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aims: we present a comprehensive dataset of optical and near-infrared photometry and spectroscopy of type ia supernova (sn) 2016hnk, combined with integral field spectroscopy (ifs) of its host galaxy, mcg -01-06-070, and nearby environment. our goal with this complete dataset is to understand the nature of this peculiar object.methods: properties of the sn local environment are characterized by means of single stellar population synthesis applied to ifs observations taken two years after the sn exploded. we performed detailed analyses of sn photometric data by studying its peculiar light and color curves. sn 2016hnk spectra were compared to other 1991bg-like sne ia, 2002es-like sne ia, and ca-rich transients. in addition, we used abundance stratification modeling to identify the various spectral features in the early phase spectral sequence and also compared the dataset to a modified non-lte model previously produced for the sublumnious sn 1999by.results: sn 2016hnk is consistent with being a subluminous (mb = -16.7 mag, sbv=0.43 ± 0.03), highly reddened object. the ifs of its host galaxy reveals both a significant amount of dust at the sn location, residual star formation, and a high proportion of old stellar populations in the local environment compared to other locations in the galaxy, which favors an old progenitor for sn 2016hnk. inspection of a nebular spectrum obtained one year after maximum contains two narrow emission lines attributed to the forbidden [ca ii] λλ7291,7324 doublet with a doppler shift of 700 km s-1. based on various observational diagnostics, we argue that the progenitor of sn 2016hnk was likely a near chandrasekhar-mass (mch) carbon-oxygen white dwarf that produced 0.108 m⊙ of 56ni. our modeling suggests that the narrow [ca ii] features observed in the nebular spectrum are associated with 48ca from electron capture during the explosion, which is expected to occur only in white dwarfs that explode near or at the mch limit. tables c.1-c.7 are also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/630/a76 | evidence for a chandrasekhar-mass explosion in the ca-strong 1991bg-like type ia supernova 2016hnk |
we present alma observations of 101 protoplanetary disks within the star-forming region lynds 1641 in the orion molecular cloud a. our observations include 1.33 mm continuum emission and spectral windows covering the j = 2-1 transition of 12co, 13co, and c18o. we detect 89 protoplanetary disks in the dust continuum at the 4σ level (∼88% detection rate) and 31 in 12co, 13 in 13co, and 4 in c18o. our sample contains 23 transitional disks, 20 of which are detected in the continuum. we target infrared-bright class ii objects, which biases our sample toward massive disks. we determine dust masses or upper limits for all sources in our sample and compare our sample to protostars in this region. we find a decrease in dust mass with evolutionary state. we also compare this sample to other regions surveyed in the (sub)millimeter and find that lynds 1641 has a relatively massive dust disk population compared to regions of similar and older ages, with a median dust mass of ${11.1}_{-4.6}^{+32.9}$ m⊕ and 27% with dust masses equal to or greater than the minimum solar nebula dust mass value of ∼30 m⊕. we analyze the disk mass-accretion rate relationship in this sample and find that the viscous disk lifetimes are similar to the age of the region, though with a large spread. one object, [mgm2012] 512, shows a large-scale (>5000 au) structure in both the dust continuum and the three gas lines. we discuss potential origins for this emission, including an accretion streamer with large dust grains. | an alma survey of protoplanetary disks in lynds 1641 |
the diffuse ionized gas (dig) contributes to the nebular emission of galaxies, resulting in emission line flux ratios that can be significantly different from those produced by h ii regions. comparing the emission of [sii]λ6717,31 between pointed observations of h ii regions in nearby galaxies and integrated spectra of more distant galaxies, it has been recently claimed that the dig can also deeply affect the emission of bright, star-forming galaxies, and that a large correction must be applied to observed line ratios to recover the genuine contribution from h ii regions. here, we show instead that the e?ect of dig on the integrated spectra of star-forming galaxies is lower than assumed in previous work. here we show that, in contrast, aperture effects on the spectroscopy of nearby h ii regions are largely responsible for the observed difference: when spectra of local h ii regions are extracted using large enough apertures while still avoiding the dig, the observed line ratios are the same as in more distant galaxies. this result is highly relevant for the use of strong-line methods to measure metallicity. | the diffuse ionized gas (dig) in star-forming galaxies: the influence of aperture effects on local h ii regions |
the lyman alpha emission line (lyα) of neutral hydrogen (hi) is intrinsically the brightest emission feature in the spectrum of astrophysical nebulae, making it a very attractive observational feature with which to survey galaxies. moreover as an ultraviolet resonance line, lyα possesses several unique characteristics that make it useful to study the properties of the interstellar medium and ionising stellar population at all cosmic epochs. in this review, i present a summary of lyα observations of galaxies in the nearby universe. by ultraviolet continuum selection, at the magnitudes reachable with current facilities, only ≈ 5% of the local galaxy population shows a lyα equivalent width (w lyα) that exceeds 20 å. this fraction increases dramatically at higher redshifts, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. i discuss many local lyα observations, showing that when galaxies show net lyα emission, they ubiquitously also produce large-scale halos of scattered lyα, that dominate the integrated luminosity. concerning global measurements, we discuss how w lyα and the lyα escape fraction (f lyα esc) are higher (w lyα ≳ 20 å and f lyα esc ≳ 10%) in galaxies that represent the less massive and younger end of the distribution for local objects. this is connected with various properties, such that lyα-emitting galaxies have lower metal abundances (median value of 12 + log(o/h) ~ 8.1) and dust reddening. however, the presence of galactic outflows/winds is also vital to doppler shift the lyα line out of resonance with the atomic gas, and high w lyα is found only among galaxies with winds faster than ~ 50 km s-1. the empirical evidence is then assembled into a coherent picture, and the requirement for star-formation-driven feedback is discussed in the context of an evolutionary sequence where the interstellar medium is accelerated and/or subject to hydrodynamical instabilities, which reduce the scattering of lyα. concluding remarks take the form of perspectives upon future developments, and the most pressing questions that can be answered by observation. | lyman alpha emitting galaxies in the nearby universe |
iras 00500+6713 is a hypothesized remnant of a type iax supernova sn 1181. multi-wavelength observations have revealed its complicated morphology; a dusty infrared ring is sandwiched by the inner and outer x-ray nebulae. we analyze the archival x-ray data taken by xmm-newton and chandra to constrain the angular size, mass, and metal abundance of the x-ray nebulae, and construct a theoretical model describing the dynamical evolution of iras 00500+6713, including the effects of the interaction between the sn ejecta and the intense wind enriched with carbon burning ashes from the central white dwarf (wd) j005311. we show that the inner x-ray nebula corresponds to the wind termination shock while the outer x-ray nebula to the shocked interface between the sn ejecta and the interstellar matter. the observed x-ray properties can be explained by our model with an sn explosion energy of $e_\mathrm{ej} = (0.77 \mbox{--} 1.1)\times 10^{48}$~erg, an sn ejecta mass of $m_\mathrm{ej} = 0.18\mbox{--}0.53~m_\odot$, if the currently observed wind from wd j005311 started to blow $t_\mathrm{w} \gtrsim 810$ yr after the explosion, i.e., approximately after a.d. 1990. the inferred sn properties are compatible with those of type iax sne and the timing of the wind launch may correspond to the kelvin-helmholtz contraction of the oxygen-neon core of wd j005311 that triggered a surface carbon burning. our analysis supports that iras 00500+6713 is the remnant of sn iax 1181 produced by a double degenerate merger of oxygen-neon and carbon-oxygen wds, and wd j005311 is the surviving merger product. | a dynamical model for iras 00500+6713: the remnant of a type iax supernova sn 1181 hosting a double degenerate merger product wd j005311 |
the iab iron meteorite complex consists of a main group (mg) and five chemical subgroups (sll, slm, slh, shl, and shh). here, mass-independent mo and radiogenic 182w isotope compositions are reported for iab complex meteorites to evaluate the genetics and chronology, respectively, of the mg and subgroups. osmium isotopes are used to correct for cosmic ray exposure effects on isotopes of mo and w. the mg and three subgroups (i.e., sll, slm, and slh), characterized by low au abundances, have the same mo isotopic compositions within analytical uncertainty, consistent with a common genetic origin. these meteorites, together with winonaites, are the only cosmochemical materials yet identified with mo isotopic compositions that are identical to earth. the mo isotopic compositions of two subgroups characterized by higher au abundances (shl and shh) are identical to one another within uncertainty, but differ from the low au subgroups, indicating derivation from genetically distinct materials. the mg has a 182w, post calcium-aluminum inclusion (cai) formation model age of 3.4 ± 0.7 ma. one of the low au subgroups (slm) is ∼1.7 ma younger, whereas the high au subgroups are ∼1.5-3 ma older. the new mo-w data, coupled with chemical data, indicate that the mg and the low au subgroups formed in different impact-generated melts, some of which evidently formed on a chemically disparate, but genetically identical parent body. the high au subgroups likely formed via core-formation processes on separate, internally-heated parent bodies from other iab subgroups. the iab complex meteorites fall on a linear trend defined by 94mo/96mo vs. 95mo/96mo, along with most other iron meteorite groups. variation along this line was caused by mixing between at least two nebular components. one component was likely a pure s-process enriched nucleosynthetic carrier, and the other a homogenized nebular component. sombrerete, currently classified as an shl iron, has a mo isotopic composition that is distinct from all iab complex meteorites analyzed here. along with group ivb iron meteorites and some ungrouped iron meteorites, it falls on a separate line from other meteorites which may reflect addition of an r-process-enriched component, and it should no longer be classified as a iab iron. | characterizing cosmochemical materials with genetic affinities to the earth: genetic and chronological diversity within the iab iron meteorite complex |
discs around young planets, so-called circumplanetary discs (cpds), are essential for planet growth, satellite formation, and planet detection. we study the millimetre and centimetre emission from accreting cpds by using the simple α disc model. we find that it is easier to detect cpds at shorter radio wavelengths (e.g. λ ≲ 1 mm). for example, if the system is 140 pc away from us, deep observations (e.g. 5 h) at alma band 7 (0.87 mm) are sensitive to as small as 0.03 lunar mass of dust in cpds. if the cpd is around a jupiter mass planet 20 au away from the host star and has a viscosity parameter α ≲ 0.001, alma can detect this disc when it accretes faster than 10^{-10} m_{⊙} yr^{-1}. alma can also detect the 'minimum mass sub-nebulae' disc if such a disc exists around a young planet in young stellar objects. however, to distinguish the embedded compact cpd from the circumstellar disc material, we should observe circumstellar discs with large gaps/cavities using the highest resolution possible. we also calculate the cpd fluxes at vla bands, and discuss the possibility of detecting radio emission from jets/winds launched in cpds. finally we argue that, if the radial drift of dust particles is considered, the drifting time-scale for millimetre dust in cpds can be extremely short. it only takes 102-103 yr for cpds to lose millimetre dust. thus, for cpds to be detectable at radio wavelengths, mm-sized dust in cpds needs to be replenished continuously, or the disc has a significant fraction of micron-sized dust or a high gas surface density so that the particle drifting time-scale is long, or the radial drift is prevented by other means (e.g. pressure traps). | on the radio detectability of circumplanetary discs |
aimdeforestation is rapidly altering southeast asian landscapes, resulting in some of the highest rates of habitat loss worldwide. among the many species facing declines in this region, clouded leopards rank notably for their ambassadorial potential and capacity to act as powerful levers for broader forest conservation programmes. thus, identifying core habitat and conservation opportunities are critical for curbing further neofelis declines and extending umbrella protection for diverse forest biota similarly threatened by widespread habitat loss. furthermore, a recent comprehensive habitat assessment of sunda clouded leopards (n. diardi) highlights the lack of such information for the mainland species (n. nebulosa) and facilitates a comparative assessment.locationsoutheast asia.methodsspecies–habitat relationships are scale‑dependent, yet <5% of all recent habitat modelling papers apply robust approaches to optimize multivariate scale relationships. using one of the largest camera trap datasets ever collected, we developed scale‑optimized species distribution models for two con‑generic carnivores, and quantitatively compared their habitat niches.resultswe identified core habitat, connectivity corridors, and ranked remaining habitat patches for conservation prioritization. closed‑canopy forest was the strongest predictor, with ~25% lower neofelis detections when forest cover declined from 100 to 65%. a strong, positive association with increasing precipitation suggests ongoing climate change as a growing threat along drier edges of the species' range. while deforestation and land use conversion were deleterious for both species, n. nebulosa was uniquely associated with shrublands and grasslands. we identified 800 km2 as a minimum patch size for supporting clouded leopard conservation.main conclusionswe illustrate the utility of multi‑scale modelling for identifying key habitat requirements, optimal scales of use and critical targets for guiding conservation prioritization. curbing deforestation and development within remaining core habitat and dispersal corridors, particularly in myanmar, laos and malaysia, is critical for supporting evolutionary potential of clouded leopards and conservation of associated forest biodiversity. | multi‑scale habitat modelling identifies spatial conservation priorities for mainland clouded leopards (neofelis nebulosa) |
context. ngc 7023 is a well-studied reflection nebula, which shows strong emission from polycyclic aromatic hydrocarbon (pah) molecules in the form of aromatic infrared bands (aibs). the spectral variations of the aibs in this region are connected to the chemical evolution of the pah molecules which, in turn, depends on the local physical conditions.aims: our goal is to map pah sizes in ngc 7023 with respect to the location of the star. we focus on the north west (nw) photo-dissociation region (pdr) and the south pdr of ngc 7023 to understand the photochemical evolution of pahs, using size as a proxy.methods: we use the unique capabilities of the stratospheric observatory for infrared astronomy (sofia) to observe a 3.2' × 3.4' region of ngc 7023 at wavelengths that we observe with high spatial resolution (2.7'') at 3.3 and 11.2 μm. we compare the sofia images with existing images of the pah emission at 8.0 μm (spitzer), emission from evaporating very small grains (evsg) extracted from spitzer-irs spectral cubes, the extended red emission (hubble space telescope and canadian french hawaiian telescope), and h2 (2.12 μm). we create maps of the 11.2/3.3 μm ratio to probe the morphology of the pah size distribution and the 8.0/11.2 μm ratio to probe the pah ionization. we make use of an emission model and of vibrational spectra from the nasa ames pah database to translate the 11.2/3.3 μm ratio to pah sizes.results: the 11.2/3.3 μm ratio map shows the smallest pah concentrate on the pdr surface (h2 and extended red emission) in the nw and south pdr. we estimated that pahs in the nw pdr bear, on average, a number of carbon atoms (nc) of ~70 in the pdr cavity and ~50 at the pdr surface. in the entire nebula, the results reveal a factor of 2 variation in the size of the pah. we relate these size variations to several models for the evolution of the pah families when they traverse from the molecular cloud to the pdr.conclusions: the high-resolution pah size map enables us to follow the photochemical evolution of pahs in ngc 7023. small pahs result from the photo-evaporation of vsgs as they reach the pdr surface. inside the pdr cavity, the pah abundance drops as the smallest pah are broken down. the average pah size increases in the cavity where only the largest species survive or are converted into c60 by photochemical processing. | mapping pah sizes in ngc 7023 with sofia |
strong lensing offers a precious opportunity for studying the formation and early evolution of super star clusters that are rare in our cosmic backyard. the sunburst arc, a lensed cosmic noon galaxy, hosts a young super star cluster with escaping lyman continuum radiation. analyzing archival hubble space telescope images and emission line data from very large telescope/muse and x-shooter, we construct a physical model for the cluster and its surrounding photoionized nebula. we confirm that the cluster is ≲4 myr old, is extremely massive m ⋆ ~ 107 m ⊙, and yet has a central component as compact as several parsecs, and we find a gas-phase metallicity z = (0.22 ± 0.03)z ⊙. the cluster is surrounded by ≳105 m ⊙ of dense clouds that have been pressurized to p ~ 109 k cm-3 by perhaps stellar radiation at within 10 pc. these should have large neutral columns n hi > 1022.8 cm-2 to survive rapid ejection by radiation pressure. the clouds are likely dusty as they show gas-phase depletion of silicon, and may be conducive to secondary star formation if n hi > 1024 cm-2 or if they sink farther toward the cluster center. detecting strong [n iii]λ λ 1750,1752, we infer heavy nitrogen enrichment $\mathrm{log}({\rm{n}}/{\rm{o}})=-{0.21}_{-0.11}^{+0.10}$ . this requires efficiently retaining ≳500 m ⊙ of nitrogen in the high-pressure clouds from massive stars heavier than 60 m ⊙ up to 4 myr. we suggest a physical origin of the high-pressure clouds from partial or complete condensation of slow massive star ejecta, which may have an important implication for the puzzle of multiple stellar populations in globular clusters. | nitrogen-enriched, highly pressurized nebular clouds surrounding a super star cluster at cosmic noon |
context. the multiplicity of classical cepheids (ccs) and rr lyrae stars (rrls) is still imperfectly known, particularly for rrls.aims: in order to complement the close-in short orbital period systems presented in paper i, our aim is to detect the wide, spatially resolved companions of the targets of our reference samples of galactic ccs and rrls.methods: angularly resolved common proper motion pairs were detected using a simple progressive selection algorithm to separate the most probable candidate companions from the unrelated field stars.results: we found 27 resolved, high probability gravitationally bound systems with ccs out of 456 examined stars, and one unbound star embedded in the circumstellar dusty nebula of the long-period cepheid rs pup. we found seven spatially resolved, probably bound systems with rrl primaries out of 789 investigated stars, and 22 additional candidate pairs. we report in particular new companions of three bright rrls: ov and (companion of f4v spectral type), rr leo (m0v), and ss oct (k2v). in addition, we discovered resolved companions of 14 stars that were likely misclassified as rrls.conclusions: the detection of resolved non-variable companions around ccs and rrls facilitates the validation of their gaia dr2 parallaxes. the possibility to conduct a detailed analysis of the resolved coeval companions of ccs and old population rrls will also be valuable to progress on our understanding of their evolutionary path. tables a.1-c.1 are also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/623/a117 | multiplicity of galactic cepheids and rr lyrae stars from gaia dr2. ii. resolved common proper motion pairs |
our nearest large cosmological neighbour, the andromeda galaxy (m31), is a dynamical system, and an accurate measurement of its total mass is central to our understanding of its assembly history, the life-cycles of its satellite galaxies, and its role in shaping the local group environment. here, we apply a novel approach to determine the dynamical mass of m31 using high-velocity planetary nebulae, establishing a hierarchical bayesian model united with a scheme to capture potential outliers and marginalize over tracers unknown distances. with this, we derive the escape velocity run of m31 as a function of galactocentric distance, with both parametric and non-parametric approaches. we determine the escape velocity of m31 to be 470 ± 40 km s-1 at a galactocentric distance of 15 kpc, and also, derive the total potential of m31, estimating the virial mass and radius of the galaxy to be 0.8 ± 0.1 × 1012 m⊙ and 240 ± 10 kpc, respectively. our m31 mass is on the low side of the measured range, this supports the lower expected mass of the m31-milky way system from the timing and momentum arguments, satisfying the h i constraint on circular velocity between 10 ≲ r/ kpc < 35, and agreeing with the stellar mass tully-fisher relation. to place these results in a broader context, we compare them to the key predictions of the λcdm cosmological paradigm, including the stellar-mass-halo-mass and the dark matter halo concentration-virial mass correlation, and finding it to be an outlier to this relation. | the need for speed: escape velocity and dynamical mass measurements of the andromeda galaxy |
in our solar system, terrestrial planets and meteoritical matter exhibit various bulk compositions. to understand this variety of compositions, formation mechanisms of meteorites are usually investigated via a thermodynamic approach that neglects the processes of transport throughout the protosolar nebula. here, we investigate the role played by rocklines (condensation/sublimation lines of refractory materials) in the innermost regions of the protosolar nebula to compute the composition of particles migrating inward toward the disk as a function of time. to do so, we utilize a one-dimensional accretion disk model with a prescription for dust and vapor transport, sublimation, and recondensation of refractory materials (ferrosilite, enstatite, fayalite, forsterite, iron sulfide, metal iron, and nickel). we find that the diversity of the bulk composition of cosmic spherules, chondrules, and chondrites can be explained by their formation close to rocklines, suggesting that solid matter is concentrated in the vicinity of these sublimation/condensation fronts. although our model relies a lot on the number of considered species and the availability of thermodynamic data governing state changes, it suggests that rocklines played a major role in the formation of small and large bodies in the innermost regions of the protosolar nebula. our model gives insights on the mechanisms that might have contributed to the formation of mercury's large core. | rocklines as cradles for refractory solids in the protosolar nebula |
recently two collaborations, tibet and hawc, presented new measurements of gamma-ray spectrum from crab nebula (amenomori et al. in phys rev lett 123(5):051101, 2019, arxiv:1906.05521 [astro-ph.he]; abeysekara et al. [hawc collaboration] in astrophys. j. 881, 134, (2019), arxiv:1905.12518 [astro-ph.he]) which continues beyond 100 tev. we use these data to establish two-sided constraints on parameters of lorentz invariance violation in quantum electrodynamics. the limits on lorentz violating mass scale for quartic dispersion relation are 4.1 ×1014gev (photon splitting) and 1.9 ×1013gev (photon decay) for superluminal case, and 1.4 ×1012 gev (suppression of shower formation) for subluminal case. | new constraints on lorentz invariance violation from crab nebula spectrum beyond 100 tev |
protoplanetary discs (ppds) in the orion nebula cluster (onc) are irradiated by uv fields from the massive star θ1c. this drives thermal winds, inducing mass-loss rates of up to \dot{m}_wind∼ 10^{-7} m_⊙ yr-1 in the `proplyds' (ionized ppds) close to the centre. for the mean age of the onc and reasonable initial ppd masses, such mass-loss rates imply that discs should have been dispersed. however, ∼ 80 per cent of stars still exhibit a near-infrared excess, suggesting that significant circumstellar mass remains. this `proplyd lifetime problem' has persisted since the discovery of photoevaporating discs in the core of the onc by o'dell & wen (1994). in this work, we demonstrate how an extended period of star formation can solve this problem. coupling n-body calculations and a viscous disc evolution model, we obtain high disc fractions at the present day. this is partly due to the migration of older stars outwards, and younger stars inwards such that the most strongly irradiated ppds are also the youngest. we show how the disc mass distribution can be used to test the recent claims in the literature for multiple stellar populations in the onc. our model also explains the recent finding that host mass and ppd mass are only weakly correlated, in contrast with other regions of similar age. we conclude that the status of the onc as the archetype for understanding the influence of environment on planet formation is undeserved; the complex star formation history (involving star formation episodes within ∼0.8 myr of the present day) results in confusing signatures in the ppd population. | a solution to the proplyd lifetime problem |
we present late-time spectra of eight type ia supernovae (sne ia) obtained at >200 d after peak brightness using the gemini south and keck telescopes. all of the sne ia in our sample were nearby, well separated from their host galaxy's light, and have early-time photometry and spectroscopy from the las cumbres observatory. parameters are derived from the light curves and spectra such as peak brightness, decline rate, photospheric velocity and the widths and velocities of the forbidden nebular emission lines. we discuss the physical interpretations of these parameters for the individual sne ia and the sample in general, including comparisons to well-observed sne ia from the literature. there are possible correlations between early-time and late-time spectral features that may indicate an asymmetric explosion, so we discuss our sample of sne within the context of models for an offset ignition and/or white dwarf collisions. a subset of our late-time spectra are uncontaminated by host emission, and we statistically evaluate our non-detections of h α emission to limit the amount of hydrogen in these systems. finally, we consider the late-time evolution of the iron emission lines, finding that not all of our sne follow the established trend of a redward migration at >200 d after maximum brightness. | nebular-phase spectra of nearby type ia supernovae |
i suggest a spiral-in process in which a stellar companion grazes the envelope of a giant star while both the orbital separation and the giant radius shrink simultaneously, forming a close binary system. the binary system might be viewed as evolving in a constant state of "just entering a common envelope (ce) phase." in cases where this process takes place, it can be an alternative to ce evolution where the secondary star is immersed in the giant's envelope. grazing envelope evolution (gee) is made possible only if the companion manages to accrete mass at a high rate and launches jets that remove the outskirts of the giant envelope, hence preventing the formation of a ce. the high accretion rate is made possible by the accretion disk launching jets which efficiently carry the excess angular momentum and energy from the accreted mass. the orbital decay itself is caused by the gravitational interaction of the secondary star with the envelope inward of its orbit, i.e., dynamical friction (gravitational tide). mass loss through the second lagrangian point can carry additional angular momentum and envelope mass. the gee lasts for tens to hundreds of years. the high accretion rate, with peaks lasting from months to years, might lead to a bright object referred to as the intermediate luminosity optical transient (red novae; red transients). a bipolar nebula and/or equatorial ring are formed around the binary remnant. | close stellar binary systems by grazing envelope evolution |
saturn formed beyond the snow line in the primordial solar nebula that made it possible for it to accrete a large mass. disk instability and core accretion models have been proposed for saturn's formation, but core accretion is favored on the basis of its volatile abundances, internal structure, hydrodynamic models, chemical characteristics of protoplanetary disk, etc. the observed frequency, properties and models of exoplanets provide additional supporting evidence for core accretion. the heavy elements with mass greater than 4he make up the core of saturn, but are presently poorly constrained, except for carbon. the c/h ratio is super-solar, and twice that in jupiter. the enrichment of carbon and other heavy elements in saturn and jupiter requires special delivery mechanisms for volatiles to these planets. in this chapter we will review our current understanding of the origin and evolution of saturn and its atmosphere, using a multi-faceted approach that combines diverse sets of observations on volatile composition and abundances, relevant properties of the moons and rings, comparison with the other gas giant planet, jupiter, analogies to the extrasolar giant planets, as well as pertinent theoretical models. | the origin and evolution of saturn, with exoplanet perspective |
aims: we investigate the role played by a pre-supernova (sn) ambient magnetic field in the dynamics of the expanding remnant of sn 1987a, and the origin and evolution of the radio emission from the remnant, in particular during the interaction of the blast wave with the nebula surrounding the sn.methods: we modeled the evolution of sn 1987a from the breakout of the shock wave at the stellar surface to the expansion of its remnant through the surrounding nebula using three-dimensional magnetohydrodynamic simulations. the model considers the radiative cooling, the deviations from equilibrium of ionization, the deviation from temperature-equilibration between electrons and ions, and a plausible configuration of the pre-sn ambient magnetic field. we explore the strengths of the pre-sn magnetic field ranging between 1 and 100 μg at the inner edge of the nebula and we assume an average field strength at the stellar surface b0 ≈ 3 kg. from the simulations, we synthesize the thermal x-ray and the non-thermal radio emission and compare the model results with observations.results: the presence of an ambient magnetic field with strength in the range considered does not change significantly the overall evolution of the remnant. nevertheless, the magnetic field reduces the erosion and fragmentation of the dense equatorial ring after the impact of the sn blast wave. as a result, the ring survives the passage of the blast, at least during the time covered by the simulations (40 yr). our model is able to reproduce the morphology and lightcurves of sn 1987a in both x-ray and radio bands. the model reproduces the observed radio emission if the flux originating from the reverse shock is heavily suppressed. in this case, the radio emission originates mostly from the forward shock traveling through the h ii region and this may explain why the radio emission seems to be insensitive to the interaction of the blast with the ring. possible mechanisms for the suppression of emission from the reverse shock are investigated. we find that synchrotron self-absorption and free-free absorption have negligible effects on the emission during the interaction with the nebula. we suggest that the emission from the reverse shock at radio frequencies might be limited by highly magnetized ejecta. movies associated to figs. 2 and 4 are available at http://www.aanda.org | 3d mhd modeling of the expanding remnant of sn 1987a. role of magnetic field and non-thermal radio emission |
context. lyman α blobs (labs) are large-scale radio-quiet lyman α (lyα) nebula at high-z that occur predominantly in overdense proto-cluster regions. in particular, there is the prototypical ssa22a-lab1 at z = 3.1, which has become an observational reference for labs across the electromagnetic spectrum.aims: we want to understand the powering mechanisms that drive the lab so that we may gain empirical insights into the galaxy-formation processes within a rare dense environment at high-z. thus, we need to infer the distribution, the dynamics, and the ionisation state of lab 1's lyα emitting gas.methods: lab 1 was observed for 17.2 h with the vlt/muse integral-field spectrograph. we produced optimally extracted narrow band images, in lyαλ1216, he iiλ1640, and we tried to detect c ivλ1549 emission. by utilising a moment-based analysis, we mapped the kinematics and the line profile characteristics of the blob. we also linked the inferences from the line profile analysis to previous results from imaging polarimetry.results: we map lyα emission from the blob down to surface-brightness limits of ≈6 × 10-19 erg s-1 cm-2 arcsec-2. at this depth, we reveal a bridge between lab 1 and its northern neighbour lab 8, as well as a shell-like filament towards the south of lab 1. the complexity and morphology of the lyα profile vary strongly throughout the blob. despite the complexity, we find a coherent large-scale east-west velocity gradient of ∼1000 km s-1 that is aligned perpendicular to the major axis of the blob. moreover, we observe a negative correlation of lyα polarisation fraction with lyα line width and a positive correlation with absolute line-of-sight velocity. finally, we reveal he ii emission in three distinct regions within the blob, however, we can only provide upper limits for c iv.conclusions: various gas excitation mechanisms are at play in lab 1: ionising radiation and feedback effects dominate near the embedded galaxies, while lyα scattering contributes at larger distances. however, he ii/lyα ratios combined with upper limits on c iv/lyα are not able to discriminate between active galactic nucleus ionisation and feedback- driven shocks. the alignment of the angular momentum vector parallel to the morphological principal axis appears to be at odds with the predicted norm for high-mass halos, but this most likely reflects that lab 1 resides at a node of multiple intersecting filaments of the cosmic web. lab 1 can thus be thought of as a progenitor of a present-day massive elliptical within a galaxy cluster. the reduced muse datacube, the continuum subtracted datacube, and the derived data-products (lyα narrow-band image, he ii narrow-band image, and maps from the moment based analysis) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/642/a55 based on observations made with eso telescopes at the la silla paranal observatory under programme id 094.a-0605, programme id 095.a-0570, and programme id 097.a-0831. | deciphering the lyman α blob 1 with deep muse observations |
compact nonresonant systems of sub-jovian planets are the most common outcome of the planet formation process. despite exhibiting broad overall diversity, these planets also display dramatic signatures of intrasystem uniformity in their masses, radii, and orbital spacings. although the details of their formation and early evolution are poorly known, sub-jovian planets are expected to emerge from their natal nebulae as multiresonant chains, owing to planet-disk interactions. within the context of this scenario, the architectures of observed exoplanet systems can be broadly replicated if resonances are disrupted through postnebular dynamical instabilities. here, we generate an ad hoc sample of resonant chains and use a suite of n-body simulations to show that instabilities can not only reproduce the observed period ratio distribution, but that the resulting collisions also modify the mass uniformity in a way that is consistent with the data. furthermore, we demonstrate that primordial mass uniformity, motivated by the sample of resonant chains coupled with dynamical sculpting, naturally generates uniformity in orbital period spacing similar to what is observed. finally, we find that almost all collisions lead to perfect mergers, but some form of postinstability damping is likely needed to fully account for the present-day dynamically cold architectures of sub-jovian exoplanets. | architectures of compact super-earth systems shaped by instabilities |
we present the key results from an intensive and coordinated ten-year amateur observational programme designed to uncover and confirm galactic planetary nebulae (pne). this was undertaken and led by a dedicated group of largely french amateur astronomers in collaboration with professional colleagues. over this period this group has uncovered a total of 209 spectroscopically confirmed true, likely, and possible galactic pne, with the work accelerating over the last three years in particular. these new discoveries represent ~5% of all 3831 true, likely, and possible galactic pne currently known according to the hash database as of march 2022. a further 610 pne candidates are awaiting follow-up. these figures demonstrate the power and value of the amateur community in undertaking a coordinated and focused programme such as this. tables 1-5 are only available at the cds via anonymous ftp to ftp://cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/666/a152 | amateur pn discoveries and their spectral confirmation: a significant new addition to the galactic pn inventory |
gas-phase metallicities of galaxies are typically measured through auroral or nebular emission lines, but metallicity also leaves an imprint on the overall spectral energy distribution (sed) of a galaxy and can be estimated through sed fitting. we use the prospect sed fitting code with a flexible parametric star formation history and an evolving metallicity history to self-consistently measure metallicities, stellar mass, and other galaxy properties for $\sim 90\, 000$ galaxies from the deep extragalactic visible legacy survey (devils) and galaxy and mass assembly (gama) survey. we use these to trace the evolution of the mass-metallicity relation (mzr) and show that the mzr only evolves in normalization by $\sim 0.1\,$dex at stellar mass $m_\star = 10^{10.5}\, \mathrm{m}_\odot$. we find no difference in the mzr between galaxies with and without sed evidence of active galactic nuclei emission at low redshifts ($z$ < 0.3). our results suggest an anticorrelation between metallicity and star formation activity at fixed stellar mass for galaxies with $m_\star \gt 10^{10.5}\, \mathrm{m}_\odot$ for $z$ < 0.3. using the star formation histories extracted using prospect we explore higher order correlations of the mzr with properties of the star formation history including age, width, and shape. we find that at a given stellar mass, galaxies with higher metallicities formed most of their mass over shorter time-scales, and before their peak star formation rate. this work highlights the value of exploring the connection of a galaxy's current gas-phase metallicity to its star formation history in order to understand the physical processes shaping the mzr. | devils: cosmic evolution of sed-derived metallicities and their connection to star formation histories |
the metallicity structure of the milky way disk stems from the chemodynamical evolutionary history of the galaxy. we use the national radio astronomy observatory karl g. jansky very large array to observe ∼8-10 ghz hydrogen radio recombination line and radio-continuum emission toward 82 galactic h ii regions. we use these data to derive the electron temperatures and metallicities for these nebulae. since collisionally excited lines from metals (e.g., oxygen, nitrogen) are the dominant cooling mechanism in h ii regions, the nebular metallicity can be inferred from the electron temperature. including previous single-dish studies, there are now 167 nebulae with radio-determined electron temperature and either parallax or kinematic distance determinations. the interferometric electron temperatures are systematically 10% larger than those found in previous single-dish studies, likely due to incorrect data analysis strategies, optical depth effects, and/or the observation of different gas by the interferometer. by combining the interferometer and single-dish samples, we find an oxygen abundance gradient across the milky way disk with a slope of -0.052 ± 0.004 dex kpc-1. we also find significant azimuthal structure in the metallicity distribution. the slope of the oxygen gradient varies by a factor of ∼2 when galactocentric azimuths near ∼30° are compared with those near ∼100°. this azimuthal structure is consistent with simulations of galactic chemodynamical evolution influenced by spiral arms. | metallicity structure in the milky way disk revealed by galactic h ii regions |
natures of progenitors of type ia supernovae (sne ia) have not yet been clarified. there has been long and intensive discussion on whether the so-called single degenerate (sd) scenario or the double degenerate (dd) scenario, or anything else, could explain a major population of sne ia, but the conclusion has not yet been reached. with rapidly increasing observational data and new theoretical ideas, the field of studying the sn ia progenitors has been quickly developing, and various new insights have been obtained in recent years. this paper aims at providing a summary of the current situation regarding the sn ia progenitors, both in theory and observations. it seems difficult to explain the emerging diversity seen in observations of sne ia by a single population, and we emphasize that it is important to clarify links between different progenitor scenarios and different sub-classes of sne ia. | progenitors of type ia supernovae |
measurements of stellar properties of galaxies when the universe was less than one billion years old yield some of the only observational constraints on the onset of star formation. we present here the inclusion of spitzer/irac imaging in the fitting of the spectral energy distribution of the seven highest-redshift galaxy candidates selected from the hubble space telescope (hst) imaging of the reionization lensing cluster survey. we find that for six out of eight hst-selected z ∼ 8 sources, the z ∼ 8 solutions are still strongly preferred over z ∼ 1-2 solutions after the inclusion of spitzer fluxes, and two prefer a z ∼ 7 solution, which we defer to a later analysis. we find a wide range of intrinsic stellar masses (5 × 106-4 × 109 m⊙), star formation rates (0.2-14 m⊙ yr-1), and ages (30-600 myr) among our sample. of particular interest is a1763-1434, which shows evidence of an evolved stellar population (∼500 myr) at z ∼ 8, implying that its first generation of star formation occurred <100 myr after the big bang. spt0615-jd, a spatially resolved z ∼ 10 candidate, remains at its high redshift, supported by deep spitzer/irac data, and also shows some evidence for an evolved stellar population. even with the lensed, bright apparent magnitudes of these z ≳ 8 candidates (h = 26.1-27.8 ab mag), only the james webb space telescope will be able to exclude the possibility of abnormally strong nebular emission, large dust content, or some combination thereof, and confirm the presence of evolved stellar populations early in the universe. | stellar properties of z ≳ 8 galaxies in the reionization lensing cluster survey |
we introduce project megasaura: the magellan evolution of galaxies spectroscopic and ultraviolet reference atlas. megasaura comprises medium-resolution, rest-frame ultraviolet spectroscopy of n = 15 bright gravitationally lensed galaxies at redshifts of 1.68 < z < 3.6, obtained with the mage spectrograph on the magellan telescopes. the spectra cover the observed-frame wavelength range 3200 < λo< 8280 å the average spectral resolving power is r = 3300. the median spectrum has a signal-to-noise ratio (s/n) = 21 per resolution element at 5000 å. as such, the megasaura spectra have superior s/n and wavelength coverage compared to what cos/hst provides for starburst galaxies in the local universe. this paper describes the sample, the observations, and the data reduction. we compare the measured redshifts for the stars, the ionized gas as traced by nebular lines, and the neutral gas as traced by absorption lines; we find the expected bulk outflow of the neutral gas, and no systemic offset between the redshifts measured from nebular lines and the redshifts measured from the stellar continuum. we provide the megasaura spectra to the astronomical community through a data release. | the magellan evolution of galaxies spectroscopic and ultraviolet reference atlas (megasaura). i. the sample and the spectra |
six billion years from now, while evolving on the asymptotic giant branch (agb), the sun will metamorphose from a red giant into a beautiful planetary nebula. this spectacular evolution will impact the solar system planets, but observational confirmations of the predictions of evolution models are still elusive as no planet orbiting an agb star has yet been discovered. the nearby agb red giant l2 puppis (d = 64 pc) is surrounded by an almost edge-on circumstellar dust disk. we report new observations with alma at very high angular resolution (18 × 15 mas) in band 7 (ν ≈ 350 ghz) that allow us to resolve the velocity profile of the molecular disk. we establish that the gas velocity profile is keplerian within the central cavity of the dust disk, allowing us to derive the mass of the central star l2 pup a, ma = 0.659 ± 0.011 ± 0.041 m⊙ (± 6.6%). from evolutionary models, we determine that l2 pup a had a near-solar main-sequence mass, and is therefore a close analog of the future sun in 5 to 6 gyr. the continuum map reveals a secondary source (b) at a radius of 2 au contributing fb/fa = 1.3 ± 0.1% of the flux of the agb star. l2 pup b is also detected in co emission lines at a radial velocity of vb = 12.2 ± 1.0 km s-1. the close coincidence of the center of rotation of the gaseous disk with the position of the continuum emission from the agb star allows us to constrain the mass of the companion to mb = 12 ± 16 mjup. l2 pup b is most likely a planet or low-mass brown dwarf with an orbital period of about five years. its continuum brightness and molecular emission suggest that it may be surrounded by an extended molecular atmosphere or an accretion disk. l2 pup therefore emerges as a promising vantage point on the distant future of our solar system. | alma observations of the nearby agb star l2 puppis. i. mass of the central star and detection of a candidate planet |
we present the bayesian oxygen and nitrogen abundance determinations (bond) method. bond is a bayesian code (available at: http://bond.ufsc.br) to simultaneously derive oxygen and nitrogen abundances in giant h ii regions. it compares observed emission lines to a grid of photoionization models without assuming any relation between o/h and n/o. our grid spans a wide range in o/h, n/o and ionization parameter u, and covers different starburst ages and nebular geometries. varying starburst ages accounts for variations in the ionizing radiation field hardness, which arise due to the ageing of h ii regions or the stochastic sampling of the initial mass function. all previous approaches assume a strict relation between the ionizing field and metallicity. the other novelty is extracting information on the nebular physics from semistrong emission lines. while strong lines ratios alone ([o iii]/hβ, [o ii]/hβ and [n ii]/hβ) lead to multiple o/h solutions, the simultaneous use of [ar iii]/[ne iii] allows one to decide whether an h ii region is of high or low metallicity. adding he i/hβ pins down the hardness of the radiation field. we apply our method to h ii regions and blue compact dwarf galaxies, and find that the resulting n/o versus o/h relation is as scattered as the one obtained from the temperature-based method. as in previous strong-line methods calibrated on photoionization models, the bond o/h values are generally higher than temperature-based ones, which might indicate the presence of temperature fluctuations or kappa distributions in real nebulae, or a too soft ionizing radiation field in the models. | bond: bayesian oxygen and nitrogen abundance determinations in giant h ii regions using strong and semistrong lines |
we present multiband ultraviolet and optical light curves, as well as visual-wavelength and near-infrared spectroscopy of the type ii linear (iil) supernova (sn) 2013by. we show that sn 2013by and other sne iil in the literature, after their linear decline phase that start after maximum, have a sharp light-curve decline similar to that seen in sne iip. this light-curve feature has rarely been observed in other sne iil due to their relative rarity and the intrinsic faintness of this particular phase of the light curve. we suggest that the presence of this drop could be used as a physical parameter to distinguish between subclasses of sne ii, rather than their light-curve decline rate shortly after peak. close inspection of the spectra of sn 2013by indicate asymmetric line profiles and signatures of high-velocity hydrogen. late (∼90 d after explosion) near-infrared spectra of sn 2013by exhibit oxygen lines, indicating significant mixing within the ejecta. from the late-time light curve, we estimate that 0.029 m⊙ of 56ni was synthesized during the explosion. it is also shown that the v-band light-curve slope is responsible for part of the scatter in the luminosity (v magnitude 50 d after explosion) versus 56ni relation. our observations of sn 2013by and other sne iil through the onset of the nebular phase indicate that their progenitors are similar to those of sne iip. | supernova 2013by: a type iil supernova with a iip-like light-curve drop★ |
we present results from the mosfire deep evolution field survey on broad flux from the nebular emission lines hα, [n ii], [o iii], hβ, and [s ii]. the sample consists of 127 star-forming galaxies at 1.37 < z < 2.61 and 84 galaxies at 2.95 < z < 3.80. we decompose the emission lines using narrow and broad gaussian components that we define as having fwhm < 275 km s-1 and fwhm > 300 km s-1, respectively, for both individual galaxies and stacks. for individual galaxies, broad emission is detected at >3σ in <10% of galaxies and the broad flux accounts for 10%-70% of the total flux. in the stacks, we find a slight increase in broad to narrow flux ratio with mass but note that we cannot reliably detect broad emission with fwhm < 275 km s-1, which may be significant at low masses. when placed on the n2-bpt diagram ([o iii]/hβ versus [n ii]/hα), the broad components of the stacks are shifted toward higher [o iii]/hβ and [n ii]/hα ratios compared to the narrow component. we compare the location of the broad components to shock models and find that the broad component could be explained as a shocked outflow, but we do not rule out other possibilities, such as the presence of an agn. we discuss the possible consequences of shocked emission on the galaxy location in emission line diagnostic diagrams and calculation of sfr. we attempt to estimate the mass outflow rate/star formation rate, but caution that our results strongly rely on the assumptions regarding the physical properties of the outflow. based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w. m. keck foundation. | the mosdef survey: broad emission lines at z = 1.4-3.8 |
we present new atacama large millimeter/submillimeter array band 7 observational results of a lyman-break galaxy at z = 7.15, b14-65666 ("big three dragons"), which is an object detected in [o iii] 88 μm, [c ii] 158 μm, and dust continuum emission during the epoch of reionization. our targets are the [n ii] 122 μm fine-structure emission line and the underlying 120 μm dust continuum. the dust continuum is detected with a ~19σ significance. from far-infrared spectral energy distribution sampled at 90, 120, and 160 μm, we obtain a best-fit dust temperature of 40 k (79 k) and an infrared luminosity of ${\mathrm{log}}_{10}({l}_{\mathrm{ir}}/{l}_{\odot })=11.6$ (12.1) at the emissivity index β = 2.0 (1.0). the [n ii] 122 μm line is not detected. the 3σ upper limit of the [n ii] luminosity is 8.1 × 107 l ⊙. from the [n ii], [o iii], and [c ii] line luminosities, we use the cloudy photoionization code to estimate nebular parameters as functions of metallicity. if the metallicity of the galaxy is high (z > 0.4 z ⊙), the ionization parameter and hydrogen density are ${\mathrm{log}}_{10}u\simeq -2.7\pm 0.1$ and n h ≃ 50-250 cm-3, respectively, which are comparable to those measured in low-redshift galaxies. the nitrogen-to-oxygen abundance ratio, n/o, is constrained to be subsolar. at z < 0.4 z ⊙, the allowed u drastically increases as the assumed metallicity decreases. for high ionization parameters, the n/o constraint becomes weak. finally, our cloudy models predict the location of b14-65666 on the bpt diagram, thereby allowing a comparison with low-redshift galaxies. | big three dragons: a [n ii] 122 μm constraint and new dust-continuum detection of a z = 7.15 bright lyman-break galaxy with alma |
stars form in molecular clouds in the interstellar medium (ism) with a turbulent kinematic state. newborn stars therefore should retain the turbulent kinematics of their natal clouds. gaia dr2 and apogee-2 surveys in combination provide three-dimensional (3d) positions and 3d velocities of young stars in the orion molecular cloud complex. using the full 6d measurements, we compute the velocity structure functions (vsfs) of the stars in six different groups within the orion complex. we find that the motions of stars in all diffuse groups exhibit strong characteristics of turbulence. their first-order vsfs have a power-law exponent ranging from ∼0.2-0.5 on scales of a few to a few tens of parsecs, generally consistent with larson's relation. on the other hand, dense star clusters, such as the orion nebula cluster (onc), have experienced rapid dynamical relaxation, and have lost the memory of the initial turbulent kinematics. the vsfs of several individual groups and the whole complex all show features supporting local energy injection from supernovae. the measured strength of turbulence depends on the location relative to the supernova epicenters and the formation history of the groups. our detection of turbulence traced by young stars introduces a new method of probing the turbulent kinematics of the ism. unlike previous gas-based studies with only projected measurements accessible to observations, we utilize the full 6d information of stars, presenting a more complete picture of the 3d interstellar turbulence. | measuring turbulence with young stars in the orion complex |
super star cluster (ssc) a1 ($3.1\times 10^5\, \mathrm{m}_\odot$) in ngc 3125 has one of the strongest ($ew=4.6\pm 0.5\,$ å) broad ($fwhm=1131\pm 40\,$ km s-1) he ii λ1640 emission lines in the nearby universe and constitutes an important template for interpreting observations of extreme he ii emitters out to redshifts of z ~ 2 - 3. we use cosmic origins spectrograph (cos) observations of a1 to show that there is no significant contamination of the he ii line with nebular emission and that the line is redshifted by 121 ± 17 km s-1 relative to ism lines. we compare the cos g130m + g160m observations of a1 to recent binary bpass and single-star charlot & bruzual (c&b) simple stellar population (ssp) models with very massive stars (vms) of up to $300\, \mathrm{m}_\odot$. on the other hand, we suggest why bpass models fail to reproduce a1's he ii emission. on the other hand, a c&b model with z = 0.008, age = 2.2 myr, and vms approaching the eddington limit provides an excellent fit to the he ii emission and fits reasonably well c iii λ1175, n v λλ1238, 1241, and c iv λλ1548, 1551. we present o v λ1371 line-profile predictions showing that this line constitutes an important tracer of youth and vms in galaxies. finally, we discuss the presence of vms in cdfs131717, a highly star-forming low-metallicity galaxy located at z = 3.071, which has a tentative detection of o v absorption and strong broad he ii emission. these features are rare and hint to the presence of short-lived vms in the galaxy. our results show the effect of the latest developments of stellar wind theory and the importance of accounting for vms in models. | extreme broad he ii emission at high and low redshifts: the dominant role of vms in ngc 3125-a1 and cdfs131717 |
planetary nebulae represent a potential late stage of stellar evolution, however, their central stars (cspne) are relatively faint and, therefore, pertinent information is available for merely < 20% of the galactic sample. consequently, the literature was surveyed to construct a new catalogue of 620 cspne featuring important spectral classifications and information. the catalogue supersedes the existing iteration by 25% and includes physical parameters such as luminosity, surface gravity, temperature, magnitude estimates, and references for published spectra. the marked statistical improvement enabled the following pertinent conclusions to be determined: the h-rich/h-poor ratio is 2:1, there is a deficiency of cspne with types [wc 5-6], and nearly 80% of binary central stars belong to the h-rich group. the last finding suggests that evolutionary scenarios leading to the formation of binary central stars interfere with the conditions required for the formation of h-poor cspn. approximately 50% of the sample with derived values of log l⋆, log teff, and log g, exhibit masses and ages consistent with single stellar evolutionary models. the implication is that single stars are indeed able to form planetary nebulae. moreover, it is shown that h-poor cspne are formed by higher mass progenitors. the catalogue is available through the vizier database. tables d.1 and d.2 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/640/a10 | catalogue of the central stars of planetary nebulae. expanded edition |
the atmospheric noble gas isotope and elemental bulk ratios on venus and earth provide important information on their origin and evolution. if the protoplanets grew to a certain mass (i.e. > 0.5 mearth), they could have captured h2-dominated primordial atmospheres by accreting gas from the circumstellar disk during the formation of the solar system, which were then quickly lost by hydrodynamic escape after the disk dissipated. in such a case, the euv-driven hydrodynamic flow of h atoms dragged heavier elements with it at different rates, leading to changes in their initial isotope ratios. for reproducing earth and venus present atmospheric 36ar/38ar, 20ne/22ne, 36ar/22ne, isotope and bulk k/u ratios we applied hydrodynamic upper atmosphere escape and smooth particle hydrodynamics (sph) impact models for the loss calculations of captured h2-dominated primordial atmospheres for various protoplanetary masses. we investigated a wide range of possible euv evolution tracks of the young sun and initial atmospheric compositions based on mixtures of captured nebula gas, outgassed and delivered material from ureilite, enstatite and carbonaceaous chondrites. depending on the disk lifetime of ≈ 3-5 myr (bollard et al., 2017; wang et al., 2017) and the composition of accreted material after disk dispersal, we find from the reproduction of the present atmospheric ar, ne, and bulk k/u ratios, that early earth's evolution can be explained if proto-earth had accreted masses between ≈ 0.53 - 0.58 mearth by the time the nebula gas dissipated. if proto-earth would have accreted a higher mass during the disk lifetime the present atmospheric ar and ne isotope ratios can not be reproduced with our model approach. for masses > 0.75 mearth, earth would have had a problem to get get rid of its primordial atmosphere. if proto-earth accreted ≈ 0.53 - 0.58mearth of enstatite-dominated material as suggested by dauphas (2017) during the disk lifetime, it would have captured a tiny primordial atmosphere that was lost ≈ 3 myr after the disk dissipated. in such a case we find that the present-day atmospheric ar and ne isotope ratios can be best reproduced if the post-nebula impactors contained ≈ 5% weakly depleted carbonaceous chondritic material and ≈ 95% enstatite chondrites that are strongly depleted in ar, ne and moderately volatile elements like potassium. if higher amounts of carbonaceous chondrites were involved in early earth's accretion as recently suggested by schiller et al. (2018), then the earth's present atmospheric ar and ne ratios can only be reproduced if the involved carbonaceous chondritic post-nebula material was also highly depleted in these noble gases and/or had to be partially be delivered as long as the primordial atmosphere was yet escaping. as long as primordial atmospheres surround the growing protoplanets the abundance of their volatile elements is overwritten by their respective captured solar-like atmospheric abundances. therefore the initial composition of the protoplanets at the disk dispersal time can not be identified by our method. for masses < 0.5 mearth atmospheric escape cannot explain the present-day ratios, i.e. if earth grew slower then these ratios have to be explained differently (marty, 2012). if proto-venus captured a primordial atmosphere it should have grown to masses of ≈ 0.85- 1.0 mvenus during the time until the disk dissipated and if early venus accreted its main mass during the disk lifetime than the present atmospheric ar and ne isotope ratios and the observed k/u ratios on venus surface can also be reproduced by the escape of a captured primordial atmosphere that is lost within ≤ 100 myr, if the sun was born as a weakly to moderately active young g star. new precise re-measurements of atmospheric noble gases are necessary by future venus missions to better constrain the material that was involved in the planet's accretion history and possibly also the euv activity evolution of the young sun. in addition, measurements of other moderately volatile element and isotope ratios on the surface such as rb/u, 64zn/66zn, and 39k/41k can give an insight on whether venus accreted slow or fast, i.e. almost to its final mass within the disk lifetime. | constraining the early evolution of venus and earth through atmospheric ar, ne isotope and bulk k/u ratios |
we have investigated nucleosynthetic mo isotope anomalies in 38 different bulk iron meteorites from 11 groups, to produce by far the largest and most precise dataset available to date for such samples. all magmatic iron groups were found to display deficits in s-process mo isotopes, with essentially constant anomalies within but significant variations between groups. only meteorites of the non-magmatic iab/iiicd complex revealed terrestrial mo isotopic compositions. the improved analytical precision achieved in this study enables two isotopically distinct suites of iron meteorites to be identified. of these, the r=p suite encompasses the ic, iiab, iie, iiiab, iiie and iva groups and exhibits relatively modest but 'pure' s-process deficits, relative to earth. the second r>p suite includes groups iic, iiif and ivb. these iron meteorites show larger s-process deficits than the r=p suite, coupled with an excess of r-process relative to p-process components. comparison of the results with data for other elements (e.g., cr, ni, ru, ti, zr) suggests that the mo isotope variability is most likely produced by thermal processing and selective destruction of unstable presolar phases. an updated model is proposed, which relates the iron meteorite suites to different extents of thermal processing in the solar nebula, as governed by heliocentric distance. in detail, the r=p suite of iron meteorite parent bodies is inferred to have formed closer to the sun, where the extent of thermal processing was similar to that experienced by terrestrial material, so that the meteorites exhibit only small s-process deficits relative to earth. in contrast, the r>p suite formed at greater heliocentric distance, where more subtle thermal processing removed a smaller proportion of r- and p-process host phases, thereby generating larger s-process deficits relative to the terrestrial composition. in addition, the thermal conditions enabled selective destruction of p- versus r-isotope carrier phases, to produce the observed divergence of r- and p-process mo isotope abundances. | nucleosynthetic molybdenum isotope anomalies in iron meteorites - new evidence for thermal processing of solar nebula material |
we present an analysis of a new 120 deg2 radio continuum image of the large magellanic cloud (lmc) at 888 mhz with a bandwidth of 288 mhz and beam size of 13${_{.}^{\prime\prime}}$9 × 12${_{.}^{\prime\prime}}$1 from the australian square kilometre array pathfinder processed as part of the evolutionary map of the universe survey. the median root mean squared noise is 58 $\mu$jy beam-1. we present a catalogue of 54 612 sources, divided over a gold list (30 866 sources) complete down to 0.5 mjy uniformly across the field, a silver list (22 080 sources) reaching down to <0.2 mjy, and a bronze list (1666 sources) of visually inspected sources in areas of high noise and/or near bright complex emission. we discuss detections of planetary nebulae and their radio luminosity function, young stellar objects showing a correlation between radio luminosity and gas temperature, novae and x-ray binaries in the lmc, and active stars in the galactic foreground that may become a significant population below this flux level. we present examples of diffuse emission in the lmc (h ii regions, supernova remnants, bubbles) and distant galaxies showcasing spectacular interaction between jets and intracluster medium. among 14 333 infrared counterparts of the predominantly background radio source population, we find that star-forming galaxies become more prominent below 3 mjy compared to active galactic nuclei. we combine the new 888 mhz data with archival australia telescope compact array data at 1.4 ghz to determine spectral indices; the vast majority display synchrotron emission but flatter spectra occur too. we argue that the most extreme spectral index values are due to variability. | the askap-emu early science project: 888 mhz radio continuum survey of the large magellanic cloud |
we present the identification of 34 likely binary central stars (css) of planetary nebulae (pne) from kepler/k2 data, seven of which show eclipses. of these, 29 are new discoveries. two additional css with more complicated variability are also presented. we examined the light curves of all 'possible', 'likely', and 'true' pne in every kepler/k2 campaign (0 through 19) to identify cs variability that may indicate a binary cs. for campaigns 0, 2, 7, 15, and 16, we find 6 likely or confirmed variables among 21 pne. our primary effort, though, was focused on campaign 11 which targeted a galactic bulge field containing approximately 183 pne, in which we identified 30 candidate variable css. the periods of these variables range from 2.3 h to 30 d, and based on our analysis, most are likely to be close binary star systems. we present periods and preliminary classifications (eclipsing, double degenerate, or irradiated systems) for the likely binaries based on light-curve shape. from our total sample of 204 target pne, with a correction for incompleteness due to magnitude limits, we calculate a binary fraction of pn central stars to be 20.7 per cent for all the observed pne, or 23.5 per cent if we limit our sample only to 'true' pne. however, these fractions are almost certainly lower limits due to the large angular size of the kepler pixels, which leads to reduced sensitivity in detecting variability, primarily as a result of dilution and noise from the nebula and neighbouring stars. we discuss the binary population of css based on these results as part of the total known sample of close binary css. | binary central stars of planetary nebulae identified with kepler/k2 |
we present a new integral field spectroscopic dataset of the central part of the orion nebula (m 42), observed with the muse instrument at the eso vlt. we reduced the data with the public muse pipeline. the output products are two fits cubes with a spatial size of ~5.´9×4.´9 (corresponding to ~0.76 × 0.63 pc2) and a contiguous wavelength coverage of 4595...9366 å, spatially sampled at 0.´2. we provide two versions with a sampling of 1.25 å and 0.85 å in dispersion direction. together with variance cubes these files have a size of 75 and 110 gib on disk. they are the largest integral field mosaics to date in terms of information content. we make them available for use in the community. to validate this dataset, we compare world coordinates, reconstructed magnitudes, velocities, and absolute and relative emission line fluxes to the literature values and find excellent agreement. we derive a 2d map of extinction and present de-reddened flux maps of several individual emission lines and of diagnostic line ratios. we estimate physical properties of the orion nebula, using the emission line ratios [n ii] and [s iii] (for the electron temperature te) and [s ii] and [cl iii] (for the electron density ne), and show 2d images of the velocity measured from several bright emission lines. data products are available at http://muse-vlt.eu/sciencebased on observations made with eso telescopes at the la silla paranal observatory under program id 60.a-9100(a). | a muse map of the central orion nebula (m 42) |
aims: long gamma-ray bursts (lgrbs) are associated with the deaths of massive stars and might therefore be a potentially powerful tool for tracing cosmic star formation. however, especially at low redshifts (z< 1.5) lgrbs seem to prefer particular types of environment. our aim is to study the host galaxies of a complete sample of bright lgrbs to investigate the effect of the environment on grb formation.methods: we studied host galaxy spectra of the swift/bat6 complete sample of 14 z< 1 bright lgrbs. we used the detected nebular emission lines to measure the dust extinction, star formation rate (sfr), and nebular metallicity (z) of the hosts and supplemented the data set with previously measured stellar masses m⋆. the distributions of the obtained properties and their interrelations (e.g. mass-metallicity and sfr-m⋆ relations) are compared to samples of field star-forming galaxies.results: we find that lgrb hosts at z< 1 have on average lower sfrs than if they were direct star formation tracers. by directly comparing metallicity distributions of lgrb hosts and star-forming galaxies, we find a good match between the two populations up to 12 +log ≤ft( frac{ohright)} 8.4-8.5, after which the paucity of metal-rich lgrb hosts becomes apparent. the lgrb host galaxies of our complete sample are consistent with the mass-metallicity relation at similar mean redshift and stellar masses. the cutoff against high metallicities (and high masses) can explain the low sfr values of lgrb hosts. we find a hint of an increased incidence of starburst galaxies in the swift/bat6 z< 1 sample with respect to that of a field star-forming population. given that the sfrs are low on average, the latter is ascribed to low stellar masses. nevertheless, the limits on the completeness and metallicity availability of current surveys, coupled with the limited number of lgrb host galaxies, prevents us from investigating more quantitatively whether the starburst incidence is such as expected after taking into account the high-metallicity aversion of lgrb host galaxies. based on observations at eso, program ids: 077.d-0425, 177.a-0591, 080.d-0526, 081.a-0856, 082.d-0276, 083.d-0069, 084.a-0303, 084.a-0260, 086.a-0644, 086.b-0954, 089.a-0868, 090.a-0760, 095.d-0560.the reduced spectra are available in the eso archive as phase 3 data products and in the gtc archive. | are long gamma-ray bursts biased tracers of star formation? clues from the host galaxies of the swift/bat6 complete sample of bright lgrbs. ii. star formation rates and metallicities at z < 1 |
context. extended filamentary hα emission nebulae are a striking feature of nearby galaxy clusters but the formation mechanism of the filaments, and the processes which shape their morphology remain unclear.aims: we conduct an investigation into the formation, evolution and destruction of dense gas in the centre of a simulated, perseus-like, cluster under the influence of a spin-driven jet. the jet is powered by the supermassive black hole (smbh) located in the cluster's brightest cluster galaxy. we particularly study the role played by condensation of dense gas from the diffuse intracluster medium, and the impact of direct uplifting of existing dense gas by the jets, in determining the spatial distribution and kinematics of the dense gas.methods: we present a hydrodynamical simulation of an idealised perseus-like cluster using the adaptive mesh refinement code ramses. our simulation includes a smbh that self-consistently tracks its spin evolution via its local accretion, and in turn drives a large-scale jet whose direction is based on the black hole's spin evolution. the simulation also includes a live dark matter (dm) halo, a smbh free to move in the dm potential, star formation and stellar feedback.results: we show that the formation and destruction of dense gas is closely linked to the smbh's feedback cycle, and that its morphology is highly variable throughout the simulation. while extended filamentary structures readily condense from the hot intra-cluster medium, they are easily shattered into an overly clumpy distribution of gas during their interaction with the jet driven outflows. condensation occurs predominantly onto infalling gas located 5-15 kpc from the centre during quiescent phases of the central agn, when the local ratio of the cooling time to free fall time falls below 20, i.e. when tcool/tff < 20.conclusions: we find evidence for both condensation and uplifting of dense gas, but caution that purely hydrodynamical simulations struggle to effectively regulate the cluster cooling cycle and produce overly clumpy distributions of dense gas morphologies, compared to observation. | dense gas formation and destruction in a simulated perseus-like galaxy cluster with spin-driven black hole feedback |
a review of the properties of the tarantula nebula (30 doradus) in the large magellanic cloud is presented, primarily from the perspective of its massive star content. the proximity of the tarantula and its accessibility to x-ray through radio observations permit it to serve as a rosetta stone amongst extragalactic supergiant hii regions since one can consider both its integrated characteristics and the individual properties of individual massive stars. recent surveys of its high mass stellar content, notably the vlt flames tarantula survey (vfts), are reviewed, together with vlt/muse observations of the central ionizing region ngc 2070 and hst/stis spectroscopy of the young dense cluster r136, provide a near complete hertzsprung-russell diagram of the region, and cumulative ionizing output. several high mass binaries are highlighted, some of which have been identified from a recent x-ray survey. brief comparisons with the stellar content of giant hii regions in the milky way (ngc 3372) and small magellanic cloud (ngc 346) are also made, together with green pea galaxies and star forming knots in high-z galaxies. finally, the prospect of studying massive stars in metal poor galaxies is evaluated. | massive stars in the tarantula nebula: a rosetta stone for extragalactic supergiant hii regions |
a recent survey of the inner 0.35 × 0.35 pc of the ngc 2024 star-forming region revealed two distinct millimetre continuum disc populations that appear to be spatially segregated by the boundary of a dense cloud. the eastern (and more embedded) population is ~0.2-0.5 myr old, with an alma mm continuum disc detection rate of about $45\,$ per cent. however, this drops to only $\sim 15\,$ per cent in the 1-myr western population. when these distinct populations were presented, it was suggested that the two main uv sources, irs 1 (a b0.5v star in the western region) and irs 2b (an o8v star in the eastern region, but embedded) have both been evaporating the discs in the depleted western population. in this paper, we report the firm discovery in archival hst data of four proplyds and four further candidate proplyds in ngc 2024, confirming that external photoevaporation of discs is occurring. however, the locations of these proplyds changes the picture. only three of them are in the depleted western population and their evaporation is dominated by irs 1, with no obvious impact from irs 2b. the other five proplyds are in the younger eastern region and being evaporated by irs 2b. we propose that both populations are subject to significant external photoevaporation, which happens throughout the region wherever discs are not sufficiently shielded by the interstellar medium. the external photoevaporation and severe depletion of mm grains in the 0.2-0.5 myr eastern part of ngc 2024 would be in competition even with very early planet formation. | proplyds in the flame nebula ngc 2024 |
we present optical and near-infrared (nir) observations of the type icn supernova (sn icn) 2022ann, the fifth member of its newly identified class of sne. its early optical spectra are dominated by narrow carbon and oxygen p-cygni features with absorption velocities of ~800 km s-1; slower than other sne icn and indicative of interaction with a dense, h/he-poor circumstellar medium (csm) that is outflowing slower than typical wolf-rayet wind velocities of >1000 km s-1. we identify helium in nir spectra 2 weeks after maximum and in optical spectra at 3 weeks, demonstrating that the csm is not fully devoid of helium. unlike other sne icn, the spectra of sn 2022ann never develop broad features from sn ejecta, including in the nebular phase. compared to other sne icn, sn 2022ann has a low luminosity (o-band absolute magnitude of ~-17.7), and evolves slowly. the bolometric light curve is well-modelled by 4.8 m⊙ of sn ejecta interacting with 1.3 m⊙ of csm. we place an upper limit of 0.04 m⊙ of 56ni synthesized in the explosion. the host galaxy is a dwarf galaxy with a stellar mass of 107.34 m⊙ (implied metallicity of log(z/z⊙) ≈ 0.10) and integrated star-formation rate of log (sfr) = -2.20 m⊙ yr-1; both lower than 97 per cent of galaxies observed to produce core-collapse supernovae, although consistent with star-forming galaxies on the galaxy main sequence. the low csm velocity, nickel and ejecta masses, and likely low-metallicity environment disfavour a single wolf-rayet progenitor star. instead, a binary companion is likely required to adequately strip the progenitor and produce a low-velocity outflow. | sn 2022ann: a type icn supernova from a dwarf galaxy that reveals helium in its circumstellar environment |
nebular he ii λ4686 å line emission is useful to unveil active galactic nuclei (agn) residing in actively star-forming (sf) galaxies, typically missed by the standard bpt classification. here, we adopt the he ii diagnostic to identify hidden agn in the local universe using for the first time spatially resolved data from the data release 15 of the mapping nearby galaxies at apo survey (manga dr15). by combining results from he ii and bpt diagnostics, we overall select 459 agn host candidates (~10 per cent in manga dr15), out of which 27 are identified as agn by the he ii diagram only. the he ii-only agn population is hosted by massive (m* ≳ 1010 m⊙) sf main sequence galaxies and on average less luminous than the bpt-selected agn. given the he ii line faintness, we revisit our census accounting for incompleteness effects due to the he ii sensitivity limit of manga. we thus obtain an overall increased fraction (11 per cent) of agn in manga compared to the bpt-only census (9 per cent), which further increases to 14 per cent for galaxies more massive than 1010 m⊙; interestingly, on the sf main sequence the increase is by about a factor of 2. a substantial number of agn in sf galaxies points to significant, coeval star formation and black hole accretion, consistently with results from hydrodynamical simulations and with important implications on quenching scenarios. in view of exploring unprecedented high redshifts with jwst and new ground-based facilities, revisiting the standard bpt classification through novel emission-line diagnostics is fundamental to discover agn in highly sf environments. | unveiling hidden active nuclei in manga star-forming galaxies with he ii λ4686 line emission |
we demonstrate how the stellar and nebular conditions in star-forming galaxies modulate the emission and spectral profile of h i ly α emission line. we examine the net ly α output, kinematics, and in particular emission of blueshifted ly α radiation, using spectroscopy from with the cosmic origins spectrograph on hubble space telescope (hst), giving a sample of 87 galaxies at redshift z = 0.05-0.44. we contrast the ly α spectral measurements with properties of the ionized gas (from optical spectra) and stars (from stellar modelling). we demonstrate correlations of unprecedented strength between the ly α escape fraction (and equivalent width) and the ionization parameter (p ≈ 10-15). the relative contribution of blueshifted emission to the total ly α also increases from ≈0 to ≈40 per cent over the range of o32 ratios (p ≈ 10-6). we also find particularly strong correlations with estimators of stellar age and nebular abundance, and weaker correlations regarding thermodynamic variables. low ionization stage absorption lines suggest the ly α emission and line profile are predominantly governed by the column of absorbing gas near zero velocity. simultaneous multiparametric analysis over many variables shows we can predict 80 per cent of the variance on ly α luminosity, and ~50 per cent on the ew. we determine the most crucial predictive variables, finding that for tracers of the ionization state and h β luminosity dominate the luminosity prediction whereas the ly α ew is best predicted by h β ew and the h α/h β ratio. we discuss our results with reference to high-redshift observations, focussing upon the use of ly α to probe the nebular conditions in high-z galaxies and cosmic reionization. | spectral shapes of the ly α emission from galaxies - ii. the influence of stellar properties and nebular conditions on the emergent ly α profiles |
as a novel x-ray focusing technology, lobster-eye micropore optics (mpo) feature both a wide observing field of view and true imaging capability, promising sky monitoring with significantly improved sensitivity and spatial resolution in soft x-rays. since first proposed by angel, the optics have been extensively studied, developed and trialed over the past decades. in this letter, we report on the first-light results from a flight experiment of the lobster eye imager for astronomy, a pathfinder of the wide-field x-ray telescope of the einstein probe mission. the piggyback imager, launched in 2022 july, has a mostly unvignetted field of view of 18.°6 × 18.°6. its spatial resolution is in the range of 4'-7' in fwhm and the focal spot effective area is 2-3 cm2, both showing only mild fluctuations across the field of view. we present images of the galactic center region, sco x-1, and the diffuse cygnus loop nebular taken in snapshot observations over 0.5-4 kev. these are truly wide-field x-ray images of celestial bodies observed, for the first time, by a focusing imaging telescope. initial analyses of the in-flight data show excellent agreement between the observed images and the on-ground calibration and simulations. the instrument and its characterization are briefly described, as well as the flight experiment. the results provide a solid basis for the development of the present and proposed wide-field x-ray missions using lobster-eye mpo. | first wide field-of-view x-ray observations by a lobster-eye focusing telescope in orbit |
context. white dwarfs are nowadays routinely used as reliable cosmochronometers, allowing several stellar populations to be dated.aims: we present new white dwarf evolutionary sequences for low-metallicity progenitors. this is motivated by the recent finding that residual h burning in low-mass white dwarfs resulting from z = 0.0001 progenitors is the main energy source over a significant part of their evolution.methods: white dwarf sequences have been derived from full evolutionary calculations that take the entire history of progenitor stars into account, including the thermally pulsing and the post-asymptotic giant branch (agb) phases.results: we show that for progenitor metallicities in the range 0.00003 ≲ z ≲ 0.001, and in the absence of carbon enrichment from the occurrence of a third dredge-up episode, the resulting h envelope of the low-mass white dwarfs is thick enough to make stable h burning the most important energy source even at low luminosities. this has a significant impact on white dwarf cooling times. this result is independent of the adopted mass-loss rate during the thermally-pulsing and post-agb phases and in the planetary nebulae stage.conclusions: we conclude that in the absence of third dredge-up episodes, a significant part of the evolution of low-mass white dwarfs resulting from low-metallicity progenitors is dominated by stable h burning. our study opens the possibility of using the observed white dwarf luminosity function of low-metallicity globular clusters to constrain the efficiency of third dredge up episodes during the thermally-pulsing agb phase of low-metallicity progenitors. | white dwarf evolutionary sequences for low-metallicity progenitors: the impact of third dredge-up |
the traditional picture of post-starburst galaxies as dust- and gas-poor merger remnants, rapidly transitioning to quiescence, has been recently challenged. unexpected detections of a significant interstellar medium (ism) in many post-starburst galaxies raise important questions. are they truly quiescent, and if so, what mechanisms inhibit further star formation? what processes dominate their ism energetics? we present an infrared spectroscopic and photometric survey of 33 e+a post-starbursts selected by the sloan digital sky survey, aimed at resolving these questions. we find compact, warm dust reservoirs with high pah abundances and total gas and dust masses significantly higher than expected from stellar recycling alone. both polycyclic aromatic hydrocarbon (pah)/total infrared (tir) and dust-to-burst stellar mass ratios are seen to decrease with post-burst age, indicative of the accumulating effects of dust destruction and an incipient transition to hot, early-type ism properties. their infrared spectral properties are unique, with dominant pah emission, very weak nebular lines, unusually strong h2 rotational emission, and deep [c ii] deficits. there is substantial scatter among star formation rate (sfr) indicators, and both pah and tir luminosities provide overestimates. even as potential upper limits, all tracers show that the sfr has typically experienced a decline of more than two orders of magnitude since the starburst and that the sfr is considerably lower than expected given both their stellar masses and molecular gas densities. these results paint a coherent picture of systems in which star formation was, indeed, rapidly truncated, but in which the ism was not completely expelled, and is instead supported against collapse by latent or continued injection of turbulent or mechanical heating. the resulting aging burst populations provide a “high-soft” radiation field that seemingly dominates the e+a galaxies’ unusual ism energetics. | after the fall: the dust and gas in e+a post-starburst galaxies |
aims: we present a spectroscopic study of a sample of 287 planetary nebulas (pns) around the brightest cluster galaxy (bcg) m 87 in virgo a, of which 211 are located between 40 kpc and 150 kpc from the galaxy centre. with these data we can distinguish the stellar halo from the co-spatial intracluster light (icl) and study both components separately.methods: we obtained pn velocities with a high resolution flames/vlt survey targeting eight fields in a total area of ~0.4 deg2. we identified pns from their narrow and symmetric redshifted λ5007 å [oiii] emission line, the presence of the second λ4959 å [oiii] emission line, and the absence of significant continuum. we implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify pns associated with the m 87 halo and icl. using photometric magnitudes, we construct pn luminosity functions (pnlfs), which are complete down to m5007 = 28.8.results: the velocity distribution of the spectroscopically confirmed pns is bimodal, containing a narrow component centred on the systemic velocity of the bcg and an off-centred broader component, which we identify as halo and icl, respectively. we find that 243 pns are part of the velocity distribution of the m 87 halo, while the remaining subsample of 44 pns are intracluster pns (icpns). halo and icpns have different spatial distributions: the number density of halo pns follow the galaxy's surface brightness profile, whereas the icpns are characterised by a shallower power-law profile, iicl ∝ rγ with γ in the range [-0.34, -0.04 ]. no evidence is found for an asymmetry in the halo and icpn density distributions when the nw and se fields are studied separately. a study of the composite pn number density profile confirms the superposition of different pn populations associated with the m 87 halo and the icl, characterised by different pn specific numbers α. we derive αhalo = 1.06 × 10-8npn l⊙,bol-1 and αicl = 2.72 × 10-8npn l⊙,bol-1, respectively. the m 87 halo pnlf has fewer bright pns and a steeper slope towards faint magnitudes than the icpnlf, and both are steeper than the standard pnlf for the m 31 bulge. moreover, the icpnlf has a dip at ~1-1.5 mag fainter than the bright cut-off, reminiscent of the pnlfs of systems with extended star formation history, such as m 33 or the magellanic clouds.conclusions: the bcg halo of m 87 and the virgo icl are dynamically distinct components with different density profiles and velocity distributions. moreover, the different α-parameter values and pnlf shapes of the halo and icl indicate distinct parent stellar populations, consistent with the existence of a gradient towards bluer colours at large radii. these results reflect the hierarchical build-up of the virgo cluster. based on observations made with the vlt at paranal observatory under programs 088.b-0288(a) and 093.b-066(a), and with the subaru telescope under program s10a-039. | the outer regions of the giant virgo galaxy m 87 kinematic separation of stellar halo and intracluster light |
star-forming galaxies form a sequence in the [o iii] λ5007/{{h}}β versus [n ii] λ6584/{{h}}α diagnostic diagram, with low-metallicity, highly ionized galaxies falling in the upper left corner. drawing from a large sample of uv-selected star-forming galaxies at z∼ 2 with rest-frame optical nebular emission line measurements from keck-mosfire, we select the extreme ∼5% of the galaxies lying in this upper left corner, requiring log([n ii]/{{h}}α ) ≤slant -1.1 and log([o iii]/{{h}}β ) ≥slant 0.75. these cuts identify galaxies with 12+{log}({{o/h}})≲ 8.0, when oxygen abundances are measured via the o3n2 diagnostic. we study the {ly}α properties of the resulting sample of 14 galaxies. the mean (median) rest-frame {ly}α equivalent width is 39 (36) å, and 11 of the 14 objects (79%) are {ly}α emitters (laes) with {w}{lyα } \gt 20 \mathring{{a}} . we compare the equivalent width distribution of a sample of 522 uv-selected galaxies at 2.0\lt z\lt 2.6 identified without regard to their optical line ratios; this sample has mean (median) {ly}α equivalent width -1 (-4) å, and only 9% of these galaxies qualify as laes. the extreme galaxies typically have lower attenuation at {ly}α than those in the comparison sample and have ∼50% lower median oxygen abundances. both factors are likely to facilitate the escape of {ly}α : in less dusty galaxies {ly}α photons are less likely to be absorbed during multiple scatterings, while the harder ionizing spectrum and higher ionization parameter associated with strong, low-metallicity star formation may reduce the covering fraction or column density of neutral hydrogen, further easing {ly}α escape. the use of nebular emission line ratios may prove useful in the identification of galaxies with low opacity to {ly}α photons across a range of redshifts. based on data obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and the national aeronautics and space administration and was made possible by the generous financial support of the w. m. keck foundation. | a high fraction of lyα emitters among galaxies with extreme emission line ratios at z ~2 |
a new class of faint, spectroscopically peculiar transients has emerged in the last decade. we term these events “calcium-strong transients” (casts) because of their atypically high calcium-to-oxygen nebular line ratios. previous studies have struggled to deduce the identity of their progenitors, due to a combination of their extremely extended radial distributions with respect to their host galaxies and their relatively high rate of occurrence. in this work, we find that the cast radial distribution is consistent with the radial distribution of two populations of stars: old (ages >5 gyr), low-metallicity (z/z ⊙ < 0.3) stars, and globular clusters. while no obvious progenitor scenario arises from considering old, metal-poor stars, the alternative production site of globular clusters leads us to narrow down the list of possible candidates to three binary scenarios: mergers of helium and oxygen/neon white dwarfs; tidal disruptions of helium white dwarfs by neutron stars; and stable accretion from low-mass helium-burning stars onto white dwarfs. while rare in the field, these binary systems can be formed dynamically at much higher rates in globular clusters. subsequent binary hardening both increases their interaction rate and ejects them from their parent globular clusters prior to mass transfer contact. their production in, and ejection from, globular clusters may explain their radial distribution and the absence of globular clusters at their explosion site. this model predicts a currently undiscovered high rate of casts in nuclear star clusters. alternatively, an undetermined progenitor scenario involving old, low-metallicity stars may instead hold the key to understanding casts. | the progenitors of calcium-strong transients |
we analyse maps of the spatially resolved nebular emission of ≈1500 star-forming galaxies at z ≈ 0.6-2.2 from deep k-band multi-object spectrograph and muse observations to measure the average shape of their rotation curves. we use these to test claims for declining rotation curves at large radii in galaxies at z ≈ 1-2 that have been interpreted as evidence for an absence of dark matter. we show that the shape of the average rotation curves, and the extent to which they decline beyond their peak velocities, depends upon the normalization prescription used to construct the average curve. normalizing in size by the galaxy stellar disc-scale length after accounting for seeing effects (rd^' }), we construct stacked position-velocity diagrams that trace the average galaxy rotation curve out to 6rd^' } (≈13 kpc, on average). combining these curves with average h i rotation curves for local systems, we investigate how the shapes of galaxy rotation curves evolve over ≈10 gyr. the average rotation curve for galaxies binned in stellar mass, stellar surface mass density and/or redshift is approximately flat, or continues to rise, out to at least 6rd^' }. we find a trend between the outer slopes of galaxies' rotation curves and their stellar mass surface densities, with the higher surface density systems exhibiting flatter rotation curves. drawing comparisons with hydrodynamical simulations, we show that the average shapes of the rotation curves for our sample of massive, star-forming galaxies at z ≈ 0-2.2 are consistent with those expected from lambda cold dark matter theory and imply dark matter fractions within 6rd of at least ≈60 per cent. | the shapes of the rotation curves of star-forming galaxies over the last ≈10 gyr |
newly born, rapidly spinning magnetars have been invoked as the power sources of superluminous transients, including the class of “fast blue optical transients” (fbots). the extensive multiwavelength analysis of at2018cow, the first fbot discovered in real time, is consistent with the magnetar scenario and offers an unprecedented opportunity to comprehend the nature of these sources and assess their broader implications. using at2018cow as a prototype, we investigate high-energy neutrino and cosmic-ray production from fbots and the more general class of superluminous supernovae (slsne). by calculating the interaction of cosmic rays and the time-evolving radiation field and baryon background, we find that particles accelerated in the magnetar wind may escape the ejecta at ultrahigh energies. the predicted high-energy neutrino fluence from at2018cow is below the sensitivity of the icecube observatory, and estimates of the cosmically integrated neutrino flux from fbots are consistent with the extreme-high-energy upper limits posed by icecube. high-energy γ rays exceeding gev energies are obscured for the first months to years by thermal photons in the magnetar nebula, but are potentially observable at later times. given their potentially higher volumetric rate compared to other engine-powered transients (e.g., slsne and gamma-ray bursts), we conclude that fbots are favorable targets for current and next-generation multimessenger observatories. | multimessenger implications of at2018cow: high-energy cosmic-ray and neutrino emissions from magnetar-powered superluminous transients |
we present optical spectra of nine galactic h ii regions observed with the 10.4 m gran telescopio canarias telescope and located at galactocentric distances (rg) from 4 to 8 kpc. the distances of the objects have been revised using gaia dr2 parallaxes. we determine the electron temperature for all the nebulae, which allows a precise computation of their ionic abundances. we have included published data of an additional sample of galactic h ii regions, providing a final data set of 42 objects. the shape of the radial gradients of o/h and n/h is linear and constant, discarding any substantial change of the slope, at least for rg between 4 and 17 kpc. the small dispersion of the o/h and n/h values with respect to the computed gradients imply the absence of significant azimuthal variations of the chemical abundances, at least in the quadrant covered by our observations. we find an almost flat n/o versus o/h diagram relation. this result is not observed in other nearby spiral galaxies except m31. finally, we compare our computed gradients with those obtained using far-infrared (fir) spectra. we confirm the significant offset in the n/o distribution between the optical and fir observations. possible explanations involve ionization correction factors and the strong dependence on density of the abundance determinations based on fir lines. | on the radial abundance gradients of nitrogen and oxygen in the inner galactic disc |
we present extensive observations of sn 2018zd covering the first ∼450 d after the explosion. this sn shows a possible shock-breakout signal ∼3.6 h after the explosion in the unfiltered light curve, and prominent flash-ionization spectral features within the first week. the unusual photospheric temperature rise (rapidly from ∼12 000 to above 18 000 k) within the earliest few days suggests that the ejecta were continuously heated. both the significant temperature rise and the flash spectral features can be explained by the interaction of the sn ejecta with the massive stellar wind ( $0.18^{+0.05}_{-0.10}\, \rm m_{\odot }$ ), which accounts for the luminous peak ( $l_{\rm max} = [1.36\pm 0.63] \times 10^{43}\, \rm erg\, s^{-1}$ ) of sn 2018zd. the luminous peak and low expansion velocity (v ≈ 3300 km s-1) make sn 2018zd like a member of the llev (luminous sne ii with low expansion velocities) events originating due to circumstellar interaction. the relatively fast post-peak decline allows a classification of sn 2018zd as a transition event morphologically linking sne iip and sne iil. in the radioactive-decay phase, sn 2018zd experienced a significant flux drop and behaved more like a low-luminosity sn iip both spectroscopically and photometrically. this contrast indicates that circumstellar interaction plays a vital role in modifying the observed light curves of sne ii. comparing nebular-phase spectra with model predictions suggests that sn 2018zd arose from a star of $\sim 12\, \rm m_{\odot }$ . given the relatively small amount of 56ni ( $0.013\!-\!0.035 \rm m_{\odot }$ ), the massive stellar wind, and the faint x-ray radiation, the progenitor of sn 2018zd could be a massive asymptotic giant branch star that collapsed owing to electron capture. | sn 2018zd: an unusual stellar explosion as part of the diverse type ii supernova landscape |
using the nanten2 observatory, we carried out a molecular-line study of high-mass star forming regions with reflection nebulae, ngc 2068 and ngc 2071, in orion in the $^{13}$ co( $j = 2$ -1) transition. the $^{13}$ co distribution shows that there are two velocity components at ${9.0}$ and ${10.5}\:$ km $\:$ s $^{-1}$ . the blue-shifted component is in the northeast associated with ngc 2071, whereas the red-shifted component is in the southwest associated with ngc 2068. the total intensity distribution of the two clouds shows a gap of $\sim\!\! 1\:$ pc, suggesting that they are detached at present. a detailed spatial comparison indicates that the two show complementary distributions. the blue-shifted component lies toward an intensity depression to the northwest of the red-shifted component, where we find that a displacement of ${0.8}\:$ pc makes the two clouds fit well with each other. furthermore, a new simulation of non-frontal collisions shows that observations from $60^\circ$ off the collisional axis agreed well with the velocity structure in this region. on the basis of these results, we hypothesize that the two components collided with each other at a projected relative velocity of ${3.0}\:$ km $\:$ s $^{-1}$ . the timescale of the collision is estimated to be ${0.3}\:$ myr for an assumed axis of the relative motion $60^\circ$ off the line of sight. we assume that the two most massive early b-type stars in the cloud, illuminating stars of the two reflection nebulae, were formed by collisional triggering at the interfaces between the two clouds. given the other young high-mass star-forming regions, namely, m 42, m 43, and ngc 2024 (fukui et al. 2018a, apj, 859, 166; ohama et al. 2017, arxiv: 1706.05652), it seems possible that collisional triggering has been independently working to form o-type and early b-type stars in orion in the last myr over a projected distance of ∼80 pc. | high-mass star formation in orion possibly triggered by cloud-cloud collision. iii. ngc 2068 and ngc 2071 |
it is widely believed that super-eddington accretion flow can produce powerful outflow, but where does this originate and how much mass and energy are carried away in which directions? to answer these questions, we perform a new large-box, two-dimensional radiation hydrodynamic simulation, paying special attention lest the results should depend on the adopted initial and boundary conditions. we achieve a quasi-steady state at an unprecedentedly large range, r = 2-600rs (with rs being the schwarzschild radius), from the black hole. the accretion rate onto the central 10 m⊙ black hole is $\dot{m}_{\rm bh} \sim 180 l_{\rm edd}/c^{2}$ , whereas the mass outflow rate is ${\dot{m}}_{\rm outflow} \sim 24 l_{\rm edd}/c^2$ (where ledd and c are the eddington luminosity and the speed of light, respectively). the ratio ${\dot{m}}_{\rm outflow}/{\dot{m}}_{\rm bh} \sim 0.14$ is much less than previously reported. by careful inspection we find that most of the outflowing gas reaching the outer boundary originates from the region at r ≲ 140rs, while gas at 140-230rs forms failed outflow. therefore, significant outflow occurs inside the trapping radius ∼450rs. the mechanical energy flux (or mass flux) reaches its maximum in the direction of ∼15° (∼80°) from the rotation axis. the total mechanical luminosity is lmec ∼ 0.16ledd, while the isotropic x-ray luminosity varies from $l_{\rm x}^{\rm iso}\sim 2.9 l_{\rm edd}$ (for a face-on observer) to ∼2.1ledd (for a nearly edge-on observer). the power ratio is $l_{\rm mec}/l_{\rm x}^{\rm iso}\sim 0.05$ -0.08, in good agreement with observations of ultra-luminous x-ray sources surrounded by optical nebulae. | the origins and impact of outflow from super-eddington flow |
at least one in five of all planetary nebulae are the product of a common envelope (ce) interaction, where the companion in-spirals into the envelope of an asymptotic giant branch (agb) star ejecting the nebula and leaving behind a compact binary. in this work we carry out 3d smoothed particle hydrodynamics simulations of the ce interaction between a 1.7 m⊙ agb star and a 0.6 m⊙ companion. we model the agb structure using a 1d stellar model taken at the seventh thermal pulse. the interaction takes place when the giant is on the expanding phase of the seventh thermal pulse and has a radius of 250 r⊙. the post-ce orbital separations varies between 20 and 31 r⊙, with the inclusion of recombination energy resulting in wider separations. based on the observed short in-spiral time-scales, we suggest that thermal pulses can trigger ces, extending the ability of agb stars to capture companions into ces, that would lead to the prediction of a larger population of post-agb, post-ce binaries. simulations that include a tabulated equation of state unbind a great deal more gas, likely unbinding the entire envelope on short time-scales. the shape of the ce after the in-spiral is more spherical for agb than red giant branch stars, and even more so if recombination energy is included. we expect that the planetary nebula formed from this ce will have different features compared to those formed from red giant branch stars. | common envelope binary interaction simulations between a thermally pulsating agb star and a low mass companion |
hydrogen and deuterium isotopic evidence indicates that the source of terrestrial water was mostly meteorites, with additional influx from nebula gas during accretion. there are two earth models, with large (7-12 ocean masses) and small (1-4 ocean masses) water budgets that can explain the geochemical, cosmochemical, and geological observations. geophysical and mineral physics data indicate that the upper and lower mantles are generally dry, whereas the mantle transition zone is wetter, with heterogeneous water distribution. subducting slabs are a source of water influx, and there are three major sites of deep dehydration: the base of the upper mantle, and the top and bottom of the lower mantle in addition to slabs in the shallow upper mantle. hydrated regions surround these dehydration sites. the core may be a hidden reservoir of hydrogen under the large water budget model. earth is a water planet. where and when was water delivered, and how much? how does water circulate in earth? this review looks at the current answers to these fundamental questions. | hydration and dehydration in earth's interior |
context. models of the young solar nebula assume a hot initial disk in which most volatiles are in the gas phase. water emission arising from within 50 au radius has been detected around low-mass embedded young stellar objects. the question remains whether an actively accreting disk is warm enough to have gas-phase water up to 50 au radius. no detailed studies have yet been performed on the extent of snowlines in an accreting disk embedded in a dense envelope (stage 0).aims: we aim to quantify the location of gas-phase volatiles in the inner envelope and disk system for an actively accreting embedded disk.methods: two-dimensional physical and radiative transfer models were used to calculate the temperature structure of embedded protostellar systems. heating due to viscous accretion was added through the diffusion approximation. gas and ice abundances of h2o, co2, and co were calculated using the density-dependent thermal desorption formulation.results: the midplane water snowline increases from 3 to ~55 au for accretion rates through the disk onto the star between 10-9-10-4m⊙ yr-1. co2 can remain in the solid phase within the disk for ṁ ≤ 10-5m⊙ yr-1 down to ~20 au. most of the co is in the gas phase within an actively accreting disk independent of disk properties and accretion rate. the predicted optically thin water isotopolog emission is consistent with the detected h218o emission toward the stage 0 embedded young stellar objects, originating from both the disk and the warm inner envelope (hot core). an accreting embedded disk can only account for water emission arising from r< 50 au, however, and the extent rapidly decreases for ṁ ≤ 10-5m⊙ yr-1. thus, the radial extent of the emission can be measured with future alma observations and compared to this 50 au limit.conclusions: volatiles such as h2o, co2, co, and the associated complex organics sublimate out to 50 au in the midplane of young disks and, thus, can reset the chemical content inherited from the envelope in periods of high accretion rates (>10-5m⊙ yr-1). a hot young solar nebula out to 30 au can only have occurred during the deeply embedded stage 0, not during the t tauri phase of our early solar system. appendices are available in electronic form at http://www.aanda.org | volatile snowlines in embedded disks around low-mass protostars |
context. we have modelled the abundance distribution and ir emission of the first 3 members of the coronene family in the north-west photodissociation region of the well-studied reflection nebulae ngc 7023.aims: our aim was 3-fold: i) analyze the distribution of abundances; (ii) examine the spectral footprints from the hydrogenation state of polycyclic aromatic hydrocarbons (pahs); and (iii) assess the role of pahs in the formation of h2 in photodissociation regions.methods: to model the physical conditions inside the cloud, we used the meudon pdr code, and we gave this as input to our kinetic model. we used specific molecular properties for each pah, based on the latest data available at the present time. we considered the loss of an h atom or an h2 molecule as multiphoton processes, and we worked under the premise that pahs with extra h atoms can form h2 through an eley-rideal abstraction mechanism.results: in terms of abundances, we can distinguish clear differences with pah size. the smallest pah, coronene (c24h12), is found to be easily destroyed down to the complete loss of all of its h atoms. the largest species circumcircumcoronene (c96h24), is found in its normal hydrogenated state. the intermediate size molecule, circumcoronene (c54h18), shows an intermediate behaviour with respect to the other two, where partial dehydrogenation is observed inside the cloud. regarding spectral variations, we find that the emission spectra in ngc 7023 are dominated by the variation in the ionization of the dominant hydrogenation state of each species at each point inside the cloud. it is difficult to "catch" the effect of dehydrogenation in the emitted pah spectra since, for any conditions, only pahs within a narrow size range will be susceptible to dehydrogenation, being quickly stripped off of all h atoms (and may isomerize to cages or fullerenes). the 3 μm region is the most sensitive one towards the hydrogenation level of pahs.conclusions: based on our results, we conclude that pahs with extra h atoms are not the carriers of the 3.4 μm band observed in ngc 7023, since these species are only found in very benign environments. finally, concerning the role of pahs in the formation of h2 in photodissociation regions, we find that h2 abstraction from pahs with extra h atoms is an inefficient process compared to grains. instead, we propose that photodissociation of pahs of small-to-intermediate sizes could contribute to h2 formation in pdr surfaces, but they cannot account by themselves for the inferred high h2 formation rates in these regions. | hydrogenation and dehydrogenation of interstellar pahs: spectral characteristics and h2 formation |
we present the discovery of a slowly evolving, extragalactic radio transient, first j141918.9+394036, identified by comparing a catalog of radio sources in nearby galaxies against new observations from the very large array sky survey. analysis of other archival data shows that first j141918.9+394036 faded by a factor of ∼50 over 23 years, from a flux of ∼26 mjy at 1.4 ghz in 1993 to an upper limit of 0.4 mjy at 3 ghz in 2017. first j141918.9+394036 is likely associated with the small star-forming galaxy sdss j141918.81+394035.8 at a redshift z = 0.01957 (d = 87 mpc), which implies a peak luminosity νlν≳ 3 × 1038 erg s-1. if interpreted as an isotropic synchrotron blast wave, the source requires an explosion of kinetic energy ∼1051 erg some time prior to our first detection in late 1993. this explosion is most likely associated with a long gamma-ray burst (grb), but the radio source could also be interpreted as the nebula of a newly born magnetar. the radio discovery of either of these phenomena would be unprecedented. joint consideration of the event light curve, host galaxy, lack of a counterpart grb, and volumetric rate suggests that first j141918.9+394036 is the afterglow of an off-axis (“orphan”) long grb. the long time baseline of this event offers the best available constraint in afterglow evolution as the bulk of shock-accelerated electrons become non-relativistic. the proximity, age, and precise localization of first j141918.9+394036 make it a key object for understanding the aftermath of rare classes of stellar explosion. | discovery of the luminous, decades-long, extragalactic radio transient first j141918.9+394036 |
context. the vela ob2 association is a group of ∼10 myr stars exhibiting a complex spatial and kinematic substructure. the all-sky gaia dr2 catalogue contains proper motions, parallaxes (a proxy for distance), and photometry that allow us to separate the various components of vela ob2.aims: we characterise the distribution of the vela ob2 stars on a large spatial scale, and study its internal kinematics and dynamic history.methods: we make use of gaia dr2 astrometry and published gaia-eso survey data. we apply an unsupervised classification algorithm to determine groups of stars with common proper motions and parallaxes.results: we find that the association is made up of a number of small groups, with a total current mass over 2330 m⊙. the three-dimensional distribution of these young stars trace the edge of the gas and dust structure known as the iras vela shell across ∼180 pc and shows clear signs of expansion.conclusions: we propose a common history for vela ob2 and the iras vela shell. the event that caused the expansion of the shell happened before the vela ob2 stars formed, imprinted the expansion in the gas the stars formed from, and most likely triggered star formation. the movie associated to fig. 6 is available at https://www.aanda.orgselected young stars from photometry and their membership probability are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/621/a115 | a ring in a shell: the large-scale 6d structure of the vela ob2 complex |
to what degree the cluster environment influences the sizes of protoplanetary disks surrounding young stars is still an open question. this is particularly true for the short-lived clusters typical for the solar neighborhood, in which the stellar density and therefore the influence of the cluster environment change considerably over the first 10 myr. in previous studies, the effect of the gas on the cluster dynamics has often been neglected this is remedied here. using the code nbody6++, we study the stellar dynamics in different developmental phases—embedded, expulsion, and expansion—including the gas, and quantify the effect of fly-bys on the disk size. we concentrate on massive clusters (m cl ≥ 103-6 ∗ 104 m sun), which are representative for clusters like the orion nebula cluster (onc) or ngc 6611. we find that not only the stellar density but also the duration of the embedded phase matters. the densest clusters react fastest to the gas expulsion and drop quickly in density, here 98% of relevant encounters happen before gas expulsion. by contrast, disks in sparser clusters are initially less affected, but because these clusters expand more slowly, 13% of disks are truncated after gas expulsion. for onc-like clusters, we find that disks larger than 500 au are usually affected by the environment, which corresponds to the observation that 200 au-sized disks are common. for ngc 6611-like clusters, disk sizes are cut-down on average to roughly 100 au. a testable hypothesis would be that the disks in the center of ngc 6611 should be on average ≈20 au and therefore considerably smaller than those in the onc. | cluster dynamics largely shapes protoplanetary disk sizes |
context. we wish to improve our understanding of the orion central star formation region (orion-kl) and disentangle its complexity.aims: we collected data with alma during cycle 2 in 16 ghz of total bandwidth spread between 215.1 and 252.0 ghz with a typical sensitivity of 5 mjy/beam (2.3 mjy/beam from 233.4 to 234.4 ghz) and a typical beam size of 1.̋7 × 1.̋0 (average position angle of 89°). we produced a continuum map and studied the emission lines in nine remarkable infrared spots in the region including the hot core and the compact ridge, plus the recently discovered ethylene glycol peak.methods: we present the data, and report the detection of several species not previously seen in orion, including n- and i-propyl cyanide (c3h7cn), and the tentative detection of a number of other species including glycolaldehyde (ch2(oh)cho). the first detections of ggg' ethylene glycol (ggg' (ch2oh)2) and of acetic acid (ch3cooh) in orion are presented in a companion paper. we also report the possible detection of several vibrationally excited states of cyanoacetylene (hc3n), and of its 13c isotopologues. we were not able to detect the 16o18o line predicted by our detection of o2 with herschel, due to blending with a nearby line of vibrationally excited ethyl cyanide. we do not confirm the tentative detection of hexatriynyl (c6h) and cyanohexatriyne (hc7n) reported previously, or of hydrogen peroxide (h2o2) emission.results: we report a complex velocity structure only partially revealed before. components as extreme as -7 and +19 km s-1 are detected inside the hot region. thanks to different opacities of various velocity components, in some cases we can position these components along the line of sight. we propose that the systematically redshifted and blueshifted wings of several species observed in the northern part of the region are linked to the explosion that occurred ~500 yr ago. the compact ridge, noticeably farther south displays extremely narrow lines (~1 km s-1) revealing a quiescent region that has not been affected by this explosion. this probably indicates that the compact ridge is either over 10 000 au in front of or behind the rest of the region.conclusions: many lines remain unidentified, and only a detailed modeling of all known species, including vibrational states of isotopologues combined with the detailed spatial analysis offered by alma enriched with zero-spacing data, will allow new species to be detected. this paper makes use of the following alma data: ads/jao.alma#2013.1.00533.s. alma is a partnership of eso (representing its member states), nsf (usa) and nins (japan), together with nrc (canada), nsc and asiaa (taiwan), and kasi (republic of korea), in cooperation with the republic of chile. the joint alma observatory is operated by eso, aui/nrao and naoj. the reduced alma data cubes as listed in table 1 are available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/604/a32 | the complexity of orion: an alma view. i. data and first results |
copper isotope compositions in cu-bearing metals and minerals have been measured by deep (194 nm) ultraviolet femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (uv-fsla-mc-icp-ms). pure cu-metal, brass, and several cu-rich minerals (chalcopyrite, enargite, covellite, malachite and cuprite) have been investigated. a long-term reproducibility of better than 0.08‰ at the 95% confidence limit on the nist srm 976 (national institute of standards and technology) cu-metal standard has been achieved with this technique. the δ65cu values for all samples have been calculated by standard-sample-standard bracketing with nist srm 976. all analyses have been carried out using ni as a mass discrimination monitor added by nebulization prior to entering the plasma torch. for further verification samples have been analysed by conventional solution nebulization mc-icp-ms and the results obtained have been compared with those from uv-fsla-mc-icp-ms. several potential matrix-induced molecular interferences on the mineral copper isotope ratio, such as (32s33s)+ and (32s-16o17o)+ do not affect the cu isotope measurements on sulfides, while hydrides, such as zn-h or doubly-charged sn2 + that interfere ni isotopes can be either neglected or stripped by calculation. matrix independent cu-isotope measurements are sensitive to the energy density (fluence) applied onto the sample and can produce artificial shifts in the obtained δ65cu values which are on the order of 3‰ for cu-metal, 0.5‰ for brass and 0.3‰ for malachite when using energy density of up to 2 j/cm2 for ablation. a positive correlation between applied energy density and the magnitude of the isotope ratio shift has been found in the energy density range from 0.2 to 1.3 j/cm2 which is below the ablation threshold for ns-laser ablation. the results demonstrate that by using appropriate low fluence it is possible to measure cu isotopic ratios in native copper and cu-bearing sulfides, carbonates and oxides in situ with a precision of better than 0.1‰ (2sd) without using a matrix-matched standard during laser ablation analyses. thus, this is a suitable tool to resolve cu isotopic zoning larger than 0.1‰ in cu-sulfides, carbonates and oxides. | matrix and energy effects during in-situ determination of cu isotope ratios by ultraviolet-femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry |
aims. we investigate the role of photo-evaporation of dust exposed to the radiation field from hot young stars and planetary nebulae (pne) as a possible destruction mechanism of dust grains in the interstellar medium (ism). methods. we estimate photo-evaporation induced by the feedback of individual or clustered young stars, of pne and in the presence of a variable radiation field scaled with the interstellar radiation field. for pne we investigate dust photo-evaporation of both dust grains already present in the ism as well as those formed in the last phases of the evolution of thermally pulsing asymptotic giant branch (tp-agb) stars. we include dust photo-evaporation rate in models of dust evolution in galaxies for different assumptions of the dust growth scenario, dust-to-gas ratios, star formation histories, and initial mass functions of the stars. results. for all the cases considered, we find that both photo-evaporation from young stars and from pne are negligible with respect to other dust removal processes such as destruction from supernovae shocks, astration and possibly outflow. grains are stable against photo-evaporation if they are exposed to a radiation field which is up to 10^7 times the interstellar radiation field. conclusions. dust grains of size >= 0.01 microns are not efficiently destroyed by photo-evaporation also in the presence of a strong radiation field. | dust survival in harsh environments -- is photo-evaporation an important destruction mechanism? |
the build up of heavy elements and the stellar mass assembly are fundamental processes in the formation and evolution of galaxies. although they have been extensively studied through observations and simulations, the key elements that govern these processes, such as gas accretion and outflows, are not fully understood. this is especially true for luminous and massive galaxies, which usually suffer strong feedback in the form of massive outflows, and large-scale gas accretion triggered by galaxy interactions. for a sample of 77 luminous infrared (ir) galaxies, we derive chemical abundances using new diagnostics based on nebular ir lines, which peer through the dusty medium of these objects and allow us to include the obscured metals in our abundance determinations. in contrast to optical-based studies, our analysis reveals that most luminous ir galaxies remain close to the mass-metallicity relation. nevertheless, four galaxies with extreme star-formation rates ($> 60$m$_{\odot }$yr$^{-1}$) in their late merger stages show heavily depressed metallicities of 12+log(o/h) $\sim 7.7$--$8.1$ along with solar-like n/o ratios, indicative of gas mixing processes affecting their chemical composition. this evidence suggests the action of a massive infall of metal-poor gas in a short phase during the late merger stages, eventually followed by a rapid enrichment. these results challenge the classical gas equilibrium scenario usually applied to main-sequence galaxies, suggesting that the chemical enrichment and stellar-mass growth in luminous ir galaxies are regulated by different processes. | merger-driven infall of metal-poor gas in luminous infrared galaxies: a deep dive beneath the mass-metallicity relation |
during the first four all-sky surveys erass:4 carried out from december 2019 to 2021, the extended roentgen survey with an imaging telescope array (erosita) on board spektrum-roentgen-gamma (spektr-rg, srg) observed the galactic hii region carina nebula. we analysed the erass:4 data to study the distribution and the spectral properties of the hot interstellar plasma and the bright stellar sources in the carina nebula. spectral extraction regions of the diffuse emission were defined based on x-ray spectral morphology and multi-wavelength data. the spectra were fit with a combination of thermal and non-thermal emission models. x-ray bright point sources in the carina nebula are the colliding wind binary $\eta$ car, several o stars, and wolf-rayet (wr) stars. we extracted the spectrum of the brightest stellar sources, which can be well fit with a multi-component thermal plasma model. the spectra of the diffuse emission in the brighter parts of the carina nebula is well reproduced by two thermal models, a lower-temperature component ($\sim$0.2 kev) and a higher-temperature component (0.6 - 0.8 kev). an additional non-thermal component dominates the emission above $\sim$1 kev in the central region around $\eta$ car and the other massive stars. significant orbital variation of the x-ray flux was measured for $\eta$ car, wr22 and wr25. $\eta$ car requires an additional time-variable thermal component in the spectral model, which is associated to the wind-wind-collision zone. properties like temperature, pressure, and luminosity of the x-ray emitting plasma in the carina nebula derived from the erosita data are consistent with theoretical calculations of emission from superbubbles. it confirms that the x-ray emission is caused by the hot plasma inside the carina nebula which has been shocked-heated by the stellar winds of the massive stars, in particular, of $\eta$ car. | erosita studies of the carina nebula |
high-resolution spectroscopy of the core of the perseus cluster of galaxies, using the hitomi satellite above 2 kev and the xmm-newton reflection grating spectrometer at lower energies, provides reliable constraints on the abundances of o, ne, mg, si, s, ar, ca, cr, mn, fe, and ni. accounting for all known systematic uncertainties, the ar/fe, ca/fe, and ni/fe ratios are determined with a remarkable precision of less than 10 per cent, while the constraints on si/fe, s/fe, and cr/fe are at the 15 per cent level, and mn/fe is measured with a 20 per cent uncertainty. the average biases in determining the chemical composition using archival ccd spectra from xmm-newton and suzakutypically range from 15 to 40 per cent. a simple model in which the enrichment pattern in the perseus cluster core and the protosolar nebula are identical gives a surprisingly good description of the high-resolution x-ray spectroscopy results, with χ2 = 10.7 for 10 degrees of freedom. however, this pattern is challenging to reproduce with linear combinations of existing supernova nucleosynthesis calculations, particularly given the precise measurements of intermediate α-elements enabled by hitomi. we discuss in detail the degeneracies between various supernova progenitor models and explosion mechanisms, and the remaining uncertainties in these theoretical models. we suggest that including neutrino physics in the core-collapse supernova yield calculations may improve the agreement with the observed pattern of α-elements in the perseus cluster core. our results provide a complementary benchmark for testing future nucleosynthesis calculations required to understand the origin of chemical elements. | constraints on the chemical enrichment history of the perseus cluster of galaxies from high-resolution x-ray spectroscopy |
we present ultraviolet, optical, and near-infrared observations of sn 2012ap, a broad-lined type ic supernova in the galaxy ngc 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. photometry and spectroscopy follow the flux evolution from -13 to +272 days past the b-band maximum of -17.4 ± 0.5 mag. the spectra are dominated by fe ii, o i, and ca ii absorption lines at ejecta velocities of v ≈ 20,000 km s-1 that change slowly over time. other spectral absorption lines are consistent with contributions from photospheric he i, and hydrogen may also be present at higher velocities (v >~ 27,000 km s-1). we use these observations to estimate explosion properties and derive a total ejecta mass of ~2.7 m ⊙, a kinetic energy of ~1.0 × 1052 erg, and a 56ni mass of 0.1-0.2 m ⊙. nebular spectra (t > 200 days) exhibit an asymmetric double-peaked [o i] λλ6300, 6364 emission profile that we associate with absorption in the supernova interior, although toroidal ejecta geometry is an alternative explanation. sn 2012ap joins sn 2009bb as another exceptional supernova that shows evidence for a central engine (e.g., black hole accretion or magnetar) capable of launching a non-negligible portion of ejecta to relativistic velocities without a coincident gamma-ray burst detection. defining attributes of their progenitor systems may be related to notable observed properties including environmental metallicities of z >~ z ⊙, moderate to high levels of host galaxy extinction (e(b - v) > 0.4 mag), detection of high-velocity helium at early epochs, and a high relative flux ratio of [ca ii]/[o i] >1 at nebular epochs. these events support the notion that jet activity at various energy scales may be present in a wide range of supernovae. | the broad-lined type ic sn 2012ap and the nature of relativistic supernovae lacking a gamma-ray burst detection |
we present nirspec ifs observations of a galaxy group around the massive gs_4891 galaxy at z=3.7 in goods-south that includes two other two systems, gs_4891_n to the north and gs_28356 to the east. these observations, obtained as part of the gto ga-nifs program, allow for the first time to study the spatially resolved properties of the interstellar medium (ism) and ionized gas kinematics of a galaxy at this redshift. leveraging the wide wavelength range spanned with the high-dispersion grating (with resolving power r=2700) observations, covering from [oii]$\lambda$$\lambda$3726,29 to [sii]$\lambda$$\lambda$6716,31, we explore the spatial distribution of star-formation rate, nebular attenuation and gas metallicity, together with the mechanisms responsible for the excitation of the ionized gas. gs_4891 presents a clear gradient of gas metallicity (as traced by 12 + log(o/h)) by more than 0.2dex from the south-east (where a star-forming clump is identified) to the north-west. the gas metallicity in the less-massive northern system, gs_4891_n, is also higher by 0.2 dex than at the center of gs_4891, suggesting that inflows of lower-metallicity gas might be favoured in higher-mass systems. the kinematic analysis shows that gs_4891 presents velocity gradients in the ionized gas consistent with rotation. the region between gs_4891 and gs_4891_n does not present high gas turbulence which, together with the difference in gas metallicities, suggests that these two systems might be in a pre-merger stage. finally, gs_4891 hosts an ionized outflow that extends out to r_out=1.2 kpc from the nucleus and reaches maximum velocities v_out of approximately 400 km/s. despite entraining an outflowing mass rate of m_out$\sim$2msun/yr, the low associated mass-loading factor, $\eta$=0.05, implies that the outflow does not have a significant impact on the star-formation activity of the galaxy. | ga-nifs: co-evolution within a highly star-forming galaxy group at z=3.7 witnessed by jwst/nirspec ifs |
we present nebular spectroscopy of sn 2020hvf, a type ia supernova (sn ia) with an early bump in its light curve. sn 2020hvf shares many spectroscopic and photometric similarities to the carbon-rich high-luminosity "03fg-like" sne ia. at >240 days after peak brightness, we detect unambiguous emission from [ca ii] λ λ7291, 7324, which is rarely observed in normal sne ia and only seen in peculiar subclasses. sn 2020hvf displays "sawtooth" emission profiles near 7300 å that cannot be explained with single symmetric velocity components of [fe ii], [ni ii], and [ca ii], indicating an asymmetric explosion. the broad [ca ii] emission is best modeled by two velocity components offset by 1220 km s-1, which could be caused by ejecta associated with each star in the progenitor system, separated by their orbital velocity. for the first time in an sn ia, we identify narrow (fwhm = 180 ± 40 km s-1) [ca ii] emission, which we associate with a wind from a surviving, puffed-up companion star. few published spectra have sufficient resolution and the signal-to-noise ratio necessary to detect similar narrow [ca ii] emission; however, we have detected similar line profiles in other 03fg-like sne ia. the extremely narrow velocity width of [ca ii] has only otherwise been observed in sne iax at late times. since this event likely had a double-degenerate "super-chandrasekhar" mass progenitor system, we suggest that a single white dwarf (wd) was fully disrupted and a wind from a surviving companion wd is producing the observed narrow emission. it is unclear whether this unique progenitor and explosion scenario can explain the diversity of 03fg-like sne ia, potentially indicating that multiple progenitor channels contribute to this subclass. | an asymmetric double-degenerate type ia supernova explosion with a surviving companion star |
we present results from daily monitoring of gamma-rays in the energy range from ∼0.5 to ∼100 tev with the first 17 months of data from the high altitude water cherenkov (hawc) observatory. its wide field of view of 2 steradians and duty cycle of > 95% are unique features compared to other tev observatories that allow us to observe every source that transits over hawc for up to ∼6 hr each sidereal day. this regular sampling yields unprecedented light curves from unbiased measurements that are independent of seasons or weather conditions. for the crab nebula as a reference source, we find no variability in the tev band. our main focus is the study of the tev blazars markarian (mrk) 421 and mrk 501. a spectral fit for mrk 421 yields a power-law index {{γ }}=2.21+/- {0.14}{stat}+/- {0.20}{sys} and an exponential cut-off {e}0=5.4+/- {1.1}{stat}+/- {1.0}{sys} tev. for mrk 501, we find an index {{γ }}=1.60+/- {0.30}{stat}+/- {0.20}{sys} and exponential cut-off {e}0=5.7+/- {1.6}{stat}+/- {1.0}{sys} tev. the light curves for both sources show clear variability and a bayesian analysis is applied to identify changes between flux states. the highest per-transit fluxes observed from mrk 421 exceed the crab nebula flux by a factor of approximately five. for mrk 501, several transits show fluxes in excess of three times the crab nebula flux. in a comparison to lower energy gamma-ray and x-ray monitoring data with comparable sampling, we cannot identify clear counterparts for the most significant flaring features observed by hawc. | daily monitoring of tev gamma-ray emission from mrk 421, mrk 501, and the crab nebula with hawc |
recently, frb 190520b, which has the largest extragalactic dispersion measure (dm), was discovered by the five-hundred-meter aperture spherical radio telescope (fast). the dm excess over the intergalactic medium and galactic contributions is estimated as ~900 pc cm-3, which is nearly ten times higher than that of other fast-radio-burst (frb) host galaxies. the dm decreases with the rate ~0.1 pc cm-3 per day. it is the second frb associated with a compact persistent radio source (prs). the rotation measure (rm) is found to be larger than 1.8 × 105rad m-2. in this letter, we argue that frb 190520b is powered by a young magentar formed by core collapse of massive stars, embedded in a composite of a magnetar wind nebula (mwn) and supernova remnant (snr). the energy injection of the magnetar drives the mwn and sn ejecta to evolve together and the prs is generated by the synchrotron radiation of the mwn. the magnetar has an interior magnetic field b int ~ (2-4) × 1016 g and an age t age ~ 14-22 yr. the dense sn ejecta and the shocked shell contribute a large fraction of the observed dm and rm. our model can naturally and simultaneously explain the luminous prs, decreasing dm, and extreme rm of frb 190520b. | frb 190520b embedded in a magnetar wind nebula and supernova remnant: a luminous persistent radio source, decreasing dispersion measure, and large rotation measure |
context. the andromeda (m 31) galaxy displays several substructures in its inner halo. different simulations associate their origin with either a single relatively massive merger, or with a larger number of distinct, less massive accretions.aims: the origin of these substructures as remnants of accreted satellites or perturbations of the pre-existing disc would be encoded in the properties of their stellar populations (sps). the metallicity and star formation history of these distinct populations leave traces on their deep [o iii] 5007 å planetary nebulae luminosity function (pnlf). by characterizing the morphology of the pnlfs, we constrain their origin.methods: from our 54 sq. deg. deep narrow-band [o iii] survey of m 31, we identify planetary nebulae in six major inner-halo substructures: the giant stream, north east shelf, g1 clump, northern clump, western shelf, and stream d. we obtain their pnlfs and those in two disc annuli, with galactocentric radii of rgc = 10-20 kpc and rgc = 20-30 kpc. we measure pnlf parameters from cumulative fits and statistically compare the pnlfs in each substructure and disc annulus. we link these deep pnlf parameters and those for the large magellanic cloud (lmc) to published metallicities and resolved stellar population-age measurements for their parent sps.results: the absolute magnitudes (m*) of the pnlf bright cut-off for these sub-populations span a significant magnitude range, despite being located at the same distance and having a similar line-of-sight extinction. the m* values of the giant stream, w shelf, and stream d pnlfs are fainter than those predicted by pn evolution models by 0.6, 0.8, and 1.5 mag, respectively, assuming the measured metallicity of the parent stellar populations. the faint-end slope of the pnlf increases linearly with decreasing fraction of stellar mass younger than 5 gyr across the m 31 regions and the lmc. from their pnlfs, the giant stream and ne shelf are consistent with being stellar debris from an infalling satellite, while the g1 clump appears to be linked with the pre-merger disc with an additional contribution from younger stars.conclusions: the sps of the substructures are consistent with those predicted by simulations of a single fairly massive merger event that took place 2-3 gyr ago in m31. stream d has an unrelated, distinct origin. furthermore, this study provides independent evidence that the faint-end of the pnlf is preferentially populated by planetary nebulae evolved from older stars. | the survey of planetary nebulae in andromeda (m 31). iii. constraints from deep planetary nebula luminosity functions on the origin of the inner halo substructures in m 31 |
planetary nebulae—the ejected envelopes of red giant stars—provide us with a history of the last, mass-losing phases of 90% of stars initially more massive than the sun. here we analyse images of the planetary nebula ngc 3132 from the james webb space telescope (jwst) early release observations. a structured, extended hydrogen halo surrounding an ionized central bubble is imprinted with spiral structures, probably shaped by a low-mass companion orbiting the central star at about 40-60 au. the images also reveal a mid-infrared excess at the central star, interpreted as a dusty disk, which is indicative of an interaction with another closer companion. including the previously known a-type visual companion, the progenitor of the ngc 3132 planetary nebula must have been at least a stellar quartet. the jwst images allow us to generate a model of the illumination, ionization and hydrodynamics of the molecular halo, demonstrating the power of jwst to investigate complex stellar outflows. furthermore, new measurements of the a-type visual companion allow us to derive the value for the mass of the progenitor of a central star with excellent precision: 2.86 ± 0.06 m⊙. these results serve as pathfinders for future jwst observations of planetary nebulae, providing unique insight into fundamental astrophysical processes including colliding winds and binary star interactions, with implications for supernovae and gravitational-wave systems. | the messy death of a multiple star system and the resulting planetary nebula as observed by jwst |
context. recent jwst observations of the type ia supernova (sn ia) 2021aefx in the nebular phase have paved the way for late-time studies covering the full optical to mid-infrared (mir) wavelength range, and with it the hope to better constrain sn ia explosion mechanisms.aims: we investigate whether public sn ia models covering a broad range of progenitor scenarios and explosion mechanisms (chandrasekhar-mass, or mch, delayed detonations, pulsationally assisted gravitationally confined detonations, sub-mch double detonations, and violent mergers) can reproduce the full optical-mir spectrum of sn 2021aefx at ∼270 days post explosion.methods: we consider spherically averaged 3d models available from the heidelberg supernova model archive with a 56ni yield in the range 0.5-0.8 m⊙. we performed 1d steady-state non-local thermodynamic equilibrium simulations with the radiative-transfer code cmfgen, and compared the predicted spectra to sn 2021aefx.results: the models can explain the main features of sn 2021aefx over the full wavelength range. however, no single model, or mechanism, emerges as a preferred match, and the predicted spectra are similar to each other despite the very different explosion mechanisms. we discuss possible causes for the mismatch of the models, including ejecta asymmetries and ionisation effects. our new calculations of the collisional strengths for ni iii have a major impact on the two prominent lines at 7.35 μm and 11.00 μm, and highlight the need for more accurate collisional data for forbidden transitions. using updated atomic data, we identify a strong feature due to [ca iv] 3.21 μm, attributed to [ni i] in previous studies. we also provide a tentative identification of a forbidden line due to [ne ii] 12.81 μm, whose peaked profile indicates the presence of neon all the way to the innermost region of the ejecta, as predicted for instance in violent merger models. contrary to previous claims, we show that the [ar iii] 8.99 μm line can be broader in sub-mch models compared to near-mch models. last, the total luminosity in lines of ni is found to correlate strongly with the stable nickel yield, although ionisation effects can bias the inferred abundance.conclusions: our models suggest that key physical ingredients are missing from either the explosion models, or the radiative-transfer post-processing, or both. nonetheless, they also show the potential of the near- and mir to uncover new spectroscopic diagnostics of sn ia explosion mechanisms. full tables f.1 and f.2 are available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/678/a170 | nebular spectra from type ia supernova explosion models compared to jwst observations of sn 2021aefx |
ultra-high-energy (uhe, >0.1 pev) γ-ray astronomy is rapidly evolving into an expanding branch of γ-ray astronomy with the surprising discovery of 12 pevatrons and the detection of a handful of photons above 1 pev. nearly all known celestial object types that have emissions in the tev band are found also to emit uhe photons. uhe γ-rays have a well-defined horizon inside our galaxy due to the absorption of infrared and cosmic microwave backgrounds in the universe. in the last 30 years, traditional cosmic ray (cr) measurement techniques have enabled the detection of uhe γ-rays and opened the last observation window. for leptonic sources, uhe radiation is in the deep klein-nishina regime, which is largely suppressed. therefore, uhe γ-ray detection will be helpful in locating and identifying hadronic radiation sources, tracing the historic pursuit for the origin of crs around the knee of the spectrum. the crab nebula is the focus of attention with measured photon emissions up to 1 pev. in the absence of hadronic processes, these emissions may indicate the existence of an extreme accelerator of e+e-. use of cr extensive air shower detection techniques broadens the field of view of the source observations, enabling measurement of uhe radiation surrounding the sources. these observations can probe the particle propagation inside and outside the accelerators and the subsequent injection/escape into the interstellar medium. | ultra-high-energy gamma-ray astronomy |
the infrared spectrograph (irs) on the spitzer space telescope observed nearly 800 point sources in the large magellanic cloud (lmc), taking over 1000 spectra. 197 of these targets were observed as part of the sage-spec spitzer legacy program; the remainder are from a variety of different calibration, guaranteed time and open time projects. we classify these point sources into types according to their infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, using a decision-tree classification method. we then refine the classification using supplementary information from the astrophysical literature. we find that our irs sample is comprised substantially of yso and h ii regions, post-main-sequence low-mass stars: (post-)asymptotic giant branch stars and planetary nebulae and massive stars including several rare evolutionary types. two supernova remnants, a nova and several background galaxies were also observed. we use these classifications to improve our understanding of the stellar populations in the lmc, study the composition and characteristics of dust species in a variety of lmc objects, and to verify the photometric classification methods used by mid-ir surveys. we discover that some widely used catalogues of objects contain considerable contamination and others are missing sources in our sample. | the sage-spec spitzer legacy program: the life-cycle of dust and gas in the large magellanic cloud. point source classification - iii |
we present an overview and the first data release of zfire, a spectroscopic redshift survey of star-forming galaxies that utilizes the mosfire instrument on keck-i to study galaxy properties in rich environments at 1.5 < z < 2.5. zfire measures accurate spectroscopic redshifts and basic galaxy properties derived from multiple emission lines. the galaxies are selected from a stellar mass limited sample based on deep near infrared imaging ({k}{ab}\lt 25) and precise photometric redshifts from the zfourge and ukidss surveys as well as grism redshifts from 3dhst. between 2013 and 2015, zfire has observed the cosmos and uds legacy fields over 13 nights and has obtained 211 galaxy redshifts over 1.57 < z < 2.66 from a combination of nebular emission lines (such as hα, [n ii], hβ, [o ii], [o iii], and [s ii]) observed at 1-2 μm. based on our medium-band near infrared photometry, we are able to spectrophotometrically flux calibrate our spectra to ∼10% accuracy. zfire reaches 5σ emission line flux limits of ∼3 × 10-18 erg s-1 cm-2 with a resolving power of r = 3500 and reaches masses down to ∼109 m ⊙. we confirm that the primary input survey, zfourge, has produced photometric redshifts for star-forming galaxies (including highly attenuated ones) accurate to {{δ }}z/(1+{z}{spec})=0.015 with 0.7% outliers. we measure a slight redshift bias of <0.001, and we note that the redshift bias tends to be larger at higher masses. we also examine the role of redshift on the derivation of rest-frame colors and stellar population parameters from sed fitting techniques. the zfire survey extends spectroscopically confirmed z ∼ 2 samples across a richer range of environments, here we make available the first public release of the data for use by the community.7 | zfire: a keck/mosfire spectroscopic survey of galaxies in rich environments at z ∼ 2 |
t pyx is one of the most enigmatic recurrent novae, and it has been proposed as a potential galactic type-ia supernova progenitor. using spatially-resolved data obtained with muse, we characterized the geometrical distribution of the material expelled in previous outbursts surrounding the white dwarf progenitor. we used a 3d model for the ejecta to determine the geometric distribution of the extended remnant. we have also calculated the nebular parallax distance ($d = 3.55 \pm 0.77$ kpc) based on the measured velocity and spatial shift of the 2011 bipolar ejecta. these findings confirm previous results, including data from the gaia mission. the remnant of t pyx can be described by a two-component model, consisting of a tilted ring at $i = 63.7$ deg, relative to its normal vector and by fast bipolar ejecta perpendicular to the plane of the equatorial ring. we find an upper limit for the bipolar outflow ejected mass in 2011 of the bipolar outflow of $m_{ej,b} < (3.0 \pm 1.0) \times 10^{-6}$ m$_{\odot}$, which is lower than previous estimates given in the literature. however, only a detailed physical study of the equatorial component could provide an accurate estimate of the total ejecta of the last outburst, a fundamental step to understand if t pyx will end its life as a type-ia supernova. | the physical properties of t pyx as measured by muse i. the geometrical distribution of the ejecta and the distance to the remnant |
the solar nebula contained a number of short-lived radionuclides (slrs) with half-lives of tens of myr or less, comparable to the timescales for formation of protostars and protoplanetary disks. therefore, determining the origins of slrs would provide insights into star formation and the sun's astrophysical birth environment. in this chapter, we review how isotopic studies of meteorites reveal the existence and abundances of these now-extinct radionuclides; and the evidence that the slr ${}^{10}{\rm be}$, which uniquely among the slrs is not produced during typical stellar nucleosynthesis, was distributed homogeneously in the solar nebula. we review the evidence that the slrs ${}^{26}{\rm al}$, ${}^{53}{\rm mn}$, and ${}^{182}{\rm hf}$, and other radionuclides, were also homogeneously distributed and can be used to date events during the solar system's planet-forming epoch. the homogeneity of the slrs, especially ${}^{10}{\rm be}$, strongly suggests they were all inherited from the sun's molecular cloud, and that production by irradiation within the solar nebula was very limited, except for ${}^{36}{\rm cl}$. we review astrophysical models for the origin of ${}^{10}{\rm be}$, showing that it requires that the sun formed in a spiral arm of the galaxy with higher star formation rate than the galaxy-wide average. likewise, we review the astrophysical models for the origins of the other slrs and show that they likely arose from contamination of the sun's molecular cloud by massive stars over tens of myr, most likely dominated by ejecta from wolf-rayet stars. the other slrs also demand formation of the sun in a spiral arm of the galaxy with a star formation rate as high as demanded by the solar system initial ${}^{10}{\rm be}$ abundance. we discuss the astrophysical implications, and suggest further tests of these models and future directions for the field. | short-lived radionuclides in meteorites and the sun's birth environment |
angrites are silica-undersaturated achondrites formed very early in the history of the solar system, and the most volatile-depleted known meteorites. as such, the study of angrites can provide critical insights into the early stages of planetary formation, melting and differentiation. yet, understanding the origins of angrites and the nature of their parent body has long been hindered by the initially small number of specimens available. here, we leverage (i) the rapidly growing number of known angrites, and (ii) equilibrium crystallization experiments at various pressure, temperature and oxygen fugacity conditions (p-t-fo2), to revisit the petrogenesis of angrites and constrain key features of the angrite parent body (apb), such as its composition and size. we observe that quenched (i.e., volcanic) angrites define two compositional groups, which we show are readily related by fractional crystallization. this crystallization trend converges on an olivine-clinopyroxene-plagioclase (ol + cpx + plag) multiple saturation boundary, whose composition is sampled by d'orbigny, sahara 99555 and nwa 1296. using the observation that some quenched specimens represent primitive angritic melts, we derive a self-consistent bulk composition for the apb. we find that this composition matches the proposed mg/si ratio of 1.3 derived from the angrite δ30si values, and yields a core size (18 ± 6 wt%) in agreement with the siderophile elements depletion in the apb mantle. our results support a primary control of nebular fractionation (i.e., partial condensation) on the composition of the apb. to establish the liquid phase equilibria of angrites, a series of 1 atmosphere and high-pressure crystallization experiments (piston cylinder and internally heated pressure vessel) were performed on a synthetic powder of d'orbigny. the results suggest that the apb was a large (possibly moon-sized) body, formed from materials condensed at relatively high-temperature (∼1300-1400 k), and whose fo2 changed from mildly reducing (∼iw-1.5) to relatively oxidizing (∼iw+1 ± 1) in the ∼ 3 myr between its core formation and the crystallization of d'orbigny-like (group 2) angrites. based on its timing of accretion and differentiation, its composition, redox, and size, we argue that the apb represents the archetype of the first-generation of refractory-enriched planetesimals and embryos formed in the innermost part of the inner solar system (<1 au), and which accreted in the telluric planets. | the case for the angrite parent body as the archetypal first-generation planetesimal: large, reduced and mg-enriched |
geophysical and geochemical evidence suggests that earth's core is predominantly made of iron (or iron-nickel alloy) with several percent of light elements. however, earth's solid inner core transmits shear waves at a much lower velocity than expected from mineralogical models that are consistent with geochemical constraints. here we investigate the effect of hydrogen on the elastic properties of iron and iron-silicon alloys using ab initio molecular dynamic simulations. we find that these h-bearing alloys maintain a superionic state under inner-core conditions and that their shear moduli exhibit a strong shear softening due to the superionic effect, with a corresponding reduction in vs. several hcp-iron-silicon-hydrogen compositions can explain the observed density, vp, vs, and poisson's ratio of the inner core simultaneously. our results indicate that hydrogen is a significant component of the earth's core, and that it may contain at least four ocean masses of water. this indicates that the earth may have accreted wet and obtained its water from chondritic and/or nebular materials before or during core formation. | strong shear softening induced by superionic hydrogen in earth's inner core |
the stratospheric observatory for infrared astronomy (sofia) is a boeing 747sp aircraft modified to accommodate a 2.7 meter gyro-stabilized telescope, which is mainly focused to studying the universe at infrared wavelengths. as part of the strategic director's discretionary time (s-ddt) program, sofia performs observations of relevant science cases and immediately offers science-ready data products to the astronomical community. we present the first data release of the s-ddt program on far-infrared imaging polarimetric observations of 30 doradus using the high-resolution airborne wideband camera-plus (hawc+) at 53, 89, 154, and 214 micron. we present the status and quality of the observations, an overview of the sofia data products, and examples of working with hawc+ polarimetric data that will enhance the scientific analysis of this, and future, data sets. these observations illustrate the potential influence of magnetic fields and turbulence in a star-forming region within the tarantula nebula. | sofia community science i: hawc+ polarimetry of 30 doradus |
we model the radiatively driven flow from im lup - a large protoplanetary disc expected to be irradiated by only a weak external radiation field (at least 104 times lower than the ultraviolet field irradiating the orion nebula cluster proplyds). we find that material at large radii (>400 au) in this disc is sufficiently weakly gravitationally bound that significant mass-loss can be induced. given the estimated values of the disc mass and accretion rate, the viscous time-scale is long (∼10 myr) so the main evolutionary behaviour for the first myr of the disc's lifetime is truncation of the disc by photoevaporation, with only modest changes effected by viscosity. we also produce approximate synthetic observations of our models, finding substantial emission from the flow that can explain the co halo observed about im lup out to ≥1000 au. solutions that are consistent with the extent of the observed co emission generally imply that im lup is still in the process of having its disc outer radius truncated. we conclude that im lup is subject to substantial external photoevaporation, which raises the more general possibility that external irradiation of the largest discs can be of significant importance even in low mass star forming regions. | first evidence of external disc photoevaporation in a low mass star forming region: the case of im lup |
the orion complex is a notable star-forming region fragmented into several different populations with substantial differences in their phase space. i propose a model that attempts to explain the how the complex has evolved into this current configuration. in the model presented here, the large-scale expansion can be attributable to a supernova that exploded 6 myr ago. the remnants of this explosion can be seen as barnard's loop, as the center of the expansion is consistent with the geometrical center of the h ii bubble. this is similar to the h ii bubble and the ballistic expansion that is associated with λ ori, a region that was also the site of an ancient supernova. assuming that the orion complex originally formed as one long filament spanning from the bottom of orion a to ψ2 ori (or potentially as far as λ ori), barnard's loop supernova could have split the cloud, which led to the formation of orion c & d. furthermore, the shockwave that propagated into the filament could have swept along the gas through several parsecs, which led to the formation of the singularly most massive cluster in the solar neighborhood, the orion nebula cluster. i also discuss other related nearby events, such as the formation of the monogem ring and various runaways that have been ejected from the orion complex. | supernovae in orion: the missing link in the star-forming history of the region |
we analyze a keck i/low resolution imager and spectrograph nebular spectrum taken 268 days after b-band maximum of asassn-18bt (sn 2018oh), a type ia supernova observed by k2 at the time of explosion. asassn-18bt exhibited a two-component rise to peak brightness, possibly the signature of an interaction between the supernova ejecta and a large (≳20 r ⊙) nearby, non-degenerate companion. we search for emission signatures of stripped material from a non-degenerate companion in the nebular spectrum and find no evidence for any unbound material. we place an upper limit of <0.006 m ⊙ on the amount of stripped/ablated h-rich material that could go undetected in our spectrum, effectively ruling out all hydrogen-rich donor stars. additionally, we place a more tentative upper limit on he i emission in the observed spectrum of ≲0.02 m ⊙ which also rules out helium star companions. our deep limits rule out a non-degenerate companion as the explanation for the early-time feature in asassn-18bt. | no stripped companion material in the nebular spectrum of the “two-component” type ia supernova asassn-18bt |
we present new optical spectra of the nearby, bright, planetary nebula ngc 6778. the nebula has been known to emit strong recombination lines for more than 40 years but this is the first detailed study of its abundances. heavy element abundances derived from recombination lines are found to exceed those from collisionally excited lines by a factor of ∼20 in an integrated spectrum of the nebula, which is among the largest known abundance discrepancy factors. spatial analysis of the spectra shows that the abundance discrepancy factor is strongly, centrally peaked, reaching ∼40 close to the central star. the central star of ngc 6778 is known to be a short-period binary, further strengthening the link between high nebular abundance discrepancy factors and central star binarity. | ngc 6778: strengthening the link between extreme abundance discrepancy factors and central star binarity in planetary nebulae |
recent work suggests that strong emission line, star-forming galaxies (sfgs) may be significant lyman continuum leakers. we combine archival hubble space telescope broadband ultraviolet and optical imaging (f275w and f606w, respectively) with emission line catalogs derived from wfc3 ir g141 grism spectroscopy to search for escaping lyman continuum (lyc) emission from homogeneously selected z ∼ 2.5 sfgs. we detect no escaping lyman continuum from sfgs selected on [o ii] nebular emission (n = 208) and, within a narrow redshift range, on [o iii]/[o ii]. we measure 1σ upper limits to the lyc escape fraction relative to the non-ionizing uv continuum from [o ii] emitters, f esc ≲ 5.6%, and strong [o iii]/[o ii] > 5 elgs, f esc ≲ 14.0%. our observations are not deep enough to detect f esc ∼ 10% typical of low-redshift lyman continuum emitters. however, we find that this population represents a small fraction of the star-forming galaxy population at z ∼ 2. thus, unless the number of extreme emission line galaxies grows substantially to z ≳ 6, such galaxies may be insufficient for reionization. deeper survey data in the rest-frame ionizing uv will be necessary to determine whether strong line ratios could be useful for pre-selecting lyc leakers at high redshift. | the lyman continuum escape fraction of emission line-selected z ∼ 2.5 galaxies is less than 15% |
the extreme, time-variable faraday rotation observed in the repeating fast radio burst (frb) 121102 and its associated persistent synchrotron source demonstrates that some frbs originate in dense, dynamic, and possibly relativistic magneto-ionic environments. besides rotation of the linear polarization vector (faraday rotation), such media can generally convert linear to circular polarization (faraday conversion). we use non-detection of faraday conversion, and the temporal variation in faraday rotation and dispersion in bursts from frb 121102 to constrain models where the progenitor inflates a relativistic nebula (persistent source) confined by a cold dense medium (e.g. supernova ejecta). we find that the persistent synchrotron source, if composed of an electron-proton plasma, must be an admixture of relativistic and non-relativistic (lorentz factor γ < 5) electrons. furthermore, we independently constrain the magnetic field in the cold confining medium, which provides the faraday rotation, to be between 10 and 30 mg. this value is close to the equipartition magnetic field of the confined persistent source implying a self-consistent and overconstrained model that can explain the observations. | faraday conversion and magneto-ionic variations in fast radio bursts |
circumstellar discs are the precursors of planetary systems and develop shortly after their host star has formed. in their early stages, these discs are immersed in an environment rich in gas and neighbouring stars, which can be hostile for their survival. there are several environmental processes that affect the evolution of circumstellar discs, and external photoevaporation is arguably one of the most important ones. theoretical and observational evidence point to circumstellar discs losing mass quickly when in the vicinity of massive, bright stars. in this work, we simulate circumstellar discs in clustered environments in a range of stellar densities, where the photoevaporation mass-loss process is resolved simultaneously with the stellar dynamics, stellar evolution, and the viscous evolution of the discs. our results indicate that external photoevaporation is efficient in depleting disc masses and that the degree of its effect is related to stellar density. we find that a local stellar density lower than 100 stars pc-2 is necessary for discs massive enough to form planets to survive for 2.0 myr. there is an order of magnitude difference in the disc masses in regions of projected density 100 versus 104 stars pc-2. we compare our results to observations of the lupus clouds, the orion nebula cluster, the orion molecular cloud-2, taurus, and ngc 2024, and find that the trends observed between region density and disc masses are similar to those in our simulations. | effects of stellar density on the photoevaporation of circumstellar discs |
the early stages of dynamical evolution of planetary systems are often shaped by dissipative processes that drive orbital migration. in multi-planet systems, convergent amassing of orbits inevitably leads to encounters with rational period ratios, which may result in establishment of mean-motion resonances. the success or failure of resonant capture yields exceedingly different subsequent evolutions, and thus plays a central role in determining the ensuing orbital architecture of planetary systems. in this work, we employ an integrable hamiltonian formalism for first order planetary resonances that allows both secondary bodies to have finite masses and eccentricities, and construct a comprehensive theory for resonant capture. particularly, we derive conditions under which orbital evolution lies within the adiabatic regime, and provide a generalized criterion for guaranteed resonant locking as well as a procedure for calculating capture probabilities when capture is not certain. subsequently, we utilize the developed analytical model to examine the evolution of jupiter and saturn within the protosolar nebula, and investigate the origins of the dominantly non-resonant orbital distribution of sub-jovian extrasolar planets. our calculations show that the commonly observed extrasolar orbital structure can be understood if planet pairs encounter mean-motion commensurabilities on slightly eccentric (e ∼ 0.02) orbits. accordingly, we speculate that resonant capture among low-mass planets is typically rendered unsuccessful due to subtle axial asymmetries inherent to the global structure of protoplanetary discs. | capture of planets into mean-motion resonances and the origins of extrasolar orbital architectures |
the luminosity of young giant planets can inform about their formation and accretion history. the directly imaged planets detected so far are consistent with the `hot-start' scenario of high entropy and luminosity. if nebular gas passes through a shock front before being accreted into a protoplanet, the entropy can be substantially altered. to investigate this, we present high-resolution, three-dimensional radiative hydrodynamic simulations of accreting giant planets. the accreted gas is found to fall with supersonic speed in the gap from the circumstellar disc's upper layers on to the surface of the circumplanetary disc and polar region of the protoplanet. there it shocks, creating an extended hot supercritical shock surface. this shock front is optically thick; therefore, it can conceal the planet's intrinsic luminosity beneath. the gas in the vertical influx has high entropy which when passing through the shock front decreases significantly while the gas becomes part of the disc and protoplanet. this shows that circumplanetary discs play a key role in regulating a planet's thermodynamic state. our simulations furthermore indicate that around the shock surface extended regions of atomic - sometimes ionized - hydrogen develop. therefore, circumplanetary disc shock surfaces could influence significantly the observational appearance of forming gas giants. | thermodynamics of giant planet formation: shocking hot surfaces on circumplanetary discs |
the virgil fossae region on pluto exhibits three spatially coincident properties that are suggestive of recent cryovolcanic activity over an area approximately 300 by 200 km. situated in the fossae troughs or channels and in the surrounding terrain are exposures of h2o ice in which there is entrained opaque red-colored matter of unknown composition. the h2o ice is also seen to carry spectral signatures at 1.65 and 2.2 μm of nh3 in some form, possibly as a hydrate, an ammoniated salt, or some other compound. model calculations of nh3 destruction in h2o ice by galactic cosmic rays suggest that the maximum lifetime of nh3 in the uppermost meter of the exposed surface is 109 years, while considerations of lyman-α ultraviolet and solar wind charged particles suggest shorter timescales by a factor of 10 or 10000. thus, 109 y is taken as an upper limit to the age of the emplacement event, and it could be substantially younger. the red colorant in the ammoniated h2o in virgil fossae and surroundings may be a macromolecular organic material (tholin) thought to give color to much of pluto's surface, but probably different in composition and age. owing to the limited spectral range of the new horizons imaging spectrometer and the signal precision of the data, apart from the h2o and nh3 signatures there are no direct spectroscopic clues to the chemistry of the strongly colored deposit on pluto. we suggest that the colored material was a component of the fluid reservoir from which the material now on the surface in this region was erupted. although other compositions are possible, if it is indeed a complex organic material it may incorporate organics inherited from the solar nebula, further processed in a warm aqueous environment inside pluto. a planet-scale stress pattern in pluto's lithosphere induced by true polar wander, freezing of a putative interior ocean, and surface loading has caused fracturing in a broad arc west of sputnik planitia, consistent with the structure of virgil fossae and similar extensional features. this faulting may have facilitated the ascent of fluid in subsurface reservoirs to reach the surface as flows and as fountains of cryoclastic materials, consistent with the appearance of colored, ammoniated h2o ice deposits in and around virgil fossae. models of a cryoflow emerging from sources in virgil fossae indicate that the lateral extent of the flow can be several km (umurhan et al., 2019). the deposit over the full length (>200 km) of the main trough in the virgil fossae complex and extending through the north rim of elliot crater and varying in elevation over a range of 2.5 km, suggests that it debouched from multiple sources, probably along the length of the strike direction of the normal faults defining the graben. the source or sources of the ammoniated h2o are one or more subsurface reservoirs that may or may not connect to the global ocean postulated for pluto's interior. alternatives to cryovolcanism in producing the observed characteristics of the region around virgil fossae are explored in the discussion section of the paper. | recent cryovolcanism in virgil fossae on pluto |
aims: we present a kinematic study of a sample of 298 planetary nebulas (pns) in the outer halo of the central virgo galaxy m 87 (ngc 4486). the line-of-sight velocities of these pns are used to identify subcomponents, to measure the angular momentum content of the main m 87 halo, and to constrain the orbital distribution of the stars at these large radii.methods: we use gaussian mixture modelling to statistically separate distinct velocity components and identify the m 87 smooth halo component, its unrelaxed substructures, and the intra-cluster (ic) pns. we compute probability weighted velocity and velocity dispersion maps for the smooth halo, and its specific angular momentum profile (λr) and velocity dispersion profile.results: the classification of the pns into smooth halo and icpns is supported by their different pn luminosity functions. based on a kolmogorov-smirnov (k-s) test, we conclude that the icpn line-of-sight velocity distribution (losvd) is consistent with the losvd of the galaxies in virgo subcluster a. the surface density profile of the icpns at 100 kpc radii has a shallow logarithmic slope, -αicl ≃ -0.8, dominating the light at the largest radii. previous b - v colour and resolved star metallicity data indicate masses for the icpn progenitor galaxies of a few ×108 m⊙. the angular momentum-related λr profile for the smooth halo remains below 0.1, in the slow rotator regime, out to 135 kpc average ellipse radius (170 kpc major axis distance). combining the pn velocity dispersion measurements for the m 87 halo with literature data in the central 15 kpc, we obtain a complete velocity dispersion profile out to ravg = 135 kpc. the σhalo profile decreases from the central 400 km s-1 to about 270 km s-1 at 2-10 kpc, then rises again to ≃300 ± 50 km s-1 at 50-70 kpc, to finally decrease sharply to σhalo ∼ 100 km s-1 at ravg = 135 kpc. the steeply decreasing outer σhalo profile and the surface density profile of the smooth halo can be reconciled with the circular velocity curve inferred from assuming hydrostatic equilibrium for the hot x-ray gas. because this rises to νc,x ∼ km s-1 at 200 kpc, the orbit distribution of the smooth m 87 halo is required to change strongly from approximately isotropic within ravg ∼ 60 kpc to very radially anisotropic at the largest distances probed.conclusions: the extended losvd of the pns in the m 87 halo allows the identification of several subcomponents: the icpns, the "crown" accretion event, and the smooth m 87 halo. in galaxies like m 87, the presence of these subcomponents needs to be taken into account to avoid systematic biases in estimating the total enclosed mass. the dynamical structure inferred from the velocity dispersion profile indicates that the smooth halo of m 87 steepens beyond ravg = 60 kpc and becomes strongly radially anisotropic, and that the velocity dispersion profile is consistent with the x-ray circular velocity curve at these radii without non-thermal pressure effects. based on observations made with the vlt at paranal observatory under programmes 088.b-0288(a) and 093.b-066(a), and with the subaru telescope under programme s10a-039.table b.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/620/a111 | kinematics of the outer halo of m 87 as mapped by planetary nebulae⋆ |
planetary embryos form protoplanets via mutual collisions, which can lead to the development of magma oceans. during their solidification, significant amounts of the mantles' volatile contents may be outgassed. the resulting h2o/co2 dominated steam atmospheres may be lost efficiently via hydrodynamic escape due to the low gravity of these moon- to mars-sized objects and the high stellar euv luminosities of the young host stars. protoplanets forming from such degassed building blocks after nebula dissipation could therefore be drier than previously expected. we model the outgassing and subsequent hydrodynamic escape of steam atmospheres from such embryos. the efficient outflow of h drags along heavier species like o, co2, and noble gases. the full range of possible euv evolution tracks of a young solar-mass star is taken into account to investigate the atmospheric escape from mars-sized planetary embryos at different orbital distances. the estimated envelopes are typically lost within a few to a few tens of myr. furthermore, we study the influence on protoplanetary evolution, exemplified by venus. in particular, we investigate different early evolution scenarios and constrain realistic cases by comparing modeled noble gas isotope ratios with present observations. isotope ratios of ne and ar can be reproduced, starting from solar values, under hydrodynamic escape conditions. solutions can be found for different solar euv histories, as well as assumptions about the initial atmosphere, assuming either a pure steam atmosphere or a mixture with accreted hydrogen from the protoplanetary nebula. our results generally favor an early accretion scenario with a small amount of residual hydrogen from the protoplanetary nebula and a low-activity sun, because in other cases too much co2 is lost during evolution, which is inconsistent with venus' present atmosphere. important issues are likely the time at which the initial steam atmosphere is outgassed and/or the amount of co2 which may still be delivered at later evolutionary stages. a late accretion scenario can only reproduce present isotope ratios for a highly active young sun, but then unrealistically massive steam atmospheres (few kbar) would be required. | escape and fractionation of volatiles and noble gases from mars-sized planetary embryos and growing protoplanets |
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