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we present bolometric and broadband light curves and spectra for a suite of core-collapse supernova models exploded self-consistently in spherical symmetry within the push framework. we analyze broad trends in these light curves and categorize them based on morphology. we find that these morphological categories relate simply to the progenitor radius and mass of the hydrogen envelope. we present a proof-of-concept sensitive-variable analysis, indicating that an important determining factor in the properties of a light curve within a given category is 56ni mass. we follow spectra from the photospheric to the nebular phase. these spectra show characteristic iron-line blanketing at short wavelengths and doppler-shifted fe ii and ti ii absorption lines. to enable this analysis, we develop a first-of-its-kind pipeline from a massive progenitor model, through a self-consistent explosion in spherical symmetry, to electromagnetic counterparts. this opens the door to more detailed analyses of the collective properties of these observables. we provide a machine-readable database of our light curves and spectra online at go.ncsu.edu/astrodata. | core-collapse supernovae: from neutrino-driven 1d explosions to light curves and spectra |
pair-instability supernovae (pisne) are very luminous explosions of massive, low-metallicity stars. they can potentially be observed out to high redshifts due to their high explosion energies, thus providing a probe of the universe prior to reionization. the near-infrared camera (nircam) on board the james webb space telescope is ideally suited for detecting their redshifted ultraviolet emission. we calculate the photometric signature of high-redshift pisne and derive the optimal detection strategy for identifying their prompt emission and possible afterglow. we differentiate between pisne and other sources that could have a similar photometric signature, such as active galactic nuclei or high-redshift galaxies. we demonstrate that the optimal strategy, which maximizes the visibility time of the pisn light curve per invested exposure time, consists of the two wide-band filters f200w and f356w with an exposure time of 600 s. for such exposures, we expect one pisn at z ≲ 7.5 per at least 50000 different field of view, which can be accomplished with parallel observations and an extensive archival search. the pisn afterglow, caused by nebular emission and reverberation, is very faint and requires unfeasibly long exposure times to be uniquely identified. however, this afterglow would be visible for several hundred years, about two orders of magnitude longer than the prompt emission, rendering pisne promising targets for future, even more powerful telescopes. | detection strategies for the first supernovae with jwst |
volatiles are vital ingredients for a habitable planet. angrite meteorites sample the most volatile-depleted planetesimal in the solar system, particularly for the alkali elements. they are prime targets for investigating the formation of volatile-poor rocky planets, yet their exceptionally low volatile content presents a major analytical challenge. here, we leverage improved sensitivity and precision of k isotopic analysis to constrain the mechanism of extreme k depletion (>99.8%) in angrites. in contrast with the isotopically heavy moon and vesta, we find that angrites are strikingly depleted in the heavier k isotopes, which is best explained by partial recondensation of vaporized k following extensive evaporation on the angrite parent body (apb) during magma-ocean stage. therefore, the apb may provide a rare example of isotope fractionation controlled by condensation, rather than evaporation, at a planetary scale. furthermore, nebula-wide k isotopic variations primarily reflect volatility-driven fractionations instead of presolar nucleosynthetic heterogeneity proposed previously. | potassium isotope heterogeneity in the early solar system controlled by extensive evaporation and partial recondensation |
intraperitoneal (ip) aerosolized anticancer drug delivery was recently introduced in the treatment of patients with peritoneal metastases. however, little is known on the effect of treatment parameters on the spatial distribution of the aerosol droplets in the peritoneal cavity. here, computational fluid dynamics (cfd) modeling was used in conjunction with experimental validation in order to investigate the effect of droplet size, liquid flow rate and viscosity, and the addition of an electrostatic field on the homogeneity of ip aerosol. we found that spatial distribution is optimal with small droplet sizes (1-5 µm). using the current clinically used technology (droplet size of 30 µm), the optimal spatial distribution of aerosol is obtained with a liquid flow rate of 0.6 ml s−1. compared to saline, nebulization of higher viscosity liquids results in less homogeneous aerosol distribution. the addition of electrostatic precipitation significantly improves homogeneity of aerosol distribution, but no further improvement is obtained with voltages higher than 6.5 kv. the results of the current study will allow to choose treatment parameters and settings in order to optimize spatial distribution of ip aerosolized drug, with a potential to enhance its anticancer effect. | optimization of intraperitoneal aerosolized drug delivery using computational fluid dynamics (cfd) modeling |
the paris meteorite is one of the most primitive carbonaceous chondrites. it is reported to be the least aqueously altered cm chondrite, and to have experienced only weak thermal metamorphism. we have analyzed for the first time the amino acid and hydrocarbon contents of this pristine meteorite by gas chromatography-mass spectrometry (gc-ms). when plotting the relative amino acids abundances of several cm chondrites according to the increasing hydrothermal scale (petrologic subtypes), from the cm2.7/2.8 paris to the cm2.0 met 01070, paris has the lowest relative abundance of β-alanine/glycine (0.15), which fits with the relative abundances of β-alanine/glycine increasing with increasing aqueous alteration for cm chondrites. these results confirm the influence of aqueous alteration on the amino acid abundances and distribution. the amino acid analysis shows that the isovaline detected in this meteorite is racemic (d/l = 0.99 ± 0.08; l-enantiomer excess = 0.35 ± 0.5%; corrected d/l = 1.03; corrected l-enantiomer excess = -1.4 ± 2.6%). the identified hydrocarbons show that paris has n-alkanes ranging from c16 to c25 and 3- to 5-ring nonalkylated polycyclic aromatic hydrocarbons (pahs). the lack of alkylated pahs in paris seems to be also related to this low degree of aqueous alteration on its parent body. the extraterrestrial hydrocarbon content, suggested by the absence of any biomarker, may well have a presolar origin. the chemistry of the paris meteorite may thus be closely related to the early stages of the solar nebula with a contribution from interstellar (molecular cloud) precursors. | the amino acid and hydrocarbon contents of the paris meteorite: insights into the most primitive cm chondrite |
strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. however, different observational setups can affect these lines, and the derivation of the physical nebular properties. we analyze 12 local star-forming galaxies from the cos legacy spectroscopy survey (classy) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. we compare optical spectra observed with the sloan digital sky survey data release aperture, which has a 3″ diameter similar to cos, ifu, and long-slit spectra, including new lbt/mods observations of five classy galaxies. we calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (ews). we find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. however, using ifu observations of three galaxies, we find that the e(b - v) values derived from the balmer ratios decrease (by up to 53%) with increasing aperture size. the values change most significantly in the center of the galaxies, and level out near the cos aperture diameter of 2.″5. we examine the relative contributions from the gas and stars using the hα and [o iii] λ5007 ews as a function of aperture light fraction, but find little to no variations within a given galaxy. these results imply that the optical spectra provide nebular properties appropriate for the far-uv classy spectra, even when narrow 1.″0 long-slit observations are used. | classy v: the impact of aperture effects on the inferred nebular properties of local star-forming galaxies |
context. the age-velocity dispersion relation is an important tool to understand the evolution of the disc of the andromeda galaxy (m 31) in comparison with the milky way.aims: we use planetary nebulae (pne) to obtain the age-velocity dispersion relation in different radial bins of the m 31 disc.methods: we separate the observed pne sample based on their extinction values into two distinct age populations in the m 31 disc. the observed velocities of our high- and low-extinction pne, which correspond to higher- and lower-mass progenitors, respectively, are fitted in de-projected elliptical bins to obtain their rotational velocities, vϕ, and corresponding dispersions, σϕ. we assign ages to the two pn populations by comparing central-star properties of an archival sub-sample of pne, that have models fitted to their observed spectral features, to stellar evolution tracks.results: for the high- and low-extinction pne, we find ages of ∼2.5 and ∼4.5 gyr, respectively, with distinct kinematics beyond a deprojected radius rgc = 14 kpc. at rgc = 17-20 kpc, which is the equivalent distance in disc scale lengths of the sun in the milky way disc, we obtain σϕ, 2.5 gyr = 61 ± 14 km s-1 and σϕ, 4.5 gyr = 101 ± 13 km s-1. the age-velocity dispersion relation for the m 31 disc is obtained in two radial bins, rgc = 14-17 and 17-20 kpc.conclusions: the high- and low-extinction pne are associated with the young thin and old thicker disc of m 31, respectively, whose velocity dispersion values increase with age. these values are almost twice and three times that of the milky way disc stellar population of corresponding ages, respectively. from comparison with simulations of merging galaxies, we find that the age-velocity dispersion relation in the m 31 disc measured using pne is indicative of a single major merger that occurred 2.5-4.5 gyr ago with an estimated merger mass ratio ≈1:5. | the survey of planetary nebulae in andromeda (m 31). ii. age-velocity dispersion relation in the disc from planetary nebulae |
we present mid-infrared photometry of the orion bar obtained with the faint object infrared camera for the sofia telescope (forcast) on board sofia at 6.4, 6.6, 7.7, 19.7, 31.5, and 37.1 μm. by complementing this observation with archival forcast and herschel/pacs images, we are able to construct a complete infrared spectral energy distribution of the huygens region in the orion nebula. comparing the infrared images with gas tracers, we find that pacs maps trace the molecular cloud, while the forcast data trace the photodissociation region (pdr) and the h ii region. analysis of the energetics of the region reveal that the pdr extends for 0.28 pc along the line of sight and that the bar is inclined at an angle of 4°. the infrared and submillimeter images reveal that the orion bar represents a swept-up shell with a thickness of 0.1 pc. the mass of the shell implies a shock velocity of ≃3 km s-1 and an age of ≃105 years for the h ii region. our analysis shows that the uv and infrared dust opacities in the h ii region and the pdr are a factor 5 to 10 lower than in the diffuse interstellar medium. in the ionized gas, lyα photons are a major source of dust heating at distances larger than ≃0.06 pc from θ 1 ori c. dust temperatures can be explained if the size of the grains is between 0.1 and 1 μm. we derive the photoelectric heating efficiency of the atomic gas in the orion bar. the results are in good qualitative agreement with models and the quantitative differences indicate a decreased polycyclic aromatic hydrocarbon abundance in this region. | the orion hii region and the orion bar in the mid-infrared |
calcium-rich gap transients represent an intriguing new class of faint and fast-evolving supernovae that exhibit strong [ca ii] emission in their nebular phase spectra. in this paper, we present the discovery and follow-up observations of a faint and fast-evolving transient, iptf 16hgs, that exhibited a double-peaked light curve. exhibiting a type ib spectrum in the photospheric phase and an early transition to a [ca ii] dominated nebular phase, iptf 16hgs shows properties consistent with the class of ca-rich gap transients, with two important exceptions. first, while the second peak of the light curve is similar to other ca-rich gap transients, the first blue and fast-fading peak (declining over ≈2 days) is unique to this source. second, we find that iptf 16hgs occurred in the outskirts (projected offset of ≈6 kpc ≈ 1.9 r eff) of a low-metallicity (≈0.4 z ⊙), star-forming, dwarf spiral galaxy. deep limits from late-time radio observations suggest a low-density environment for the source. if iptf 16hgs shares explosion physics with the class of ca-rich gap transients, the first peak can be explained by the presence of 0.01 m ⊙ of 56ni in the outer layers the ejecta, reminiscent of some models of he-shell detonations on wds. however, if iptf 16hgs is physically unrelated to the class, the first peak is consistent with shock cooling emission (of an envelope with a mass of ≈0.08 m ⊙ and radius of ≈13 r ⊙) in a core-collapse explosion of a highly stripped massive star in a close binary system. | iptf 16hgs: a double-peaked ca-rich gap transient in a metal-poor, star-forming dwarf galaxy |
we report the detection of diffuse lyα emission, or lyα halos (lahs), around star-forming galaxies at z ≈ 3.78 and 2.66 in the noao deep wide-field survey boötes field. our samples consist of a total of ∼1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. they provide a unique opportunity to investigate how the lah characteristics vary with host galaxy large-scale environment and physical properties. we stack lyα images of different samples defined by these properties and measure their median lah sizes by decomposing the stacked lyα radial profile into a compact galaxy-like and an extended halo-like component. we find that the exponential scale-length of lahs depends on uv continuum and lyα luminosities, but not on lyα equivalent widths or galaxy overdensity parameters. the full samples, which are dominated by low uv-continuum luminosity lyα emitters (m uv ≳ -21), exhibit lah sizes of 5-6 kpc. however, the most uv- or lyα-luminous galaxies have more extended halos with scale-lengths of 7-9 kpc. the stacked lyα radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. however, the lah extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. the observed trends of lah sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, h i column density, and outflow velocity) change with halo mass and/or star formation rates. | the diversity of diffuse lyα nebulae around star-forming galaxies at high redshift |
the massive o4.5 v + o5.5 v binary vfts 352 in the tarantula nebula is one of the shortest-period and most massive overcontact binaries known. recent theoretical studies indicate that some of these systems could ultimately lead to the formation of gravitational waves via black hole binary mergers through the chemically homogeneous evolution pathway. by analyzing ultraviolet-optical phase-resolved spectroscopic data, we aim to constrain atmospheric and wind properties that could be later used to confront theoretical predictions from binary evolution. in particular, surface abundances are powerful diagnostics of the evolutionary status, mass transfer, and internal mixing processes. from a set of 32 very large telescope/flames visual and eight hubble space telescope/cosmic origins spectrograph ultraviolet spectra, we used spectral disentangling to separate the primary and secondary components. using a genetic algorithm wrapped around the nlte model atmosphere and the spectral synthesis code fastwind, we perform an 11-parameter optimization to derive the atmospheric and wind parameters of both components, including the surface abundances of he, c, n, o, and si. we find that both components are hotter than expected compared to single-star evolutionary models, indicating that additional mixing processes may be at play. however, the derived chemical abundances do not show significant indications of mixing when adopting baseline values typical of the system environment. | clues on the origin and evolution of massive contact binaries: atmosphere analysis of vfts 352 |
the first water cherenkov detector of the lhaaso experiment (wcda-1) has been operating since april, 2019. the first 10 months of data have been analyzed to test its performance by observing the crab nebula as a standard candle. the wcda-1 achieves the sensitivity of 65 mcu per year with a statistical threshold of 5 $\sigma$. in order to do so, 97.7\% cosmic ray background rejection rate around 1 tev and 99.8\% around 6 tev with an approximately photon acceptance about 50\% by using the $compactness$ of the shower footprints to be greater than 10 as the discriminator between gamma induced showers and the cosmic ray backgrounds. the angular resolution is measured using the crab nebula as a point source about 0.45$^\circ$ at 1 tev and better than 0.2$^\circ$ above 6 tev with the pointing accuracy better than 0.05$^\circ$. they are all matching the design specifications. the energy resolution is found 33\% for gamma rays around 6 tev. the spectral energy distribution of the crab nebula in the range from 500 gev and 15.8 tev is measured and in agreement with results of other tev gamma ray observatories. | performance of lhaaso-wcda and observation of crab nebula as a standard candle |
we present the deepest constraints yet on the median rest-uv+optical spectral energy distribution (sed) of z ~ 10 galaxies prior to james webb space telescope science operations. we constructed stacks based on four robust j 125 dropouts, previously identified across the goods fields. we used archival hubble space telescope/wide field camera 3 data and the full-depth spitzer/irac mosaics from the greats program, the deepest coverage at ~3-5 μm to date. the most remarkable feature of the sed is a blue irac [3.6]-[4.5] = -0.18 ± 0.25 mag color. we also find a nearly flat h 160 - [3.6] = 0.07 ± 0.22 mag color, corresponding to a uv slope β = -1.92 ± 0.25. this is consistent with previous studies and indicative of minimal dust absorption. the observed blue irac color and sed fitting suggest that z ~ 10 galaxies have very young (few × 10 myr) stellar populations, with 80% of stars being formed in the last ≲160 myr (2σ). while an exciting result, the uncertainties on the sed are too large to allow us to place strong constraints on the presence of a nebular continuum in z ~ 10 galaxies (as might be suggested by the blue [3.6]-[4.5] < 0 mag color). the resulting ssfr is consistent with the specific accretion rate of dark matter halos, indicative of a star formation efficiency showing quite limited evolution at such early epochs. | deep spitzer/irac data for z 10 galaxies reveal blue balmer break colors: young stellar populations at500 myr of cosmic time |
a large fraction of core-collapse supernovae (ccsne), 30-50 per cent, are expected to originate from the low-mass end of progenitors with mzams = 8-12 m⊙. however, degeneracy effects make stellar evolution modelling of such stars challenging, and few predictions for their supernova light curves and spectra have been presented. here, we calculate synthetic nebular spectra of a 9 m⊙ fe ccsn model exploded with the neutrino mechanism. the model predicts emission lines with fwhm ∼ 1000 km s-1, including signatures from each deep layer in the metal core. we compare this model to the observations of the three subluminous iip sne with published nebular spectra; sn 1997d, sn 2005cs and sn 2008bk. the predictions of both line profiles and luminosities are in good agreement with sn 1997d and sn 2008bk. the close fit of a model with no tuning parameters provides strong evidence for an association of these objects with low-mass fe ccsne. for sn 2005cs, the interpretation is less clear, as the observational coverage ended before key diagnostic lines from the core had emerged. we perform a parametrized study of the amount of explosively made stable nickel, and find that none of these three sne show the high 58ni/56ni ratio predicted by current models of electron capture sne (ecsne) and ecsn-like explosions. combined with clear detection of lines from o and he shell material, these sne rather originate from fe core progenitors. we argue that the outcome of self-consistent explosion simulations of low-mass stars, which gives fits to many key observables, strongly suggests that the class of subluminous type iip sne is the observational counterpart of the lowest mass ccsne. | emission line models for the lowest mass core-collapse supernovae - i. case study of a 9 m⊙ one-dimensional neutrino-driven explosion |
since the discovery of jupiter-sized planets in extremely close orbits around sun-like stars, several mechanisms have been proposed to produce these "hot jupiters". here we address their pile-up at 0.05 au observed in stellar radial velocity surveys, their long-term orbital stability in the presence of stellar tides, and their occurrence rate of 1.2 ± 0.38% in one framework. we calculate the combined torques on the planet from the stellar dynamical tide and from the protoplanetary disk in the type-ii migration regime. the disk is modeled as a 2d nonisothermal viscous disk parameterized to reproduce the minimum-mass solar nebula. we simulate an inner disk cavity at various radial positions near the star and simulate stellar rotation periods according to observations of young star clusters. the planet is on a circular orbit in the disk midplane and in the equatorial plane of the star. we show that the two torques can add up to zero beyond the corotation radius around young, solar-type stars and stop inward migration. monte carlo simulations with plausible variations of our nominal parameterization of the star-disk-planet model predict hot-jupiter survival rates between about 3% (for an α disk viscosity of 10-1) and 15% (for α = 10-3) against consumption by the star. once the protoplanetary disk has been fully accreted, the surviving hot jupiters are pushed outward from their tidal migration barrier and pile up at about 0.05 au, as we demonstrate using a numerical implementation of a stellar dynamical tide model coupled with stellar evolution tracks. orbital decay is negligible on a one-billion-year timescale due to the contraction of highly dissipative convective envelopes in young sun-like stars. we find that the higher pile-up efficiency around metal-rich stars can at least partly explain the observed positive correlation between stellar metallicity and hot-jupiter occurrence rate. combined with the observed hot-jupiter occurrence rate, our results for the survival rate imply that ≲8% (α = 10-3) to ≲43% (α = 10-1) of sun-like stars initially encounter an inwardly migrating hot jupiter. our scenario reconciles models and observations of young spinning stars with the observed hot-jupiter pile up and hot-jupiter occurrence rates. | formation of hot jupiters through disk migration and evolving stellar tides |
we present the first direct comparison between balmer line and panchromatic spectral energy distribution (sed)-based star formation rates (sfrs) for z∼ 2 galaxies. for this comparison, we used 17 star-forming galaxies selected from the mosfire deep evolution field (mosdef) survey, with 3σ detections for hα and at least two ir bands (spitzer/mips 24 μm and herschel/pacs 100 and 160 μm, and in some cases herschel/spire 250, 350, and 500 μm). the galaxies have total ir (8-1000 μm) luminosities of ∼ 1011.4-1012.4 l⊙ and sfrs of ∼ 30-250 m⊙ yr-1. we fit the uv-to-far-ir seds with flexible stellar population synthesis (fsps) models—which include both stellar and dust emission—and compare the inferred sfrs with the sfr(hα, hβ) values corrected for dust attenuation using balmer decrements. the two sfrs agree with a scatter of 0.17 dex. our results imply that the balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate sfrs for star-forming galaxies at z∼ 2 with sfrs up to ∼ 200 m⊙ yr-1. we also use our data to assess sfr indicators based on modeling the uv-to-mid-ir seds or by adding sfr(uv) and sfr(ir), for which the latter is based on the mid-ir only or on the full ir sed. all these sfrs show a poorer agreement with sfr(hα, hβ) and in some cases large systematic biases are observed. finally, we show that the sfr and dust attenuation derived from the uv-to-near-ir sed alone are unbiased when assuming a delayed exponentially declining star formation history. based on observations made with 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. | the mosdef survey: the strong agreement between hα and uv-to-fir star formation rates for z ~ 2 star-forming galaxies |
one of the key physical processes that helps prevent strong cooling flows in galaxy clusters is the continued energy input from the central active galactic nucleus (agn) of the cluster. however, it remains unclear how this energy is thermalised so that it can effectively prevent global thermal instability. one possible option is that a fraction of the agn energy is converted into cosmic rays (crs), which provide non-thermal pressure support, and can retain energy even as thermal energy is radiated away. by means of magneto-hydrodynamical simulations, we investigate how cr injected by the agn jet influence cooling flows of a massive galaxy cluster. we conclude that converting a fraction of the agn luminosity as low as 10% into cr energy prevents cooling flows on timescales of billion years, without significant changes in the structure of the multi-phase intra-cluster medium. cr-dominated jets, by contrast, lead to the formation of an extended, warm central nebula that is supported by cr pressure. we report that the presence of crs is not able to suppress the onset of thermal instability in massive galaxy clusters, but cr-dominated jets do significantly change the continued evolution of gas as it continues to cool from isobaric to isochoric. the cr redistribution in the cluster is dominated by advection rather than diffusion or streaming, but the heating by cr streaming helps maintain gas in the hot and warm phase. observationally, self-regulating, cr-dominated jets produce a γ-ray flux in excess of current observational limits, but low cr fractions in the jet are not ruled out. | cosmic rays and thermal instability in self-regulating cooling flows of massive galaxy clusters |
orion source i (“srci”) is the protostar at the center of the kleinmann-low nebula. alma observations of srci with 0.″2 angular resolution were made at 350 and 660 ghz to search for the h26α and h21α hydrogen recombination lines and to measure the continuum flux densities. the recombination lines were not detected, ruling out the possibility that srci is a hypercompact h ii region. the deconvolved size of the continuum source is approximately 0.″23 × 0.″07 (∼100 × 30 au); it is interpreted as a disk viewed almost edge-on. optically thick thermal emission from ∼500 k dust is the most plausible source of the continuum, even at frequencies as low as 43 ghz; the disk mass is most likely in the range 0.02-0.2 {m}⊙ . a rich spectrum of molecular lines is detected, mostly from sulfur- and silicon-rich molecules like so, so2, and sis, but also including vibrationally excited co and several unidentified transitions. lines with upper energy levels {e}{{u}}\gt 500 k appear in emission and are symmetric about the source’s lsr velocity of 5 {km} {{{s}}}-1, while lines with {e}{{u}}\lt 500 k appear as blueshifted absorption features against the continuum, indicating that they originate in outflowing gas. the emission lines exhibit a velocity gradient along the major axis of the disk that is consistent with rotation around a 5-7 {m}⊙central object. the relatively low mass of srci and the existence of a 100 au disk around it are difficult to reconcile with the model in which srci and the nearby becklin-neugebauer object were ejected from a multiple system 500 years ago. | alma observations of orion source i at 350 and 660 ghz |
the ionizing radiation of massive stars sculpts the surrounding neutral gas into pillar-like structures. direct signatures of star formation through outflows and jets are observed in these structures, typically at their tips. recent numerical simulations have suggested that this star formation could potentially be triggered by photoionizing radiation, driving compressive modes of turbulence in the pillars. in this study, we use recent high-resolution alma observations of 12co, 13co, and c18o, j = 2 - 1 emission to test this hypothesis for pillars in the carina nebula. we analyse column density and intensity-weighted velocity maps, and subtract any large-scale bulk motions in the plane of the sky to isolate the turbulent motions. we then reconstruct the dominant turbulence driving mode in the pillars, by computing the turbulence driving parameter b, characterized by the relation $\sigma _{\rho /\rho _0} = b \mathcal {m}$ between the standard deviation of the density contrast $\sigma _{\rho /\rho _0}$ (with gas density ρ and its average ρ0) and the turbulent mach number $\mathcal {m}$ . we find values of b ∼ 0.7-1.0 for most of the pillars, suggesting that predominantly compressive modes of turbulence are driven in the pillars by the ionizing radiation from nearby massive stars. we find that this range of b values can produce star formation rates in the pillars that are a factor ∼3 greater than with b ∼ 0.5, a typical average value of b for spiral-arm molecular clouds. our results provide further evidence for the potential triggering of star formation in pillars through compressive turbulent motions. | on the compressive nature of turbulence driven by ionizing feedback in the pillars of the carina nebula |
there are currently few approved effective treatments for sars-cov-2, the virus responsible for the covid-19 pandemic. nanobodies are 12-15 kda single-domain antibody fragments that can be delivered by inhalation and are amenable to relatively inexpensive large scale production compared to other biologicals. we have isolated nanobodies that bind to the sars-cov-2 spike protein receptor binding domain and block spike protein interaction with the angiotensin converting enzyme 2 (ace2) with 1-5 nm affinity. the lead nanobody candidate, nih-covnb-112, blocks sars-cov-2 spike pseudotyped lentivirus infection of hek293 cells expressing human ace2 with an ec50 of 0.3 µg/ml. nih-covnb-112 retains structural integrity and potency after nebulization. furthermore, nih-covnb-112 blocks interaction between ace2 and several high affinity variant forms of the spike protein. these nanobodies and their derivatives have therapeutic, preventative, and diagnostic potential. | high affinity nanobodies block sars-cov-2 spike receptor binding domain interaction with human angiotensin converting enzyme |
we present an optical spectroscopic study of the black hole x-ray transient v4641 sgr (=sax j1819.3-2525) covering the 1999, 2002, and 2004 outbursts. the spectra were taken over 22 different epochs during the low-luminosity phases that follow the sharp and bright outburst peaks displayed by the system. the data reveal the frequent presence of wind-related features in h (balmer) and he i emission lines in the form of p-cygni profiles and strong emission lines with broad wings. the terminal velocity of the wind, as measured in the blue-shifted absorption (p-cygni) components, is in the range of ∼ 900-1600 km s-1 , while the broad emission line wings (so-called nebular phases) imply outflow velocities of up to ∼3000 km s-1 . we show that, at least for several of the wind detections, the radio jet was active and the system was likely in the hard state. this, together with previous detections reported in the literature, shows that v4641 sgr is the second source of this class, after v404 cyg, where the presence of these cold wind outflows has been clearly established. we discuss the similar phenomenology observed in both systems as well as the possible nature of the outflow and its impact on the accretion process. | the low-luminosity accretion disc wind of the black hole transient v4641 sagittarii |
context. l1630 in the orion b molecular cloud, which includes the iconic horsehead nebula, illuminated by the star system σ ori, is an example of a photodissociation region (pdr). in pdrs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes.aims: observations toward l1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate uv radiation field. contrary to the well-studied orion molecular cloud 1 (omc1), which hosts much harsher conditions, l1630 has little star formation. our goal is to relate the [c ii] fine-structure line emission to the physical conditions predominant in l1630 and compare it to studies of omc1.methods: the [c ii] 158 μm line emission of l1630 around the horsehead nebula, an area of 12' × 17', was observed using the upgraded german receiver for astronomy at terahertz frequencies (upgreat) onboard the stratospheric observatory for infrared astronomy (sofia).results: of the [c ii] emission from the mapped area 95%, 13 l⊙, originates from the molecular cloud; the adjacent h ii region contributes only 5%, that is, 1 l⊙. from comparison with other data (co (1 - 0)-line emission, far-infrared (fir) continuum studies, emission from polycyclic aromatic hydrocarbons (pahs)), we infer a gas density of the molecular cloud of nh 3 × 103 cm-3, with surface layers, including the horsehead nebula, having a density of up to nh 4 × 104 cm-3. the temperature of the surface gas is t 100 k. the average [c ii] cooling efficiency within the molecular cloud is 1.3 × 10-2. the fraction of the mass of the molecular cloud within the studied area that is traced by [c ii] is only 8%. our pdr models are able to reproduce the fir-[c ii] correlations and also the co (1 - 0)-[c ii] correlations. finally, we compare our results on the heating efficiency of the gas with theoretical studies of photoelectric heating by pahs, clusters of pahs, and very small grains, and find the heating efficiency to be lower than theoretically predicted, a continuation of the trend set by other observations.conclusions: in l1630 only a small fraction of the gas mass is traced by [c ii]. most of the [c ii] emission in the mapped area stems from pdr surfaces. the layered edge-on structure of the molecular cloud and limitations in spatial resolution put constraints on our ability to relate different tracers to each other and to the physical conditions. from our study, we conclude that the relation between [c ii] emission and physical conditions is likely to be more complicated than often assumed. the theoretical heating efficiency is higher than the one we calculate from the observed [c ii] emission in the l1630 molecular cloud. | [c ii] emission from l1630 in the orion b molecular cloud |
we extend the range of validity of the artis 3d radiative transfer code up to hundreds of days after explosion, when type ia supernovae (sne ia) are in their nebular phase. to achieve this, we add a non-local thermodynamic equilibrium population and ionization solver, a new multifrequency radiation field model, and a new atomic data set with forbidden transitions. we treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionization, and heating. we validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known one-dimensional w7 model with the results of other studies. as an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-chandrasekhar white dwarf (wd) in which the possible effects of gravitational settling of 22ne prior to explosion have been explored. specifically, we compare synthetic nebular spectra for a 1.06 m⊙ wd model obtained when 5.5 gyr of very efficient settling is assumed to a similar model without settling. we find that this degree of 22ne settling has only a modest effect on the resulting nebular spectra due to increased 58ni abundance. due to the high ionization in sub-chandrasekhar models, the nebular [ni ii] emission remains negligible, while the [ni iii] line strengths are increased and the overall ionization balance is slightly lowered in the model with 22ne settling. in common with previous studies of sub-chandrasekhar models at nebular epochs, these models overproduce [fe iii] emission relative to [fe ii] in comparison to observations of normal sne ia. | monte carlo radiative transfer for the nebular phase of type ia supernovae |
we explore the observational appearance of the merger of a low-mass star with a white dwarf (wd) binary companion. we are motivated by recent work finding that multiple tensions between the observed properties of cataclysmic variables (cvs) and standard evolution models are resolved if a large fraction of cv binaries merge as a result of unstable mass transfer. tidal disruption of the secondary forms a geometrically thick disk around the wd, which subsequently accretes at highly super-eddington rates. analytic estimates and numerical hydrodynamical simulations reveal that outflows from the accretion flow unbind a large fraction ≳90% of the secondary at velocities ~500-1000 km s-1 within days of the merger. hydrogen recombination in the expanding ejecta powers optical transient emission lasting about a month with a luminosity ≳1038 erg s-1, similar to slow classical novae and luminous red novae from ordinary stellar mergers. over longer timescales the mass accreted by the wd undergoes hydrogen shell burning, inflating the remnant into a giant of luminosity ~300-5000 l ⊙, effective temperature t eff ≈ 3000 k, and lifetime ~104-105 yr. we predict that ~103-104 milky way giants are cv merger products, potentially distinguishable by atypical surface abundances. we explore whether any galactic historical slow classical novae are masquerading cv mergers by identifying four such post-nova systems with potential giant counterparts for which a cv merger origin cannot be ruled out. we address whether the historical transient ck vul and its gaseous/dusty nebula resulted from a cv merger. | transients from the cataclysmic deaths of cataclysmic variables |
jets are ubiquitous in the universe and are seen from a large number of astrophysical objects including active galactic nuclei, gamma ray bursters, micro-quasars, proto-planetary nebulae, young stars and even brown dwarfs. in every case they seem to be accompanied by an accretion disk and, while the detailed physics may change, it has been suggested that the same basic mechanism is responsible for generating the jet. although we do not understand what that mechanism is, or even if it is universal, it is thought to involve the centrifugal ejection of matter from the disk along magnetic field lines. for a number of reasons, in particular their proximity and the abundant range of diagnostics to determine their characteristics, jets from young stars and their associated outflows may offer us the best opportunity to discover how jets are generated and the nature of the link between outflows and their accretion disks. recently it has become clear that jets may be fundamental to the star formation process in removing angular momentum from the surrounding protoplanetary disk thereby allowing accretion to proceed. moreover, with the realization that planetary formation begins much earlier than previously thought, jets may also help forge planets by determining initial environmental characteristics. this seems to be particularly true within the so-called terrestrial planet forming zone. here we review observations of jets from young stars which have greatly benefitted from new facilities such as alma, space observatories like spitzer, herschel and hst, and radio facilities like lofar and the vla. interferometers such as chara and gravity are starting to make inroads into resolving how they are launched, and we can look forward to a bright future in our understanding of this phenomenon when jwst and the ska come on stream. in addition, we examine the various magnetohydrodynamic models for how jets from young stars are thought to be generated and how observations may help us select between these various options. | jets from young stars |
calcium-rich supernovae (ca-rich sne) are peculiar low-luminosity sne ib with relatively strong ca spectral lines at ∼2 months after peak brightness. this class also has an extended projected offset distribution, with several members of the class offset from their host galaxies by 30-150 kpc. there is no indication of any stellar population at the sn positions. using a sample of 13 ca-rich sne, we present kinematic evidence that the progenitors of ca-rich sne originate near the centres of their host galaxies and are kicked to the locations of the sn explosions. specifically, sne with small projected offsets have large line-of-sight velocity shifts as determined by nebular lines, while those with large projected offsets have no significant velocity shifts. therefore, the velocity shifts must not be primarily the result of the sn explosion. additionally, nearly every ca-rich sn is hosted by a galaxy with indications of a recent merger and/or is in a dense environment. we propose a progenitor model which fits all current data: the progenitor system for a ca-rich sn is a double white dwarf (wd) system where at least one wd has a significant he abundance. this system, through an interaction with a super-massive black hole (smbh) is ejected from its host galaxy and the binary is hardened, significantly reducing the merger time. after 10-100 myr (on average), the system explodes with a large physical offset. the rate for such events is significantly enhanced for galaxies which have undergone recent mergers, potentially making ca-rich sne new probes of both the galaxy merger rate and (binary) smbh population. | kinematics and host-galaxy properties suggest a nuclear origin for calcium-rich supernova progenitors |
six planetary nebulae (pn) are known in the kepler space telescope field of view, three of which are newly identified. of the five central stars of pn with useful kepler data, one, j193110888+4324577, is the first short-period, post-common envelope binary exhibiting relativistic beaming effects. a second, the central star of the newly identified pn pa 5, has a rare o(he) spectral type and a periodic variability consistent with an evolved companion, where the orbital axis is almost aligned with the line of sight. the third pn, ngc 6826, has a fast rotating central star, something that can only be achieved in a merger. fourth, the central star of the newly identified pn kn 61, has a pg1159 spectral type and a mysterious semi-periodic light variability which we conjecture to be related to the interplay of binarity with a stellar wind. finally, the central star of the circular pn a61 does not appear to have a photometric variability above 2 mmag. with the possible exception of the variability of kn 61, all other variability behaviour, would not easily have been detected from the ground. we conclude, based on very low numbers, that there may be many more close binary or close binary products to be discovered with ultra-high-precision photometry. with a larger number of high-precision photometric observations, we will be able to determine how much higher than the currently known 15 per cent, the short-period binary fraction for central stars of pn is likely to be. | identifying close binary central stars of pn with kepler |
we report on the extensive multi-wavelength observations of the blazar markarian 421 (mrk 421) covering radio to γ-rays, during the 4.5 year period of argo-ybj and fermi common operation time, from 2008 august to 2013 february. these long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of mrk 421. in particular, due to the argo-ybj and fermi data, the entire energy range from 100 mev to 10 tev is covered without any gap. in the observation period, mrk 421 showed both low- and high-activity states at all wavebands. the correlations among flux variations in different wavebands were analyzed. the x-ray flux is clearly correlated with the tev γ-ray flux, while the gev γ-rays only show a partial correlation with the tev γ-rays. radio and uv fluxes seem to be weakly or not correlated with the x-ray and γ-ray fluxes. seven large flares, including five x-ray flares and two gev γ-ray flares with variable durations (3-58 days), and one x-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. during the outburst phase and the seven flaring episodes, the peak energy in x-rays is observed to increase from sub-kev to a few kev. the tev γ-ray flux increases up to 0.9-7.2 times the flux of the crab nebula. the behavior of gev γ-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the gev flux variation. finally, the one-zone synchrotron self-compton model was adopted to describe the emission spectra. two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. the underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties. | 4.5 years of multi-wavelength observations of mrk 421 during the argo-ybj and fermi common operation time |
the orion nebula cluster (onc) is the nearest site of ongoing massive star formation, which allows us to study the kinematics and dynamics of the region in detail and constrain star formation theories. using hst acs/wfpc2/wfc3ir and keck ii nirc2 data, we have measured the proper motions of 701 stars within an ∼6‧ × 6‧ field of view around the center of the onc. we have found more than 10 escaping star candidates, concentrated predominantly at the core of the cluster. the proper motions of the bound stars are consistent with a normal distribution, albeit elongated north-south along the orion filament, with proper-motion dispersions of ({σ }μ ,{α * },{σ }μ ,δ )=(0.83+/- 0.02,1.12+/- 0.03) mas yr-1 or intrinsic velocity dispersions of ({σ }v,{α * },{σ }v,δ )=(1.57+/- 0.04,2.12+/- 0.06) km s-1 assuming a distance of 400 pc to the onc. the cluster shows no evidence for tangential-to-radial anisotropy. our velocity dispersion profile agrees with the prediction from the observed stellar + gas density profile from da rio et al., indicating that the onc is in virial equilibrium. this finding suggests that the cluster was formed with a low star formation efficiency per dynamical timescale based on comparisons with current star formation theories. our survey also recovered high-velocity ir sources bn, x and n in the bn/kl region. the estimated location of the first two sources ∼500 yr ago agrees with that of the radio source i, consistent with their proposed common origin from a multistellar disintegration. however, source n appears to have a small proper motion and is unlikely to have been involved in the event. | stellar proper motions in the orion nebula cluster |
the orion nebula cluster (onc) is the nearest dense star-forming region at ~400 pc away, making it an ideal target to study the impact of high stellar density and proximity to massive stars (the trapezium) on protoplanetary disk evolution. the omc1 molecular cloud is a region of high extinction situated behind the trapezium in which actively forming stars are shielded from the trapezium's strong radiation. in this work, we survey disks at high resolution with atacama large millimeter/submillimeter array at three wavelengths with resolutions of 0.″095 (3 mm; band 3), 0.″048 (1.3 mm; band 6), and 0.″030 (0.85 mm; band 7) centered on radio source i. we detect 127 sources, including 15 new sources that have not previously been detected at any wavelength. 72 sources are spatially resolved at 3 mm, with sizes from ~8-100 au. we classify 76 infrared-detected sources as foreground onc disks and the remainder as embedded omc1 disks. the two samples have similar disk sizes, but the omc1 sources have a dense and centrally concentrated spatial distribution, indicating they may constitute a spatially distinct subcluster. we find smaller disk sizes and a lack of large (>75 au) disks in both our samples compared to other nearby star-forming regions, indicating that environmental disk truncation processes are significant. while photoevaporation from nearby massive trapezium stars may account for the smaller disks in the onc, the embedded sources in omc1 are hidden from this radiation and thus must truncated by some other mechanism, possibly dynamical truncation or accretion-driven contraction. | small protoplanetary disks in the orion nebula cluster and omc1 with alma |
getman et al. report the discovery, energetics, frequencies, and effects on environs of >1000 x-ray superflares with x-ray energies ex ~ 1034-1038 erg from pre-main-sequence (pms) stars identified in the chandra mystix and sfincs surveys. here we perform detailed plasma evolution modeling of 55 bright mystix/sfincs superflares from these events. they constitute a large sample of the most powerful stellar flares analyzed in a uniform fashion. they are compared with published x-ray superflares from young stars in the orion nebula cluster, older active stars, and the sun. several results emerge. first, the properties of pms x-ray superflares are independent of the presence or absence of protoplanetary disks inferred from infrared photometry, supporting the solar-type model of pms flaring magnetic loops with both footpoints anchored in the stellar surface. second, most pms superflares resemble solar long-duration events that are associated with coronal mass ejections. slow-rise pms superflares are an interesting exception. third, strong correlations of superflare peak emission measure and plasma temperature with the stellar mass are similar to established correlations for the pms x-ray emission composed of numerous smaller flares. fourth, a new correlation of loop geometry is linked to stellar mass; more massive stars appear to have thicker flaring loops. finally, the slope of a long-standing relationship between the x-ray luminosity and magnetic flux of various solar-stellar magnetic elements appears steeper in pms superflares than for solar events. | x-ray superflares from pre-main-sequence stars: flare modeling |
a significative fraction of all massive stars in the milky way move supersonically through their local interstellar medium (ism), producing bow shock nebulae by wind-ism interaction. the stability of these observed astrospheres around cool massive stars challenges precedent 2d (magneto-)hydrodynamical (mhd) simulations of their surroundings. we present 3d mhd simulations of the circumstellar medium of runaway m-type red supergiant stars moving with velocity $v_{\star }=50\, \rm km\, \rm s^{-1}$. we treat the stellar wind with a parker spiral and assume a $7\, \rm \mu g$ magnetization of the ism. our free parameter is the angle θmag between ism flow and magnetization, taken to 0°, 45°, and 90°. it is found that simulation dimension, coordinate systems, and grid effects can greatly affect the development of the modelled astrospheres. nevertheless, as soon as the ism flow and magnetization directions differs by more than a few degrees (θmag ≥ 5°), the bow shock is stabilized, most clumpiness and ragged structures vanishing. the complex shape of the bow shocks induce important projection effects, e.g. at optical h α line, producing complex of astrospheric morphologies. we speculate that those effects are also at work around earlier-type massive stars, which would explain their diversity of their observed arc-like nebula around runaway ob stars. our 3d mhd models are fitting well observations of the astrospheres of several runaway red supergiant stars. the results interpret the smoothed astrosphere of irc-10414 and betelgeuse (αori) are stabilized by an organized non-parallel ambient magnetic field. our findings suggest that irc-10414 is currently in a steady state of its evolution, and that betelgeuse's bar is of interstellar origin. | 3d mhd astrospheres: applications to irc-10414 and betelgeuse |
mev gamma-rays provide a unique window for the direct measurement of line emissions from radioisotopes, but observations have made little significant progress since comptel on board the compton gamma-ray observatory (cgro). to observe celestial objects in this band, we are developing an electron-tracking compton camera (etcc) that realizes both bijective imaging spectroscopy and efficient background reduction gleaned from the recoil-electron track information. the energy spectrum of the observation target can then be obtained by a simple on-off method using a correctly defined point-spread function on the celestial sphere. the performance of celestial object observations was validated on the second balloon smile-2+ , on which an etcc with a gaseous electron tracker was installed that had a volume of 30 × 30 × 30 cm3. gamma-rays from the crab nebula were detected with a significance of 4.0σ in the energy range 0.15-2.1 mev with a live time of 5.1 hr, as expected before launch. additionally, the light curve clarified an enhancement of gamma-ray events generated in the galactic center region, indicating that a significant proportion of the final remaining events are cosmic gamma-rays. independently, the observed intensity and time variation were consistent with the prelaunch estimates except in the galactic center region. the estimates were based on the total background of extragalactic diffuse, atmospheric, and instrumental gamma-rays after accounting for the variations in the atmospheric depth and rigidity during the level flight. the crab results and light curve strongly support our understanding of both the detection sensitivity and the background in real observations. this work promises significant advances in mev gamma-ray astronomy. | first observation of the mev gamma-ray universe with bijective imaging spectroscopy using the electron-tracking compton telescope on board smile-2+ |
primordial black holes (pbhs) formed in the early universe constitute an attractive candidate for dark matter. within the gaseous environment of the interstellar medium, pbhs with accretion discs naturally launch outflows such as winds and jets. we discuss for the first time how pbhs with significant spin can sustain powerful relativistic jets and generate associated cocoons. jets and winds can efficiently deposit their kinetic energies and heat the surrounding gas through shocks. focusing on the leo t dwarf galaxy, we demonstrate that these effects form novel tests and set new limits on pbhs over a significant ~10-2 -106 m⊙ mass range, including the parameter space associated with gravitational wave observations by the ligo and virgo collaborations. observing the morphology of emission will allow to distinguish between jet and wind contributions, and hence establishes a new method for identifying spinning pbhs. | impacts of jets and winds from primordial black holes |
detailed observational characterization of transiting exoplanet systems has revealed that the spin-axes of massive (m≳ 1.2{m}⊙ ) stars often exhibit substantial misalignments with respect to the orbits of the planets they host. conversely, lower-mass stars tend to only have limited obliquities. a similar trend has recently emerged within the observational data set of young stars’ magnetic field strengths: massive t-tauri stars tend to have dipole fields that are ∼10 times weaker than their less-massive counterparts. here we show that the associated dependence of magnetic star-disk torques upon stellar mass naturally explains the observed spin-orbit misalignment trend, provided that misalignments are obtained within the disk-hosting phase. magnetic torques act to realign the stellar spin-axes of lower-mass stars with the disk plane on a timescale significantly shorter than the typical disk lifetime, whereas the same effect operates on a much longer timescale for massive stars. cumulatively, our results point to a primordial excitation of extrasolar spin-orbit misalignment, signalling consistency with disk-driven migration as the dominant transport mechanism for short-period planets. furthermore, we predict that spin-orbit misalignments in systems where close-in planets show signatures of dynamical, post-nebular emplacement will not follow the observed correlation with stellar mass. | magnetic origins of the stellar mass-obliquity correlation in planetary systems |
ts34 is a type b1 ca-al-rich inclusion (cai) from the allende cv3 chondrite, consisting of spinel, melilite, ti-al-rich clinopyroxene (fassaite) and minor anorthite in an igneous texture. oxygen and magnesium isotopic compositions were measured by secondary ion mass spectrometry in spots of known chemical composition in all major minerals in ts34. using the sequence of formation from dynamic crystallization experiments and from chemical compositions of melilite and fassaite, the oxygen isotopic evolution of the cai melt was established. oxygen isotopic compositions of the constituent minerals plot along the carbonaceous chondrite anhydrous mineral line. the spinel grains are uniformly 16o-rich (δ17o = -22.7 ± 1.7‰, 2sd), while the melilite grains are uniformly 16o-poor (δ17o = -2.8 ± 1.8‰) irrespective of their åkermanite content and thus their relative time of crystallization. the fassaite crystals exhibit growth zoning overprinting poorly-developed sector zoning; they generally grow from ti-rich to ti-poor compositions. the fassaite crystals also show continuous variations in δ17o along the inferred directions of crystal growth, from 16o-poor (δ17o ∼ -3‰) to 16o-rich (δ17o ∼ -23‰), covering the full range of oxygen isotopic compositions observed in ts34. the early-crystallized 16o-poor fassaite and the melilite are in oxygen isotope equilibrium and formed simultaneously. the correlation of oxygen isotopic compositions with ti content in the fassaite imply that the oxygen isotopic composition of the cai melt evolved from 16o-poor to 16o-rich during fassaite crystallization, presumably due to oxygen isotope exchange with a surrounding 16o-rich nebular gas. formation of spinel, the liquidus phase in melts of this composition, predates crystallization of all other phases, so its 16o-rich composition is a relic of an earlier stage. anorthite exhibits oxygen isotopic compositions between δ17o ∼ -2‰ and -9‰, within the range of those of fassaite, indicating co-crystallization of these two minerals during the earliest to intermediate stage of fassaite growth. the melilite and fassaite yield an 26al-26mg mineral isochron with an initial value of (26al/27al)0 = (5.003 ± 0.075) × 10-5, corresponding to a relative age of 0.05 ± 0.02 myr from the canonical al-mg age of cais. these data demonstrate that both 16o-rich and 16o-poor reservoirs existed in the solar nebula at least ∼0.05 myr after the birth of the solar system. | crystal growth and disequilibrium distribution of oxygen isotopes in an igneous ca-al-rich inclusion from the allende carbonaceous chondrite |
measured and modeled ca and ti isotopic fractionation effects in a diverse suite of refractory inclusions are used to understand processes of condensation in the solar protoplanetary disk where they and their precursor materials formed. this coordinated approach reveals largely decoupled isotopic signatures and implies that few, if any, of the studied inclusions can be considered primary condensates. all studied inclusions are enriched in light ca isotopes (∼-0.2 to - 2.8 ‰ /amu), but only two show correspondingly light ti isotopes. studied inclusions exhibit both heavy and light ti isotope enrichments (∼0.3 to - 0.4 ‰ /amu). these refractory element isotopic signatures, therefore, suggest admixture and reprocessing of earlier formed materials with distinct condensation histories. along with coordinated measurements of 50ti isotopic anomalies, which span a range from ∼0 to ∼40 epsilon-unit excesses, the comparison of measured and modeled fractionation of ca and ti isotopes provides a powerful approach to understanding primitive nebular processes and environments in the protoplanetary disk. remarkable evidence for ca isotopic zoning within a typical type b1 inclusion exemplifies the potential record of the earliest solar nebula that is likely lost and/or overprinted in the isotopic compositions of more volatile elements (e.g., mg, si, and o) by later modification processes. | calcium and titanium isotope fractionation in refractory inclusions: tracers of condensation and inheritance in the early solar protoplanetary disk |
aims: so far, only one rotating disk has been clearly identified and studied in agb or post-agb objects (in the red rectangle), by means of observations with high spectral and spatial resolution. however, disks are thought to play a key role in the late stellar evolution and are suspected to surround many evolved stars. we aim to extend our knowledge on these structures.methods: we present interferometric observations of 12co j = 2-1 emission from the nebula surrounding the post-agb star ac her, a source belonging to a class of objects that share properties with the red rectangle and show hints of keplerian disks.results: we clearly detect the keplerian dynamics of a second disk orbiting an evolved star. its main properties (size, temperature, central mass) are derived from direct interpretation of the data and model fitting. with this we confirm that there are disks orbiting the stars of this relatively wide class of post-agb objects. | detection of keplerian dynamics in a disk around the post-agb star ac herculis |
the high energy stereoscopic system (h.e.s.s.) phase i instrument was an array of four $100\,\mathrm{m}^2$ mirror area imaging atmospheric cherenkov telescopes (iacts) that has very successfully mapped the sky at photon energies above $\sim 100\,$gev. recently, a $600\,\mathrm{m}^2$ telescope was added to the centre of the existing array, which can be operated either in standalone mode or jointly with the four smaller telescopes. the large telescope lowers the energy threshold for gamma-ray observations to several tens of gev, making the array sensitive at energies where the fermi-lat instrument runs out of statistics. at the same time, the new telescope makes the h.e.s.s. phase ii instrument. this is the first hybrid iact array, as it operates telescopes of different size (and hence different trigger rates) and different field of view. in this contribution we present results of h.e.s.s. phase ii observations of the crab nebula, compare them to earlier observations, and evaluate the performance of the new instrument with monte carlo simulations. | observations of the crab nebula with h.e.s.s. phase ii |
context. sulphur is one of the most abundant elements in the universe (s/h 1.3 × 10-5) and plays a crucial role in biological systems on earth. the understanding of its chemistry is therefore of major importance.aims: our goal is to complete the inventory of s-bearing molecules and their abundances in the prototypical photodissociation region (pdr) the horsehead nebula to gain insight into sulphur chemistry in uv irradiated regions. based on the whisper (wide-band high-resolution iram-30 m surveys at two positions with emir receivers) millimeter (mm) line survey, our goal is to provide an improved and more accurate description of sulphur species and their abundances towards the core and pdr positions in the horsehead.methods: the monte carlo markov chain (mcmc) methodology and the molecular excitation and radiative transfer code radex were used to explore the parameter space and determine physical conditions and beam-averaged molecular abundances.results: a total of 13 s-bearing species (cs, so, so2, ocs, h2cs - both ortho and para - hdcs, c2s, hcs+, so+, h2s, s2h, ns and ns+) have been detected in the two targeted positions. this is the first detection of so+ in the horsehead and the first detection of ns+ in any pdr. we find a differentiated chemical behaviour between c-s and o-s bearing species within the nebula. the c-s bearing species c2s and o-h2cs present fractional abundances a factor of > two higher in the core than in the pdr. in contrast, the o-s bearing molecules so, so2, and ocs present similar abundances towards both positions. a few molecules, so+, ns, and ns+, are more abundant towards the pdr than towards the core, and could be considered as pdr tracers.conclusions: this is the first complete study of s-bearing species towards a pdr. our study shows that cs, so, and h2s are the most abundant s-bearing molecules in the pdr with abundances of approximately a few 10-9. we recall that sh, sh+, s, and s+ are not observable at the wavelengths covered by the whisper survey. at the spatial scale of our observations, the total abundance of s atoms locked in the detected species is <10-8, only 0.1% of the cosmic sulphur abundance. | abundances of sulphur molecules in the horsehead nebula. first ns+ detection in a photodissociation region |
in 2013, nustar observed the sgr b2 region and for the first time resolved its hard x-ray emission on subarcminute scales. two prominent features are detected above 10 kev: a newly emerging cloud, g0.66-0.13, and the central 90″ radius region containing two compact cores, sgr b2(m) and sgr b2(n), surrounded by diffuse emission. it is inconclusive whether the remaining level of sgr b2 emission is still decreasing or has reached a constant background level. a decreasing x-ray emission can be best explained by the x-ray reflection nebula scenario, where the cloud reprocesses a past giant outburst from sgr a{}\star . in the x-ray reflection nebula (xrn) scenario, the 3-79 kev sgr b2 spectrum allows us to self-consistently test the xrn model using both the fe kα line and the continuum emission. the peak luminosity of the past sgr a{}\staroutburst is constrained to {l}3-79{kev}∼ 5× {10}38 {erg} {{{s}}}-1. a newly discovered cloud feature, g0.66-0.13, shows different timing variability. we suggest that it could be a molecular clump located in the sgr b2 envelope reflecting the same sgr a{}\staroutburst. in contrast, if the sgr b2 x-ray emission has reached a constant background level, it would imply an origin of low-energy cosmic-ray (cr) proton bombardment. in this scenario, from the nustar measurements we infer a cr ion power of {dw}/{dt}=(1-4)× {10}39 {erg} {{{s}}}-1 and a cr ionization rate of {\zeta }{{h}}=(6-10)× {10}-15 {{{h}}}-1\quad {{{s}}}-1. these measurements can become powerful tools to constrain the gc cr population. | hard x-ray morphological and spectral studies of the galactic center molecular cloud sgr b2: constraining past sgr a* flaring activity |
we study the stellar population properties of the irac-detected 6 ≲ z ≲ 10 galaxy candidates from the spitzer ultra faint survey program. using the lyman break selection technique, we find a total of 17 galaxy candidates at 6 ≲ z ≲ 10 from hubble space telescope images (including the full-depth images from the hubble frontier fields program for macs 1149 and macs 0717) that have detections at signal-to-noise ratios ≥ 3 in at least one of the irac 3.6 and 4.5 μm channels. according to the best mass models available for the surveyed galaxy clusters, these irac-detected galaxy candidates are magnified by factors of ∼1.2-5.5. due to the magnification of the foreground galaxy clusters, the rest-frame uv absolute magnitudes m1600 are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 × 108m⊙ and 2.9 × 109m⊙. we identify two lyα emitters in our sample from the keck deimos spectra, one at zlyα = 6.76 (in rxj 1347) and one at zlyα = 6.32 (in macs 0454). we find that 4 out of 17 z ≳ 6 galaxy candidates are favored by z ≲ 1 solutions when irac fluxes are included in photometric redshift fitting. we also show that irac [3.6]-[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows. | spitzer ultra faint survey program (surfs up). ii. irac-detected lyman-break galaxies at 6 ≲ z ≲ 10 behind strong-lensing clusters |
we present mid- and far-ir imaging of four famous hypergiant stars: the red supergiants μ cep and vy cma, and the warm hypergiants irc +10420 and ρ cas. our 11-37 μm sofia/forcast imaging probes cool dust not detected in visual and near-ir imaging studies. adaptive optics 8-12 μm imaging of μ cep and irc +10420 with mmt/mirac reveals extended envelopes that are the likely sources of these stars’ strong silicate emission features. we find μ cep’s mass-loss rate to have declined by about a factor of five over a 13,000 year history, ranging from 5 × 10-6 down to ∼1× 10-6 m⊙ yr-1. the morphology of vy cma indicates a cooler dust component coincident with the highly asymmetric reflection nebulae seen in the visual and near-ir. the lack of cold dust at greater distances around vy cma indicates that its mass-loss history is limited to the last ∼1200 years, with an average rate of 6 × 10-4 m⊙ yr-1. we find two distinct periods in the mass-loss history of irc +10420 with a high rate of 2 × 10-3 m⊙ yr-1 until approximately 2000 years ago, followed by an order of magnitude decrease in the recent past. we interpret this change as evidence of its evolution beyond the rsg stage. our new infrared photometry of ρ cas is consistent with emission from the expanding dust shell ejected in its 1946 eruption, with no evidence of newer dust formation from its more recent events. based on observations obtained with: (1) the nasa/dlr stratospheric observatory for infrared astronomy (sofia). sofia is jointly operated by the universities space research association, inc. (usra), under nasa contract nas2-97001, and the deutsches sofia institut (dsi) under dlr contract 50 ok 0901 to the university of stuttgart; and (2) the mmt observatory on mt. hopkins, az, a joint facility of the smithsonian institution and the university of arizona. | searching for cool dust in the mid-to-far infrared: the mass-loss histories of the hypergiants μ cep, vy cma, irc+10420, and ρ cas |
outflows are a pervasive feature of mechanical feedback from super star clusters (sscs) in starburst galaxies, playing a fundamental role in galaxy evolution. observations are now starting to confirm that outflows can undergo catastrophic cooling, suppressing adiabatic superwinds. here we present a suite of one-dimensional, hydrodynamic simulations that study the ionization structure of these outflows and the resulting line emission generated by the cooling gas. we use the non-equilibrium atomic chemistry package within maihem, our modified version of flash, which evolves the ionization state of the gas and computes the total cooling rate on an ion-by-ion basis. we find that catastrophically cooling models produce strong nebular line emission compared to adiabatic outflows. we also show that such models exhibit non-equilibrium conditions, thereby generating more highly ionized states than equivalent equilibrium models. when including photoionization from the parent ssc, catastrophically cooling models show strong c iv λ1549 and o vi λ1037 emission. for density-bounded photoionization, he ii λ1640, λ4686, c iii] λ1908, si iv λ1206, and si iii λ1400 are also strongly enhanced. these lines are seen in extreme starbursts where catastrophic cooling is likely to occur, suggesting that they may serve as diagnostics of such conditions. the higher ionization generated by these flows may help to explain line emission that cannot be attributed to ssc photoionization alone. | catastrophic cooling in superwinds: line emission and non-equilibrium ionization |
we use gaia dr2 to hunt for runaway stars from the orion nebula cluster (onc). we search a region extending 45° around the onc and out to 1 kpc to find sources that have overlapped in angular position with the cluster in the last ∼10 myr. we find ∼17,000 runaway/walkaway candidates that satisfy this 2d traceback condition. most of these are expected to be contaminants, e.g., caused by galactic streaming motions of stars at different distances. we thus examine six further tests to help identify real runaways, namely: (1) possessing young stellar object (yso) colors and magnitudes based on gaia optical photometry; (2) having ir excess consistent with ysos based on 2mass and wide-field infrared survey explorer photometry; (3) having a high degree of optical variability; (4) having closest approach distances well-constrained to within the cluster half-mass radius; (5) having ejection directions that avoid the main galactic streaming contamination zone; and (6) having a required radial velocity (rv) for 3d overlap of reasonable magnitude (or, for the 7% of candidates with measured rvs, satisfying 3d traceback). thirteen sources, not previously noted as orion members, pass all these tests, while another twelve are similarly promising, except they are in the main galactic streaming contamination zone. among these 25 ejection candidates, ten with measured rvs pass the most restrictive 3d traceback condition. we present full lists of runaway/walkaway candidates, estimate the high-velocity population ejected from the onc, and discuss its implications for cluster formation theories via comparison with numerical simulations. | hunting for runaways from the orion nebula cluster |
we present results from the remaining sources in our search for near-infrared (nir) candidate counterparts to ultraluminous x-ray sources (ulxs) within ≃10 mpc. we observed 23 ulxs in 15 galaxies and detected nir candidate counterparts to 6 of them. two of these have an absolute magnitude consistent with a single red supergiant (rsg). three counterparts are too bright for an rsg and spatially extended, and thus we classify them as stellar clusters. the other candidate is too faint for an rsg. additionally, we present the results of our nir spectroscopic follow-up of five sources: four originally classified as rsg and one as a stellar cluster on the basis of previous photometry. the stellar cluster candidate is actually a nebula. of the four rsg candidates, one source has a broad h α emission line redshifted by ∼z = 1, making it a background active galactic nucleus (agn). two other sources show stellar spectra consistent with them being rsgs. the final rsg candidate is too faint to classify, but does not show strong (nebular) emission lines in its spectrum. after our search for nir counterparts to 113 ulxs, where we detected a candidate counterpart for 38 ulxs, we have spectroscopically confirmed the nature of 12: 5 sources are nebulae, 1 source is not classified, 1 source is an agn, and 5 are rsgs. these possible five ulx-rsg binary systems would constitute ${\simeq} (4 \pm 2){{\ \rm per\ cent}}$ of the observed ulxs, a fraction almost four times larger than what was predicted by binary evolution simulations. | nir counterparts to ulxs (iii): completing the photometric survey and selected spectroscopic results |
we present results on the properties of neon emission in z ∼ 2 star-forming galaxies drawn from the mosfire deep evolution field (mosdef) survey. doubly ionized neon ([ne iii]λ3869) is detected at ≥3σ in 61 galaxies, representing ∼25% of the mosdef sample with hα, hβ, and [o iii]λ5007 detections at similar redshifts. we consider the neon emission-line properties of both individual galaxies with [ne iii]λ3869 detections and composite z ∼ 2 spectra binned by stellar mass. with no requirement of [ne iii]λ3869 detection, the latter provide a more representative picture of neon emission-line properties in the mosdef sample. the [ne iii]λ3869/[o ii]λ3727 ratio (ne3o2) is anticorrelated with stellar mass in z ∼ 2 galaxies, as expected based on the mass-metallicity relation. it is also positively correlated with the [o iii]λ5007/[o ii]λ3727 ratio (o32), but z ∼ 2 line ratios are offset toward higher ne3o2 at fixed o32, compared with both local star-forming galaxies and individual h ii regions. despite the offset toward higher ne3o2 at fixed o32 at z ∼ 2, biases in inferred ne3o2-based metallicity are small. accordingly, ne3o2 may serve as an important metallicity indicator deep into the reionization epoch. analyzing additional rest-optical line ratios including [ne iii]λ3869/[o iii]λ5007 (ne3o3) and [o iii]λ5007/hβ (o3hβ), we conclude that the nebular emission-line ratios of z ∼ 2 star-forming galaxies suggest a harder ionizing spectrum (lower stellar metallicity, i.e., fe/h) at fixed gas-phase oxygen abundance, compared to systems at z ∼ 0. these new results based on neon lend support to the physical picture painted by oxygen, nitrogen, hydrogen, and sulfur emission of an ionized interstellar medium in high-redshift star-forming galaxies irradiated by chemically young, α-enhanced massive stars. * 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. | the mosdef survey: neon as a probe of ism physical conditions at high redshift |
we performed the deepest search for an x-ray emission line at between 0.5 and 7 kev from non-baryonic dark matter by the suzaku xis. dark matter associated with the milky way was selected as the target to obtain the best signal-to-noise ratio. from the suzaku archive, we selected 187 data sets of blank-sky regions that were dominated by the x-ray diffuse background. the data sets were from 2005 to 2013. the instrumental responses were adjusted by multiple calibration data sets of the crab nebula. we also improved the technique of subtracting lines of instrumental origin. these energy spectra were well described by x-ray emission due to charge exchange around the solar system, hot plasma in and around the milky way, and the superposition of extra-galactic point sources. a signal of a narrow emission-line was searched for, and the significance of detection was evaluated in consideration of the blind search method (the look-elsewhere effect). our results exhibited no significant detection of an emission line feature from dark matter. the 3 σ upper limit for the emission line intensity between 1 and 7 kev was ∼ 10-2 photons cm-2 s-1 sr-1, or ∼ 5 × 10-4 photons cm-2 s-1 sr-1 per m⊙ pc-2, assuming a dark matter distribution with the galactic rotation curve. the parameters of sterile neutrinos as candidates of dark-matter were also constrained. | a search for a kev signature of radiatively decaying dark matter with suzaku xis observations of the x-ray diffuse background |
primitive meteorites preserve the chemical and isotopic composition of the first aggregates that formed from dust and gas in the solar nebula during the earliest stages of solar system evolution. gradual increase in the size of solid bodies from dust to aggregates and then to planetesimals finally led to the formation of planets within a few to tens of million years after the start of condensation. thus the rocky planets of the inner solar system are likely the result of the accumulation of numerous smaller primitive as well as differentiated bodies. the chemically most primitive known meteorites are chondrites and they consist mostly of metal and silicates. chondritic meteorites are derived from distinct primitive planetary bodies that experienced only limited element fractionation during formation and subsequent differentiation. different chondrite classes show distinct chemical and isotopic characteristics, which may reflect heterogeneities in the solar nebula and the slightly different pathways of their formation. to a first approximation the chemical composition of the bulk earth bears great similarities to primitive meteorites. however, for some elements there are striking and significant differences. the earth shows a much stronger depletion of the moderate to highly volatile elements compared to chondrites. in addition, mixing trends of specific isotopes reveal that the earth is most enriched in s -process isotopes compared to all other analysed bulk solar system materials. it is currently not possible to fully define and quantify the different chemical and isotopic materials that formed the earth, because a major component seems missing in the extant collections of extraterrestrial samples. variations in nucleosynthetic isotope compositions as well as the strong depletion of moderately and strongly volatile elements points towards a source in the inner solar system for this missing material. it is conceivable that venus and mercury contain a much larger fraction of this missing component. thus, for a complete reconstruction of the conditions that led to the formation of the inner solar system planets (mercury to mars) samples from the inner planets venus and mercury are of great interest and importance. high precision chemical and isotopic analyses in the laboratory of rocky material from inner solar system bodies could complete the knowledge on the chemical, isotopic and mineralogical make-up of the solar nebula just prior to planet formation and enhance our understanding of the evolution of the solar nebula in general and the formation of the rocky planets in particular. | accretion of the earth—missing components? |
in this study, we present one-dimensional, non-local-thermodynamic-equilibrium, radiative transfer simulations (using cmfgen) in which we introduce micro-clumping at nebular times into two type ia supernova ejecta models. we use one sub-chandrasekhar (sub-mch) ejecta model with 1.04 m⊙ and one chandrasekhar (mch) ejecta model with 1.40 m⊙. we introduce clumping factors f = 0.33, 0.25, and 0.10, which are constant throughout the ejecta, and compare results to the unclumped f = 1.0 case. we find that clumping is a natural mechanism to reduce the ionization of the ejecta, reducing emission from [fe iii], [ar iii], and [s iii] by a factor of a few. for decreasing values of the clumping factor f, the [ca ii] λλ7291,7324 doublet became a dominant cooling line for our mch model but remained weak in our sub-mch model. strong [ca ii] λλ7291,7324 indicates non-thermal heating in that region and may constrain explosion modelling. due to the low abundance of stable nickel, our sub-mch model never showed the [ni ii] 1.939-μm diagnostic feature for all clumping values. | understanding nebular spectra of type ia supernovae |
the theory of optical thermodynamics provides a comprehensive framework that enables a self-consistent description of the intricate dynamics of nonlinear multimoded photonic systems. this theory, among others, predicts a pressurelike intensive quantity (p ^) that is conjugate to the system's total number of modes (m )—its corresponding extensive variable. yet at this point, the nature of this intensive quantity is still nebulous. in this letter, we elucidate the physical origin of the optical thermodynamic pressure and demonstrate its dual essence. in this context, we rigorously derive an expression that splits p ^ into two distinct components, a term that is explicitly tied to the electrodynamic radiation pressure and a second entropic part that is responsible for the entropy change. we utilize this result to establish a formalism that simplifies the quantification of radiation pressure under nonlinear equilibrium conditions, thus eliminating the need for a tedious evaluation of the maxwell stress tensor. our theoretical analysis is corroborated by numerical simulations carried out in highly multimoded nonlinear optical structures. these results may provide a novel way in predicting and controlling radiation pressure processes in a variety of nonlinear electromagnetic settings. | nature of optical thermodynamic pressure exerted in highly multimoded nonlinear systems |
volatiles from the solar nebula are known to be present in earth's deep mantle. the core also may contain solar nebula-derived volatiles, but in unknown amounts. here we use calculations of volatile ingassing and degassing to estimate the abundance of primordial 3he now in the core and track the rate of 3he exchange between the core and mantle through earth history. we apply an ingassing model that includes a silicate magma ocean and an iron-rich proto-core coupled to a nebular atmosphere of solar composition to calculate the amounts of 3he acquired by the mantle and core during accretion and core formation. using experimentally determined partitioning between core-forming metals and silicate magma, we find that dissolution from the nebular atmosphere deposits one or more petagrams of 3he into the proto-core. following accretion, 3he exchange depends on the convective history of the coupled core-mantle system. we combine determinations of the present-day surface 3he flux with estimates of the present-day mantle 3he abundance, mantle and core heat fluxes, and our ingassed 3he abundances in a convective degassing model. according to this model, the mantle 3he abundance is evolving toward a statistical steady state, in which surface losses are compensated by enrichments from the core. | primordial helium-3 exchange between earth's core and mantle |
the most massive stars dominate the chemical enrichment, mechanical and radiative feedback, and energy budget of their host environments. yet how massive stars initially form and how they evolve throughout their lives is ambiguous. the mass loss of the most massive stars remains a key unknown in stellar physics, with consequences for stellar feedback and populations. in this work, we compare grids of very massive star (vms) models with masses ranging from 80 to 1000 m⊙, for a range of input physics. we include enhanced winds close to the eddington limit as a comparison to standard o-star winds, with consequences for present-day observations of ~50-100 m⊙ stars. we probe the relevant surface h abundances (xs) to determine the key traits of vms evolution compared to o stars. we find fundamental differences in the behaviour of our models with the enhanced-wind prescription, with a convergence on the stellar mass at 1.6 myr, regardless of the initial mass. it turns out that xs is an important tool in deciphering the initial mass due to the chemically homogeneous nature of vms above a mass threshold. we use xs to break the degeneracy of the initial masses of both components of a detached binary, and a sample of wnh stars in the tarantula nebula. we find that for some objects, the initial masses are unrestricted and, as such, even initial masses of the order 1000 m⊙ are not excluded. coupled with the mass turnover at 1.6 myr, xs can be used as a 'clock' to determine the upper stellar mass. | the hydrogen clock to infer the upper stellar mass |
thermal refuges are thermally distinct riverscape features used by aquatic organisms during unfavourable thermal events, facilitating resilience in marginal environments. however, the thermal refuge concept is nebulous, and the often interchangeable use of the term 'thermal refugia' creates additional ambiguity. we argue that lexical differences resulting from divergent scholarly trainings hinder holistic understanding of thermal refuges; thus, existing studies would benefit from a structured framework for thermal refuge conceptualization. herein, we articulate an ecohydrological typology for defining and characterizing thermal refuges in streams and rivers by identifying key hydrological and thermal characteristics and variations in ecological function described in the literature. we use concepts that are easily definable, measurable and transferable across disciplines, riverscapes and species to discriminate among thermal refuge types. future work can use our typology as a basis for more informed interdisciplinary discussion and interpretation of thermal refuges' role in riverscapes through more hypothesis‑driven research and conservation‑focused management. | an ecohydrological typology for thermal refuges in streams and rivers |
we present spitzer space telescope 3.6 and 4.5 μm observations of the binary neutron star merger gw170817 at 43, 74, and 264 days post-merger. using the final observation as a template, we uncover a source at the position of gw170817 at 4.5 μm with a brightness of 22.9 ± 0.3 ab mag at 43 days and 23.8 ± 0.3 ab mag at 74 days (the uncertainty is dominated by systematics from the image subtraction); no obvious source is detected at 3.6 μm to a 3σ limit of >23.3 ab mag in both epochs. the measured brightness is dimmer by a factor of about 2-3 times compared to our previously published kilonova model, which is based on uv, optical, and near-infrared data at ≲30 days. however, the observed fading rate and color (m 3.6-m 4.5 ≳ 0 ab mag) are consistent with our model. we suggest that the discrepancy is likely due to a transition to the nebular phase, or a reduced thermalization efficiency at such late time. using the spitzer data as a guide, we briefly discuss the prospects of observing future binary neutron star mergers with spitzer (in the laser interferometer gravitational-wave observatory (ligo)/virgo observing run 3) and the james webb space telescope (in ligo/virgo observing run 4 and beyond). | spitzer space telescope infrared observations of the binary neutron star merger gw170817 |
the physical origin of the near-ultraviolet mg ii emission remains an underexplored domain, unlike more typical emission lines that are detected in the spectra of star-forming galaxies. we explore the nebular and physical properties of a sample of 381 galaxies between 0.70 < z < 2.34 drawn from the muse hubble ultra deep survey. the spectra of these galaxies show a wide variety of profiles of the mg ii λλ2796, 2803 resonant doublet, from absorption to emission. we present a study on the main drivers for the detection of mg ii emission in galaxy spectra. by exploiting photoionization models, we verified that the emission-line ratios observed in galaxies with mg ii in emission are consistent with nebular emission from hii regions. from a simultaneous analysis of muse spectra and ancillary hubble space telescope information through spectral energy distribution fitting, we find that galaxies with mg ii in emission have lower stellar masses, smaller sizes, bluer spectral slopes, and lower optical depth than those with absorption. this leads us to suggest that mg ii emission is a potential tracer of physical conditions that are not merely related to those of the ionized gas. we show that these differences in mg ii emission and absorption can be explained in terms of a higher dust and neutral gas content in the interstellar medium (ism) of galaxies showing mg ii in absorption, which confirms the extreme sensitivity of mg ii to the presence of the neutral ism. we conclude with an analogy between the mg ii doublet and the ly α line that lies in their resonant nature. further investigations with current and future facilities, including the james webb space telescope, are promising because the detection of mg ii emission and its potential connection with lyα could provide new insights into the ism content in the early universe. based on observations made with eso telescopes at the la silla paranal observatory under programs 094.a-0289(b), 095.a-0010(a), 096.a-0045(a) and 096.a-0045(b). | the muse hubble ultra deep field survey. xii. mg ii emission and absorption in star-forming galaxies |
we stack the rest-frame ultraviolet spectra of n = 14 highly magnified gravitationally lensed galaxies at redshifts 1.6< z< 3.6. the resulting new composite spans 900< {λ }{rest}< 3000 å, with a peak signal-to-noise ratio (s/n) of 103 per spectral resolution element (∼100 km s-1). it is the highest s/n, highest spectral resolution composite spectrum of z ∼ 2-3 galaxies yet published. the composite reveals numerous weak nebular emission lines and stellar photospheric absorption lines that can serve as new physical diagnostics, particularly at high redshift with the james webb space telescope (jwst). we report equivalent widths to aid in proposing for and interpreting jwst spectra. we examine the velocity profiles of strong absorption features in the composite, and in a matched composite of z∼ 0 cos/hst galaxy spectra. we find remarkable similarity in the velocity profiles at z∼ 0 and z∼ 2, suggesting that similar physical processes control the outflows across cosmic time. while the maximum outflow velocity depends strongly on ionization potential, the absorption-weighted mean velocity does not. as such, the bulk of the high-ionization absorption traces the low-ionization gas, with an additional blueshifted absorption tail extending to at least -2000 km s-1. we interpret this tail as arising from the stellar wind and photospheres of massive stars. starburst99 models are able to replicate this high-velocity absorption tail. however, these theoretical models poorly reproduce several of the photospheric absorption features, indicating that improvements are needed to match observational constraints on the massive stellar content of star-forming galaxies at z∼ 2. we publicly release our composite spectra. | the magellan evolution of galaxies spectroscopic and ultraviolet reference atlas (megasaura). ii. stacked spectra |
the decomposition of the rotation curve of galaxies into contribution from the disc and dark halo remains uncertain and depends on the adopted mass-to-light ratio (m/l) of the disc. given the vertical velocity dispersion of stars and disc scale height, the disc surface mass density and hence the m/l can be estimated. we address a conceptual problem with previous measurements of the scale height and dispersion. when using this method, the dispersion and scale height must refer to the same population of stars. the scale height is obtained from near-infrared (ir) studies of edge-on galaxies and is weighted towards older kinematically hotter stars, whereas the dispersion obtained from integrated light in the optical bands includes stars of all ages. we aim to extract the dispersion for the hotter stars, so that it can then be used with the correct scale height to obtain the disc surface mass density. we use a sample of planetary nebulae (pne) as dynamical tracers in the face-on galaxy ngc 628. we extract two different dispersions from its velocity histogram - representing the older and younger pne. we also present complementary stellar absorption spectra in the inner regions of this galaxy and use a direct pixel fitting technique to extract the two components. our analysis concludes that previous studies, which do not take account of the young disc, underestimate the disc surface mass density by a factor of ∼2. this is sufficient to make a maximal disc for ngc 628 appear like a submaximal disc. | resolving the disc-halo degeneracy - i: a look at ngc 628 |
mirror stars are a generic prediction of dissipative dark matter models, including minimal atomic dark matter and twin baryons in the mirror twin higgs. mirror stars can capture regular matter from the interstellar medium through extremely suppressed kinetic mixing interactions between the regular and the dark photon. this accumulated "nugget" will draw heat from the mirror star core and emit highly characteristic x-ray and optical signals. in this work, we devise a general parameterization of mirror star nugget properties that is independent of the unknown details of mirror star stellar physics, and use the cloudy spectral synthesis code to obtain realistic and comprehensive predictions for the thermal emissions from optically thin mirror star nuggets. we find that mirror star nuggets populate an extremely well-defined and narrow region of the hr diagram that only partially overlaps with the white dwarf population. our detailed spectral predictions, which we make publicly available, allow us to demonstrate that optically thin nuggets can be clearly distinguished from white dwarf stars by their continuum spectrum shape, and from planetary nebulae and other optically thin standard sources by their highly exotic emission line ratios. our work will enable realistic mirror star telescope searches, which may reveal the detailed nature of dark matter. | electromagnetic signatures of mirror stars |
the multi-unit spectroscopic explorer (muse) has enabled a renaissance of the planetary nebula luminosity function (pnlf) as a standard candle. in the case of ngc 300, we learned that the precise spectrophotometry of muse was crucial to obtain an accurate pnlf distance. we present the advantage of the integral field spectrograph compared to the slit spectrograph in delivering precise spectrophotometry by simulating a slit observation on integral field spectroscopy data. we also discuss the possible systematic shift in measuring the pnlf distance using the least-square method, especially when the pnlf cutoff is affected by small number statistics. | precision spectrophotometry for pnlf distances: the case of ngc 300 |
we present an early-phase g-band light curve and visual-wavelength spectra of the normal type ia supernova (sn) 2013gy. the light curve is constructed by determining the appropriate s-corrections to transform kait natural-system b- and v-band photometry and carnegie supernova project natural-system g-band photometry to the pan-starrs1 g-band natural photometric system. a markov chain monte carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of 2.16+0.06-0.06 and a time of first light of mjd 56629.4+0.1-0.1, which is 1.93+0.12-0.13 days (i.e., < 48 h) before the discovery date (2013 december 4.84 ut) and -19.10+0.12-0.13 days before the time of b-band maximum (mjd 56648.5 ± 0.1). the estimate of the time of first light is consistent with the explosion time inferred from the evolution of the si iiλ6355 doppler velocity. furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to rc ≤ 4 r⊙. in addition to our early-time constraints, we used a deep +235 day nebular-phase spectrum from magellan/imacs to place a stripped h-mass limit of < 0.018 m⊙. combined, these limits effectively rule out h-rich nondegenerate companions. the spectra 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/627/a174. | discovery and progenitor constraints on the type ia supernova 2013gy |
molecular d/h ratios are frequently used to probe the chemical past of solar system volatiles. yet it is unclear which parts of the solar nebula hosted an active deuterium fractionation chemistry. to address this question, we present 0"2-0"4 atacama large millimeter/submillimeter array (alma) observations of dco+ and dcn 2-1, 3-2, and 4-3 toward the nearby protoplanetary disk around tw hya, taken as part of the tw hya rosetta stone project, augmented with archival data. dco+ is characterized by an excitation temperature of ∼40 k across the 70 au radius pebble disk, indicative of emission from a warm, elevated molecular layer. tentatively, dcn is present at even higher temperatures. both dco+ and dcn present substantial emission cavities in the inner disk, while in the outer disk the dco+ and dcn morphologies diverge: most dcn emission originates from a narrow ring peaking around 30 au, with some additional diffuse dcn emission present at larger radii, while dco+ is present in a broad structured ring that extends past the pebble disk. based on a set of simple parametric disk abundance models, these emission patterns can be explained by a near-constant dcn abundance exterior to the cavity, and an increasing dco+ abundance with radius. in conclusion, the alma observations reveal an active deuterium fractionation chemistry in multiple disk regions around tw hya, but not in the cold planetesimal-forming midplane and in the inner disk. more observations are needed to explore whether deuterium fractionation is actually absent in these latter regions, and if its absence is a common feature or something peculiar to the old tw hya disk. | the tw hya rosetta stone project. i. radial and vertical distributions of dcn and dco+ |
we present a new clustering method, significance mode analysis (sigma), for extracting co-spatial and co-moving stellar populations from large-scale surveys such as esa gaia. the method studies the topological properties of the density field in the multidimensional phase space. we validated sigma on simulated clusters and find that it outperforms competing methods, especially in cases where many clusters are closely spaced. we applied the new method to gaia dr3 data of the closest ob association to earth, scorpio-centaurus (sco-cen), and find more than 13 000 co-moving young objects, about 19% of which have a substellar mass. sigma finds 37 co-moving clusters in sco-cen. these clusters are independently validated by their narrow hertzsprung-russell diagram sequences and, to a certain extent, by their association with massive stars too bright for gaia, and are hence unknown to sigma. we compared our results with similar recent work and find that the sigma algorithm recovers richer populations, is able to distinguish clusters with velocity differences down to about 0.5 km s−1, and reaches cluster volume densities as low as 0.01 sources pc−3. the 3d distribution of these 37 coeval clusters implies a larger extent and volume for the sco-cen ob association than typically assumed in the literature. additionally, we find the association more actively star-forming and dynamically complex than previously thought. we confirm that the star-forming molecular clouds in the sco-cen region, namely, ophiuchus, l134/l183, pipe nebula, corona australis, lupus, and chamaeleon, are part of the sco-cen association. the application of sigma to sco-cen demonstrates that advanced machine learning tools applied to the superb gaia data allows an accurate census of the young populations to be constructed, which in turn allows us to quantify their dynamics and recreate the recent star formation history of the local milky way. full table e.1 is only 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/677/a59 interactive figs. 10, 12, and 13 are available at https://www.aanda.org. | significance mode analysis (sigma) for hierarchical structures. an application to the sco-cen ob association |
photoionization models obtained with numerical codes are widely used to study the physics of the interstellar medium (planetary nebulae, hii regions, etc). grids of models are performed to understand the effects of the different parameters used to describe the regions on the observables (mainly emission line intensities). most of the time, only a small part of the computed results of such grids are published, and they are sometimes hard to obtain in a user-friendly format. we present here the mexican million models database (3mdb), an effort to resolve both of these issues in the form of a database of photoionization models, easily accessible through the mysql protocol, and containing a lot of useful outputs from the models, such as the intensities of 178 emission lines, the ionic fractions of all the ions, etc. some examples of the use of the 3mdb are also presented. | a virtual observatory for photoionized nebulae: the mexican million models database (3mdb). |
we find capillary wave turbulence (wt) spanning multiple dynamical regimes and geometries, all within a 40 μ l volume microfluidic system. this study is made viable with recent advances in ultra-high-speed digital holographic microscopy, providing 10 μ s time and 10 nm spatial resolutions for images across the entire field at speeds sufficient to capture the salient wave phenomena. the observed wt types are: (i) discrete wave turbulence (dwt) dominated by finite domain effects, (ii) kinetic wave turbulence (kwt) that approximately satisfies weak wave turbulence (wwt) theory, and (iii) intermediate wave turbulence (iwt) that exhibits features from both dwt and kwt. we show that wt regime depends on input power and wavenumber, and we provide simple nondimensional parameters - derived from wwt theory - for intra-spectrum regime classification. using the nondimensional parameters, a bulk nonlinearity metric is defined that employs bicoherence-based weighting. analysis of experimental results reveals a correspondence between the theoretical regime classifiers and the observed phenomena. at sufficiently high input powers, the phenomena substantially depart from the wwt theory and reveal a regime of strongly nonlinear wave turbulence (swt) defined by shallower spectral slopes that achieve a constant slope value over a range of input powers. this may suggest a corresponding power-law solution to the governing equations. this work augments current understanding of wt regimes and behaviors, and directly applies to many fields beyond fluid mechanics. for example, swt appears upon the fluid interface at powers less than required for atomization, indicating that further study of swt is needed to properly understand ultrasound-driven fuel spray atomization and drug and agricultural nebulization. | identification of weakly to strongly-turbulent three-wave processes in a micro-scale system |
we present extensive ultraviolet (uv) and optical photometric and optical spectroscopic follow-up of supernova (sn) 2021gno by the 'precision observations of infant supernova explosions' (poise) project, starting less than 2 d after the explosion. given its intermediate luminosity, fast photometric evolution, and quick transition to the nebular phase with spectra dominated by [ca ii] lines, sn 2021gno belongs to the small family of calcium-rich transients. moreover, it shows double-peaked light curves, a phenomenon shared with only four other calcium-rich events. the projected distance from the centre of the host galaxy is not as large as other objects in this family. the initial optical light-curve peaks coincide with a very quick decline of the uv flux, indicating a fast initial cooling phase. through hydrodynamical modelling of the bolometric light curve and line velocity evolution, we found that the observations are compatible with the explosion of a highly stripped massive star with an ejecta mass of $0.8\, m_\odot$ and a 56ni mass of 0.024 m⊙. the initial cooling phase (first light-curve peak) is explained by the presence of an extended circumstellar material comprising ~$10^{-2}\, {\rm m}_{\odot }$ with an extension of $1100\, r_{\odot }$. we discuss if hydrogen features are present in both maximum-light and nebular spectra, and their implications in terms of the proposed progenitor scenarios for calcium-rich transients. | sn 2021gno: a calcium-rich transient with double-peaked light curves |
we report on the spectroscopic confirmation of 68 new bright (g = 13.5-17.2 mag) and blue (pre-)white dwarfs (wds). this finding has allowed us to almost double the number of the hottest (teff ≥ 60 kk) known wds brighter than g = 16 mag. we increased the number of known ultra-high excitation (uhe) wds by 20%, found one unambiguous close binary system consisting of one da wd with an irradiated low-mass companion, one dao, and one doa wd that are likely in their transformation phase of becoming pure da wds, one rare, naked o(h) star, two da and two dao wds with teff possibly in excess of 100 kk, three new doz wds, and three of our targets are central stars of (possible) planetary nebulae. using non-local thermodynamic equilibrium models, we derived the atmospheric parameters of these stars and by fitting their spectral energy distribution we derived their radii, luminosities, and gravity masses. in addition, we derived their masses in the kiel and hertzsprung-russell diagram (hrd). we find that kiel, hrd, and gravity mass agree only in half of the cases. this is not unexpected and we attribute this to the neglect of metal opacities, possibly stratified atmospheres, as well as possible uncertainties of the parallax zero point determination. furthermore, we carried out a search for photometric variability in our targets using archival data, finding that 26% of our targets are variable. this includes 15 new variable stars, with only one of them being clearly an irradiation effect system. strikingly, the majority of the variable stars exhibit non-sinusoidal light-curve shapes, which are unlikely explained in terms of close binary systems. we propose that a significant fraction of all (not just uhe) wds develop spots when entering the wd cooling phase. we suggest that this could be related to the on-set of weak magnetic fields and possibly diffusion. | the bright blue side of the night sky: spectroscopic survey of bright and hot (pre-) white dwarfs |
the luminous type iin sn 2010jl shows strong signs of interaction between the sn ejecta and dense circumstellar material. dust may be present in the unshocked ejecta; the cool, dense shell (cds) between the shocks in the interaction region; or in the circumstellar medium (csm). we present and model new optical and infrared photometry and spectroscopy of sn 2010jl from 82 to 1367 days since explosion. we evaluate the photometric and spectroscopic evolution using the radiative transfer codes mocassin and damocles, respectively. we propose an interaction scenario and investigate the resulting dust formation scenarios and dust masses. we find that sn 2010jl has been continuously forming dust based on the evolution of its infrared emission and optical spectra. there is evidence for preexisting dust in the csm as well as new dust formation in the cds and/or ejecta. we estimate that 0.005-0.01 m⊙ of predominantly carbon dust grains has formed in sn 2010jl by ∼1400 days post-outburst. | disentangling dust components in sn 2010jl: the first 1400 days |
we report the detection of emission in the v = 1 - 0 p(1) (3.51629 μm) and p(2) (3.60776 μm) rovibrational lines of the helium hydride cation (heh+) from the planetary nebula ngc 7027. these detections were obtained with the ishell spectrograph on nasa's infrared telescope facility on maunakea. they confirm the discovery of heh+ reported recently by güsten et al., who used the great instrument on the sofia airborne observatory to observe its pure rotational j = 1 - 0 transition at 149.137 μm. the flux measured for the heh+ v = 1 - 0 p(1) line is in good agreement with our model for the formation, destruction, and excitation of heh+ in ngc 7027. the measured strength of the j = 1 - 0 pure rotational line, however, exceeds the model prediction significantly, as does that of the v = 1 - 0 p(2) line, by factors of 2.9 and 2.3 respectively. possible causes of these discrepancies are discussed. our observations of ngc 7027, covering the 3.26-3.93 μm spectral region, have led to the detection of more than 60 spectral lines including nine rovibrational emissions from ch+. the latter are detected for the first time in an astronomical source. | detection of vibrational emissions from the helium hydride ion (heh+) in the planetary nebula ngc 7027 |
we here report the detection of the nebular he ii λ4686 line in 32 h ii regions in the metal-poor collisional ring galaxy cartwheel using the multi-unit spectroscopic explorer (muse) data set. the measured i(he ii λ4686)/i(h β) ratio varies from 0.004 to 0.07, with a mean value of 0.010 ± 0.003. ten of these 32 h ii regions are coincident with the location of an ultra luminous x-ray (ulx) source. we used the flux ratios of important diagnostic lines and results of photoionization by simple stellar populations (ssps) to investigate the likely physical mechanisms responsible for the ionization of he+. we find that the majority of the regions (27) are consistent with photoionization by star clusters in their wolf-rayet (wr) phase with initial ionization parameter -3.5 < log ⟨u⟩ < -2.0. blue bump (bb), the characteristic feature of the wr stars, however, is not detected in any of the spectra. we demonstrate that this non-detection is due to the relatively low equivalent width (ew) of the bb in metal-poor ssps, in spite of containing sufficient number of wr stars to reproduce the observed i(he ii λ4686)/i(h β) ratio of ≤1.5 per cent at the cartwheel metallicity of z = 0.004. the h ii regions in the wr phase that are coincident with a ulx source do not show line ratios characteristic of ionization by x-ray sources. however, the ulx sources may have a role to play in the ionization of he+ in two (#99, 144) of the five regions that are not in the wr phase. ionization by radiative shocks along with the presence of channels for the selective leakage of ionizing photons are the likely scenarios in #17 and #148, the two regions with the highest observed i(he ii λ4686)/i(h β) ratio. | detection of he++ ion in the star-forming ring of the cartwheel using muse data and ionizing mechanisms |
recently, the discovery of galactic frb 200428 associated with an x-ray burst (xrb) of sgr 1935+2154 has built a bridge between frbs and magnetar activities. in this letter, we assume that the xrb occurs in the magnetar magnetosphere. we show that the observational properties of frb 200428 and the associated xrb are consistent with the predictions of synchrotron maser emission at ultrarelativistic magnetized shocks, including radiation efficiency, similar energy occurrence frequency distributions, and simultaneous arrive times. it requires that the upstream medium is a mildly relativistic baryonic shell ejected by a previous flare. the energy injection by flares responsible for the radio bursts will produce a magnetar wind nebula, which has been used to explain the persistent radio source associated with frb 121102. we find that the radio continuum around sgr 1935+2154 can be well understood in the magnetar wind nebula model, by assuming the same energy injection rate $\dot{e}\propto {t}^{-1.37}$ as frb 121102. the required baryonic mass is also estimated form the observations of frb 121102 by the green bank telescope and the five-hundred-meter aperture spherical telescope. by assuming the same radiation efficiency $\eta \sim {10}^{-5}$ , the total baryonic mass ejected from the central magnetar is about 0.005 solar mass. this value is much larger than the typical mass of a magnetar outer crust, but is comparable to the total mass of a magnetar crust. | understanding frb 200428 in the synchrotron maser shock model: consistency and possible challenge |
dwarf spheroidal galaxies (dsphs) have been extensively investigated in the local group, but their low luminosity and surface brightness make similar work in more distant galaxy groups challenging. modern instrumentation unlocks the possibility of scrutinizing these faint systems in other environments, expanding the parameter space of group properties. we use muse spectroscopy to study the properties of 14 known or suspected dsph satellites of cen a. twelve targets are confirmed to be group members based on their radial velocities. two targets are background galaxies at ∼50 mpc: kk 198 is a face-on spiral galaxy, and dw1315-45 is an ultra-diffuse galaxy with an effective radius of ∼2300 pc. the 12 confirmed dsph members of the cen a group have old and metal-poor stellar populations and follow the stellar metallicity-luminosity relation defined by the dwarf galaxies in the local group. in the three brightest dwarf galaxies (kk 197, kks 55, and kks 58), we identify globular clusters, as well as a planetary nebula in kk 197, although its association with this galaxy and/or the extended halo of cen a is uncertain. using four discrete tracers, we measure the velocity dispersion and dynamical mass of kk 197. this dsph appears dark matter dominated and lies on the radial acceleration relation of star-forming galaxies within the uncertainties. it also is consistent with predictions stemming from modified newtonian dynamics. surprisingly, in the dwarf kk 203 we find an extended hα ring. careful examination of hubble space telescope photometry reveals a very low level of star formation at ages between 30 and 300 myr. the hα emission is most likely linked to a ∼40 myr old supernova remnant, although other possibilities for its origin cannot be entirely ruled out. the fully reduced data cubes 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/645/a92 based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso program 0101.a-0193(a) and 0101.a-0193(b). | the properties of dwarf spheroidal galaxies in the cen a group. stellar populations, internal dynamics, and a heart-shaped hα ring |
we study the utility of the [o i] 6300 å forbidden line for identifying and interpreting externally driven photoevaporative winds in different environments and at a range of distances. thermally excited [o i] 6300 å is a well-known tracer of inner disc winds, so any external contribution needs to be distinguishable. in external winds, the line is not thermally excited and instead results from the dissociation of oh, and we study how the line luminosity resulting from that process scales with the disc/environmental parameters. we find that the line luminosity increases dramatically with fuv radiation field strength above around 5000 g0. the predicted luminosities from our models are consistent with measurements of the line luminosity of proplyds in the orion nebula cluster. the high luminosity in strong uv environments alone may act as a diagnostic, but a rise in the [o i]-to-accretion luminosity ratio is predicted to better separate the two contributions. this could provide a means of identifying external photoevaporation in distant clusters where the proplyd morphology of evaporating discs cannot be spatially resolved. | [o i] 6300 å emission as a probe of external photoevaporation of protoplanetary discs |
we present explosive transient spectral simulator (extrass), a newly developed code aimed at generating 3d spectra for supernovae in the nebular phase by using modern multidimensional explosion models as input. it is well established that supernovae are asymmetric by nature, and that the morphology is encoded in the line profiles during the nebular phase, months after the explosion. in this work, we use extrass to study one such simulation of a $3.3\, \mathrm{ m}_\odot$ he-core explosion ($m_\text{ejecta}=1.3\, m_\odot$, $e_\text{kin}=1.05\times 10^{51}\,$erg) modelled with the prometheus-hotb code and evolved to the homologous phase. our code calculates the energy deposition from the radioactive decay of 56ni → 56co → 56fe and uses this to determine the non-local-thermodynamic-equilibrium temperature, excitation, and ionization structure across the nebula. from the physical condition solutions we generate the emissivities to construct spectra depending on viewing angles. our results show large variations in the line profiles with viewing angles, as diagnosed by the first three moments of the line profiles; shifts, widths, and skewness. we compare line profiles from different elements, and study the morphology of line-of-sight slices that determine the flux at each part of a line profile. we find that excitation conditions can sometimes make the momentum vector of the ejecta emitting in the excited states significantly different from that of the bulk of the ejecta of the respective element, thus giving blueshifted lines for bulk receding material, and vice versa. we compare the 3.3 m⊙ he-core model to observations of the type ib supernova sn 2007y. | modelling supernova nebular lines in 3d with extrass |
thermonuclear and core-collapse supernova remnants (snrs) are the nebular leftovers of defunct stars. their morphology and emission properties provide insights into the evolutionary history of the progenitor star. but while some snrs are spherical, as expected from a point-like explosion expanding into a roughly uniform medium, many others exhibit complex non-spherical morphologies that are often not easily explained. in this work, we use 3d magnetohydrodynamic simulations to show that rectangular and jet-like morphologies can be explained by supernovae (sne), either type ia or type ii, expanding within anisotropic, bipolar stellar wind bubbles driven by the progenitor star. the stellar wind has an anisotropic density distribution, which channels the sn ejecta differently depending on the anisotropy characteristics. we compute synthetic thermal (x-ray) and non-thermal (synchrotron) emission maps from our numerical simulations to compare with observations. we find rectangular morphologies are generated when the stellar wind has a high-mass loss rate and forms a dense, narrow disc at the equatorial region. instead, a jet-like or ear-like morphology is obtained when the stellar wind develops a wide, dense disc. stellar winds with low mass-loss rates do not strongly influence the snr morphology. finally, our synthetic synchrotron and x-ray maps for the high mass-loss rate case qualitatively agree with the observations of the snrs g332.5-5.6 and g290.1-0.8. | the sculpting of rectangular and jet-like morphologies in supernova remnants by anisotropic equatorially confined progenitor stellar winds |
we present [c ii] 158 μm and [o i] 63 μm observations of the bipolar h ii region rcw 36 in the vela c molecular cloud, obtained within the sofia legacy project feedback, which is complemented with apex 12/13co (3-2) and chandra x-ray (0.5-7 kev) data. this shows that the molecular ring, forming the waist of the bipolar nebula, expands with a velocity of 1-1.9 km s-1. we also observe an increased line width in the ring, indicating that turbulence is driven by energy injection from the stellar feedback. the bipolar cavity hosts blueshifted expanding [c ii] shells at 5.2 ± 0.5 ± 0.5 km s-1 (statistical and systematic uncertainty), which indicates that expansion out of the dense gas happens nonuniformly and that the observed bipolar phase might be relatively short (~0.2 myr). the x-ray observations show diffuse emission that traces a hot plasma, created by stellar winds, in and around rcw 36. at least 50% of the stellar wind energy is missing in rcw 36. this is likely due to leakage that is clearing even larger cavities around the bipolar rcw 36 region. lastly, the cavities host high-velocity wings in [c ii], which indicates relatively high mass ejection rates (~5 × 10-4 m ⊙ yr-1). this could be driven by stellar winds and/or radiation but remains difficult to constrain. this local mass ejection, which can remove all mass within 1 pc of rcw 36 in 1-2 myr, and the large-scale clearing of ambient gas in the vela c cloud indicate that stellar feedback plays a significant role in suppressing the star formation efficiency. | the sofia feedback legacy survey dynamics and mass ejection in the bipolar h ii region rcw 36 |
on 2017 september 22, the icecube neutrino observatory reported the detection of the high-energy neutrino event ic 170922a, of potential astrophysical origin. it was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar txs 0506+056 (3fgl j0509.4+0541), which was in an elevated gamma-ray emission state as measured by the fermi satellite. very energetic radiation imaging telescope array system (veritas) observations of the neutrino/blazar region started on 2017 september 23 in response to the neutrino alert and continued through 2018 february 6. while no significant very-high-energy (vhe; e > 100 gev) emission was observed from the blazar by veritas in the two-week period immediately following the icecube alert, txs 0506+056 was detected by veritas with a significance of 5.8 standard deviations (σ) in the full 35 hr data set. the average photon flux of the source during this period was (8.9 ± 1.6) × 10-12 cm-2 s-1, or 1.6% of the crab nebula flux, above an energy threshold of 110 gev, with a soft spectral index of 4.8 ± 1.3. | veritas observations of the bl lac object txs 0506+056 |
aims: we study the dynamics and growth of dust particles in circumstellar disks of different masses that are prone to gravitational instability during the critical first myr of their evolution.methods: we solved the hydrodynamics equations for a self-gravitating and viscous circumstellar disk in a thin-disk limit using the feosad numerical hydrodynamics code. the dust component is made up of two different components: micron-sized dust and grown dust of evolving size. for the dust component, we considered the dust coagulation, fragmentation, momentum exchange with the gas, and dust self-gravity.results: we found that the micron-sized dust particles grow rapidly in the circumstellar disk, reaching a few cm in size in the inner 100 au of the disk during less than 100 kyr after the disk formation, provided that fragmentation velocity is 30 ms-1. due to the accretion of micron dust particles from the surrounding envelope, which serves as a micron dust reservoir, the approximately cm-sized dust particles continue to be present in the disk for more than 900 kyr after the disk formation and maintain a dust-to-gas ratio close to 0.01. we show that a strong correlation exists between the gas and pebble fluxes in the disk. we find that radial surface density distribution of pebbles in the disk shows power-law distribution with an index similar to that of the minimum-mass solar nebula regardless the disk mass. we also show that the gas surface density in our models agrees well with measurements of dust in protoplanetary disks of as 209, hd 163296, and doar 25 systems.conclusions: pebbles are formed during the very early stages of protoplanetary disk evolution. they play a crucial role in the planet formation process. our disc simulations reveal the early onset (<105 yr) of an inwards-drifting flux of pebble-sized particles that makes up approximately between one hundredth and one tenth of the gas mass flux, which appears consistent with mm-observations of discs. such a pebble flux would allow for the formation of planetesimals by streaming instability and the early growth of embryos by pebble accretion. we conclude that unlike the more common studies of isolated steady-state protoplanetary disks, more sophisticated global numerical simulations of circumstellar disk formation and evolution, including the pebble formation from the micron dust particles, are needed for performing realistic planet formation studies. | gravitoviscous protoplanetary disks with a dust component. iii. evolution of gas, dust, and pebbles |
context. radio continuum surveys of the galactic plane are an excellent way to identify different source populations such as planetary nebulae, h ii regions, and radio stars and characterize their statistical properties. the global view of star formation in the milky way (glostar) survey will study the star formation in the galactic plane between -2° < ℓ < 85° and |b| < 1° with unprecedented sensitivity in both flux density (∼40 μjy beam-1) and range ofangular scales (∼1".5 to the largest radio structures in the galaxy).aims: in this paper we present the first results obtained from a radio continuum map of a 16-square-degree-sized region of the galactic plane centered on ℓ = 32° and b = 0° (28° < ℓ < 36° and |b| < 1°). this map has a resolution of 18″ and a sensitivity of ∼60-150 μjy beam-1.methods: we present data acquired in 40 h of observations with the vla in d-configuration. two 1 ghz wide sub-bands were observed simultaneously and they were centered at 4.7 and 6.9 ghz. these data were calibrated and imaged using the obit software package. the source extraction was performed using the blobcat software package and verified through a combination of visual inspection and cross-matching with other radio and mid-infrared surveys.results: the final catalog consists of 1575 discrete radio sources and 27 large scale structures (including w43 and w44). by cross-matching with other catalogs and calculating the spectral indices (s(ν) ∝ να), we have classified 231 continuum sources as h ii regions, 37 as ionization fronts, and 46 as planetary nebulae. the longitude and latitude distribution and negative spectral indices are all consistent with the vast majority of the unclassified sources being extragalactic background sources.conclusions: we present a catalog of 1575 radio continuum sources and discuss their physical properties, emission nature, and relation to previously reported data. these first glostar results have increased the number of reliable h ii regions in this part of the galaxy by a factor of four. full version of table 7 and data from figs. 7, 9, and 17 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/627/a175 | glostar: radio source catalog i. 28° < ℓ < 36° and |b| < 1° |
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 10be, 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 26al, 53mn, and 182hf, 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 10be, 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 36cl. we review astrophysical models for the origin of 10be, 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 10be 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 |
planetary nebulae (pne) are essential tracers of the kinematics of the diffuse halo and intracluster light where stellar spectroscopy is unfeasible, due to their strong emission lines. however, that is not all they can reveal about the underlying stellar population. in recent years, it has also been found that pne in the metal-poor halos of galaxies have different properties (specific frequency, luminosity function), than pne in the more metal-rich galaxy centers. a more quantitative understanding of the role of age and metallicity in these relations would turn pne into valuable stellar-population tracers. in order to do that, a full characterization of pne in regions where the stellar light can also be analysed in detail is necessary. in this work, we make use of integral-field spectroscopic data covering the central regions of galaxies, which allow us to measure both stellar ages and metallicities as well as to detect pne. this analysis is fundamental to calibrate pne as stellar population tracers and to push our understanding of galaxy properties at unprecedented galactocentric distances. | planetary nebulae as tracers of stellar population properties: unlocking their potential with integral-field spectroscopy |
ly α nebulae ubiquitously found around z > 2 quasars can supply unique constraints on the properties of the circumgalactic medium, such as its density distribution, provided the quasar halo mass is known. we present a new method to constrain quasar halo masses based on the line-of-sight velocity dispersion maps of ly α nebulae. by using muse-like mock observations obtained from cosmological hydrodynamic simulations under the assumption of maximal quasar fluorescence, we show that the velocity dispersion radial profiles of ly α emitting gas are strongly determined by gravity and that they are thus self-similar with respect to halo mass when rescaled by the virial radius. through simple analytical arguments and by exploiting the kinematics of he ii1640 å emission for a set of observed nebulae, we show that ly α radiative transfer effects plausibly do not change the shape of the velocity dispersion profiles but only their normalization without breaking their self-similarity. taking advantage of these results, we define the variable $\eta ^{140-200}_{40-100}$ as the ratio of the median velocity dispersion in two specifically selected annuli and derive an analytical relation between $\eta ^{140-200}_{40-100}$ and the halo mass which can be directly applied to observations. we apply our method to 37 observed quasar ly α nebulae at 3 < z < 4.7 and find that their associated quasars are typically hosted by ~1012.16 ± 0.14m⊙ haloes independent of redshift within the explored range. this measurement, which is completely independent of clustering methods, is consistent with the lowest mass estimates based on quasar autocorrelation clustering at z~3 and with quasar-galaxies cross-correlation results. | resolving the physics of quasar ly α nebulae (rephyne): i. constraining quasar host halo masses through circumgalactic medium kinematics |
connecting the gas in h ii regions to the underlying source of the ionizing radiation can help us constrain the physical processes of stellar feedback and how h ii regions evolve over time. with phangs-muse, we detect nearly 24 000 h ii regions across 19 galaxies and measure the physical properties of the ionized gas (e.g. metallicity, ionization parameter, and density). we use catalogues of multiscale stellar associations from phangs-hst to obtain constraints on the age of the ionizing sources. we construct a matched catalogue of 4177 h ii regions that are clearly linked to a single ionizing association. a weak anticorrelation is observed between the association ages and the $\mathrm{h}\, \alpha$ equivalent width $\mathrm{ew}(\mathrm{h}\, \alpha)$, the $\mathrm{h}\, \alpha/\mathrm{fuv}$ flux ratio, and the ionization parameter, log q. as all three are expected to decrease as the stellar population ages, this could indicate that we observe an evolutionary sequence. this interpretation is further supported by correlations between all three properties. interpreting these as evolutionary tracers, we find younger nebulae to be more attenuated by dust and closer to giant molecular clouds, in line with recent models of feedback-regulated star formation. we also observe strong correlations with the local metallicity variations and all three proposed age tracers, suggestive of star formation preferentially occurring in locations of locally enhanced metallicity. overall, $\mathrm{ew}(\mathrm{h}\, \alpha)$ and log q show the most consistent trends and appear to be most reliable tracers for the age of an h ii region. | stellar associations powering h ii regions - i. defining an evolutionary sequence |
fine-grained ca-al-rich inclusions (fgis) in cv chondrites are suggested to be condensates formed directly from the solar nebular gas. al-mg mineral isochrons of seven fgis from reduced cv chondrites efremovka, vigarano, thiel mountains 07007, and northwest africa 8613 were obtained via in situ al-mg isotope measurements using secondary ion mass spectrometry. the slopes of the mineral isochrons for seven fgis exhibit statistically significant variations in initial 26al/27al ratios, (26al/27al)0, ranging from (5.19 ± 0.17) to (3.35 ± 0.21) × 10-5, which correspond to a relative age spread of 0.44 ± 0.07 myr. inferred upper limit of (26al/27al)0 for the fgis is identical to the solar system (26al/27al)0 of ∼5.2 × 10-5 as determined by whole-rock al-mg isochron studies for cais in cv chondrites. the intercepts of the mineral isochrons, the initial 26mg/24mg ratios the fgis formed with, are consistent with mg-isotope evolution path of a solar-composition nebular gas. the observed variations in (26al/27al)0 for fgis are essentially similar to those (∼5.2 to ∼4.2 × 10-5) for coarse-grained, igneous cais of cv chondrites that are formed by melting and solidification. if 26al was distributed homogeneously in the forming region, then our data indicate that thermal processes of condensation and melting for cai formation occurred contemporaneously and continued for at least ∼0.4 myr at the very beginning of the solar system. alternatively, the observed variations in (26al/27al)0 also indicate the possibility of heterogeneous distributions of 26al in the forming region, corresponding to a range of over at least 3.4 × 10-5 < (26al/27al)0 < 5.2 × 10-5. | variations in initial 26al/27al ratios among fine-grained ca-al-rich inclusions from reduced cv chondrites |
we use a semi-empirical model to reproduce the 0.1-10μm spectral energy distribution (sed) of a sample of 85 luminous quasars. in the model, the continuum emission from the accretion disk as well as the nebular lines are represented by a single empirical template (disk), where differences in the optical spectral index are reproduced by varying the amount of extinction. the near- and mid-infrared emission of the agn-heated dust is modelled as the combination of two black-bodies (dust). the model fitting shows that the disk and dust components are remarkably uniform among individual quasars, with differences in the observed sed largely accounted for by varying levels of obscuration in the disk as well as differences in the relative luminosity of the disk and dust components. by combining the disk-subtracted seds of the 85 quasars, we generate a template for the 1-10μm emission of the agn-heated dust. additionally, we use a sample of local seyfert 1 galaxies with full spectroscopic coverage in the 0.37μm to 39μm range to demonstrate a method for stitching together spectral segments obtained with different psf and extraction apertures. we show that the disk and dust templates obtained from luminous quasars also reproduce the optical-to-mid-infrared spectra of local seyfert 1s when the contribution from the host galaxy is properly subtracted. | disentangling accretion disk and dust emissions in the infrared spectrum of type 1 agn |
context. young terrestrial planets, when they are still embedded in a circumstellar disk, accumulate an atmosphere of nebula gas. the evolution and eventual evaporation of the protoplanetary disk affect the structure and dynamics of the planetary atmosphere. these processes, combined with other mass loss mechanisms, such as thermal escape driven by extreme ultraviolet and soft x-ray radiation from the young host star, determine how much of the primary atmosphere, if anything at all, survives into later stages of planetary evolution.aims: our aim is to explore the structure and the dynamic outflow processes of nebula-accreted atmospheres in dependency on changes in the planetary environment.methods: we integrate stationary hydrostatic models and perform time-dependent dynamical simulations to investigate the effect of a changing nebula environment on the atmospheric structure and the timescales on which the protoatmosphere reacts to these changes.results: we find that the behavior of the atmospheres strongly depends on the mass of the planetary core. for planets of about mars-mass the atmospheric structure, and in particular the atmospheric mass, changes drastically and on very short timescales whereas atmospheres around higher mass planets are much more robust and inert. | hydrodynamic simulations of captured protoatmospheres around earth-like planets |
context. how the diffuse medium of molecular clouds condenses in dense cores and how many of these cores will evolve in protostars is still a poorly understood step of the star formation process. much progress is being made in this field, thanks to the extensive imaging of star-forming regions carried out with the herschel space observatory.aims: the herschel gould belt survey key project mapped the bulk of nearby star-forming molecular clouds in five far-infrared bands with the aim of compiling complete census of prestellar cores and young, embedded protostars. from the complete sample of prestellar cores, we aim at defining the core mass function and studying its relationship with the stellar initial mass function. young stellar objects (ysos) with a residual circumstellar envelope are also detected.methods: in this paper, we present the catalogue of the dense cores and ysos/protostars extracted from the herschel maps of the lupus i, iii, and iv molecular clouds. the physical properties of the detected objects were derived by fitting their spectral energy distributions.results: a total of 532 dense cores, out of which 103 are presumably prestellar in nature, and 38 ysos/protostars have been detected in the three clouds. almost all the prestellar cores are associated with filaments against only about one third of the unbound cores and ysos/protostars. prestellar core candidates are found even in filaments that are on average thermally subcritical and over a background column density lower than that measured in other star-forming regions so far. the core mass function of the prestellar cores peaks between 0.2 and 0.3 m⊙, and it is compatible with the log-normal shape found in other regions. herschel data reveal several, previously undetected, protostars and new candidates of class 0 and class ii with transitional disks. we estimate the evolutionary status of the ysos/protostars using two independent indicators: the α index and the fitting of the spectral energy distribution from near- to far-infrared wavelengths. for 70% of the objects, the evolutionary stages derived with the two methods are in agreement.conclusions: lupus is confirmed to be a very low-mass star-forming region, in terms of both the prestellar condensations and the diffuse medium. noticeably, in the lupus clouds we have found star formation activity associated with interstellar medium at low column density, usually quiescent in other (more massive) star-forming regions. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa.full tables a.1 and a.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/qcat?j/a+a/619/a52 | a catalogue of dense cores and young stellar objects in the lupus complex based on herschel. gould belt survey observations |
the morphologies of planetary nebula have long been believed to be due to wind shaping processes in which a "fast wind" from the central star impacts a previously ejected envelope. it is assumed that asymmetries existing in the "slow wind" envelope would lead to inertial confinement, shaping the resulting interacting wind flow. we present new results demonstrating the effectiveness of common envelope evolution (cee) at producing aspherical envelopes which, when impinged upon by a spherical fast stellar wind, produce highly bipolar, jet-like outflows. we have run two simple cases using the output of a single phantom sph cee simulation. our work uses the adaptive mesh refinement code astrobear to track the interaction of the fast wind and cee ejecta allows us to follow the morphological evolution of the outflow lobes at high resolution in 3-d. our two models bracket low and high momentum output fast winds. we find the interaction leads to highly collimated bipolar outflows. in addition, the bipolar morphology depends on the fast wind momentum injection rate. with this dependence comes the initiation of significant symmetry breaking between the top and bottom bipolar lobes. our simulations, though simplified, confirm the long-standing belief that cee can plan a major role in ppn and pn shaping. these simulations are intended as an initial exploration of the post-ce/ppn flow patterns that can be expected from central source outflows and ce ejecta. | planetary nebulae shaped by common envelope evolution |
this work presents an interferometric study of the massive-binary fraction in the orion trapezium cluster with the recently comissioned gravity instrument. we observed a total of 16 stars of mainly ob spectral type. we find three previously unknown companions for θ1 ori b, θ2 ori b, and θ2 ori c. we determined a separation for the previously suspected companion of nu ori. we confirm four companions for θ1 ori a, θ1 ori c, θ1 ori d, and θ2 ori a, all with substantially improved astrometry and photometric mass estimates. we refined the orbit of the eccentric high-mass binary θ1 ori c and we are able to derive a new orbit for θ1 ori d. we find a system mass of 21.7 m⊙ and a period of 53 days. together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. we obtain a total number of 22 companions with separations up to 600 au. the companion fraction of the early b and o stars in our sample is about two, significantly higher than in earlier studies of mostly ob associations. the separation distribution hints toward a bimodality. such a bimodality has been previously found in a stars, but rarely in ob binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. we also do not find a substantial population of equal-mass binaries. the observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. again, this is in contrast to earlier findings of flat mass ratio distributions in ob associations. we excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion. | multiple star systems in the orion nebula |
hertzsprung-russell diagrams of star-forming regions show a large luminosity spread. this is incompatible with well-defined isochrones based on classic non-accreting protostellar evolution models. protostars do not evolve in isolation of their environment, but grow through accretion of gas. in addition, while an age can be defined for a star-forming region, the ages of individual stars in the region will vary. we show how the combined effect of a protostellar age spread, a consequence of sustained star formation in the molecular cloud, and time-varying protostellar accretion for individual protostars can explain the observed luminosity spread. we use a global magnetohydrodynamic simulation including a sub-scale sink particle model of a star-forming region to follow the accretion process of each star. the accretion profiles are used to compute stellar evolution models for each star, incorporating a model of how the accretion energy is distributed to the disc, radiated away at the accretion shock, or incorporated into the outer layers of the protostar. using a modelled cluster age of 5 myr, we naturally reproduce the luminosity spread and find good agreement with observations of the collinder 69 cluster, and the orion nebular cluster. it is shown how stars in binary and multiple systems can be externally forced creating recurrent episodic accretion events. we find that in a realistic global molecular cloud model massive stars build up mass over relatively long time-scales. this leads to an important conceptual change compared to the classic picture of non-accreting stellar evolution segmented into low-mass hayashi tracks and high-mass henyey tracks. | explaining the luminosity spread in young clusters: proto and pre-main sequence stellar evolution in a molecular cloud environment |
nebular phase spectra of core-collapse supernovae (sne) provide critical and unique information on the progenitor massive star and its explosion. we present a set of one-dimensional steady-state non-local thermodynamic equilibrium radiative transfer calculations of type ii sne at 300 d after explosion. guided by the results obtained from a large set of stellar evolution simulations, we craft ejecta models for type ii sne from the explosion of a 12, 15, 20, and 25 m⊙ star. the ejecta density structure and kinetic energy, the 56ni mass, and the level of chemical mixing are parametrized. our model spectra are sensitive to the adopted line doppler width, a phenomenon we associate with the overlap of fe ii and o i lines with ly α and ly β. our spectra show a strong sensitivity to 56ni mixing since it determines where decay power is absorbed. even at 300 d after explosion, the h-rich layers reprocess the radiation from the inner metal rich layers. in a given progenitor model, variations in 56ni mass and distribution impact the ejecta ionization, which can modulate the strength of all lines. such ionization shifts can quench ca ii line emission. in our set of models, the [o i] λλ 6300, 6364 doublet strength is the most robust signature of progenitor mass. however, we emphasize that convective shell merging in the progenitor massive star interior can pollute the o-rich shell with ca, which would weaken the o i doublet flux in the resulting nebular sn ii spectrum. this process may occur in nature, with a greater occurrence in higher mass progenitors, and this may explain in part the preponderance of progenitor masses below 17 m⊙ that are inferred from nebular spectra. | radiative-transfer modeling of nebular-phase type ii supernovae. dependencies on progenitor and explosion properties |
we present an optical nebular spectrum of the nearby type ia supernova 2011fe, obtained 981 d after explosion. sn 2011fe exhibits little evolution since the +593 d optical spectrum, but there are several curious aspects in this new extremely late-time regime. we suggest that the persistence of the ∼5800 å feature is due to na i d, and that a new emission feature at ∼7300 å may be [ca ii]. also, we discuss whether the new emission feature at ∼6400 å might be [fe i] or the high-velocity hydrogen predicted by mazzali et al. the nebular feature at 5200 å exhibits a linear velocity evolution of ∼350 km s- 1 per 100 d from at least +220 to +980 d, but the line's shape also changes in this time, suggesting that line blending contributes to the evolution. at ∼1000 d after explosion, flux from the sn has declined to a point where contribution from a luminous secondary could be detected. in this work, we make the first observational tests for a post-impact remnant star and constrain its temperature and luminosity to t ≳ 104 k and l ≲ 104 l⊙. additionally, we do not see any evidence for narrow h α emission in our spectrum. we conclude that observations continue to strongly exclude many single-degenerate scenarios for sn 2011fe. | constraining the progenitor companion of the nearby type ia sn 2011fe with a nebular spectrum at +981 d |
we present results from a survey of the internal kinematics of 49 star-forming galaxies at z∼ 2 in the candels fields with the keck/mosfire spectrograph, survey in the near-infrared of galaxies with multiple position angles (sigma). kinematics (rotation velocity v rot and gas velocity dispersion {σ }g) are measured from nebular emission lines which trace the hot ionized gas surrounding star-forming regions. we find that by z∼ 2, massive star-forming galaxies ({log} {m}* /{m}⊙ ≳ 10.2) have assembled primitive disks: their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a tully-fisher relation. these massive galaxies have values of {v}{rot}/{σ }g that are factors of 2-5 lower than local well-ordered galaxies at similar masses. such results are consistent with findings by other studies. we find that low-mass galaxies ({log} {m}* /{m}⊙ ≲ 10.2) at this epoch are still in the early stages of disk assembly: their kinematics are often dominated by gas velocity dispersion and they fall from the tully-fisher relation to significantly low values of v rot. this “kinematic downsizing” implies that the process(es) responsible for disrupting disks at z∼ 2 have a stronger effect and/or are more active in low-mass systems. in conclusion, we find that the period of rapid stellar mass growth at z∼ 2 is coincident with the nascent assembly of low-mass disks and the assembly and settling of high-mass disks. | kinematic downsizing at z ∼ 2 |
we present a new model describing the evolution of triple stars that undergo common envelope evolution, using a combination of analytical and numerical techniques. the early stages of evolution are driven by dynamical friction with the envelope, which causes the outer triple orbit to shrink faster than the inner binary. in most cases, this leads to a chaotic dynamical interaction between the three stars, culminating in the ejection of one of the stars from the triple. this ejection and resulting recoil on the remnant binary are sufficient to eject all three stars from the envelope, which expands and dissipates after the stars have escaped. these results have implications for the properties of post-common envelope triples: they may only exist in cases where the envelope was ejected before the onset of dynamical instability, the likelihood of which depends on the initial binary separation and the envelope structure. in cases where the triple becomes dynamically unstable, the triple does not survive and the envelope dissipates without forming a planetary nebula. | estimating the outcomes of common envelope evolution in triple stellar systems |
we analyse a sample of eight highly magnified galaxies at redshift 0.6 < z < 1.5 observed with muse, exploring the resolved properties of these galaxies at sub-kiloparsec scales. combining multiband hst photometry and muse spectra, we derive the stellar mass, global star formation rates (sfrs), extinction and metallicity from multiple nebular lines, concluding that our sample is representative of z ∼ 1 star-forming galaxies. we derive the 2d kinematics of these galaxies from the [o ii ] emission and model it with a new method that accounts for lensing effects and fits multiple images simultaneously. we use these models to calculate the 2d beam-smearing correction and derive intrinsic velocity dispersion maps. we find them to be fairly homogeneous, with relatively constant velocity dispersions between 15 and 80 km s-1 and gini coefficient of {≲ }0.3. we do not find any evidence for higher (or lower) velocity dispersions at the positions of bright star-forming clumps. we derive resolved maps of dust attenuation and attenuation-corrected sfrs from emission lines for two objects in the sample. we use this information to study the relation between resolved sfr and velocity dispersion. we find that these quantities are not correlated, and the high-velocity dispersions found for relatively low star-forming densities seems to indicate that, at sub-kiloparsec scales, turbulence in high-z discs is mainly dominated by gravitational instability rather than stellar feedback. | kinematics, turbulence, and star formation of z ∼ 1 strongly lensed galaxies seen with muse |
context. the kleinmann-low nebula in orion (orion-kl) is the nearest example of a high-mass star-forming environment. studying the resolved chemical substructures of this complex region provides important insight into the chemistry of high-mass star-forming regions (hmsfrs), as it relates to their evolutionary states.aims: the goal of this work is to resolve the molecular line emission from individual substructures of orion-kl at high spectral and spatial resolution and to infer the chemical properties of the associated gas.methods: we present a line survey of orion-kl obtained from combined submillimeter array (sma) interferometric and iram 30 m single-dish observations. covering a 4 ghz bandwidth in total, this survey contains over 160 emission lines from 20 species (25 isotopologues), including 11 complex organic molecules (coms). spectra are extracted from individual substructures and the intensity-integrated distribution map for each species is provided. we then estimate the rotation temperature for each substructure, along with their molecular column densities and abundances.results: for the first time, we complement 1.3 mm interferometric data with single-dish observations of the orion-kl region and study small-scale chemical variations in this region. (1) we resolve continuum substructures on ~3'' angular scale. (2) we identify lines from the low-abundance coms ch3coch3 and ch3ch2oh, as well as tentatively detect ch3cho and long carbon-chain molecules c6h and hc7n. (3) we find that while most coms are segregated by type, peaking either towards the hotcore (e.g., nitrogen-bearing species) or the compact ridge (e.g., oxygen-bearing species like hcooch3 and ch3och3), the distributions of others do not follow this segregated structure (e.g., ch3ch2oh, ch3oh, ch3coch3). (4) we find a second velocity component of hnco, so2, 34so2, and so lines, which may be associated with a strong shock event in the low-velocity outflow. (5) temperatures and molecular abundances show large gradients between central condensations and the outflow regions, illustrating a transition between hot molecular core and shock-chemistry dominated regimes.conclusions: our observations of spatially resolved abundance variations in orion-kl provide the nearest reference source for hot molecular core and outflow chemistry, which will be an important example for interpreting the chemistry of more distant hmsfrs. appendices are available in electronic form at http://www.aanda.orgmerged maps (data cubes) 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/581/a71 | resolving the chemical substructure of orion-kl |
the depletion pattern of volatile elements on earth and other differentiated terrestrial bodies provides a unique insight as to the nature and origin of planetary building blocks. the processes responsible for the depletion of volatile elements range from the early incomplete condensation in the solar nebula to the late de-volatilization induced by heating and impacting during planetary accretion after the dispersion of the h2-rich nebular gas. furthermore, as many volatile elements are also siderophile (metal-loving), it is often difficult to deconvolve the effect of volatility from core formation. with the notable exception of the earth, all the differentiated terrestrial bodies for which we have samples have non-chondritic mn/na ratios, taken as a signature of post-nebular volatilization. the bulk silicate earth (bse) is unique in that its mn/na ratio is chondritic, which points to a nebular origin for the depletion; unless the mn/na in the bse is not that of the bulk earth (be), and has been affected by core formation through the partitioning of mn in earth's core. here we quantify the metal-silicate partitioning behavior of mn at deep magma ocean pressure and temperature conditions directly applicable to core formation. the experiments show that mn becomes more siderophile with increasing pressure and temperature. modeling the partitioning of mn during core formation by combining our results with previous data at lower p-t conditions, we show that the core likely contains a significant fraction (20 to 35%) of earth's mn budget. however, we show that the derived mn/na value of the bulk earth still lies on the volatile-depleted end of a trend defined by chondritic meteorites in a mn/na vs mn/mg plot, which tend to higher mn/na with increasing volatile depletion. this suggests that the material that formed the earth recorded similar chemical fractionation processes for moderately volatile elements as chondrites in the solar nebula, and experienced limited post nebular volatilization. | chondritic mn/na ratio and limited post-nebular volatile loss of the earth |
we analyse the morphologies of three core collapse supernova remnants (ccsnrs) and the energy of jets in other ccsnrs and in super luminous supernovae (slsne) of type ib/ic/iib, and conclude that these properties are well explained by the last jets' episode as expected in the jet feedback explosion mechanism of core collapse supernovae (ccsne). the presence of two opposite protrusions, termed ears, and our comparison of the ccsnr morphologies with morphologies of planetary nebulae strengthen the claim that jets play a major role in the explosion mechanism of ccsne. we crudely estimate the energy that was required to inflate the ears in two ccsnrs and assume that the ears were inflated by jets. we find that the energies of the jets which inflated ears in 11 ccsnrs span a range that is similar to that of jets in some energetic ccsne (slsne) and that this energy, only of the last jets' episode, is much less than the explosion energy. this finding is compatible with the jet feedback explosion mechanism of ccsne, where only the last jets, which carry a small fraction of the total energy carried by earlier jets, are expected to influence the outer parts of the ejecta. we reiterate our call for a paradigm shift from neutrino-driven to jet-driven explosion models of ccsne. | the imprints of the last jets in core collapse supernovae |
we report on the detection of flaring activity from the fanaroff-riley i radio galaxy ngc 1275 in very-high-energy (vhe, e > 100 gev) gamma rays with the major atmospheric gamma imaging cherenkov (magic) telescopes. the observations were performed between 2016 september and 2017 february, as part of a monitoring programme. the brightest outburst, with ∼1.5 times the crab nebula flux above 100 gev (c.u.), was observed during the night between 2016 december 31 and 2017 january 1. the flux is fifty times higher than the mean flux previously measured in two observational campaigns between 2009 october and 2010 february and between 2010 august and 2011 february. significant variability of the day-by-day light curve was measured. the shortest flux-doubling timescale was found to be of (611 ± 101) min. the spectra calculated for this period are harder and show a significant curvature with respect to the ones obtained in the previous campaigns. the combined spectrum of the magic data during the strongest flare state and simultaneous data from the fermi-lat around 2017 january 1 follows a power law with an exponential cutoff at the energy (492 ± 35) gev. we further present simultaneous optical flux density measurements in the r-band obtained with the kungliga vetenskaps akademien (kva) telescope and investigate the correlation between the optical and gamma-ray emission. due to possible internal pair-production, the fast flux variability constrains the doppler factor to values that are inconsistent with a large viewing angle as observed in the radio band. we investigate different scenarios for the explanation of fast gamma-ray variability, namely emission from magnetospheric gaps, relativistic blobs propagating in the jet (mini-jets), or an external cloud (or star) entering the jet. we find that the only plausible model to account for the luminosities here observed would be the production of gamma rays in a magnetospheric gap around the central black hole, only in the eventuality of an enhancement of the magnetic field threading the hole from its equipartition value with the gas pressure in the accretion flow. the observed gamma-ray flare therefore challenges all the discussed models for fast variability of vhe gamma-ray emission in active galactic nuclei. | gamma-ray flaring activity of ngc1275 in 2016-2017 measured by magic |
lenticular galaxies are generally thought to have descended from spirals via morphological transformation, although recent numerical simulations have shown that minor or even major mergers can also lead to an s0-like remnant. these mechanisms, however, are active in a dense environment such as a group or a cluster of galaxies—making it harder to explain the remarkable fraction of s0s found in the field. here, we propose a new mechanism to form such lenticular galaxies. we show that an isolated cold disk settled into rotational equilibrium becomes violently unstable—leading to fragmentation and formation of stellar clumps that, in turn, not only cause the bulge to grow, but also increase the stellar disk velocity dispersion optimally in less than a billion years. subsequently, the galaxy evolves passively without any conspicuous spiral structure. the final galaxy models resemble remarkably well the morphology and stellar kinematics of the present-day s0s observed by the planetary nebulae spectrograph. our findings suggest a natural link between the high-redshift clumpy progenitors and the present-day s0 galaxies. | forming lenticular galaxies via violent disk instability |
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