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applying dendrogram analysis to the carma-nro c18o (j = 1-0) data having an angular resolution of ∼8″, we identified 692 dense cores in the orion nebula cluster region. using this core sample, we compare the core and initial stellar mass functions in the same area to quantify the step from cores to stars. about 22% of the identified cores are gravitationally bound. the derived core mass function (cmf) for starless cores has a slope similar to salpeter's stellar initial mass function (imf) for the mass range above 1 m⊙, consistent with previous studies. our cmf has a peak at a subsolar mass of ∼0.1 m⊙, which is comparable to the peak mass of the imf derived in the same area. we also find that the current star formation rate is consistent with the picture in which stars are born only from self-gravitating starless cores. however, the cores must gain additional gas from the surroundings to reproduce the current imf (e.g., its slope and peak mass), because the core mass cannot be accreted onto the star with 100% efficiency. thus, the mass accretion from the surroundings may play a crucial role in determining the final stellar masses of stars. | the core mass function in the orion nebula cluster region: what determines the final stellar masses? |
context. the fate of a massive star during the latest stages of its evolution is highly dependent on its mass-loss rate and geometry and therefore knowing the geometry of the circumstellar material close to the star and its surroundings is crucial.aims: we aim to provide insight into the nature (i.e. geometry, rates) of mass-loss episodes, and in particular, the connection between the observed asymmetries due to the mass lost in a fast wind or during a previous, prodigious mass-losing phase. in this context, yellow hypergiants offer a good opportunity to study mass-loss events.methods: we analysed a large set of optical and near-infrared data in spectroscopic and photometric, spectropolarimetric, and interferometric (gravity/vlti) modes, towards the yellow hypergiant iras 17163-3907. we used x-shooter optical observations to determine the spectral type of this yellow hypergiant and we present the first model-independent, reconstructed images of iras 17163-3907 at these wavelengths tracing milli-arcsecond scales. lastly, we applied a 2d radiative transfer model to fit the dereddened photometry and the radial profiles of published diffraction-limited visir images at 8.59 μm, 11.85 μm, and 12.81 μm simultaneously, adopting a revised distance determination using gaia data release 2 measurements.results: we constrain the spectral type of iras 17163-3907 to be slightly earlier than a6ia (teff ∼ 8500 k). the interferometric observables around the 2 μm window towards iras 17163-3907 show that the brγ emission appears to be more extended and asymmetric than the na i and the continuum emission. interestingly, the spectrum of iras 17163-3907 around 2 μm shows mg ii emission that is not previously seen in other objects of its class. in addition, brγ shows variability in a time interval of four months that is not seen towards na i. lastly, in addition to the two known shells surrounding iras 17163-3907, we report on the existence of a third hot inner shell with a maximum dynamical age of only 30 yr.conclusions: the 2 μm continuum originates directly from the star and not from hot dust surrounding the stellar object. the observed spectroscopic variability of brγ could be a result of variability in the mass-loss rate. the interpretation of the presence of na i emission at closer distances to the star compared to brγ has been a challenge in various studies. to address this, we examine several scenarios. we argue that the presence of a pseudo-photosphere, which was traditionally considered to be the prominent explanation, is not needed and that it is rather an optical depth effect. the three observed distinct mass-loss episodes are characterised by different mass-loss rates and can inform theories of mass-loss mechanisms, which is a topic still under debate both in theory and observations. we discuss these in the context of photospheric pulsations and wind bi-stability mechanisms. reduced gravity and amber data (fits files) 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/635/a183 | optical and near-infrared observations of the fried egg nebula. multiple shell ejections on a 100 yr timescale from a massive yellow hypergiant |
eight planetary nebulae have been identified as 'born-again', a class of object typified by knotty secondary ejecta having low masses (${\sim}10^{-4}$ m⊙) with nearly no hydrogen. abell 30, the archetype of the class, also belongs to a small subset of planetary nebulae that exhibit extreme abundance discrepancy factors (where abell 30 is the most extreme), a phenomenon strongly linked to binary star interactions. we report the presence of light curve brightness variations having a period of 1.060 d that are highly suggestive of a binary central star in abell 30. if confirmed, this detection supports the proposed link between binary central stars and extreme abundance discrepancies. | abell 30 - a binary central star among the born-again planetary nebulae |
we present a study of 323 photometrically variable young stellar objects that are likely members of the north america and pelican nebulae star-forming region. to do so, we utilize over two years of data in the g and r photometric bands from the zwicky transient facility. we first investigate periodic variability, finding 46 objects (~15% of the sample) with significant periods that phase well and can be attributed to stellar rotation. we then use the quasiperiodicity (q) and flux asymmetry (m) variability metrics to assign morphological classifications to the remaining aperiodic light curves. another ~39% of the variable star sample beyond the periodic (low q) sources are also flux-symmetric, but with a quasiperiodic (moderate q) or stochastic (high q) nature. concerning flux-asymmetric sources, our analysis reveals ~14% bursters (high negative m) and ~29% dippers (high positive m). we also investigate the relationship between variability slopes in the g versus g - r color-magnitude diagram, and the light-curve morphological classes. burster-type objects have shallow slopes, while dipper-type variables tend to have higher slopes that are consistent with extinction-driven variability. our work is one of the earliest applications of the q and m metrics to ground-based data. we therefore contrast the q values of high-cadence and high-precision space-based data, for which these metrics were designed, with q determinations resulting from degraded space-based light curves that have the cadence and photometric precision characteristic of ground-based data. | a zwicky transient facility look at optical variability of young stellar objects in the north america and pelican nebulae complex |
we have conducted laboratory experiments with analog crystalline silicon carbide (sic) grains using transmission electron microscopy (tem) and electron energy-loss spectroscopy (eels). the 3c polytype of sic was used—the type commonly produced in the envelopes of asymptotic giant branch (agb) stars. we rapidly heated small (∼50 nm) synthetic sic crystals under vacuum to ∼1300 k and bombarded them with 150 kev xe ions. tem imaging and eels spectroscopic mapping show that such heating and bombardment leaches silicon from the sic surface, creating layered graphitic sheets. surface defects in the crystals were found to distort the six-membered rings characteristic of graphite, creating hemispherical structures with diameters matching that of c60. such nonplanar features require the formation of five-membered rings. we also identified a circumstellar grain, preserved inside the murchison meteorite, that contains the remnant of an sic core almost fully encased by graphite, contradicting long-standing thermodynamic predictions of material condensation. our combined laboratory data suggest that c60 can undergo facile formation from shock heating and ion bombardment of circumstellar sic grains. such heating/bombardment could occur in the protoplanetary nebula phase, accounting for the observation of c60 in these objects, in planetary nebulae (pns) and other interstellar sources receiving pn ejecta. the synthesis of c60 in astronomical sources poses challenges, as the assembly of 60 pure carbon atoms in an h-rich environment is difficult. the formation of c60 from the surface decomposition of sic grains is a viable mechanism that could readily occur in the heterogeneous, hydrogen-dominated gas of evolved circumstellar shells. | formation of interstellar c60 from silicon carbide circumstellar grains |
pulsar wind nebulae (pwne) are outstanding accelerators in nature, in the sense that they accelerate electrons up to the radiation reaction limit. motivated by this observation, this paper examines the possibility that young pulsar wind nebulae can accelerate ions to ultra-high energies at the termination shock of the pulsar wind. we consider here powerful pwne, fed by pulsars born with ~ millisecond periods. assuming that such pulsars exist, at least during a few years after the birth of the neutron star, and that they inject ions into the wind, we find that protons could be accelerated up to energies of the order of the greisen-zatsepin-kuzmin cut-off, for a fiducial rotation period p ~ 1 msec and a pulsar magnetic field b⋆ ~ 1013 g, implying a fiducial wind luminosity lp ~ 1045 erg/s and a spin-down time tsd ~ 3× 107 s. the main limiting factor is set by synchrotron losses in the nebula and by the size of the termination shock; ions with z⩾ 1 may therefore be accelerated to even higher energies. we derive an associated neutrino flux produced by interactions in the source region. for a proton-dominated composition, our maximum flux lies slightly below the 5-year sensitivity of icecube-86 and above the 3-year sensitivity of the projected askaryan radio array. it might thus become detectable in the next decade, depending on the exact level of contribution of these millisecond pulsar wind nebulae to the ultra-high energy cosmic ray flux. | on ultra-high energy cosmic ray acceleration at the termination shock of young pulsar winds |
aims: the nonthermal radiative properties of 18 pulsar wind nebulae (pwne) are studied in the 1d leptonic model.methods: the dynamical and radiative evolution of a pwn in a nonradiative supernova remnant are self-consistently investigated in this model. the leptons (electrons/positrons) are injected with a broken power-law form, and nonthermal emission from a pwn is mainly produced by time-dependent relativistic leptons through synchrotron radiation and inverse compton process.results: observed spectral energy distributions (seds) of all 18 pwne are reproduced well, where the indexes of low-energy electron components lie in the range of 1.0-1.8 and those of high-energy electron components in the range of 2.1-3.1. our results show that fx/fγ > 10 for young pwne; 1 <fx/fγ ≤ 10 for evolved pwne, except for g292.0+1.8; and fx/fγ ≤ 1 for mature/old pwne, except for cta 1. moreover, most pwne are particle-dominated. statistical analysis for the sample of 14 pwne further indicate that (1) not all pulsar parameters have correlations with electron injection parameters, but electron maximum energy and pwn magnetic field correlate with the magnetic field at the light cylinder, the potential difference at the polar cap, and the spin-down power; (2) the spin-down power positively correlates with radio, x-ray, bolometric, and synchrotron luminosities, but does not correlate with gamma-ray luminosity; (3) the spin-down power positively correlates with radio, x-ray, and γ-band surface brightness; and (4) the pwn radius and the pwn age negatively correlate with x-ray luminosity, the ratio of x-ray to gamma-ray luminosities, and the synchrotron luminosity. | multiband nonthermal radiative properties of pulsar wind nebulae |
stellar shells around galaxies could provide precious insights into their assembly history. however, their formation mechanism remains poorly empirically constrained, regarding in particular the type of galaxy collisions at their origin. we present muse at vlt data of the most prominent outer shell of ngc 474, to constrain its formation history. the stellar shell spectrum is clearly detected, with a signal-to-noise ratio of ∼65 pix-1. we used a full spectral fitting method to determine the line-of-sight velocity and the age and metallicity of the shell and associated point-like sources within the muse field of view. we detect six globular cluster (gc) candidates and eight planetary nebula (pn) candidates that are all kinematically associated with the stellar shell. we show that the shell has an intermediate metallicity, [m/h] = -0.83-0.12+0.12, and a possible α-enrichment, [α/fe] ∼ 0.3. assuming the material of the shell comes from a lower mass companion, and that the latter had no initial metallicity gradient, such a stellar metallicity would constrain the mass of the progenitor at around 7.4 × 108 m⊙, implying a merger mass ratio of about 1:100. however, our census of pne and earlier photometry of the shell would suggest a much higher ratio, around 1:20. given the uncertainties, this difference is only significant at the ≃1σ level. we discuss the characteristics of the progenitor, and in particular whether the progenitor could also be composed of stars from the low-metallicity outskirts of a more massive galaxy. ultimately, the presented data do not allow us to put a firm constraint on the progenitor mass. we show that at least two gc candidates possibly associated with the shell are quite young, with ages below 1.5 gyr. we also note the presence of a young (∼1 gyr) stellar population in the center of ngc 474. the two may have resulted from the same event. based on data from eso program 099.b-0328(a) (pi: fensch). | shedding light on the formation mechanism of shell galaxy ngc 474 with muse |
though the low-ionization small-scale structures (liss) such as knots, filaments and jets of planetary nebulae (pne) are known for ∼30 yr, some of their observational properties are not well established. in consequence, our ability to include them in the wider context of the formation and evolution of pne is directly affected. why most structures have lower densities than the pn shells hosting them? is their intense emission in low-ionization lines the key to their main excitation mechanism? therefore, if considered altogether, can liss line ratios, chemical abundances and kinematics enlighten the interplay between the different excitation and formation processes? here we present a spectroscopic analysis of five pne that possess liss confirming that all nebular components have comparable electron temperatures, whereas the electron density is systematically lower in liss than in the surrounding nebula. chemical abundances of liss versus other pn components do not show significant differences as well. by using diagnostic diagrams from shock models, we demonstrate that liss' main excitation is due to shocks, whereas the other components are mainly photoionized. we also propose new diagnostic diagrams involving a few emission lines ([n ii], [o iii], [s ii]) and log(fshocks/f*), where fshocks and f* are the ionization photon fluxes due to the shocks and the central star ionizing continuum, respectively. a robust relation differentiating the structures is found, with the shock-excited clearly having log(fshocks/f*) > -1; while the photoionized structures have log(fshocks/f*) < -2. a transition zone, with -2 < log(fshocks/f*) < -1, where both mechanisms are equally important, is also defined. | low-ionization structures in planetary nebulae - i. physical, kinematic and excitation properties |
we report on the mineralogy, petrography, and o-isotope compositions of ∼60 ca, al-rich inclusions (cais) incompletely melted during formation of porphyritic chondrules from the ch metal-rich carbonaceous chondrites and isheyevo (ch/cb). these include (i) relict polymineralic cais in porphyritic chondrules, (ii) cais surrounded by chondrule-like igneous rims, (iii) igneous pyroxene-rich and type c-like cais, and (iv) plagioclase-rich chondrules with clusters of relict spinel grains. 26al-26mg systematics were measured in 10 relict cais and 11 cai-bearing plagioclase-rich chondrules. based on the mineralogy, the ch cais incompletely melted during chondrule formation can be divided into grossite-rich (n = 13), hibonite-rich (n = 11), spinel ± melilite-rich (n = 33; these include plagioclase-rich chondrules with clusters of relict spinel grains) types. mineralogical observations indicate that these cais were mixed with different proportions of ferromagnesian silicates and experienced incomplete melting and gas-melt interaction during chondrule formation. these processes resulted in partial or complete destruction of the cai wark-lovering rims, replacement of melilite by na-bearing plagioclase, and dissolution and overgrowth of nearly end-member spinel by chromium- and iron-bearing spinel. only two relict cais and two cai-bearing chondrules show resolvable excess of radiogenic 26mg; the inferred initial 26al/27al ratios are (1.7 ± 1.3) × 10-6, (3.7 ± 3.1) × 10-7, (1.9 ± 0.9) × 10-6 and (4.9 ± 2.6) × 10-6. there is a large range of δ17o among the ch cais incompletely melted during chondrule formation, from ∼-37‰ to ∼-5‰; the unmelted minerals in individual cais, however, are isotopically uniform and systematically 16o-enriched relative to the host chondrules and chondrule-like igneous rims, which have δ17o ranging from ∼-7‰ to ∼+4‰. most of the ch cais incompletely melted during chondrule formation are mineralogically and isotopically similar to the ch cais surrounded by wark-lovering rims and apparently unaffected by chondrule melting. the mineralogy and o-isotope compositions of the ch cai-bearing chondrules are similar to those of the ch porphyritic chondrules without relict cais. we conclude that ch porphyritic chondrules formed by incomplete melting of isotopically diverse solid precursors, including mineralogically and isotopically unique cais commonly observed only in ch chondrites. therefore, the ch porphyritic chondrules must have formed in a distinct disk region, where the ch cais were present at the time of chondrule formation. because most ch cais avoided chondrule melting, we infer that chondrule formation was highly localized. these observations preclude formation of ch porphyritic chondrules by splashing of molten planetesimals, by impact processing of differentiated planetesimals, and by large scale nebular shocks, e.g., shocks driven by disk gravitational instabilities or by x-ray flares. instead, they are consistent with small-scale chondrule-forming mechanisms proposed in the literature, such as nebular processing of dust balls by bow shocks and by current sheets. | calcium-aluminum-rich inclusions recycled during formation of porphyritic chondrules from ch carbonaceous chondrites |
we aim at investigating whether the chemical composition of the outer region of the protosolar nebula can be consistent with current estimates of the elemental abundances in the ice giants. to do so, we use a self-consistent evolutionary disc and transport model to investigate the time and radial distributions of h2o, co, co2, ch3oh, ch4, n2 and h2s, i.e. the main o-, c-, n and s-bearing volatiles in the outer disc. we show that it is impossible to accrete a mixture composed of gas and solids from the disc with a c/h ratio presenting enrichments comparable to the measurements (approx. 70 times protosolar). we also find that the c/n and c/s ratios measured in uranus and neptune are compatible with those acquired by building blocks agglomerated from solids condensed in the 10-20 au region of the protosolar nebula. by contrast, the presence of protosolar c/n and c/s ratios in uranus and neptune would imply that their building blocks agglomerated from particles condensed at larger heliocentric distances. our study outlines the importance of measuring the elemental abundances in the ice giant atmospheres, as they can be used to trace the planetary formation location, the origin of their building blocks and/or the chemical and physical conditions of the protosolar nebula. this article is part of a discussion meeting issue `future exploration of ice giant systems'. | the role of ice lines in the formation of uranus and neptune |
since sep. 2018, lamost has started the medium-resolution (r ~ 7500) spectral survey (mrs). we proposed the spectral survey of galactic nebulae, including h ii regions, hh objects, supernova remnants, planetary nebulae and the special stars with mrs (lamost mrs-n). lamost mrs-n covers about 1700 square degrees of the northern galactic plane within 40° < l < 215° and -5° < b < 5°. in this 5-year survey, we plan to observe about 500 thousand nebulae spectra. according to the commissioning observations, the nebulae spectra can provide precise radial velocity with uncertainty less than 1 km s-1. these high-precision spectral data are of great significance to our understanding of star formation and evolution. | lamost medium-resolution spectral survey of galactic nebulae (lamost mrs-n): an overview of scientific goals and survey plan |
we present an analysis to disentangle the connection between physical quantities that characterize the conditions of ionized h ii regions - metallicity (z), ionization parameter (u), and electron density (ne) - and the global stellar mass (m*) and specific star formation rate (ssfr = sfr/m*) of the host galaxies. we construct composite spectra of galaxies at 0.027 ≤ z ≤ 0.25 from sloan digital sky survey, separating the sample into bins of m* and ssfr, and estimate the nebular conditions from the emission-line flux ratios. specially, metallicity is estimated from the direct method based on the faint auroral lines [o iii]λ4363 and [o ii]λλ7320,7330. the derived metallicities cover a range of 12 + log o/h ∼ 7.6-8.9. it is found that the three nebular parameters, z, u, and ne, are tightly correlated with the location in the m*-ssfr plane. with simple physically motivated ansätze, we derive scaling relations between these physical quantities by performing multiregression analysis. in particular, we find that u is primarily controlled by ssfr, as u∝ssfr0.43, but also depends significantly on both z and ne. the derived partial dependence of u∝z-0.36 is weaker than the apparent correlation (u∝z-1.52). the partial dependence of u on ne is found to be u ∝ n_e^{-0.29}. the scaling relations we derived are in agreement with predictions from theoretical models and observations of each aspect of the link between these quantities. our results provide a useful set of equations to predict the nebular conditions and emission-line fluxes of galaxies in semi-analytic models. | disentangling the physical parameters of gaseous nebulae and galaxies |
psr j1509-5850 is a middle-aged pulsar with a period of p ≈ 89 ms and spin-down power of \dot{e}=5.1× {10}35 erg s-1, at a distance of about 3.8 kpc. we report on deep chandra x-ray observatory observations of this pulsar and its pulsar wind nebula (pwn). in addition to the previously detected tail extending up to 7‧ southwest from the pulsar (the southern outflow), the deep images reveal similarly long, faint, diffuse emission stretched toward the north (the northern outflow) and the fine structure of the compact nebula (cn) in the pulsar vicinity. the cn is resolved into two lateral tails and one axial tail pointing southwest (a morphology remarkably similar to that of the geminga pwn), which supports the assumption that the pulsar moves toward the northeast. the luminosities of the southern and northern outflows are about 1× {10}33 and 4× {10}32 erg s-1, respectively. the spectra extracted from four regions of the southern outflow do not show any softening with increasing distance from the pulsar. the lack of synchrotron cooling suggests a high flow speed or in situ acceleration of particles. the spectra extracted from two regions of the northern outflow show a hint of softening with distance from the pulsar, which may indicate slower particle propagation. we speculate that the northern outflow is associated with particle leakage from the bow-shock apex into the ism, while the southern outflow represents the tail of the shocked pulsar wind behind the moving pulsar. we estimate the physical parameters of the observed outflows and compare the j1509-5850 pwn with pwne of other supersonically moving pulsars. | chandra observations of outflows from psr j1509-5850 |
we develop a model of gamma-ray flares of the crab nebula resulting from the magnetic reconnection events in a highly magnetised relativistic plasma. we first discuss physical parameters of the crab nebula and review the theory of pulsar winds and termination shocks. we also review the principle points of particle acceleration in explosive reconnection events [lyutikov et al., j. plasma phys., vol. 83(6), p. 635830601 (2017a); j. plasma phys., vol. 83(6), p. 635830602 (2017b)]. it is required that particles producing flares are accelerated in highly magnetised regions of the nebula. flares originate from the poleward regions at the base of the crab's polar outflow, where both the magnetisation and the magnetic field strength are sufficiently high. the post-termination shock flow develops macroscopic (not related to the plasma properties on the skin-depth scale) kink-type instabilities. the resulting large-scale magnetic stresses drive explosive reconnection events on the light-crossing time of the reconnection region. flares are produced at the initial stage of the current sheet development, during the x-point collapse. the model has all the ingredients needed for crab flares: natural formation of highly magnetised regions, explosive dynamics on the light travel time, development of high electric fields on macroscopic scales and acceleration of particles to energies well exceeding the average magnetic energy per particle. | particle acceleration in explosive relativistic reconnection events and crab nebula gamma-ray flares |
we use the gas-grain chemistry code uclchem to explore the impact of cosmic-ray feedback on the chemistry of circumstellar disks. we model the attenuation and energy losses of the cosmic rays as they propagate outward from the star and also consider ionization due to stellar radiation and radionuclides. for accretion rates typical of young stars of {\dot{m}}* ∼ {10}-9{--}{10}-6 m ⊙ yr-1, we show that cosmic rays accelerated by the stellar accretion shock produce an ionization rate at the disk surface ζ ≳ 10-15 s-1, at least an order of magnitude higher than the ionization rate associated with the galactic cosmic-ray background. the incident cosmic-ray flux enhances the disk ionization at intermediate to high surface densities (σ > 10 g cm-2), particularly within 10 au of the star. we find that the dominant ions are c+, s+, and mg+ in the disk surface layers, while the {{{h}}}3+ ion dominates at surface densities above 1.0 g cm-2. we predict the radii and column densities at which the magnetorotational instability (mri) is active in t tauri disks and show that ionization by cosmic-ray feedback extends the mri-active region toward the disk midplane. however, the mri is only active at the midplane of a minimum-mass solar nebula disk if cosmic rays propagate diffusively (ζ ∝ r -1) away from the star. the relationship between accretion, which accelerates cosmic rays, the dense accretion columns, which attenuate cosmic rays, and the mri, which facilitates accretion, creates a cosmic-ray feedback loop that mediates accretion and may produce variable luminosity. | impact of cosmic-ray feedback on accretion and chemistry in circumstellar disks |
deuterium-to-hydrogen (d/h) enrichments in molecular species provide clues about their original formation environment. the organic materials in primitive solar system bodies generally have higher d/h ratios and show greater d/h variation when compared to d/h in solar system water. we propose this difference arises at least in part due to (1) the availability of additional chemical fractionation pathways for organics beyond that for water, and (2) the higher volatility of key carbon reservoirs compared to oxygen. we test this hypothesis using detailed disk models, including a sophisticated, new disk ionization treatment with a low cosmic-ray ionization rate, and find that disk chemistry leads to higher deuterium enrichment in organics compared to water, helped especially by fractionation via the precursors ch2d+/ch3+. we also find that the d/h ratio in individual species varies significantly depending on their particular formation pathways. for example, from ∼20-40 au, ch4 can reach {{d}}/{{h}}∼ 2× {10}-3, while d/h in ch3oh remains locally unaltered. finally, while the global organic d/h in our models can reproduce intermediately elevated d/h in the bulk hydrocarbon reservoir, our models are unable to reproduce the most deuterium-enriched organic materials in the solar system, and thus our model requires some inheritance from the cold interstellar medium from which the sun formed. | exploring the origins of deuterium enrichments in solar nebular organics |
using deep multi-wavelength photometry of galaxies from zfourge, we group galaxies at 2.5< z< 4.0 by the shape of their spectral energy distributions (seds). we identify a population of galaxies with excess emission in the ks -band, which corresponds to [o iii]+hβ emission at 2.95< z< 3.65. this population includes 78% of the bluest galaxies with uv slopes steeper than β =-2. we de-redshift and scale this photometry to build two composite seds, enabling us to measure equivalent widths of these extreme [o iii]+hβ emission line galaxies (eelgs) at z∼ 3.5. we identify 60 galaxies that comprise a composite sed with a [o iii]+hβ rest-frame equivalent width of 803 ± 228 å and another 218 galaxies in a composite sed with an equivalent width of 230 ± 90 å. these eelgs are analogous to the “green peas” found in the sdss and are thought to be undergoing their first burst of star formation due to their blue colors (β < -1.6), young ages ({log}({age} {{yr}}-1)∼ 7.2), and low dust attenuation values. their strong nebular emission lines and compact sizes (typically ∼1.4 kpc) are consistent with the properties of the star-forming galaxies possibly responsible for reionizing the universe at z> 6. many of the eelgs also exhibit lyα emission. additionally, we find that many of these sources are clustered in an overdensity in the chandra deep field south, with five spectroscopically confirmed members at z=3.474+/- 0.004. the spatial distribution and photometric redshifts of the zfourge population further confirm the overdensity highlighted by the eelgs. this letter includes data gathered with the 6.5 m magellan telescopes located at las campanas observatory, chile. | discovery of extreme [o iii]+hβ emitting galaxies tracing an overdensity at z ∼ 3.5 in cdf-south |
context. micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size, and shape) and play a key role in numerous phenomena in the interstellar medium (ism). the large disparity in physical conditions (i.e. density and gas temperature) in the ism triggers an evolution of dust properties. the analysis of how dust evolves with the physical conditions is a stepping stone towards a more thorough understanding of interstellar dust.aims: we highlight dust evolution in the horsehead nebula photon-dominated region.methods: we used spitzer/irac (3.6, 4.5, 5.8 and 8 μm) and spitzer/mips (24 μm) together with herschel/pacs (70 and 160 μm) and herschel/spire (250, 350 and 500 μm) to map the spatial distribution of dust in the horsehead nebula over the entire emission spectral range. we modelled dust emission and scattering using the themis interstellar dust model together with the 3d radiative transfer code soc.results: we find that the nano-grain dust-to-gas ratio in the irradiated outer part of the horsehead is 6-10 times lower than in the diffuse ism. the minimum size of these grains is 2-2.25 times larger than in the diffuse ism, and the power-law exponent of their size distribution is 1.1-1.4 times lower than in the diffuse ism. in the denser part of the horsehead nebula, it is necessary to use evolved grains (i.e. aggregates, with or without an ice mantle).conclusions: it is not possible to explain the observations using grains from the diffuse medium. we therefore propose the following scenario to explain our results. in the outer part of the horsehead nebula, all the nano-grain have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallest of the nano-grain that are sensitive to the radiation field are photo-destroyed. in the inner part of the horsehead nebula, grains most likely consist of multi-compositional mantled aggregates. | dust evolution across the horsehead nebula |
green peas (gps) are a class of extreme star-forming galaxies (sfgs) at intermediate redshifts, originally discovered via color selection using multifilter, wide-field survey imaging data. they are commonly thought of as being analogs of high-redshift lyα-emitting galaxies. the defining characteristic of gp galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that gp-like galaxies can also be identified in samples of emission-line galaxies. here we compare the properties a sample of [o iii]-selected sfgs (z = 0.29-0.41) from the kpno international spectroscopic survey (kiss) with the color-selected gps. we find that the kiss [o iii]-selected galaxies overlap with the parameter space defined by the color-selected gps; the two samples appear to be drawn from the same population of objects. we compare the kiss gps with the full hα-selected kiss sfg sample (z < 0.1) and find that they are extreme systems. many appear to be young systems at their observed look-back times (3-4 gyr), with more than 90% of their rest-frame b-band luminosity coming from the starburst population. we compute the volume density of the kiss red (kissr) gps at z = 0.29-0.41 and find that they are extremely rare objects. we do not see galaxies as extreme as the kissr gps in the local universe, although we recognize several lower-luminosity systems at z < 0.1. | properties of the kiss green pea galaxies |
the shaping of various morphological features of planetary nebulae is increasingly linked to the role of binary central stars. identifying a binary within a planetary nebula offers a powerful tool with which to directly investigate the formation mechanisms behind these features. the etched hourglass nebula, mycn 18, is the archetype for several binary-linked morphological features, yet it has no identified binary nucleus. it has the fastest jets seen in a planetary nebula of 630 km s-1, a central star position offset from the nebula centre, and a bipolar nebula with a very narrow waist. here we report on the southern african large telescope high resolution spectrograph detection of radial velocity variability in the nucleus of mycn 18 with an orbital period of 18.15 ± 0.04 d and a semi-amplitude of 11.0 ± 0.3 km s-1. adopting an orbital inclination of 38 ± 5° and a primary mass of 0.6 ± 0.1 m⊙ yields a secondary mass of 0.19 ± 0.05 m⊙ corresponding to an m5v companion. the detached nature of the binary rules out a classical nova as the origin of the jets and the offset central star as hypothesised in the literature. furthermore, scenarios that produce the offset central star during the agb and that form narrow waist bipolar nebulae result in orbital separations 80-800 times larger than observed in mycn 18. the inner hourglass and jets may have formed from part of the common envelope ejecta that remained bound to the binary system in a circumbinary disk, whereas the offset central star position may best be explained by proper motion. detailed simulations of mycn 18 are encouraged that are compatible with the binary nucleus to further investigate its complex formation history. | salt hrs discovery of the binary nucleus of the etched hourglass nebula mycn 18 |
bow shock pulsar wind nebulae (bspwne) are known to show a large variety of shapes and morphologies, both when comparing different objects, and for the same object in different energy bands. it is unclear if such a variety is related to differences in the pulsar wind properties, or to differences in the conditions of the ambient medium. we present here a set of full 3d, relativistic and magneto-hydrodynamic simulations of bspwne, with the intention of determining how differences in the injection conditions by the pulsar wind reflect in the nebular dynamics. to achieve a good coverage of the available parameter space, we have run several simulations varying those parameters that are most representative of the wind properties: the latitudinal anisotropy of the wind energy flux with respect to the pulsar spin axis, the level of magnetization, the inclination of the pulsar spin axis with respect to the pulsar direction of motion. we have followed the dynamics in these systems, not just in the very head, but also in the tail, trying to assess if and how the system retains memory of the injection at large distances from the pulsar itself. in this work, we focus our attention on the characterization of the fluid structure and magnetic field properties. we have tried to evaluate the level of turbulence in the tail, and its relation to injection, the survival of current sheets, and the degree of mixing between the shocked ambient medium and the relativistic pulsar wind material. | full-3d relativistic mhd simulations of bow shock pulsar wind nebulae: dynamics |
many processes within galaxy clusters, such as those believed to govern the onset of thermally unstable cooling and active galactic nucleus feedback, are dependent upon local dynamical timescales. however, accurate mapping of the mass distribution within individual clusters is challenging, particularly toward cluster centers where the total mass budget has substantial radially dependent contributions from the stellar (m *), gas (m gas), and dark matter (m dm) components. in this paper we use a small sample of galaxy clusters with deep chandra observations and good ancillary tracers of their gravitating mass at both large and small radii to develop a method for determining mass profiles that span a wide radial range and extend down into the central galaxy. we also consider potential observational pitfalls in understanding cooling in hot cluster atmospheres, and find tentative evidence for a relationship between the radial extent of cooling x-ray gas and nebular hα emission in cool-core clusters. at large radii the entropy profiles of our clusters agree with the baseline power law of k ∝ r 1.1 expected from gravity alone. at smaller radii our entropy profiles become shallower but continue with a power law of the form k ∝ r 0.67 down to our resolution limit. among this small sample of cool-core clusters we therefore find no support for the existence of a central flat “entropy floor.” | mass distribution in galaxy cluster cores |
we present a study of stellar populations in a sample of spectroscopically confirmed lyman-break galaxies (lbgs) and lyα emitters (laes) at 5.7< z< 7. these galaxies have deep images from subaru, the hubble space telescope, and spitzer/irac. we focus on 27 galaxies with irac detections, and characterize their stellar populations based on the multi-band data and secure redshifts. by estimating nebular emission from the observed lyα flux, we break the strong model degeneracy between young galaxies with prominent nebular emission and older galaxies with strong balmer breaks. the results show that our galaxies cover a wide range of ages from several to a few hundred million years (myr), and stellar masses from ∼108 to ∼10{}11 {m}⊙ . these galaxies can be roughly divided into two subsamples: an “old” subsample consisting of galaxies older than 100 myr, with stellar masses higher than {10}9 {m}⊙ , and a “young” subsample consisting of galaxies younger than ∼30 myr, with masses ranging between ∼108 and ∼ 3× {10}9 {m}⊙ . both subsamples display a correlation between stellar mass and star formation rate (sfr), but with very different normalizations. the average specific sfr (ssfr) of the “old” subsample is 3-4 gyr-1, consistent with previous studies of “normal” star-forming galaxies at z≥slant 6. the average ssfr of the “young” subsample is an order of magnitude higher, likely due to starburst activity. our results also indicate little dust extinction in the majority of the galaxies, as already suggested by their steep rest-frame uv slopes. finally, laes and lbgs with strong lyα emission are indistinguishable in terms of age, stellar mass, and sfr. based in part on observations made with the nasa/esa hubble space telescope, obtained from the data archive at the space telescope science institute, which is operated by the association of universities for research in astronomy, inc., under nasa contract nas 5-26555. based in part on observations made with the spitzer space telescope, which is operated by the jet propulsion laboratory, california institute of technology under a contract with nasa. based in part on data collected at subaru telescope and obtained from the smoka, which is operated by the astronomy data center, national astronomical observatory of japan. | physical properties of spectroscopically confirmed galaxies at z ≥ 6. iii. stellar populations from sed modeling with secure lyα emission and redshifts |
we investigate a novel bayesian analysis method, based on the stochastically lighting up galaxies (slug) code, to derive the masses, ages, and extinctions of star clusters from integrated light photometry. unlike many analysis methods, slug correctly accounts for incomplete initial mass function (imf) sampling, and returns full posterior probability distributions rather than simply probability maxima. we apply our technique to 621 visually confirmed clusters in two nearby galaxies, ngc 628 and ngc 7793, that are part of the legacy extragalactic uv survey (legus). legus provides hubble space telescope photometry in the nuv, u, b, v, and i bands. we analyze the sensitivity of the derived cluster properties to choices of prior probability distribution, evolutionary tracks, imf, metallicity, treatment of nebular emission, and extinction curve. we find that slug's results for individual clusters are insensitive to most of these choices, but that the posterior probability distributions we derive are often quite broad, and sometimes multi-peaked and quite sensitive to the choice of priors. in contrast, the properties of the cluster population as a whole are relatively robust against all of these choices. we also compare our results from slug to those derived with a conventional non-stochastic fitting code, yggdrasil. we show that slug's stochastic models are generally a better fit to the observations than the deterministic ones used by yggdrasil. however, the overall properties of the cluster populations recovered by both codes are qualitatively similar. | star cluster properties in two legus galaxies computed with stochastic stellar population synthesis models |
we use the large cosmological hydro-dynamic simulation bluetides to predict the photometric properties of galaxies during the epoch of reionization (z = 8-15). these properties include the rest-frame uv to near-ir broad-band spectral energy distributions, the lyman continuum (lyc) photon production, the uv star formation rate calibration, and intrinsic uv continuum slope. in particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis (sps) model, initial mass function, and the escape fraction of lyc photons, upon these quantities. we find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. for example, at z = 8 we predict that nebular emission can account for up to 50 per cent of the rest-frame r-band luminosity, while the choice of sps model can change the lyc production rate up to a factor of ×2. | the photometric properties of galaxies in the early universe |
we present an analysis of multi-wavelength observations from various data sets and galactic plane surveys to study the star-formation process in the w42 complex. a bipolar appearance of the w42 complex is evident due to the ionizing feedback from the o5-o6 type star in a medium that is highly inhomogeneous. the very large telescope/naco adaptive-optics k and l‧ images (resolutions ∼0.″2-0.″1) resolved this ionizing source into multiple point-like sources below ∼5000 au scale. the position angle ∼15° of the w42 molecular cloud is consistent with the h-band starlight mean polarization angle, which in turn is close to the galactic magnetic field, suggesting the influence of the galactic field on the evolution of the w42 molecular cloud. herschel sub-millimeter data analysis reveals three clumps located along the waist axis of the bipolar nebula, with the peak column densities of ∼(3-5) × 1022 cm-2 corresponding to visual extinctions of av ∼ 32-53.5 mag. the herschel temperature map traces a temperature gradient in w42, revealing regions of 20 k, 25 k, and 30-36 k. herschel maps reveal embedded filaments (length ∼1-3 pc) that appear to be radially pointed to the denser clump associated with the o5-o6 star, forming a hub-filament system. a total of 512 candidate young stellar objects (ysos) are identified in the complex, ∼40% of which are present in clusters distributed mainly within the molecular cloud, including the herschel filaments. our data sets suggest that the yso clusters, including the massive stars, are located at the junction of the filaments, similar to those seen in the rosette molecular cloud. | the physical environment of the massive star-forming region w42 |
elemental abundance patterns in the galactic disk constrain theories of the formation and evolution of the milky way. h ii region abundances are the result of billions of years of chemical evolution. we made radio recombination line and continuum measurements of 21 h ii regions located between galactic azimuth az = 90°-130°, a previously unexplored region. we derive the plasma electron temperatures using the line-to-continuum ratios and use them as proxies for the nebular [o/h] abundances, because in thermal equilibrium the abundance of the coolants (o, n, and other heavy elements) in the ionized gas sets the electron temperature, with high abundances producing low temperatures. combining these data with our previous work produces a sample of 90 h ii regions with high-quality electron temperature determinations. we derive kinematic distances in a self-consistent way for the entire sample. the radial gradient in [o/h] is -0.082+/- 0.014 {dex} {{kpc}}-1 for az = 90°-130°, about a factor of 2 higher than the average value between az = 0°-60°. monte carlo simulations show that the azimuthal structure we reported for az = 0°-60° is not significant because kinematic distance uncertainties can be as high as 50% in this region. nonetheless, the flatter radial gradients between az = 0°-60° compared with az = 90°-130° are significant within the uncertainty. we suggest that this may be due to radial mixing from the galactic bar whose major axis is aligned toward az ∼ 30°. | azimuthal metallicity structure in the milky way disk |
the gum nebula is 36°-wide shell-like emission nebula at a distance of only ∼450 pc. it has been hypothesized to be an old supernova remnant, fossil h ii region, wind-blown bubble, or combination of multiple objects. here we investigate the magneto-ionic properties of the nebula using data from recent surveys: radio-continuum data from the nrao vla and s-band parkes all sky surveys, and h α data from the southern h-alpha sky survey atlas. we model the upper part of the nebula as a spherical shell of ionized gas expanding into the ambient medium. we perform a maximum-likelihood markov chain monte carlo fit to the nvss rotation measure data, using the h α data to constrain average electron density in the shell ne. assuming a latitudinal background gradient in rotation measure, we find {{n}e}=1.3-0.4+0.4 c{{m}-3}, angular radius {{φ }outer}=22\buildrel{\circ}\over{.} 7-0.1+0.1, shell thickness dr=18.5-1.4+1.5 pc, ambient magnetic field strength {{b}0}=3.9-2.2+4.9 μ g, and warm gas filling factor f=0.3-0.1+0.3. we constrain the local, small-scale (∼260 pc) pitch-angle of the ordered galactic magnetic field to +7{}^\circ ≲ \wp ≲ +44{}^\circ , which represents a significant deviation from the median field orientation on kiloparsec scales (∼-7.°2). the moderate compression factor x=6.0-2.5+5.1 at the edge of the h α shell implies that the “old supernova remnant” origin is unlikely. our results support a model of the nebula as a h ii region around a wind-blown bubble. analysis of depolarization in 2.3 ghz s-pass data is consistent with this hypothesis and our best-fitting values agree well with previous studies of interstellar bubbles. | a radio-polarisation and rotation measure study of the gum nebula and its environment |
the stellar population of the milky way bulge is thoroughly studied, with a plethora of measurements from virtually the full suite of instruments available to astronomers. it is thus perhaps surprising that alongside well-established results lies some substantial uncertainty in its star-formation history. cosmological models predict the bulge to host the galaxy's oldest stars for [fe/h] ≲ -1, and this is demonstrated by rr lyrae stars and globular cluster observations. there is consensus that bulge stars with [fe/h] ≲ 0 are older than t ≈ 10 gyr. however, at super-solar metallicity, there is a substantial unresolved discrepancy. data from spectroscopic measurements of the main-sequence turnoff and subgiant branch, the abundances of asymptotic giant branch stars, the period distribution of mira variables, the chemistry and central-star masses of planetary nebulae, all suggest a substantial intermediate-age population (t ≈ 3 gyr). this is in conflict with predictions from cosmologically motivated chemical evolution models and photometric studies of the main-sequence turnoff region, which both suggest virtually no stars younger than t ≈ 8 gyr. a possible resolution to this conflict is enhanced helium-enrichment, as this would shift nearly all of the age estimates in the direction of decreasing discrepancy. | the controversial star-formation history and helium enrichment of the milky way bulge |
second only to initial mass, the rate of wind-driven mass loss determines the final mass of a massive star and the nature of its remnant. motivated by the need to reconcile observational values and theory, we use a recently vetted technique to analyze the mass-loss rates in a sample of ob stars that generate bow shock nebulae. we measure peculiar velocities from new gaia parallax and proper motion data and their spectral types from new optical and infrared spectroscopy. for our sample of 70 central stars in morphologically selected bow shock nebulae, 67 are ob stars. the median peculiar velocity is 11 km s-1, significantly smaller than classical “runaway star” velocities. mass-loss rates for these o and early b stars agree with recently lowered theoretical predictions, ranging from ≃10-7 m ⊙ yr-1 for mid-o dwarfs to 10-9 m ⊙ yr-1 for late o dwarfs—a factor of about 2.7 lower than the often-used vink et al. formulation. our results provide the first observational mass-loss rates for b0-b3 dwarfs and giants—10-9 to 10-8 m ⊙ yr-1. we find evidence for an increase in the mass-loss rates below a critical effective temperature, consistent with predictions of the bistability phenomenon in the range t eff = 19,000-27,000 k. the sample exhibits a correlation between modified wind momentum and luminosity, consistent in slope but lower by 0.43 dex in magnitude compared to canonical wind-luminosity relations. we identify a small subset of objects deviating most significantly from theoretical expectations as probable radiation-driven bow wave nebulae by virtue of their low stellar-to-nebular luminosity ratios. for these, the inferred mass-loss rates must be regarded as upper limits. | mass-loss rates for o and early b stars powering bow shock nebulae: evidence for bistability behavior |
the relative abundance of deuterium and hydrogen is a potent tracer of planet formation and evolution. jupiter and saturn have protosolar atmospheric d/h ratios, a relic of substantial gas accretion from the nebula, while the atmospheres of neptune and uranus are enhanced in d by accretion of ices into their envelopes. for terrestrial planets, d/h ratios are used to determine the mechanisms of volatile delivery and subsequent atmosphere loss over the lifetime of the planet. planets and brown dwarfs more massive than ∼13 m j quickly fuse their initial d reservoir. here, we simulate spectra for giant exoplanets and brown dwarfs (2 m neptune to ∼10 m jupiter) from t eff = 200-1800 k including both ch3d and hdo to determine the observability of these dominant deuterium isotopologues in mid-infrared thermal emission spectra. colder objects have stronger molecular features in their spectra, due to the temperature dependence of molecular cross sections. ch3d is easier to observe than hdo at all temperatures considered, due to the strength of its absorption bands and locations of features at wavelengths with few other strong absorption features. we predict that for nearby cool brown dwarfs, the ch3d abundance can be measured at high signal to noise with the james webb space telescope (jwst); for objects from 200 to 800 k closer than 10 pc, a protosolar d/h ratio would be readily observable in 2.5 hr. moderately young jupiter-mass planets (100-300 myr) and young neptunes (10 myr) may be discovered with jwst and provide the best targets for detecting deuterium on an exoplanet in the coming decade. future telescope designs should consider the importance of isotopes for understanding the formation and evolution of planetary atmospheres. | measuring the d/h ratios of exoplanets and brown dwarfs |
due to the small amount of hydrogen (≤0.1 m ⊙) remaining on the surface of their progenitors, sne iib are sensitive probes of the mass-loss processes of massive stars toward the ends of their lives, including the role of binarity. we report late-time hubble space telescope observations of sn 2011dh in m51, and a brief period of rebrightening and plateau in the photometric light curve, from 1.8 to 6.2 yr after the explosion. these observations exclude the role of circumstellar interaction, however, a slow rotating magnetar, a significant quantity of radioactive elements, or a light echo could be responsible for the late-time luminosity observed at t > 1000 days. if the late-time light curve is powered by the decay of radioactive elements, sn 2011dh is required to have produced ∼2.6 × 10-3 m ⊙ of 44ti, which is significantly in excess of the amount inferred from earlier nebular spectra of sn 2011dh itself or measured in the cas a sn remnant. the evolution of the brightness and the color of the late-time light curve also supports the role of a light echo originating from dust with a preferred geometry of a disk of extent ∼1.8 to ∼2.7 pc from the sn, consistent with a wind-blown bubble. accounting for the long-term photometric evolution due to a light echo, the flux contribution from a surviving binary companion at ultraviolet wavelengths can be isolated and corresponds to a star of ∼9-10 m ⊙. | the origin of the late-time luminosity of supernova 2011dh |
we have carried out a new photometric v,rcstudy of 12 protoplanetary nebulae, objects in the short-lived transition between the asymptotic giant branch and planetary nebula phases of stellar evolution. these had been the subjects of an earlier study, using data from 1994-2007, that found that all 12 varied periodically, with pulsation periods in the range of ~38 to ~150 days. they are all carbon-rich, with f-g spectral types. we combined our new (2008-2018) data with publicly available all-sky automated survey for supernovae data and determined new periods for their variability. the older and newer period values were compared to investigate evidence of period change, for which there is theoretical support that it might be detectable in a decade or two in some cases. such a detection is challenging since the light curves are complicated, with multiple periods, changing amplitudes, and evidence of shocks. nevertheless, we found one, and possibly two, such cases, which are associated with the higher-temperature stars in the sample (7250 and 8000 k). these results are most consistent with the evolution of stars at the lower end of the mass range of carbon stars, ~1.5-2 m ☉. several of the stars show longer-term trends of increasing (six cases) or decreasing (one case) brightness, which we think is most likely due to changes in the circumstellar dust opacity. there is one case of a possible ~1.8 yr period in addition to the shorter pulsation. this is interpreted as possible evidence of an orbiting companion. | variability in protoplanetary nebulae. ix. evidence for evolution in a decade |
we report on the variability of a multi-component broad absorption line (bal) system observed in the hyper-luminous quasar j1538+0855 at z = 3.6. observations from the sloan digital sky survey (sdss), very large telescope (vlt), large binocular telescope (lbt), and subaru telescope taken at five different epochs, spanning 17 yr in the observed frame, are presented. we detect three (a, b, and c) civ variable troughs exhibiting extreme velocities (∼40 000-54 000 km s−1) similar to the ultra-fast outflows (ufos) typically observed in the x-ray spectra. the a component of the bal ufo (vufo ∼ 0.17c) shows strength variations, while b (vufo ∼ 0.15c) and c (vufo ∼ 0.13c) components show changes both in shape and strength, appearing and disappearing at different epochs. in addition, during the last observation on june 2021, the entire bal system disappeared. the variability trends observed during the first two epochs (1.30 yr rest frame) in the civ, siiv, ovi, and nv absorption spectral regions are the same for b and c troughs, while the a component of the bal varies independently. this suggests a change in the ionization state of the absorbing gas for b and c components and tangential motion for the a component, as the cause of this temporal behaviour. accordingly, it is possible to provide an upper limit for distance of the gas responsible for the a component of routa ≤ 58 pc and, in turn, a kinetic power of ėk,ufo ≤ 1.37 × 1045 erg s−1. we also obtain routb,c ≤ 1.9 kpc for b and c components, which implies an upper limit estimation of ėk,ufo ≤ 1.94 × 1046 erg s−1 and ėk,ufo ≤ 1.33 × 1046 erg s−1, respectively. future spectral monitoring with high-resolution instruments is mandatory to accurately constrain physical properties of the bal ufo discovered in the uv spectrum of j1538+0855 and investigate its role as a promising mechanism for the origin of the extended (∼75 kpc) civ nebula surrounding this hyper-luminous quasar. | the wissh quasars project. x. discovery of a multi-component and highly variable uv ultra-fast outflow in a z = 3.6 quasar |
if high-mass stars (≳20 − 25 m⊙) are the progenitors of stripped-envelope (se) supernovae (sne), their massive ejecta should lead to broad, long-duration lightcurves. instead, literature samples of se sne have reported relatively narrow lightcurves corresponding to ejecta masses between 1 − 4 m⊙ that favor intermediate-mass progenitors (≲20 − 25 m⊙). working with an untargeted sample from a single telescope to better constrain their rates, we searched the palomar transient factory (ptf) and intermediate-ptf (iptf) sample of sne for se sne with broad lightcurves. using a simple observational marker of g- or r-band lightcurve stretch compared to a template to measure broadness, we identified eight significantly broader type ibc sne after applying quantitative sample selection criteria. the lightcurves, broad-band colors, and spectra of these sne are found to evolve more slowly relative to typical type ibc sne, proportional with the stretch parameter. bolometric lightcurve modeling and their nebular spectra indicate high ejecta masses and nickel masses, assuming radioactive decay powering. additionally, these objects are preferentially located in low-metallicity host galaxies with high star formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. our study thus supports the link between broad lightcurves (as measured by stretch) and high-mass progenitor stars in se sne with independent evidence from bolometric lightcurve modeling, nebular spectra, host environment properties, and photometric evolution. in the first systematic search of its kind using an untargeted sample, we used the stretch distribution to identify a higher than previously appreciated fraction of se sne with broad lightcurves (∼13%). correcting for malmquist and lightcurve duration observational biases, we conservatively estimate that a minimum of ∼6% of se sne are consistent with high-mass progenitors. this result has implications for the progenitor channels of se sne, including late stages of massive stellar evolution, the origin of the observed oxygen fraction in the universe, and formation channels for stellar-mass black holes. | a population of type ibc supernovae with massive progenitors. broad lightcurves not uncommon in (i)ptf |
the resonantly scattered lyα line illuminates the extended halos of neutral hydrogen in the circumgalactic medium of galaxies. we present integral field keck cosmic web imager observations of double-peaked, spatially extended lyα emission in 12 relatively low-mass (m ⋆ ~ 109 m⊙) z ~ 2 galaxies characterized by extreme nebular emission lines. using individual spaxels and small bins as well as radially binned profiles of larger regions, we find that for most objects in the sample the lyα blue-to-red peak ratio increases, the peak separation decreases, and the fraction of flux emerging at line center increases with radius. we use new radiative transfer simulations to model each galaxy with a clumpy, multiphase outflow with radially varying outflow velocity, and self-consistently apply the same velocity model to the low-ionization interstellar absorption lines. these models reproduce the trends of peak ratio, peak separation, and trough depth with radius, and broadly reconcile outflow velocities inferred from lyα and absorption lines. the galaxies in our sample are well-described by a model in which neutral, outflowing clumps are embedded in a hotter, more highly ionized inter-clump medium (icm), whose residual neutral content produces absorption at the systemic redshift. the peak ratio, peak separation, and trough flux fraction are primarily governed by the line-of-sight component of the outflow velocity, the h i column density, and the residual neutral density in the icm respectively. the azimuthal asymmetries in the line profile further suggest nonradial gas motions at large radii and variations in the h i column density in the outer halos. *based on data obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and nasa, and was made possible by the generous financial support of the w.m. keck foundation. | the circumgalactic medium of extreme emission line galaxies at z 2: resolved spectroscopy and radiative transfer modeling of spatially extended lyα emission in the kbss-kcwi survey |
fluffy type a ca-al-rich inclusions (cais) containing reversely zoned melilite crystals are suggested to be aggregates of direct condensates from solar nebular gas. we conducted an investigation of 26al-26mg systematics of a fluffy type a cai from vigarano, named v2-01, with known oxygen isotopic distributions of reversely zoned melilite crystals; we also conducted oxygen isotope measurements of coexisting minerals. two of six reversely zoned melilite crystals show continuous variations in magnesium isotopic composition, with δ25mg decreasing along the inferred direction of crystal growth, which supports the idea that they originated through condensation. petrography suggests that the constituent minerals of v2-01 formed in the following order: first spinel and fassaite enclosed by melilite, then reversely zoned melilite crystals, and spinel and diopside in the wark-lovering rim. the spinel enclosed by melilite has 16o-rich compositions (δ17o ∼ -24‰) and on an al-mg evolutionary diagram plots along model isochron with an initial value of (26al/27al)0 = (5.6 ± 0.2) × 10-5. the fassaite enclosed by melilite crystals shows variable oxygen isotopic compositions (δ17o ∼ -12‰ and -17‰) and plots on an isochron with (26al/27al)0 = (5.6 ± 0.2) × 10-5. the oxygen isotopic compositions of reversely zoned melilite showed continuous variations in δ17o along the inferred direction of crystal growth, suggesting that surrounding nebular gas, during the formation of the reversely zoned melilite, changed from 16o-poor (δ17o values larger than -10‰) to 16o-rich (δ17o ∼ -25‰). the six reversely zoned melilite crystals show indistinguishable initial 26al/27al values with an average (26al/27al)0 of (4.7 ± 0.3) × 10-5, which is clearly distinguishable from the value of enclosed spinel and fassaite, indicating a younger formation age than the enclosed spinel and fassaite. the spinel and diopside from the wark-lovering rim show 16o-rich compositions (δ17o ∼ -23‰) with (26al/27al)0 = (4.5 ± 0.4) × 10-5. the values of (26al/27al)0 are consistent with the formation sequence inferred from petrography. the formation period for the v2-01 cai is estimated to be 0.18 ± 0.07 myr from the difference in initial 26al/27al values. these data suggest that the oxygen isotopic composition of solar nebular gas surrounding the cai changed from 16o-rich to 16o-poor and back to 16o-rich during the first ∼0.2 myr of solar system formation. | chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy type a cai from vigarano |
the sagittarius b2 (sgr b2) molecular cloud complex is an x-ray reflection nebula whose nonthermal x-ray emissions have continued to decrease since 2001 as it reprocesses one or more past energetic outbursts from the supermassive black hole sagittarius a* at the galactic center. the x-ray reflection model explains the observed time variability of sgr b2 and provides a window into the luminous evolutionary history of our nearest supermassive black hole. in light of evidence of elevated cosmic particle populations in the galactic center, x-rays from sgr b2 are also of interest as a probe of low-energy (sub-gev) cosmic rays, which may be responsible for an increasing relative fraction of the nonthermal emission as the contribution from x-ray reflection decreases. here, we present the most recent nustar and xmm-newton observations of sgr b2, from 2018, and we emphasize the kα fluorescence line of neutral fe. these 2018 observations reveal small-scale variations within lower-density portions of the complex, including brightening features, yet still enable upper limits on x-rays from low-energy cosmic-ray interactions in sgr b2. we present fe kα line fluxes from cloud regions of different densities, facilitating comparison with models of ambient low-energy cosmic-ray interactions throughout the cloud. | new constraints on cosmic particle populations at the galactic center using x-ray observations of the molecular cloud sagittarius b2 |
we investigate the physical conditions of the co gas, based on the submillimeter imaging spectroscopy from a 2' × 7' (1.5 × 5 pc2) area near the young star cluster, trumpler 14 of the carina nebula. the observations presented in this work are taken with the fourier transform spectrometer (fts) of the spectral and photometric imaging receiver (spire) onboard the herschel space observatory. the newly observed spectral lines include [ci] 370 μm [ci] 609 μm, and co transitions from j = 4-3 to j = 13-12. our field of view covers the edge of a cavity carved by trumpler 14 about 1 myr ago and marks the transition from h ii regions to photo-dissociation regions. the observed co intensities are the most prominent at the northwest region, car i-e. with the state-of-the-art meudon pdr code, we successfully derive the physical conditions, which include the thermal pressure (p) and the scaling factor of radiation fields (guv), from the observed co spectral line energy distributions (sleds) in the observed region. the derived guv values generally show excellent agreement with the uv radiation fields created by nearby ob-stars and thus confirm that the main excitation source of the observed co emission is the uv-photons provided by the massive stars. the derived thermal pressure is in the range 0.5-3 × 108 k cm-3 with the highest values found along the ionization front in car i-e region facing trumpler 14, hinting that the cloud structure is similar to the recent observations of the orion bar. we also note a discrepancy at a local position (<0.17 × 0.17 pc2) between the photo-dissociation region (pdr) modeling result and the uv radiation fields estimated from nearby massive stars, which requires further investigation on nearby objects that could contribute to local heating, including outflow. comparing the derived thermal pressure with the radiation fields, we report the first observationally derived and spatially resolved p ~ 2 × 104 guv relationship. as direct comparisons of the modeling results to the observed 13co, [o i] 63 μm, and [c ii] 158 μm intensities are not straightforward, we urge the reader to be cautious when constraining the physical conditions of pdrs with combinations of 12co, 13co, [c i], [o i] 63 μm, and [c ii] 158 μm observations. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. datacubes 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/618/a53 | constraining physical conditions for the pdr of trumpler 14 in the carina nebula |
the mgro j2019+37 region is one of the brightest sources in the sky at tev energies. it was detected in the second hawc catalog as 2hwc j2019+367 and here we present a detailed study of this region using data from hawc. this analysis resolves the region into two sources: hawc j2019+368 and hawc j2016+371. we associate hawc j2016+371 with the evolved supernova remnant ctb 87, although its low significance in this analysis prevents a detailed study at this time. an investigation of the morphology (including possible energy-dependent morphology) and spectrum for hawc j2019+368 is the focus of this work. we associate hawc j2019+368 with psr j2021+3651 and its x-ray pulsar wind nebula, the dragonfly nebula. modeling the spectrum measured by hawc and suzaku reveals a ∼7 kyr pulsar and nebula system producing the observed emission at x-ray and γ-ray energies. | spectrum and morphology of the very-high-energy source hawc j2019+368 |
while chandrasekhar-mass (mch) models with a low 56ni yield can match the peak luminosities of fast-declining, 91bg-like type ia supernovae (sne ia), they systematically fail to reproduce their faster light-curve evolution. here, we illustrate the impact of a low ejecta mass on the radiative display of low-luminosity sne ia, by comparing a sub-mch model resulting from the pure central detonation of a c-o white dwarf (wd) to an mch delayed-detonation model with the same 56ni yield of 0.12 m⊙. our sub-mch model from a 0.90 m⊙ wd progenitor has a ∼5 d shorter rise time in the integrated uv-optical-ir (uvoir) luminosity, as well as in the b band, and a ∼20 per cent higher peak uvoir luminosity (∼1 mag brighter peak mb). this sub-mch model also displays bluer maximum-light colours due to the larger specific heating rate, and larger post-maximum uvoir and b-band decline rates. the luminosity decline at nebular times is also more pronounced, reflecting the enhanced escape of gamma rays resulting from the lower density of the progenitor wd. the deficit of stable nickel in the innermost ejecta leads to a notable absence of forbidden lines of [ni ii] in the nebular spectra. in contrast, the mch model displays a strong line due to [ni ii] 1.939 μm, which could in principle serve to distinguish between different progenitor scenarios. our sub-mch model offers an unprecedented agreement with optical and near-infrared observations of the 91bg-like sn 1999by, making a strong case for a wd progenitor significantly below the chandrasekhar-mass limit for this event and other low-luminosity sne ia. | the detonation of a sub-chandrasekhar-mass white dwarf at the origin of the low-luminosity type ia supernova 1999by |
we calculate dust spectral energy distributions (seds) for a range of grain sizes and compositions, using physical properties appropriate for five pulsar wind nebulae (pwne) from which dust emission associated with the ejecta has been detected. by fitting the observed dust sed with our models, with the number of grains of different sizes as the free parameters, we are able to determine the grain size distribution and total dust mass in each pwn. we find that all five pwne require large (≥ 0.1 {μ m}) grains to make up the majority of the dust mass, with strong evidence for the presence of micron-sized or larger grains. only two pwne contain non-negligible quantities of small (< 0.01 {μ m}) grains. the size distributions are generally well-represented by broken power laws, although our uncertainties are too large to rule out alternative shapes. we find a total dust mass of 0.02{-}0.28 m_⊙ for the crab nebula, depending on the composition and distance from the synchrotron source, in agreement with recent estimates. for three objects in our sample, the pwn synchrotron luminosity is insufficient to power the observed dust emission, and additional collisional heating is required, either from warm, dense gas as found in the crab nebula, or higher temperature shocked material. for g54.1+0.3, the dust is heated by nearby ob stars rather than the pwn. inferred dust masses vary significantly depending on the details of the assumed heating mechanism, but in all cases large mass fractions of micron-sized grains are required. | dust masses and grain size distributions of a sample of galactic pulsar wind nebulae |
we study the hydrodynamics and nucleosynthesis in the double-detonation model of type ia supernovae (sne ia) and the interaction between the ejecta and a surviving white dwarf (wd) companion in the double-degenerate scenario. we set up a binary star system with 1.0 and 0.6 m ⊙ carbon-oxygen (co) wds, where the primary wd consists of a co core and helium (he) shell with 0.95 and 0.05 m ⊙, respectively. we follow the evolution of the binary star system from the initiation of an he detonation, ignition and propagation of a co detonation, and the interaction of sn ejecta with the companion wd. the companion (or surviving) wd gets a flung-away velocity of ∼1700 km s-1 and captures 56ni of ∼0.03 m ⊙ and he of 3× {10}-4 {m}⊙ . such he can be detected on the surface of surviving wds. the sn ejecta contains a “companion-origin stream” and unburned materials stripped from the companion wd (∼ 3× {10}-3 {m}⊙ ), although the stream compositions would depend on the he shell mass of the companion wd. the ejecta has also a velocity shift of ∼1000 km s-1 due to the binary motion of the exploding primary wd. these features would be prominent in nebular-phase spectra of oxygen emission lines from the unburned materials like sn 2010lp and iptf14atg and of blue- or redshifted fe-group emission lines from the velocity shift like a part of subluminous sne ia. we expect that sn ia counterparts to the d6 model would leave these fingerprints for sn ia observations. | three-dimensional simulation of double detonations in the double-degenerate model for type ia supernovae and interaction of ejecta with a surviving white dwarf companion |
data augmentation (da) has emerged as an indispensable strategy in time series classification (tsc), primarily due to its capacity to amplify training samples, thereby bolstering model robustness, diversifying datasets, and curtailing overfitting. however, the current landscape of da in tsc is plagued with fragmented literature reviews, nebulous methodological taxonomies, inadequate evaluative measures, and a dearth of accessible, user-oriented tools. in light of these challenges, this study embarks on an exhaustive dissection of da methodologies within the tsc realm. our initial approach involved an extensive literature review spanning a decade, revealing that contemporary surveys scarcely capture the breadth of advancements in da for tsc, prompting us to meticulously analyze over 100 scholarly articles to distill more than 60 unique da techniques. this rigorous analysis precipitated the formulation of a novel taxonomy, purpose-built for the intricacies of da in tsc, categorizing techniques into five principal echelons: transformation-based, pattern-based, generative, decomposition-based, and automated data augmentation. our taxonomy promises to serve as a robust navigational aid for scholars, offering clarity and direction in method selection. addressing the conspicuous absence of holistic evaluations for prevalent da techniques, we executed an all-encompassing empirical assessment, wherein upwards of 15 da strategies were subjected to scrutiny across 8 ucr time-series datasets, employing resnet and a multi-faceted evaluation paradigm encompassing accuracy, method ranking, and residual analysis, yielding a benchmark accuracy of 88.94 +- 11.83%. our investigation underscored the inconsistent efficacies of da techniques, with... | data augmentation for time-series classification: an extensive empirical study and comprehensive survey |
approximately one hundred sources of very-high-energy (vhe) gamma rays are known in the milky way. a survey of the entire galactic plane in the energy range from a few tens of gev to a few hundred tev has been proposed as a key science project for the upcoming cherenkov telescope array observatory (ctao). this article presents the status of the studies towards the galactic plane survey (gps). we build and make publicly available a sky model that combines data from observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the main classes of established galactic vhe sources, as well as of interstellar emission from cosmic-ray interactions in the milky way. we also perform an optimisation of the observation strategy. we use the improved sky model and observation strategy to simulate gps data that are analysed using the methods and software tools under development for real data. we show that the gps has the potential to increase the number of known galactic vhe emitters by almost a factor of five. this corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 tev, therefore opening the possibility to perform unprecedented population studies. the gps also has the potential to provide new vhe detections of binary systems and pulsars, and to identify any bright pevatrons. furthermore, the gps will constitute a pathfinder for deeper follow-up observations of these source classes. finally, we show that we can extract from gps data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. (abridged) | prospects for a survey of the galactic plane with the cherenkov telescope array |
i examine the morphologies of the brightest planetary nebulae (pne) in the milky way galaxy and conclude that violent binary interaction processes eject the main nebulae of the brightest pne. the typical morphologies of the brightest pne are multipolar, namely have been shaped by two or more major jet-launching episodes at varying directions, and possess small to medium departures from pure point symmetry. i discuss some scenarios, including a rapid onset of a common envelope interaction and the merger of the companion, mainly a white dwarf, with the asymptotic giant branch core at the termination of the common envelope. some of these might be progenitors of type ia supernovae (sne ia), as i suggest for snr g1.9+0.3, the youngest sn ia in the galaxy. | violent mass ejection by the progenitors of the brightest planetary nebulae: supernova progenitors |
the entire southern sky (declination, $δ< 30^{\circ}$ ) has been observed using the murchison widefield array (mwa), which provides radio imaging of $∼$ 2 arcmin resolution at low frequencies (72-231 mhz). this is the galactic and extragalactic all-sky mwa (gleam) survey, and we have previously used a combination of visual inspection, cross-checks against the literature, and internal matching to identify the `brightest' radio-sources ( $s_{151 mhz}>4$ jy) in the extragalactic catalogue (galactic latitude, $|b| >10^{\circ}$ ). we refer to these 1 863 sources as the gleam 4-jy (g4jy) sample, and use radio images (of ${≤}45$ arcsec resolution), and multi-wavelength information, to assess their morphology and identify the galaxy that is hosting the radio emission (where appropriate). details of how to access all of the overlays used for this work are available at https://github.com/svw26/g4jy. alongside this we conduct further checks against the literature, which we document here for individual sources. whilst the vast majority of the g4jy sample are active galactic nuclei with powerful radio-jets, we highlight that it also contains a nebula, two nearby, star-forming galaxies, a cluster relic, and a cluster halo. there are also three extended sources for which we are unable to infer the mechanism that gives rise to the low-frequency emission. in the g4jy catalogue we provide mid-infrared identifications for 86% of the sources, and flag the remainder as: having an uncertain identification (129 sources), having a faint/uncharacterised mid-infrared host (126 sources), or it being inappropriate to specify a host (2 sources). for the subset of 129 sources, there is ambiguity concerning candidate host-galaxies, and this includes four sources (b0424-728, b0703-451, 3c 198, and 3c 403.1) where we question the existing identification. | the gleam 4-jy (g4jy) sample: ii. host galaxy identification for individual sources |
as a candidate `super-chandrasekhar' or 09dc-like type ia supernova (sn ia), sn 2012dn shares many characteristics with other members of this remarkable class of objects but lacks their extraordinary luminosity. here, we present and discuss the most comprehensive optical data set of this sn to date, comprised of a densely sampled series of early-time spectra obtained within the nearby supernova factory project, plus photometry and spectroscopy obtained at the very large telescope about 1 yr after the explosion. the light curves, colour curves, spectral time series, and ejecta velocities of sn 2012dn are compared with those of other 09dc-like and normal sne ia, the overall variety within the class of 09dc-like sne ia is discussed, and new criteria for 09dc-likeness are proposed. particular attention is directed to additional insight that the late-phase data provide. the nebular spectra show forbidden lines of oxygen and calcium, elements that are usually not seen in late-time spectra of sne ia, while the ionization state of the emitting iron plasma is low, pointing to low ejecta temperatures and high densities. the optical light curves are characterized by an enhanced fading starting ∼60 d after maximum and very low luminosities in the nebular phase, which is most readily explained by unusually early formation of clumpy dust in the ejecta. taken together, these effects suggest a strongly perturbed ejecta density profile, which might lend support to the idea that 09dc-like characteristics arise from a brief episode of interaction with a hydrogen-deficient envelope during the first hours or days after the explosion. | sn 2012dn from early to late times: 09dc-like supernovae reassessed |
we present new estimates of protosolar elemental abundances based on an improved combination of solar photospheric abundances and ci chondritic abundances. these new estimates indicate ci chondrites and solar abundances are consistent for 60 elements. our estimate of the protosolar "metallicity" (i.e. mass fraction of metals, z) is 1.40%, which is consistent with a value of z that has been decreasing steadily over the past three decades from ∼1.9%. we compare our new protosolar abundances with our recent estimates of bulk earth composition (normalized to aluminium), thereby quantifying the devolatilization in going from the solar nebula to the formation of the earth. the quantification yields a linear trend log (f) = α log (tc) + β, where f is the earth-to-sun abundance ratio and tc is the 50% condensation temperature of elements. the best fit coefficients are: α = 3.676 ± 0.142 and β = - 11.556 ± 0.436. the quantification of these parameters constrains models of devolatilization processes. for example, the coefficients α and β determine a critical devolatilization temperature for the earth td(e) = 1391 ± 15 k. the terrestrial abundances of elements with tc < td(e) are depleted compared with solar abundances, whereas the terrestrial abundances of elements with tc > td(e) are indistinguishable from solar abundances. the abundances of noble gases and hydrogen are depleted more than a prediction based on the extrapolation of the best-fit volatility trend. the terrestrial abundance of hg (tc = 252 k) appears anomalously high under the assumption that solar and ci chondrite hg abundances are identical. to resolve this anomaly, we propose that ci chondrites have been depleted in hg relative to the sun by a factor of 13 ± 7. we use the best-fit volatility trend to derive the fractional distribution of carbon and oxygen between volatile and refractory components (fvol, fref). for carbon we find (0.91 ± 0.08, 0.09 ± 0.08); for oxygen we find (0.80 ± 0.04, 0.20 ± 0.04). our preliminary estimate gives ci chondrites a critical devolatilization temperature td(ci) = 550-100+20 k. | the volatility trend of protosolar and terrestrial elemental abundances |
this work presents the observations and analysis of atlas19dqr/sn 2019bkc, an extraordinary rapidly evolving transient event located in an isolated environment, tens of kiloparsecs from any likely host. its light curves rise to maximum light in 5-6 d and then display a decline of δm15 ∼ 5 mag. with such a pronounced decay, it has one of the most rapidly evolving light curves known for a stellar explosion. the early spectra show similarities to normal and "ultra-stripped" type ic sne, but the early nebular phase spectra, which were reached just over two weeks after explosion, display prominent calcium lines, marking sn 2019bkc as a ca-rich transient. the ca emission lines at this phase show an unprecedented and unexplained blueshift of 10 000-12 000 km s-1. modelling of the light curve and the early spectra suggests that the transient had a low ejecta mass of 0.2-0.4 m⊙ and a low kinetic energy of (2-4) × 1050 erg, giving a specific kinetic energy ek/mej ∼ 1 [1051 erg]/m⊙. the origin of this event cannot be unambiguously defined. while the abundance distribution used to model the spectra marginally favours a progenitor of white dwarf origin through the tentative identification of ar ii, the specific kinetic energy, which is defined by the explosion mechanism, is found to be more similar to an ultra-stripped core-collapse events. sn 2019bkc adds to the diverse range of physical properties shown by ca-rich events. partially based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programmes 199.d-0143 and 0102.d-0137(a). | the rise and fall of an extraordinary ca-rich transient. the discovery of atlas19dqr/sn 2019bkc |
cross-correlation techniques have been used since 1974 and, since 1979, the analysis based on the fourier method has been applied. however, we are currently obtaining data with spectral resolution higher than those for which this technique was developed, hence some revision seems timely. the principal aim of this work is to adapt tonry and davis' method and implementing it for the treatment of very high spectral resolution data. we have applied this technique to two different sets of spectroscopic data of moderate and high resolutions obtained with the muse and megara spectrographs respectively. using stellar spectra obtained with these two instruments (i) we have optimised the input parameters; (ii) we have analysed the method assumptions; and (iii) we have compared the results for the two sets of data. the optimal method parameters applied to muse data are $k_{min}$ $\sim$ 3, $k_{max}$ $\sim$ 60 and 512 bins, which correspond to a uniform velocity shift value of $\delta $v = 27.1 km/s. for megara data, we propose the values $k_{min}$ $\sim$ 3, $k_{max}$ $\sim$ 350 and 4096 bins finding that the cross-correlation function lost its gaussian behavior at higher resolutions. thus, we have developed an equivalent mathematical method that can be used for this kind of data. additionally, the velocity dispersion error analysis suggests that the greatest error introduced in this method is due to the subtraction or masking of the nebular lines. for the application cross-correlation techniques to high spectral resolution data, we propose to calculate the galaxy-galaxy and star-galaxy correlations, with widths $\mu_{gg}$ and $\mu_{gt}$ respectively. then, the width of the broadening function can be calculated as $\sigma = \sqrt{\mu_{gg}^2 - \mu_{gt}^2}$. | revising the cross correlation technique at high spectral resolution |
models of core accretion assume that in the radiative zones of accreting gas envelopes, radiation diffuses. but super-earths/sub-neptunes (1-4 r⊕, 2-20 m⊕) point to formation conditions that are optically thin: their modest gas masses are accreted from short-lived and gas-poor nebulae reminiscent of the transparent cavities of transitional discs. planetary atmospheres born in such environments can be optically thin to both incident starlight and internally generated thermal radiation. we construct time-dependent models of such atmospheres, showing that super-earths/sub-neptunes can accrete their ∼1 per cent-by-mass gas envelopes, and super-puffs/sub-saturns their ∼20 per cent-by-mass envelopes, over a wide range of nebular depletion histories requiring no fine tuning. although nascent atmospheres can exhibit stratospheric temperature inversions affected by atomic fe and various oxides that absorb strongly at visible wavelengths, the rate of gas accretion remains controlled by the radiative-convective boundary (rcb) at much greater pressures. for dusty envelopes, the temperature at the rcb trcb ≃ 2500 k is still set by h2 dissociation; for dust-depleted envelopes, trcb tracks the temperature of the visible or thermal photosphere, whichever is deeper, out to at least ∼5 au. the rate of envelope growth remains largely unchanged between the old radiative diffusion models and the new optically thin models, reinforcing how robustly super-earths form as part of the endgame chapter in disc evolution. | optically thin core accretion: how planets get their gas in nearly gas-free discs |
we investigate pathways for the formation of icy super-earth mass planets orbiting at 125-250 au around a 1 {{m}⊙ } star. an extensive suite of coagulation calculations demonstrates that swarms of 1 cm-10 m planetesimals can form super-earth mass planets on timescales of 1-3 gyr. collisional damping of 10-2-102 cm particles during oligarchic growth is a highlight of these simulations. in some situations, damping initiates a second runaway growth phase where 1000-3000 km protoplanets grow to super-earth sizes. our results establish the initial conditions and physical processes required for in situ formation of super-earth planets at large distances from the host star. for nearby dusty disks in hd 107146, hd 202628, and hd 207129, ongoing super-earth formation at 80-150 au could produce gaps and other structures in the debris. in the solar system, forming a putative planet x at a≲ 300 au (a≳ 1000 au) requires a modest (very massive) protosolar nebula. | formation of super-earth mass planets at 125-250 au from a solar-type star |
planetary nebulae mark the end of the active life of 90% of all stars. they trace the transition from a red giant to a degenerate white dwarf. stellar models1,2 predicted that only stars above approximately twice the solar mass could form a bright nebula. but the ubiquitous presence of bright planetary nebulae in old stellar populations, such as elliptical galaxies, contradicts this: such high-mass stars are not present in old systems. the planetary nebula luminosity function, and especially its bright cut-off, is almost invariant between young spiral galaxies, with high-mass stars, and old elliptical galaxies, with only low-mass stars. here, we show that new evolutionary tracks of low-mass stars are capable of explaining in a simple manner this decades-old mystery. the agreement between the observed luminosity function and computed stellar evolution validates the latest theoretical modelling. with these models, the planetary nebula luminosity function provides a powerful diagnostic to derive star formation histories of intermediate-age stars. the new models predict that the sun at the end of its life will also form a planetary nebula, but it will be faint. | the mysterious age invariance of the planetary nebula luminosity function bright cut-off |
we present a catalog of 840 x-ray sources and first results from a 100 ks chandra x-ray observatory imaging study of the filamentary infrared (ir) dark cloud g014.225-00.506, which forms the central regions of a larger cloud complex known as the m17 southwest extension (m17 swex). in addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by archival data from the spitzer space telescope, we discover a population of x-ray-emitting, intermediate-mass pre-main-sequence stars that lack ir excess emission from circumstellar disks. we model the ir spectral energy distributions of this source population to measure its mass function and place new constraints on the destruction timescales for the inner dust disk for 2-8 m ⊙ stars. we also place a lower limit on the star formation rate (sfr) and find that it is quite high (\dot{m}≥slant 0.007 m ⊙ yr-1), equivalent to several orion nebula clusters in g14.225-0.506 alone, and likely accelerating. the cloud complex has not produced a population of massive, o-type stars commensurate with its sfr. this absence of very massive (≳20 m ⊙) stars suggests that either (1) m17 swex is an example of a distributed mode of star formation that will produce a large ob association dominated by intermediate-mass stars but relatively few massive clusters, or (2) the massive cores are still in the process of accreting sufficient mass to form massive clusters hosting o stars. | rapid circumstellar disk evolution and an accelerating star formation rate in the infrared dark cloud m17 swex |
type ia sn 2014j exploded in the nearby starburst galaxy m82 = ngc 3032 and was discovered at earth about seven days later on 2014 january 21, reaching maximum light in v around 2014 february 5. sn 2014j is the closest sn ia in at least four decades and probably many more. recent hubble space telescope/wfc3 imaging (2014 september 5 and 2015 february 2) of m82 in the vicinity of sn 2014j reveals a light echo at radii of about 0.6 arcsec from the supernova (sn; corresponding to about 12 pc at the distance of m82). likely additional light echoes reside at a smaller radii of about 0.4 arcsec the major echo signal corresponds to echoing material about 330 pc in the foreground of sn 2014j and tends to be bright where pre-existing nebular structure in m82 is also bright. the second, likely echo corresponds to foreground distances of 80 pc in front of the sn. even one year after maximum light, there are indications of further echo structures appearing at smaller radii, and future observations may show how extinction in these affect detected echo farther from the sn, which will affect interpretation of details of the three-dimensional structure of this gas and dust. given enough data, we might even use these considerations to constrain the near-sn material’s shadowing on distant echoing clouds, even without directly observing the foreground structure. this is in addition to echoes in the near future that might also reveal circumstellar structure around sn 2014j’s progenitor star from direct imaging observations and other techniques. | light echoes from supernova 2014j in m82 |
we present a near-ir survey of the trapezium cluster and inner orion nebula using the nasa/esa/csa james webb space telescope. the survey with the nircam instrument covers 10.9 x 7.5 arcminutes (~1.25 x 0.85 pc) in twelve wide-, medium-, and narrow-band filters from 1-5 microns and is diffraction-limited at all wavelengths, providing a maximum spatial resolution of 0.063 arcsec at 2 microns, corresponding to ~25 au at orion. the suite of filters chosen was designed to address a number of scientific questions including the form of the extreme low-mass end of the imf into the planetary-mass range to 1 jupiter mass and below; the nature of ionised and non-ionised circumstellar disks and associated proplyds in the near-ir with a similar resolution to prior hst studies; to examine the large fragmented outflow from the embedded bn-kl region at very high resolution and fidelity; and to search for new jets and outflows from young stars in the trapezium cluster and the orion molecular cloud 1 behind. in this paper, we present a description of the design of the observational programme, explaining the rationale for the filter set chosen and the telescope and detector modes used to make the survey; the reduction of the data using the jwst pipeline and other tools; the creation of large colour mosaics covering the region; and an overview of the discoveries made in the colour images and in the individual filter mosaics. highlights include the discovery of large numbers of free-floating planetary-mass candidates as low as 0.6 jupiter masses, a significant fraction of which are in wide binaries; new emission phenomena associated with the explosive outflow from the bn-kl region; and a mysterious "dark absorber" associated with a number of disparate features in the region, but which is seen exclusively in the f115w filter. further papers will examine those discoveries and others in more detail. | a jwst survey of the trapezium cluster & inner orion nebula. i. observations & overview |
hess j1825-137 is a pulsar wind nebula (pwn) whose tev emission extends across ∼1 . its large asymmetric shape indicates that its progenitor supernova interacted with a molecular cloud located in the north of the pwn as detected by previous co galactic survey (e.g. lemiere, terrier & djannati-ataï). here, we provide a detailed picture of the interstellar medium (ism) towards the region north of hess j1825-137, with the analysis of the dense molecular gas from our 7 and 12 mm mopra survey and the more diffuse molecular gas from the nanten co(1-0) and grs 13co(1-0) surveys. our focus is the possible association between hess j1825-137 and the unidentified tev source to the north, hess j1826-130. we report several dense molecular regions whose kinematic distance matched the dispersion measured distance of the pulsar. among them, the dense molecular gas located at (ra, dec.) = (18h421h,-13.282°) shows enhanced turbulence and we suggest that the velocity structure in this region may be explained by a cloud-cloud collision scenario. furthermore, the presence of a h α rim may be the first evidence of the progenitor supernova remnant (snr) of the pulsar psr j1826-1334 as the distance between the h α rim and the tev source matched with the predicted snr radius rsnr ∼ 120 pc. from our ism study, we identify a few plausible origins of the hess j1826-130 emission, including the progenitor snr of psr j1826-1334 and the pwn g018.5-0.4 powered by psr j1826-1256. a deeper tev study however, is required to fully identify the origin of this mysterious tev source. | ism gas studies towards the tev pwn hess j1825-137 and northern region |
we present the results of 3d particle-in-cell simulations that explore relativistic magnetic reconnection in pair plasma with strong synchrotron cooling and a small mass fraction of nonradiating ions. our results demonstrate that the structure of the current sheet is highly sensitive to the dynamic efficiency of radiative cooling. specifically, stronger cooling leads to more significant compression of the plasma and magnetic field within the plasmoids. we demonstrate that ions can be efficiently accelerated to energies exceeding the plasma magnetization parameter, ≫σ, and form a hard power-law energy distribution, fi∝ γ -1. this conclusion implies a highly efficient proton acceleration in the magnetospheres of young pulsars. conversely, the energies of pairs are limited to either σ in the strong cooling regime or the radiation burnoff limit, γ syn, when cooling is weak. we find that the high-energy radiation from pairs above the synchrotron burnoff limit, ɛc≈ 16 mev, is only efficiently produced in the strong cooling regime, γ syn < σ. in this regime, we find that the spectral cutoff scales as ɛ cut ≈ ɛc (σ/γ syn) and the highest energy photons are beamed along the direction of the upstream magnetic field, consistent with the phenomenological models of gamma-ray emission from young pulsars. furthermore, our results place constraints on the reconnection-driven models of gamma-ray flares in the crab nebula. | high-energy radiation and ion acceleration in three-dimensional relativistic magnetic reconnection with strong synchrotron cooling |
the recent detection of the geminga pulsar wind nebula (pwn) by hawc in the multi-tev band allows us to infer precious information about the transport of pairs in the immediate surroundings of the pulsar and on the spectrum of pairs contributed by a geminga-like pulsar to the spectrum of pairs in the cosmic radiation. moreover, this detection allows us to address the issue of how typical are the so-called tev halos associated to pulsar wind nebulae. our calculations confirm the need to have suppressed diffusion in a region of at least 20-50 pc around the pulsar, and are used here to infer precious constraints on the spectrum of pairs accelerated at the termination shock: more specifically, we discuss the conditions under which such a spectrum is consistent with that typically expected in a pwn and how it gets modified once it escapes the halo. finally, we discuss the implications of the existence of a tev halo around geminga in terms of acceleration of protons in the pulsar environment, a topic of profound relevance for the whole field of particle acceleration and physics of pulsars. | tev halos and the role of pulsar wind nebulae as sources of cosmic-ray positrons |
we perform numerical simulations to investigate the stellar wind from interacting binary stars. our aim is to find analytical formulae describing the outflow structure. in each binary system the more massive star is in the asymptotic giant branch (agb) and its wind is driven by a combination of pulsations in the stellar surface layers and radiation pressure on dust, while the less massive star is in the main sequence. time averages of density and outflow velocity of the stellar wind are calculated and plotted as profiles against distance from the centre of mass and colatitude angle. we find that mass is lost mainly through the outer lagrangian point l2. the resultant outflow develops into a spiral at low distances from the binary. the outflowing spiral is quickly smoothed out by shocks and becomes an excretion disc at larger distances. this leads to the formation of an outflow structure with an equatorial density excess, which is greater in binaries with smaller orbital separation. the pole-to-equator density ratio reaches a maximum value of ∼105 at roche lobe overflow state. we also find that the gas stream leaving l2 does not form a circumbinary ring for stellar mass ratios above 0.78, when radiation pressure on dust is taken into account. analytical formulae are obtained by curve fitting the two-dimensional, azimuthally averaged density and outflow velocity profiles. the formulae can be used in future studies to set-up the initial outflow structure in hydrodynamic simulations of common-envelope evolution and formation of planetary nebulae. | agb winds in interacting binary stars |
the bubble nebula (or ngc 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved o star bd+60°2522. the young dynamical age of the nebula and significant space velocity of the star suggest that the bubble nebula might be a bow shock. we ran 2d hydrodynamic simulations to model the interaction of the wind of the central star with the interstellar medium (ism). the models cover a range of possible ism number densities of n = 50-200 cm-3 and stellar velocities of v* = 20-40 km s-1. synthetic hα and 24 μm emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. the synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. the best-matching simulation had v* ≈ 20 km s-1 into an ism with n ∼ 100 cm-3, at an angle of 60° with respect to the line of sight. synthetic maps of soft (0.3-2 kev) and hard (2-10 kev) x-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. the unabsorbed soft x-rays have a luminosity of ∼1032-1033 erg s-1. the hard x-rays are fainter: ∼1030-1031 erg s-1, and may be too faint for current x-ray instruments to successfully observe. our results imply that the o star creates a bow shock as it moves through the ism and in turn creates an asymmetric bubble visible at optical and infrared wavelengths and predicted to be visible in x-rays. the bubble nebula does not appear to be unique; it could simply be a favourably oriented, very dense bow shock. the dense ism surrounding bd+60°2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission. | thermal emission from bow shocks. i. 2d hydrodynamic models of the bubble nebula |
we present a synthetic galaxy lightcone specially designed for narrow-band optical photometric surveys. to reduce time-discreteness effects, unlike previous works, we directly include the lightcone construction in the l-galaxies semi-analytic model applied to the subhalo merger trees of the millennium simulation. additionally, we add a model for the nebular emission in star-forming regions, which is crucial for correctly predicting the narrow- and medium-band photometry of galaxies. specifically, we consider, individually for each galaxy, the contribution of 9 different lines: lyα (1216 å), hβ (4861 å), hα (6563 å), [o ii] (3727 å, 3729 å), [o iii] (4959 å, 5007 å), [ne iii] (3870 å), [o i] (6300 å), [n ii] (6548 å, 6583 å), and [s ii] (6717 å, 6731 å). we validate our lightcone by comparing galaxy number counts, angular clustering, and hα, hβ, [o ii], and [o iii]5007 luminosity functions to a compilation of observations. as an application of our mock lightcones, we generated catalogues tailored for j-plus, a large optical galaxy survey featuring five broad-band and seven medium-band filters. we study the ability of the survey to correctly identify, with a simple three-filter method, a population of emission-line galaxies at various redshifts. we show that the 4000 å break in the spectral energy distribution of galaxies can be misidentified as line emission. however, all significant excess (> 0.4 mag) can be correctly and unambiguously attributed to emission-line galaxies. our catalogues are publicly released to facilitate their use in interpreting narrow-band surveys and in quantifying the impact of line emission in broad-band photometry. | j-plus: synthetic galaxy catalogues with emission lines for photometric surveys |
one clear observational prediction of the single-degenerate progenitor scenario as the origin of type ia supernovae (sne) is the presence of relatively narrow (≈1000 km s-1) hα emission at nebular phases, although this feature is rarely seen. we present a compilation of nebular phase hα limits for sn ia in the literature and demonstrate that this heterogenous sample has been biased toward sn ia with relatively high luminosities and slow decline rates, as parameterized by δm 15(b), the difference in b-band magnitude between maximum light and 15 days afterward. motivated by the need to explore the full parameter space of sn ia and their subtypes, we present two new and six previously published nebular spectra of sn ia with δm 15(b) > 1.3 mag (including members of the transitional and sn1991bg-like subclasses) and measure nondetection limits of l hα< 0.85-9.9 × 1036 erg s-1, which we confirmed by implanting simulated hα emission into our data. based on the latest models of swept-up material stripped from a nondegenerate companion star, these l hαvalues correspond to hydrogen mass limits of m h ≲ 1-3 × 10-4 m ⊙, which are roughly three orders of magnitude below that expected for the systems modeled, although we note that no simulations of hα nebular emission in such weak explosions have yet been performed. despite the recent detection of strong hα in asassn-18tb (sn 2018fhw; δm 15(b) = 2.0 mag), we see no evidence that fast-declining systems are more likely to have late time hα emission, although a larger sample is needed to confirm this result. | nebular hα limits for fast declining sne ia |
bow shock pulsar wind nebulae are observed with a variety of complex morphologies at different wavelengths, most likely due to differences in the magnetic field strength and pulsar wind geometry. here we present a detailed analysis, showing how these differences affect the observational properties in these systems, focusing on non-thermal synchrotron emission. by adopting different prescriptions for the local emissivity, on top of the magnetic and flow patterns taken from three-dimensional (3d) high-resolution numerical simulations in relativistic magnetohydrodynamics (mhd), and considering various viewing angles, we try to characterize the main features of the emission and polarization, to verify if and how these can be used to get information, or to put constraints, on known objects. we found, for example, that conditions leading to a strong development of the turbulence in the bow shock tail produce substantial differences in the emission pattern, especially in polarized light. | full-3d relativistic mhd simulations of bow shock pulsar wind nebulae: emission and polarization |
lyman-α blobs (labs) are spatially extended nebulae of emission in the lyman-α (lyα) line of hydrogen, seen at high redshifts1,2, and most commonly found in the dense environment of star-forming galaxies3,4. a recent study showed that nearly 100% of the sky is covered by lyα emission around high-redshift galaxies5-7. the origin of lyα emission in the labs is still unclear and under debate8. it may be powered by photoionization involving galactic superwinds/outflows, resonant scattering of lyα photons from starbursts or active galactic nuclei9-16, or by cooling radiation from cold streams of gas accreting onto galaxies17,18, as demonstrated by recent simulations19. here we analyse the gas kinematics within a lab, providing rare observational evidence for infalling gas. this is consistent with the release of gravitational accretion energy as cold streams radiate lyα photons. it also provides direct evidence for possible cold streams feeding the central galaxies. the mass of the infalling gas is not important in comparison to the gas mass consumed by star formation, and is also not the major powering source of lyα emission, but it hints at another mechanism to explain the origin of the extended lyα emission around young galaxies. | infalling gas in a lyman-α blob |
context. there is a class of binary post-agb stars with a remarkable near-infrared excess that are surrounded by keplerian or quasi-keplerian disks and extended outflows composed of gas escaping from the disk. the keplerian dynamics had been well identified in four cases, namely the red rectangle, ac her, iw car, and iras 08544−4431. in these objects, the mass of the outflow represents ~10% of the nebular mass, the disk being the dominant component of the nebula.aims: we aim to study the presence of rotating disks in sources of the same class in which the outflow seems to be the dominant component.methods: we present interferometric noema maps of 12co and 13co j = 2-1 in 89 her and 12co j = 2-1 in ac her, iras 19125+0343, and r sct. several properties of the nebula are obtained from the data and model fitting, including the structure, density, and temperature distributions, as well as the dynamics. we also discuss the uncertainties on the derived values.results: the presence of an expanding component in ac her is doubtful, but thanks to new maps and models, we estimate an upper limit to the mass of this outflow of ≲3 × 10−5 m⊙, that is, the mass of the outflow is ≲5% of the total nebular mass. for 89 her, we find a total nebular mass of 1.4 × 10−2 m⊙, of which ~50% comes from an hourglass-shaped extended outflow. in the case of iras 19125+0343, the nebular mass is 1.1 × 10−2 m⊙, where the outflow contributes ~70% of the total mass. the nebular mass of r sct is 3.2 × 10−2 m⊙, of which ~75% corresponds to a very extended outflow that surrounds the disk.conclusions: our results for iras 19125+0343 and r sct lead us to introduce a new subclass of binary post-agb stars, for which the outflow is the dominant component of the nebula. moreover, the outflow mass fraction found in ac her is smaller than those found in other disk-dominated binary post-agb stars. 89 her would represent an intermediate case between both subclasses. final datacubes are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/648/a93 based on observations with iram northern extended millimeter array (noema). iram is supported by insu/cnrs (france), mpg (germany), and ign (spain). | keplerian disks and outflows in post-agb stars: ac herculis, 89 herculis, iras 19125+0343, and r scuti |
fast-rotating pulsars and magnetars have been suggested as the central engines of superluminous supernovae (slsne) and fast radio bursts, and this scenario naturally predicts non-thermal synchrotron emission from their nascent pulsar wind nebulae (pwne). we report results of high-frequency radio observations with alma and noema for three slsne (sn 2015bn, sn 2016ard, and sn 2017egm), and present a detailed theoretical model to calculate non-thermal emission from pwne with an age of ~1-3 yr. we find that the alma data disfavours a pwn model motivated by the crab nebula for sn 2015bn and sn 2017egm, and argue that this tension can be resolved if the nebular magnetization is very high or very low. such models can be tested by future mev-gev gamma-ray telescopes such as amego. | alma and noema constraints on synchrotron nebular emission from embryonic superluminous supernova remnants and radio-gamma-ray connection |
radiation-dust driven outflows, where radiation pressure on dust grains accelerates gas, occur in many astrophysical environments. almost all previous numerical studies of these systems have assumed that the dust was perfectly coupled to the gas. however, it has recently been shown that the dust in these systems is unstable to a large class of 'resonant drag instabilities' (rdis) which de-couple the dust and gas dynamics and could qualitatively change the non-linear outcome of these outflows. we present the first simulations of radiation-dust driven outflows in stratified, inhomogeneous media, including explicit grain dynamics and a realistic spectrum of grain sizes and charge, magnetic fields and lorentz forces on grains (which dramatically enhance the rdis), coulomb and epstein drag forces, and explicit radiation transport allowing for different grain absorption and scattering properties. in this paper, we consider conditions resembling giant molecular clouds (gmcs), h ii regions, and distributed starbursts, where optical depths are modest (≲1), single-scattering effects dominate radiation-dust coupling, lorentz forces dominate over drag on grains, and the fastest-growing rdis are similar, such as magnetosonic and fast-gyro rdis. these rdis generically produce strong size-dependent dust clustering, growing non-linear on time-scales that are much shorter than the characteristic times of the outflow. the instabilities produce filamentary and plume-like or 'horsehead' nebular morphologies that are remarkably similar to observed dust structures in gmcs and h ii regions. additionally, in some cases they strongly alter the magnetic field structure and topology relative to filaments. despite driving strong micro-scale dust clumping which leaves some gas 'behind,' an order-unity fraction of the gas is always efficiently entrained by dust. | dust in the wind with resonant drag instabilities - i. the dynamics of dust-driven outflows in gmcs and h ii regions |
context. m 105 (ngc 3379) is an early-type galaxy in the nearby leo i group, the closest galaxy group to contain all galaxy types and therefore an excellent environment to explore the low-mass end of intra-group light (igl) assembly.aims: we present a new and extended kinematic survey of planetary nebulae (pne) in m 105 and the surrounding 30′×30′ in the leo i group with the planetary nebula spectrograph (pn.s) to investigate kinematically distinct populations of pne in the halo and the surrounding igl.methods: we use pne as kinematic tracers of the diffuse stellar light in the halo and igl, and employ photo-kinematic gaussian mixture models to (i) separate contributions from the companion galaxy ngc 3384, and (ii) associate pne with structurally defined halo and igl components around m 105.results: we present a catalogue of 314 pne in the surveyed area and firmly associate 93 of these with the companion galaxy ngc 3384 and 169 with m 105. the pne in m 105 are further associated with its halo (138) and the surrounding exponential envelope (31). we also construct smooth velocity and velocity dispersion fields and calculate projected rotation, velocity dispersion, and λr profiles for the different components. pne associated with the halo exhibit declining velocity dispersion and rotation profiles as a function of radius, while the velocity dispersion and rotation of the exponential envelope increase notably at large radii. the rotation axes of these different components are strongly misaligned.conclusions: based on the kinematic profiles, we identify three regimes with distinct kinematics that are also linked to distinct stellar population properties: (i) the rotating core at the centre of the galaxy (within 1reff) formed in situ and is dominated by metal-rich ([m/h] ≈ 0) stars that also likely formed in situ, (ii) the halo from 1 to 7.5reff consisting of a mixture of intermediate-metallicity and metal-rich stars ([m/h] > −1), either formed in situ or was brought in via major mergers, and (iii) the exponential envelope reaching beyond our farthest data point at 16reff, predominately composed of metal-poor ([m/h] < −1) stars. the high velocity dispersion and moderate rotation of the latter are consistent with those measured for the dwarf satellite galaxies in the leo i group, indicating that this exponential envelope traces the transition to the igl. full tables a.1 and a.2 are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/663/a12 | the halo of m 105 and its group environment as traced by planetary nebula populations. ii. using kinematics of single stars to unveil the presence of intragroup light around the leo i galaxies ngc 3384 and m 105 |
we use the hubble space telescope advanced camera for surveys to obtain the first spatially resolved, nebular imaging in the light of c iv λ λ1548, 1551 by using the f150lp and f165lp filters. these observations of the local starburst mrk 71 in ngc 2366 show emission apparently originating within the interior cavity around the dominant super star cluster (ssc), knot a. together with imaging in he ii λ4686 and supporting space telescope imaging spectrograph far-ultraviolet spectroscopy, the morphology and intensity of the c iv nebular surface brightness and the c iv/he ii ratio map provide direct evidence that the mechanical feedback is likely dominated by catastrophic radiative cooling, which strongly disrupts adiabatic superbubble evolution. the implied extreme mass loading and low kinetic efficiency of the cluster wind are reasonably consistent with the wind energy budget, which is probably enhanced by radiation pressure. in contrast, the knot b ssc lies within a well-defined superbubble with associated soft x-rays and he ii λ1640 emission, which are signatures of adiabatic, energy-driven feedback from a supernova-driven outflow. this system lacks clear evidence of c iv from the limb-brightened shell, as expected for this model, but the observations may not be deep enough to confirm its presence. we also detect a small c iv-emitting object that is likely an embedded compact h ii region. its c iv emission may indicate the presence of very massive stars (>100 m ⊙) or strongly pressure-confined stellar feedback. | nebular c iv λ1550 imaging of the metal-poor starburst mrk 71: direct evidence of catastrophic cooling |
we present evidence in support of the hypothesis that the young stellar object rno 54 is a mature-stage fu ori type source. the star was first cataloged as a "red nebulous object" in the 1980s but appears to have undergone its outburst prior to the 1890s. present-day optical and near-infrared spectra are consistent with those of other fu ori-type stars, both in the details of spectral line presence and shape, and in the overall change in spectral type from an fgk-type in the optical, to the m-type presented in the near-infrared. in addition, the spectral energy distribution of rno 54 is well-fit by a pure-accretion disk model with parameters: $\dot{m}={10}^{-3.45\pm 0.06}$ m ⊙ yr-1, m * = 0.23 ± 0.06 m ⊙, and r inner = 3.68 ± 0.76 r ⊙, though we believe r inner is likely close to its upper range of 4.5r ⊙ in order to produce a ${t}_{\max }=7000$ k that is consistent with the optical to near-infrared spectra. the resulting l acc is ~265 l ⊙. to find these values, we adopted a source distance d = 1400 pc and extinction av= 3.9 mag, along with disk inclination i = 50 deg based on the consideration of confidence intervals from our initial disk model, and in agreement with observational constraints. the new appreciation of a well-known source as an fu ori-type object suggests that other such examples may be lurking in extant samples. | rno 54: a previously unappreciated fu ori star |
we summarize the results of a spectropolarimetric survey of 56 chemically peculiar (cp) stars in the association of orion ob1. we uniformly collected the observational material with the 6-m telescope bta of the special astrophysical observatory in 2013-2021. we identify 14 new magnetic cp stars with a longitudinal magnetic field exceeding approximately 500 g. the studied sample contains 31 magnetic stars or 55 per cent of the whole cp population in orion ob1. we show that the percentage of the magnetic cp stars and the field strength drop sharply with age. the mean longitudinal magnetic field in the young subgroup ob1b (log t = 6.23) is confidently almost three times stronger than in the older subgroups ob1a (log t = 7.05) and ob1c (log t = 6.66). in the orion nebula, a place with the youngest stellar population (log t < 6.0), we detect the magnetic field only in 20 per cent of cp stars. such an occurrence drastically differs from 83 per cent of magnetic cp stars in the nearby subgroup ob1c. we consider this effect an observational bias caused by a significant portion of a very young population with the signatures of herbig ae/be stars. the technique we used for magnetic measurements and the quality of available data do not allow us to detect weak fields in the case of stars with a limited number of lines and emissions in spectra. | spectropolarimetry of magnetic chemically peculiar stars in the orion ob1 association |
here we describe a new study of the supernova remnants (snrs) and snr candidates in nearby face-on spiral galaxy m83, based primarily on muse integral field spectroscopy. our revised catalog of snr candidates in m83 has 366 objects, 81 of which are reported here for the first time. of these, 229 lie within the muse observation region, 160 of which have spectra with [s ii]:hα ratios exceeding 0.4, the value generally accepted as confirmation that an emission nebula is shock-heated. combined with 51 snr candidates outside the muse region with high [s ii]:hα ratios, there are 211 spectroscopically confirmed snrs in m83, the largest number of confirmed snrs in any external galaxy. muse's combination of relatively high spectral resolution and broad wavelength coverage has allowed us to explore two other properties of snrs that could serve as the basis of future snr searches. specifically, most of the objects identified as snrs on the basis of [s ii]:hα ratios exhibit more velocity broadening and lower ratios of [s iii]:[s ii] emission than h ii regions. a search for nebulae with the very broad emission lines expected from young, rapidly expanding remnants revealed none, except for the previously identified b12-174a. the snrs identified in m83 are, with few exceptions, middle-aged interstellar medium (ism) dominated ones. smaller-diameter candidates show a larger range of velocity broadening and a larger range of gas densities than the larger-diameter objects, as expected if the snrs expanding into denser gas brighten and then fade from view at smaller diameters than those expanding into a more tenuous ism. | supernova remnants in m83 as observed with muse |
the javalambre-physics of the accelerating universe astrophysical survey (j-pas) is a photometric survey that is poised to scan several thousands of square degrees of the sky. it will use 54 narrow-band filters, combining the benefits of low-resolution spectra and photometry. its offshoot, minijpas, is a 1 deg2 survey that uses j-pas filter system with the pathfinder camera. in this work, we study mjpc2470-1771, the most massive cluster detected in minijpas. we survey the stellar population properties of the members, their star formation rates (sfr), star formation histories (sfh), the emission line galaxy (elg) population, spatial distribution of these properties, and the ensuing effects of the environment. this work shows the power of j-pas to study the role of environment in galaxy evolution. we used a spectral energy distribution (sed) fitting code to derive the stellar population properties of the galaxy members: stellar mass, extinction, metallicity, (u − r)res and (u − r)int colours, mass-weighted age, the sfh that is parametrised by a delayed-τ model (τ, t0), and sfrs. we used artificial neural networks for the identification of the elg population via the detection of the hα, [nii], hβ, and [oiii] nebular emission. we used the ew(hα)-[nii] (whan) and [oiii]/hα-[nii]/hα (bpt) diagrams to separate them into individual star-forming galaxies and agns. we find that the fraction of red galaxies increases with the cluster-centric radius; and at 0.5r200 the red and blue fractions are both equal. the redder, more metallic, and more massive galaxies tend to be inside the central part of the cluster, whereas blue, less metallic, and less massive galaxies are mainly located outside of the inner 0.5r200. we selected 49 elg, with 65.3% of them likely to be star-forming galaxies, dominated by blue galaxies, and 24% likely to have an agn (seyfert or liner galaxies). the rest are difficult to classify and are most likely composite galaxies. these latter galaxies are red, and their abundance decreases with the cluster-centric radius; in contrast, the fraction of star-forming galaxies increases outwards up to r200. our results are compatible with an scenario in which galaxy members were formed roughly at the same epoch, but blue galaxies have had more recent star formation episodes, and they are quenching out from within the cluster centre. the spatial distribution of red galaxies and their properties suggest that they were quenched prior to the cluster accretion or an earlier cluster accretion epoch. agn feedback or mass might also stand as an obstacle in the quenching of these galaxies. | the minijpas survey. galaxy populations in the most massive cluster in minijpas: mjpc2470-1771 |
i use recent observations of circumstellar matter (csm) around type ia supernovae (sne ia) to estimate the fraction of sne ia that explode into a planetary nebula (pn) and to suggest a new delay time distribution from the common envelope evolution (cee) to the sn ia explosion for sne ia that occur shortly after the cee. under the assumption that the csm results from a cee, i crudely estimate that about 50% of all sne ia are sne ia inside pne (snips), and that the explosions of most snips occur within a cee to explosion delay (ceed) time of less than about ten thousand years. i also estimate that the explosion rate of snips, i.e., the ceed time distribution, is roughly constant within this timescale of ten thousand years. the short ceed time suggests that a fraction of snips come from the core-degenerate (cd) scenario where the merger of the core with the white dwarf takes place at the end of the cee. i present my view that the majority of snips come from the cd scenario. i list some further observations that might support or reject my claims, and describe the challenge to theoretical studies to find a process to explain a merger to explosion delay (med) time of up to ten thousand years or so. a long med will apply also to the double degenerate scenario. | common envelope to explosion delay time distribution (ceedtd) of type ia supernovae |
we present and publicly release a new star-forming regions emission library toddlers (time evolution of observables including dust diagnostics and line emission from regions containing young stars) for the publicly available radiative transfer code skirt. the library generation involves the spherical evolution of a homogeneous gas cloud around a young stellar cluster that accounts for stellar feedback processes including stellar winds, supernovae, and radiation pressure, as well as the gravitational forces on the gas. the semi-analytical evolution model is coupled with the photoionization code cloudy to calculate time-dependent uv-mm spectral energy distributions (seds) from star-forming regions of varying metallicity, star-formation efficiency, birth-cloud density, and mass. the calculated seds include the stellar, nebular, and dust continuum emission along with a wide range of emission lines originating from h ii, photodissociation, and molecular gas regimes tabulated at high resolution. the seds incorporated in skirt are generated by calculating a stellar-mass normalized luminosity, which assumes that each emission source is composed of a power-law population of star-forming clouds. when compared to the previous treatment of star-forming regions in skirt, toddlers shows a better agreement with low-redshift observational data in the ir wavelength range while offering a more comprehensive line-emission support. this paves the way for a variety of applications using simulated galaxies at low and high redshift. | toddlers: a new uv-mm emission library for star-forming regions - i. integration with skirt and public release |
the [o iii] 5007 å line is typically the brightest line in planetary nebula (pn) spectra. observations show that the brightest [o iii] 5007 å pn in a galaxy-the planetary nebula luminosity function (pnlf) bright-end cutoff-is surprisingly independent of galaxy type. to understand the origin of this puzzling uniformity, we simulate pne with a range of cloud and star parameters using the photoionization code cloudy. we find that the peak [o iii] 5007 å luminosity depends weakly on both the central stellar effective temperature at high temperature and on the total pn ejecta mass; however, the peak [o iii] 5007 å luminosity depends strongly on the central stellar luminosity and the pn dust-to-gas mass ratio. we explain these scalings physically. they imply that a higher dust-to-gas mass ratio at higher central stellar luminosity can help explain a constant bright-end cutoff in the pnlf across galaxy types. this prediction is testable with a survey of galactic pne. the surviving remnants of double white dwarf (wd) mergers should also produce photoionized nebulae analogous to pne. these may be preferentially present at the high luminosity end of the [o iii] plnf and could explain the existence of pne in early-type galaxies that are more luminous in [o iii] than expected from single-star evolutionary models. the presence of wd mergers in both young and old stellar populations could contribute to the uniformity of the [o iii] pnlf across galaxy types; such nebulae would lack the hydrogen lines otherwise characteristic of pne. | the origin of the consistent planetary nebula luminosity function bright-end cutoff |
turbulent motions in the circumgalactic medium (cgm) play a critical role in regulating the evolution of galaxies, yet their detailed characterization remains elusive. using two-dimensional velocity maps constructed from spatially-extended [oii] and [oiii] emission, chen et al. (2023b) measured the velocity structure functions (vsfs) of four quasar nebulae at $z\approx\!0.5$--1.1. one of these exhibits a spectacular kolmogorov relation. here we carry out an ensemble study using an expanded sample incorporating four new nebulae from three additional qso fields. the vsfs measured for all eight nebulae are best explained by subsonic turbulence revealed by the line-emitting gas, which in turn strongly suggests that the cool gas ($t\!\sim\!10^4$ k) is dynamically coupled to the hot ambient medium. previous work demonstrates that the largest nebulae in our sample reside in group environments with clear signs of tidal interactions, suggesting that environmental effects are vital in seeding and enhancing turbulence within the gaseous halos, ultimately promoting the formation of the extended nebulae. no discernible differences are observed in the vsf properties between radio-loud and radio-quiet qso fields. we estimate the turbulent heating rate per unit volume, $q_{\rm turb}$, in the qso nebulae to be $\sim 10^{-26}$--$10^{-22}$ erg cm$^{-3}$ s$^{-1}$ for the cool phase and $\sim 10^{-28}$--$10^{-25}$ erg cm$^{-3}$ s$^{-1}$ for the hot phase. this range aligns with measurements in the intracluster medium and star-forming molecular clouds but is $\sim10^3$ times higher than the $q_{\rm turb}$ observed inside cool gas clumps on scales $\lesssim1$ kpc using absorption-line techniques. we discuss the prospect of bridging the gap between emission and absorption studies by pushing the emission-based vsf measurements to below $\approx\!10$ kpc. | an ensemble study of turbulence in extended qso nebulae at $z\\approx0.5$--1 |
a family of unidentified infrared emission (uie) bands has been observed throughout the universe. the current observed spectral properties of the uie bands are summarized. these properties are discussed in the frameworks of different models of the chemical carriers of these bands. the uie carriers represent a large reservoir of carbon in the universe, and play a significant role in the physical and chemical processes in the interstellar medium and galactic environment. a correct identification of the carrier of the uie bands is needed to use these bands as probes of galactic evolution. | the mystery of unidentified infrared emission bands |
we present a detailed theoretical study of the rotational excitation of ch+ due to reactive and non-reactive collisions involving c+(2p), h2, ch+, h and free electrons. specifically, the formation of ch+ proceeds through the reaction between c+(2p) and h_2(ν _h_2 = 1, 2), while the collisional (de)excitation and destruction of ch+ is due to collisions with hydrogen atoms and free electrons. state-to-state and initial-state-specific rate coefficients are computed in the kinetic temperature range 10-3000 k for the inelastic, exchange, abstraction and dissociative recombination processes using accurate potential energy surfaces and the best scattering methods. good agreement, within a factor of 2, is found between the experimental and theoretical thermal rate coefficients, except for the reaction of ch+ with h atoms at kinetic temperatures below 50 k. the full set of collisional and chemical data are then implemented in a radiative transfer model. our non-lte calculations confirm that the formation pumping due to vibrationally excited h2 has a substantial effect on the excitation of ch+ in photon-dominated regions. in addition, we are able to reproduce, within error bars, the far-infrared observations of ch+ towards the orion bar and the planetary nebula ngc 7027. our results further suggest that the population of ν _h_2 = 2 might be significant in the photon-dominated region of ngc 7027. | state-to-state chemistry and rotational excitation of ch+ in photon-dominated regions |
context. measurements of internal dynamics of young clusters and star-forming regions are crucial to fully understand the process of their formation. a basic prerequisite for this is a well-established and robust list of probable members.aims: in this work, we study the 2.8° ×2.6° region in the emblematic rosette nebula, centred in the young cluster ngc 2244, with the aim of constructing the most reliable candidate member list to date. using the obtained catalogue, we can determine various structural and kinematic parameters, which can help to draw conclusions about the past and the future of the region.methods: we constructed a catalogue containing optical to mid-infrared photometry, as well as accurate positions and proper motions from gaia edr3 for the sources in the field of the rosette nebula. we applied the probabilistic random forest algorithm to derive the membership probability for each source within our field of view. based on the list of almost 3000 probable members, of which about a third are concentrated within the radius of 20′ from the centre of ngc 2244, we identified various clustered sources and stellar concentrations in the region, and estimated the average distance to the entire region at 1489 ± 37 pc, 1440 ± 32 pc to ngc 2244, and 1525 ± 36 pc to ngc 2237. the masses, extinction, and ages were derived by fitting the spectral energy distribution to the atmosphere and evolutionary models, and the internal dynamic was assessed via proper motions relative to the mean proper motion of ngc 2244.results: ngc 2244 is showing a clear expansion pattern, with an expansion velocity that increases with radius. its initial mass function (imf) is well represented by two power laws (dn/dm ∝ m−α), with slopes α = 1.05 ± 0.02 for the mass range 0.2-1.5 m⊙ and α = 2.3 ± 0.3 for the mass range 1.5-20 m⊙, and it is in agreement with slopes detected in other star-forming regions. the mean age of the region, derived from the hr diagram, is ∼2 myr. we find evidence for the difference in ages between ngc 2244 and the region associated with the molecular cloud, which appears slightly younger. the velocity dispersion of ngc 2244 is well above the virial velocity dispersion derived from the total mass (1000 ± 70 m⊙) and half-mass radius (3.4 ± 0.2 pc). from the comparison to other clusters and to numerical simulations, we conclude that ngc 2244 may be unbound and that it possibly may have even formed in a super-virial state. full table a.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/668/a19 | stellar population of the rosette nebula and ngc 2244. application of the probabilistic random forest |
the spread of invasive species continues to reduce biodiversity across all regions and habitat types globally. however, invader impact prediction can be nebulous, and approaches often fail to integrate coupled direct and indirect invader effects. here, we examine the ecological impacts of an invasive higher predator on lower trophic groups, further developing methodologies to more holistically quantify invader impact. we employ functional response (fr, resource use under different densities) and prey switching experiments to examine the trait- and density-mediated impacts of the invasive mosquitofish gambusia affinis on an endemic intermediate predator lovenula raynerae (copepoda). lovenula raynerae effectively consumed larval mosquitoes, but was naïve to mosquitofish cues, with attack rates and handling times of the intermediate predator unaffected by mosquitofish cue-treated water. mosquitofish did not switch between male and female prey, consistently displaying a strong preference for female copepods. we thus demonstrate a lack of risk-reduction activity in the presence of invasive fish by l. raynerae and, in turn, high susceptibility of such intermediate trophic groups to invader impact. further, we show that mosquitofish demonstrate sex-skewed predator selectivity towards intermediate predators of mosquito larvae, which may affect predator population demographics and, perversely, increase disease vector proliferations. we advocate the utility of frs and prey switching combined to holistically quantify invasive species impact potential on native organisms at multiple trophic levels. | intermediate predator naïveté and sex-skewed vulnerability predict the impact of an invasive higher predator |
we present the results of a study of the accretion rate of planetesimals by a growing proto-jupiter in the core-accretion model. the purpose of our study is to test the assumptions of pollack et al. regarding the flux of planetesimals and their encounter velocities with the protoplanet. using a newly developed code, we have accurately calculated planetesimals trajectories during their passage in the envelope by combining detailed three-body integrations with gas drag. to be consistent with pollack et al., our calculations do not include the effect of nebular gas. the results point to several new findings. for instance, we find that only 4-5 m⊕ is accreted in the first 1.5 myr before the onset of rapid gas accretion and ∼10 m⊕ is accreted simultaneously during this phase. we also find that mass accretion remains small (0.3-0.4 m⊕) for ∼1 myr after this time. this late accretion, together with a rapid infall of gas, could lead to a mixing of accreted material throughout the outer regions, which may explain the enhancement of high-z material in jupiter's envelope. results demonstrate that planetesimal encounters with the protoplanetary envelope become so fast that in most cases, ram pressure breaks them up. as a result, the accretion rate is largely independent of the planetesimals' size and composition. we also carried out some calculations considering nebular gas drag. as expected, the accreted mass of planetesimals depended strongly on their size and composition. in general, nebular gas lowered the amount of accreted planetesimals, although the majority of planetesimals were still accreted during the rapid gas accretion phase. | detailed calculations of the efficiency of planetesimal accretion in the core-accretion model |
radiometric dating indicates that mars accreted in the first ~4 myr of the solar system, coinciding with the formation and possible migration of jupiter. while nebular gas from the protoplanetary disk was still present, jupiter may have migrated inward and tacked at 1.5 au in a 3:2 resonance with saturn. this migration excited planetary building blocks in the inner solar system, resulting in extensive mixing and planetesimal removal. here we evaluate the plausible nature of mars's building blocks, focusing in particular on how its growth was influenced by jupiter. we use dynamical simulations and an isotopic mixing model that traces the accretion. dynamical simulations show that jupiter's migration causes the late stages of earth's and mars's accretion to be dominated by ec (enstatite chondrite)-type material due to the loss of ordinary chondrite planetesimals. our analysis of available isotopic data for mars shows that it consists of approximately 68% enstatite + 32% ordinary chondrite by mass (2σ). the large uncertainties indicate that isotopic analyses of martian samples are generally too imprecise to definitely test model predictions; in particular, it remains uncertain whether or not mars accreted predominantly ec material in the latter stages of its formation history. dynamical simulations also provide no definitive constraint on mars's accretion history due to the great variety of dynamical pathways that the martian embryo exhibits. the present work calls for new measurements of isotopic anomalies in martian meteorites targeting siderophile elements (most notably ni, mo, and ru) to constrain mars's accretion history and its formation location. | jupiter's influence on the building blocks of mars and earth |
to date, over 220 emission nebulae in m33 have been identified as supernova remnants (snrs) or snr candidates, principally through [s ii]:hα line ratios that are elevated compared to those in h ii regions. in many cases, the determination of a high [s ii]:hα line ratio was made using narrow-band interference filter images and has not been confirmed spectroscopically. here, we present mmt 6.5 m optical spectra that we use to measure [s ii]:hα and other line ratios in an attempt to determine the nature of these suggested candidates. of the 197 objects in our sample, 120 have no previously published spectroscopic observations. we confirm that the majority of candidate snrs have emission line ratios characteristic of snrs. while no candidates show doppler-broadened lines expected from young, ejecta-dominated snrs (≳1000 km s-1), a substantial number do exhibit lines that are broader than h ii regions. we argue that the majority of the objects with high [s ii]:hα line ratios (>0.4) are indeed snrs, but the distinction between h ii regions and snrs becomes less obvious at low surface brightness, and additional criteria, such as x-ray detection, are needed. we discuss the properties of the sample as a whole and compare it with similar samples in other nearby galaxies. | mmt spectroscopy of supernova remnant candidates in m33 |
using 3d radiation-hydrodynamic simulations and analytic theory, we study the orbital evolution of asymptotic giant branch (agb) binary systems for various initial orbital separations and mass ratios, and thus different initial accretion modes. the time evolution of binary separations and orbital periods are calculated directly from the averaged mass-loss rate, accretion rate and angular momentum loss rate. we separately consider spin-orbit synchronized and zero-spin agb cases. we find that the angular momentum carried away by the mass loss together with the mass transfer can effectively shrink the orbit when accretion occurs via wind-roche lobe overflow. in contrast, the larger fraction of mass lost in bondi-hoyle-lyttleton accreting systems acts to enlarge the orbit. synchronized binaries tend to experience stronger orbital period decay in close binaries. we also find that orbital period decay is faster when we account for the non-linear evolution of the accretion mode as the binary starts to tighten. this can increase the fraction of binaries that result in common envelope, luminous red novae, type ia supernovae and planetary nebulae with tight central binaries. the results also imply that planets in the habitable zone around white dwarfs are unlikely to be found. | wind-accelerated orbital evolution in binary systems with giant stars |
we present near-infrared (nir) spectroscopy of the nearby supernova 2014j obtained ∼450 d after explosion. we detect the [ni ii] 1.939 μm line in the spectra indicating the presence of stable 58ni in the ejecta. the stable nickel is not centrally concentrated but rather distributed as the iron. the spectra are dominated by forbidden [fe ii] and [co ii] lines. we used lines, in the nir spectra, arising from the same upper energy levels to place constraints on the extinction from host galaxy dust. we find that that our data are in agreement with the high av and low rv found in earlier studies from data near maximum light. using a 56ni mass prior from near maximum light γ-ray observations, we find 0.053 ± 0.018 m⊙ of stable nickel to be present in the ejecta. we find that the iron group features are redshifted from the host galaxy rest frame by ∼600 km s-1. | nebular spectroscopy of sn 2014j: detection of stable nickel in near-infrared spectra |
calcium-aluminum-rich inclusions (cais) and amoeboid olivine aggregates (aoas), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (δ17o ∼ -24‰) compositions, most likely near the protosun. here we describe a 16o-rich (δ17o ∼ -22 ± 2‰) aoa from the carbonaceous renazzo-type (cr) chondrite yamato-793261 containing both (i) an ultrarefractory cai and (ii) forsterite, low-ca pyroxene, and silica, indicating formation by gas-solid reactions over a wide temperature range from ∼1,800 to ∼1,150 k. this aoa provides direct evidence for gas-solid condensation of silica in a cai/aoa-forming region. in a gas of solar composition, the mg/si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the aoa formed in a parcel of gas with fractionated mg/si ratio, most likely due to condensation of forsterite grains. thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by ∼10× in h and he that cooled at 50 k/hour at total pressure of 10-4 bar. condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks. | first evidence for silica condensation within the solar protoplanetary disk |
context. pulsar wind nebulae are efficient particle accelerators, and yet the processes at work remain elusive. self-generated, microturbulence is too weak in relativistic magnetized shocks to accelerate particles over a wide energy range, suggesting that the global dynamics of the nebula may be involved in the acceleration process instead.aims: in this work, we study the role played by the large-scale anisotropy of the transverse magnetic field profile on the shock dynamics.methods: we performed large two-dimensional particle-in-cell simulations for a wide range of upstream plasma magnetizations, from weakly magnetized to strongly magnetized pulsar winds.results: the magnetic field anisotropy leads to a dramatically different structure of the shock front and downstream flow. a large-scale velocity shear and current sheets form in the equatorial regions and at the poles, where they drive strong plasma turbulence via kelvin-helmholtz vortices and kinks. the mixing of current sheets in the downstream flow leads to efficient nonthermal particle acceleration. the power-law spectrum hardens with increasing magnetization, akin to those found in relativistic reconnection and kinetic turbulence studies. the high end of the spectrum is composed of particles surfing on the wake produced by elongated spearhead-shaped cavities forming at the shock front and piercing through the upstream flow. these particles are efficiently accelerated via the shear-flow acceleration mechanism near the bohm limit.conclusions: magnetized relativistic shocks are very efficient particle accelerators. capturing the global dynamics of the downstream flow is crucial to understanding them, and therefore local plane parallel studies may not be appropriate for pulsar wind nebulae and possibly other astrophysical relativistic magnetized shocks. a natural outcome of such shocks is a variable and doppler-boosted synchrotron emission at the high end of the spectrum originating from the shock-front cavities, reminiscent of the mysterious crab nebula gamma-ray flares. simulation movies are available at https://www.aanda.org | a global model of particle acceleration at pulsar wind termination shocks |
some supernova (sn) explosions show evidence for an interaction with a pre-existing nonspherically symmetric circumstellar medium (csm) in their light curves, spectral line profiles, and polarization signatures. the origin of this aspherical csm is unknown, but binary interactions have often been implicated. to better understand the connection with binary stars and to aid in the interpretation of observations, we performed two-dimensional axisymmetric hydrodynamic simulations where an expanding spherical sn ejecta initialized with realistic density and velocity profiles collide with various aspherical csm distributions. we consider csm in the form of a circumstellar disk, colliding wind shells in binary stars with different orientations and distances from the sn progenitor, and bipolar lobes representing a scaled down version of the homunculus nebula of η car. we study how our simulations map onto observables, including approximate light curves, indicative spectral line profiles at late times, and estimates of a polarization signature. we find that the sn-csm collision layer is composed of normal and oblique shocks, reflected waves, and other hydrodynamical phenomena that lead to acceleration and shear instabilities. as a result, the total shock heating power fluctuates in time, although the emerging light curve might be smooth if the shock interaction region is deeply embedded in the sn envelope. sne with circumstellar disks or bipolar lobes exhibit late-time spectral line profiles that are symmetric with respect to the rest velocity and relatively high polarization. in contrast, sne with colliding wind shells naturally lead to line profiles with asymmetric and time-evolving blue and red wings and low polarization. given the high frequency of binaries among massive stars, the interaction of sn ejecta with a pre-existing colliding wind shell must occur and the observed signatures could be used to characterize the binary companion. array(0x22cff00) | supernova explosions interacting with aspherical circumstellar material: implications for light curves, spectral line profiles, and polarization |
aims: two-dimensional spectroscopic data for the whole extent of the ngc 3132 planetary nebula have been obtained. we deliver a reduced data-cube and high-quality maps on a spaxel-by-spaxel basis for the many emission lines falling within the multi-unit spectroscopic explorer (muse) spectral coverage over a range in surface brightness >1000. physical diagnostics derived from the emission line images, opening up a variety of scientific applications, are discussed.methods: data were obtained during muse commissioning on the european southern observatory (eso) very large telescope and reduced with the standard eso pipeline. emission lines were fitted by gaussian profiles. the dust extinction, electron densities, and temperatures of the ionised gas and abundances were determined using python and pyneb routines.results: the delivered datacube has a spatial size of ~63''× 123'', corresponding to ~0.26 × 0.51 pc2 for the adopted distance, and a contiguous wavelength coverage of 4750-9300 å at a spectral sampling of 1.25 å pix-1. the nebula presents a complex reddening structure with high values (c(hβ) ~ 0.4) at the rim. density maps are compatible with an inner high-ionisation plasma at moderate high density (~1000 cm-3), while the low-ionisation plasma presents a structure in density peaking at the rim with values ~700 cm-3. median te, using different diagnostics, decreases according to the sequence [n ii], [s ii] →[s iii] → [o i] → he i → paschen jump. likewise, the range of temperatures covered by recombination lines is much larger than those obtained from collisionally excited lines (cels), with large spatial variations within the nebula. if these differences were due to the existence of high density clumps, as previously suggested, these spatial variations would suggest changes in the properties and/or distribution of the clumps within the nebula. we determined a median helium abundance he/h = 0.124, with slightly higher values at the rim and outer shell. the range of measured ionic abundances for light elements are compatible with literature values. our kinematic analysis nicely illustrates the power of 2d kinematic information in many emission lines, which sheds light on the intrinsic structure of the nebula. specifically, our derived velocity maps support a geometry for the nebula that is similar to the diabolo-like model previously proposed, but oriented with its major axis roughly at pa ~ -22°. we identified two low-surface brightness arc-like structures towards the northern and southern tips of the nebula, with high extinction, high helium abundance, and strong low-ionisation emission lines. they are spatially coincident with some extended low-surface brightness mid-infrared emission. the characteristics of the features suggest that they could be the consequence of precessing jets caused by the binary star system. a simple 1d cloudy model is able to reproduce the strong lines in the integrated spectrum of the whole nebula with an accuracy of ~15%.conclusions: together with similar work with muse on ngc 7009, the present study illustrates the enormous potential of wide field integral field spectrographs for the study of galactic planetary nebulae. the reduced datacube and the derived maps 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/634/a47 | the muse view of the planetary nebula ngc 3132 |
we investigate a possible correlation between the solid surface density σ of the minimum-mass extrasolar nebula (mmen) and the host star mass m⋆ and metallicity [fe/h]. leveraging on the precise host star properties from the california-kepler survey (cks), we found that ${\rm{\sigma }}={50}_{-20}^{+33}\,{\rm{g}}\,{\mathrm{cm}}^{-2}$ (a/1 au)-1.75±0.07 (m⋆/m⊙)1.04±0.22 100.22±0.05[fe/h] for kepler-like systems (1-4r⊕; a < 1 au). the strong m⋆ dependence is reminiscent of previous dust continuum results that the solid disk mass scales with m⋆. the weaker [fe/h] dependence shows that sub-neptune planets, unlike giant planets, form readily in lower metallicity environment. the innermost region (a < 0.1 au) of an mmen maintains a smooth profile despite a steep decline of planet occurrence rate: a result that favors the truncation of disks by corotating magnetospheres with a range of rotation periods, rather than the sublimation of dust. the σ of kepler multitransiting systems shows a much stronger correlation with m⋆ and [fe/h] than singles. this suggests that the dynamically hot evolution that produced single systems also partially removed the memory of formation in disks. radial-velocity planets yielded a mmen very similar to cks planets; transit-timing-variation planets' postulated convergent migration history is supported by their poorly constrained mmen. we found that lower mass stars have a higher efficiency of forming/retaining planets: for sun-like stars, about 20% of the solid mass within ∼1 au are converted/preserved as sub-neptunes, compared to 70% for late-k to early-m stars. this may be due to the lower binary fraction, lower giant-planet occurrence, or the longer disk lifetime of lower mass stars. | california-kepler survey. ix. revisiting the minimum-mass extrasolar nebula with precise stellar parameters |
extragalactic planetary nebulae (pne) are detectable through relatively strong nebulous [o iii] emission and act as direct probes into the local stellar population. because they have an apparently universal invariant magnitude cut-off, pne are also considered to be a remarkable standard candle for distance estimation. through detecting pne within the galaxies, we aim to connect the relative abundances of pne to the properties of their host galaxy stellar population. by removing the stellar background components from fcc 167 and fcc 219, we aim to produce pn luminosity functions (pnlf) of these galaxies, and thereby also estimate the distance modulus to these two systems. finally, we test the reliability and robustness of our novel detection and analysis method. it detects unresolved point sources by their [o iii] 5007 å emission within regions that have previously been unexplored. we model the [o iii] emissions in the spatial and spectral dimensions together, as afforded to us by the multi unit spectroscopic explorer, and we draw on data gathered as part of the fornax3d survey. for each source, we inspect the properties of the nebular emission lines to remove other sources that might hinder the safe construction of the pnlf, such as supernova remnants and h ii regions. as a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach through a set of simulations. by applying this novel detection and modelling approach to integral field unit observations, we report for the distance estimates and luminosity-specific pne frequency values for the two galaxies. furthermore, we include an overview of source contamination, galaxy differences, and possible effects on the pne populations in the dense stellar environments. tables 4 and 5 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/637/a62 | fornax 3d project: automated detection of planetary nebulae in the centres of early-type galaxies and first results |
in the early, disk-embedded phase of evolution of terrestrial planets, a protoplanetary core can accumulate gas from the circumstellar disk into a planetary envelope. in order to relate the accumulation and structure of this primordial atmosphere to the thermal evolution of the planetary core, we calculated atmosphere models characterized by the surface temperature of the core. we considered cores with masses between 0.1 and 5 m ⊕ situated in the habitable zone around a solar-like star. the time-dependent simulations in 1d-spherical symmetry include the hydrodynamics equations, gray radiative transport, and convective energy transport. using an implicit time integration scheme, we can use large time steps and and thus efficiently cover evolutionary timescales. our results show that planetary atmospheres, when considered with reference to a fixed core temperature, are not necessarily stable, and multiple solutions may exist for one core temperature. as the structure and properties of nebula-embedded planetary atmospheres are an inherently time-dependent problem, we calculated estimates for the amount of primordial atmosphere by simulating the accretion process of disk gas onto planetary cores and the subsequent evolution of the embedded atmospheres. the temperature of the planetary core is thereby determined from the computation of the internal energy budget of the core. for cores more massive than about one earth mass, we obtain that a comparatively short duration of the disk-embedded phase (∼105 years) is sufficient for the accumulation of significant amounts of hydrogen atmosphere that are unlikely to be removed by later atmospheric escape processes. | dynamical accretion of primordial atmospheres around planets with masses between 0.1 and 5 m ⊕ in the habitable zone |
several decades of observations and discoveries have shown that high-redshift agn and massive galaxies are often surrounded by giant lyα nebulae extending in some cases up to 500 kpc in size. in this chapter, i review the properties of the such nebulae discovered at z > 2 and their connection with gas flows in and around galaxies and their halos. in particular, i show how current observations are used to constrain the physical properties and origin of the emitting gas in terms of the lyα photon production processes and kinematical signatures. the emerging picture from these studies suggests that recombination radiation is the most viable scenario to explain the observed lyα luminosities and surface brightness for the large majority of the nebulae and imply that a significant amount of dense (n > 1 cm-3), ionized and cold (t ∼ 104 k) "clumps" should be present within and around the halos of massive galaxies. spectroscopic studies suggest that, among the giant lyα nebulae, the one associated with radio-loud agn should have kinematics dominated by strong, ionized outflows within at least the inner 30-50 kpc. radio-quiet nebulae instead present more quiescent kinematics compatible with "stationary" situation and, in some cases, suggestive of rotating structures, while definitive evidences for gas accretion from the lyα emission are not clearly detected in current data. deep surveys currently ongoing using other bright, non-resonant line such as hα and he ii 1640 will be crucial to search for clearer signatures of cosmological gas accretion onto galaxies and agn. | gas accretion and giant lyα nebulae |
context. there are a number of methods that identify stellar sub-structure in star forming regions, but these do not quantify the degree of association of individual stars - something which is required if we are to better understand the mechanisms and physical processes that dictate structure.aims: we present the new novel statistical clustering tool "indicate" which assesses and quantifies the degree of spatial clustering of each object in a dataset, discuss its applications as a tracer of morphological stellar features in star forming regions, and to look for these features in the carina nebula (ngc 3372).methods: we employ a nearest neighbour approach to quantitatively compare the spatial distribution in the local neighbourhood of an object with that expected in an evenly spaced uniform (i.e. definitively non-clustered) field. each object is assigned a clustering index ("i") value, which is a quantitative measure of its clustering tendency. we have calibrated our tool against random distributions to aid interpretation and identification of significant i values.results: using indicate we successfully recover known stellar structure of the carina nebula, including the young trumpler 14-16, treasure chest and bochum 11 clusters. four sub-clusters contain no, or very few, stars with a degree of association above random which suggests these sub-clusters may be fluctuations in the field rather than real clusters. in addition we find: (1) stars in the nw and se regions have significantly different clustering tendencies, which is reflective of differences in the apparent star formation activity in these regions. further study is required to ascertain the physical origin of the difference; (2) the different clustering properties between the nw and se regions are also seen for ob stars and are even more pronounced; (3) there are no signatures of classical mass segregation present in the se region - massive stars here are not spatially concentrated together above random; (4) stellar concentrations are more frequent around massive stars than typical for the general population, particularly in the tr14 cluster; (5) there is a relation between the concentration of ob stars and the concentration of (lower mass) stars around ob stars in the centrally concentrated tr14 and tr15, but no such relation exists in tr16. we conclude this is due to the highly sub-structured nature of tr16.conclusions: indicate is a powerful new tool employing a novel approach to quantify the clustering tendencies of individual objects in a dataset within a user-defined parameter space. as such it can be used in a wide array of data analysis applications. in this paper we have discussed and demonstrated its application to trace morphological features of young massive clusters. | the spatial evolution of young massive clusters. i. a new tool to quantitatively trace stellar clustering |
we present two epochs of near-infrared spectroscopy of the candidate red supergiant counterpart to rx j004722.4-252051, a ulx in ngc 253. we measure radial velocities of the object and its approximate spectral type by cross-correlating our spectra with those of known red supergiants. our vlt/x-shooter spectrum is best matched by that of early m-type supergiants, confirming the red supergiant nature of the candidate counterpart. the radial velocity of the spectrum, taken on 2014 august 23, is 417 ± 4 km s-1. this is consistent with the radial velocity measured in our spectrum taken with magellan/mmirs on 2013 june 28, of 410 ± 70 km s-1, although the large error on the latter implies that a radial velocity shift expected for a black hole of tens of m⊙ can easily be hidden. using nebular emission lines we find that the radial velocity due to the rotation of ngc 253 is 351 ± 4 km s-1 at the position of the ulx. thus the radial velocity of the counterpart confirms that the source is located in ngc 253, but also shows an offset with respect to the local bulk motion of the galaxy of 66 ± 6 km s-1. we argue that the most likely origin for this displacement lies either in a sn kick, requiring a system containing a ≳ 50 m⊙ black hole, and/or in orbital radial velocity variations in the ulx binary system, requiring a ≳ 100 m⊙ black hole. we therefore conclude that rx j004722.4-252051 is a strong candidate for a ulx containing a massive stellar black hole. | discovery of a red supergiant counterpart to rx j004722.4-252051, a ulx in ngc 253 |
we report high-resolution observations of the 12co(1-0) and 13co(1-0) molecular lines in the carina nebula and the gum 31 region obtained with the 22-m mopra telescope as part of the mopra southern galactic plane co survey. we cover 8 deg2 from l = 285° to 290°, and from b = -1.5° to +0.5°. the molecular gas column density distributions from both tracers have a similar range of values. by fitting a grey-body function to the observed infrared spectral energy distribution from herschel maps, we derive gas column densities and dust temperatures. the gas column density has values in the range from 6.3 × 1020 to 1.4 × 1023 cm-2, while the dust temperature has values in the range from 17 to 43 k. the gas column density derived from the dust emission is approximately described by a lognormal function for a limited range of column densities. a high-column-density tail is clearly evident for the gas column density distribution, which appears to be a common feature in regions with active star formation. there are regional variations in the fraction of the mass recovered by the co emission lines with respect to the total mass traced by the dust emission. these variations may be related to changes in the radiation field strength, variation of the atomic to molecular gas fraction across the observed region, differences in the co molecule abundance with respect to h2, and evolutionary stage differences of the molecular clouds that compose the carina nebula-gum 31 complex. | the carina nebula and gum 31 molecular complex - i. molecular gas distribution, column densities, and dust temperatures |
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