- ID:
- ivo://CDS.VizieR/J/ApJ/857/46
- Title:
- Modelled vs observed abundances of EMP stars
- Short Name:
- J/ApJ/857/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the elemental abundance patterns of ~200 extremely metal-poor (EMP; [Fe/H]{<}-3) stars to the supernova yields of metal-free stars, in order to obtain insights into the characteristic masses of the first (Population III or Pop III) stars in the universe. The supernova yields are prepared with nucleosynthesis calculations of metal-free stars with various initial masses (M=13, 15, 25, 40 and 100M_{sun}_) and explosion energies (E_51_=E/10^51^[erg]=0.5-60), to include low-energy, normal-energy, and high-energy explosions. We adopt the mixing-fallback model, to take into account possible asymmetry in the supernova explosions, and the yields that best fit the observed abundance patterns of the EMP stars are searched by varying the model parameters. We find that the abundance patterns of the EMP stars are predominantly best- fitted by the supernova yields with initial masses M<40M_{sun}_, and that more than than half of the stars are best-fitted by the M=25M_{sun}_ hypernova (E_51_=10) models. The results also indicate that the majority of the primordial supernovae have ejected 10^-2^-10^-1^M_{sun}_ of ^56^Ni, leaving behind a compact remnant (either a neutron star or a black hole), with a mass in the range of ~1.5-5M_{sun}_. These results suggest that the masses of the first stars responsible for the first metal enrichment are predominantly <40M_{sun}_. This implies that the higher-mass first stars were either less abundant, directly collapsed into a black hole without ejecting heavy elements, or a supernova explosion of a higher-mass first star inhibits the formation of the next generation of low-mass stars at [Fe/H]{<}-3.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/746/16
- Title:
- Modelling the convection zone
- Short Name:
- J/ApJ/746/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The base of the convection zone (CZ) is a source of acoustic glitches in the asteroseismic frequency spectra of solar-like oscillators, allowing one to precisely measure the acoustic depth to the feature. We examine the sensitivity of the depth of the CZ to mass, stellar abundances, and input physics, and in particular, the use of a measurement of the acoustic depth to the CZ as an atmosphere-independent, absolute measure of stellar metallicities. We find that for low-mass stars on the main sequence with 0.4M_{sun}_<=M<=1.6M_{sun}_, the acoustic depth to the base of the CZ, normalized by the acoustic depth to the center of the star, {tau}_cz,n_, is both a strong function of mass, and varies at the 0.5%-1% per 0.1 dex level in [Z/X], and is therefore also a sensitive probe of the composition. We estimate the theoretical uncertainties in the stellar models and show that combined with reasonable observational uncertainties we can expect to measure the metallicity to within 0.15-0.3 dex for solar-like stars. We discuss the applications of this work to rotational mixing, particularly in the context of the observed mid-F star Li dip, and to distinguishing between different mixtures of heavy elements.
- ID:
- ivo://CDS.VizieR/J/A+A/453/635
- Title:
- Modelling the Galactic Interstellar Extinction
- Short Name:
- J/A+A/453/635
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Two Micron All Sky Survey (Cat. <II/246>), along with the Stellar Population Synthesis Model of the Galaxy, developed in Besancon, is used to calculate the extinction distribution along different lines of sight. The Galaxy model is used to provide the intrinsic colour of stars and their probable distances, so that the near infrared colour excess, and hence the extinction, may be calculated and its distance evaluated.
- ID:
- ivo://CDS.VizieR/J/ApJS/237/13
- Title:
- Models and yields of 13-120M_{sun}_ massive stars
- Short Name:
- J/ApJS/237/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new grid of presupernova models of massive stars extending in mass between 13 and 120M_{sun}_, covering four metallicities (i.e., [Fe/H]=0, -1, -2, and -3) and three initial rotation velocities (i.e., 0, 150, and 300km/s). The explosion has been simulated following three different assumptions in order to show how the yields depend on the remnant mass-initial mass relation. An extended network from H to Bi is fully coupled to the physical evolution of the models. The main results can be summarized as follows. (a) At solar metallicity, the maximum mass exploding as a red supergiant (RSG) is of the order of 17M_{sun}_ in the nonrotating case, with the more massive stars exploding as Wolf-Rayet (WR) stars. All rotating models, conversely, explode as WR stars. (b) The interplay between the core He-burning and the H-burning shell, triggered by the rotation-induced instabilities, drives the synthesis of a large primary amount of all the products of CNO, not just ^14^N. A fraction of them greatly enriches the radiative part of the He core (and is responsible for the large production of F), and a fraction enters the convective core, leading therefore to an important primary neutron flux able to synthesize heavy nuclei up to Pb. (c) In our scenario, remnant masses of the order of those inferred from the first detections of gravitational waves (GW 150914, GW 151226, GW 170104, GW 170814) are predicted at all metallicities for none or moderate initial rotation velocities.
- ID:
- ivo://CDS.VizieR/J/A+A/568/A7
- Title:
- Model SDSS colors for halo stars
- Short Name:
- J/A+A/568/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of tens of thousands of spectra of halo turnoff stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population "in situ" out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as flux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that best reproduces each observed spectrum. We use an optimization algorithm and evaluate model fluxes by means of interpolation in a pre-computed grid. In our analysis, we account for the spectrograph's varying resolution as a function of fiber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars at logg (cgs units) lower than 2.5. An analysis of stars in the globular cluster M13 reveals a dependence of the inferred metallicity on surface gravity for stars with logg<2.5, confirming the systematics identified in the comparison with the SSPP. We find that our metallicity estimates are significantly more precise than the SSPP results. We also find excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turnoff stars as flux calibrators efficiently excludes stars with high metallicities, but does not significantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with that expected from a dual halo system in the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/507/1409
- Title:
- Models for dynamically dissolving star clusters
- Short Name:
- J/A+A/507/1409
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The dynamical escape of stars from star clusters affects the shape of the stellar mass function (MF) in these clusters, because the escape probability of a star depends on its mass. This is found in N-body simulations and has been approximated in analytical cluster models by fitting the evolution of the MF. Both approaches are naturally restricted to the set of boundary conditions for which the simulations were performed. The objective of this paper is to provide and to apply a simple physical model for the evolution of the MF in star clusters for a large range of the parameter space. It should also offer a new perspective on the results from N-body simulations. A simple, physically self-contained model for the evolution of the stellar MF in star clusters is derived from the basic principles of two-body encounters and energy considerations. It is independent of the adopted mass loss rate or initial mass function (IMF), and contains stellar evolution, stellar remnant retention, dynamical dissolution in a tidal field, and mass segregation. The evolution of the MF affects the integrated properties of star clusters. This data catalogue provides such quantities and also lists the evolution of the MF slope in certain mass ranges.
- ID:
- ivo://CDS.VizieR/J/AZh/79/259
- Title:
- Models for Intermediate-Mass Eclipsing Binaries
- Short Name:
- J/AZh/79/259
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use estimates of ages and abundances made for a set of eclipsing binaries (Kovaleva, 2001, Cat. <J/AZh/78/1104), to re-calculate observational values of radii, effective temperatures and luminosities of these stars for solar abundance ZAMS. Geneva group evolutionary grids of models were used for this recalculation. We also present empirical and semi-empirical (for ZAMS evolutionary stage and solar metallicity) relations between mass and luminosity, temperature and radius.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A15
- Title:
- Models for massive low-Z rotating single stars
- Short Name:
- J/A+A/581/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A good understanding of low-metallicity environments requires a detailed theoretical comprehension of the evolution of their massive stars. Our models can be used to interpret observations of local star-forming dwarf galaxies and high-redshift galaxies, as well as the metal-poor components of our Milky Way and its globular clusters.
- ID:
- ivo://CDS.VizieR/J/A+A/625/A132
- Title:
- Models for massive stars in the SMC
- Short Name:
- J/A+A/625/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolution of massive stars is strongly influenced by internal mixing processes such as semiconvection, convective core overshooting, and rotationally induced mixing. None of these processes are currently well constrained. We investigate models for massive stars in the Small Magellanic Cloud (SMC), for which stellar-wind mass loss is less important than for their metal-rich counterparts. We aim to constrain the various mixing efficiencies by comparing model results to observations. For this purpose, we use the stellar-evolution code MESA to compute more than 60 grids of detailed evolutionary models for stars with initial masses of 9...100M_{sun}_, assuming different combinations of mixing efficiencies of the various processes in each grid. Our models evolve through core hydrogen and helium burning, such that they can be compared with the massive main sequence and supergiant population of the SMC. We find that for most of the combinations of the mixing efficiencies, models in a wide mass range spend core-helium burning either only as blue supergiants, or only as red supergiants. The latter case corresponds to models that maintain a shallow slope of the hydrogen/helium (H/He) gradient separating the core and the envelope of the models. Only a small part of the mixing parameter space leads to models that produce a significant number of blue and red supergiants, which are both in abundance in the SMC. Some of our grids also predict a cut-o in the number of red supergiants above logL/L_{sun}_=5...5.5. Interestingly, these models contain steep H/He gradients, as is required to understand the hot, hydrogen-rich Wolf-Rayet stars in the SMC. We find that unless it is very fast, rotation has a limited effect on the H/He profiles in our models. While we use specific implementations of the considered mixing processes, they comprehensively probe the two firstorder structural parameters, the core mass and the H/He gradient in the core-envelope interface. Our results imply that in massive stars, mixing during the main-sequence evolution leads to a moderate increase in the helium core masses, and also that the H/He gradients above the helium cores become very steep. Our model grids can be used to further refine the various mixing efficiencies with the help of future observational surveys of the massive stars in the SMC, and thereby help to considerably reduce the uncertainties in models of massive star evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/607/A118
- Title:
- Models for molecular transitions
- Short Name:
- J/A+A/607/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a method to interpret molecular observations and molecular line ratios in nearby extragalactic regions. Ab initio grids of time dependent chemical models, varying in gas density, temperature, cosmic ray ionization rate, and radiation field, are used as input to RADEX calculations. Tables of abundances, column densities, theoretical line intensities, and line ratios for some of the most used dense gas tracers are provided. The degree of correlation as well as degeneracy inherent in molecular ratios is discussed. Comparisons of the theoretical intensities with example observations are also provided. We find that, within the parameters space explored, chemical abundances can be constrained by a well defined set of gas density-gas temperature-cosmic ray ionization rate for the species we investigate here. However, line intensities, as well as, more importantly, line ratios, from different chemical models can be very similar leading to a clear degeneracy. We also find that the gas subjected to a galactic cosmic ray ionization rate will not necessarily have reached steady state by 1 million years. The species most affected by time dependency effects are HCN and CS, both high density tracers. We use our ab initio method to fit an example set of data from two galaxies (M82 and, NGC 253). We find that (i) molecular line ratios can be easily matched even with erroneous individual line intensities; (ii) no set of species can be matched by a one-component ISM; (iii) a species may be a good tracer of an energetic process but only under specific density and temperature conditions. We provide tables of chemical abundances and line intensities ratios for some of the most commonly observed extragalactic tracers of dense gas for a grid of models. We show that by taking into consideration the chemistry behind each species and the individual line intensities, many degeneracies that arise by just using molecular line ratios can be avoided. Finally we show that using a species or a ratio as a tracer of an individual energetic process (e.g. cosmic rays, UV) ought to be done with caution.
