- ID:
- ivo://CDS.VizieR/VI/118
- Title:
- Stellar Models until He burning
- Short Name:
- VI/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Grids of stellar evolutionary models published in the 4 papers referenced below are merged here. OPAL opacities with LS coupling and Grevesse composition were adopted, and Alexander's tables were used for lower temperatures. The models adopt a core overshooting with {alpha}_ov_=0.20, and mixing length parameter l/H_p_=1.52 that seems to represent well double-lined eclipsing binary stars. Mass loss during the main sequence and in the red giant phase were taken into account. The nuclear network treats 14 isotopes and optionally the lithium burning to study its depletion in less massive models during pre main sequence evolution. The initial parameters of the models are summarized in the file "grids.dat", with metal contents of Z=0.02 (solar), 0.01, 0.03 and 0.004 (Magellanic Clouds), with a wide range of initial hydrogen content around the solar composition. The mass range covered goes from 1 (0.6 for the solar composition) up to 40M_{sun}_ and the more massive models were followed until helium burning.
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- ID:
- ivo://CDS.VizieR/J/A+AS/114/549
- Title:
- Stellar models until He burning - II.
- Short Name:
- J/A+AS/114/549
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Three new grids of stellar evolutionary models with Z=0.01 are presented for the following values of initial hydrogen content X_i_=0.80, 0.73 and 0.63. The latest set of radiative opacities with spin-orbit coupling provided by the Lawrence Livermore group are used. For the lower temperatures the results by Alexander were considered. The models were computed taking into account core overshooting and mass loss. The grids cover the mass range between 1 and 40M_{sun}_. The internal structure constants (k_j_,j=2, 3,4) and the moment of inertia are also computed. These parameters are needed to investigate apsidal motions and tidal interactions in double-lined eclipsing binaries. This paper is part of a project which aims to provide grids of stellar models for a wide range of metal and hydrogen content.
633. Stellar models VI.
- ID:
- ivo://CDS.VizieR/J/A+AS/115/339
- Title:
- Stellar models VI.
- Short Name:
- J/A+AS/115/339
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New grids of models covering the evolution of low mass stars (0.8 to 1.7M{sun}) with metallicities Z=0.020 and 0.001 from the zero age main sequence up to the end of the early asymptotic giant branch are presented. The evolutionary tracks have been calculated with the new OPAL radiative opacities by Iglesias & Rogers (1992ApJ...397..717I) and Kurucz (1991). They complete the base of extensive grids of stellar models computed by the Geneva Group with up-to-date input physics (Schaller et al. 1992, Cat. J/A+AS/115/339; Schaerer et al. 1992, Cat. J/A+AS/98/523; Charbonnel et al. 1993, Cat. J/A+AS/101/415; Schaerer et al. 1993, Cat. J/A+AS/102/339; Meynet et al. 1994, Cat. J/A+AS/103/97).
- ID:
- ivo://CDS.VizieR/J/A+A/627/A24
- Title:
- Stellar models with rotation. 1.7<M<120, Z=0.0004
- Short Name:
- J/A+A/627/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The effects of rotation on stellar evolution are particularly important at low metallicity, when mass loss by stellar winds diminishes and the surface enrichment due to rotational mixing becomes relatively more pronounced than at high metallicities. Here we investigate the impact of rotation and metallicity on stellar evolution. Using a similar physics as in our previous large grids of models at Z=0.002 and Z=0.014, we compute stellar evolution models with the Geneva code for rotating and non-rotating stars with initial masses (Mini) between 1.7 and 120M_{sun}_ and Z=0.0004 (1/35 solar). This is comparable to the metallicities of the most metal poor galaxies observed so far, such as I Zw 18. Concerning massive stars, both rotating and non-rotating models spend most of their core-helium burning phase with an effective temperature higher than 8000K. Stars become red supergiants only at the end of their lifetimes, and few RSGs are expected. Our models predict very few to no classical Wolf-Rayet stars as a results of weak stellar winds at low metallicity. The most massive stars end their lifetimes as luminous blue supergiants or luminous blue variables, a feature that is not predicted by models with higher metallicities. Interestingly, due to the behavior of the intermediate convective zone, the mass domain of stars producing pair-instability supernovae is smaller at Z=0.0004 than at Z=0.002. We find that during the main sequence phase, the ratio between nitrogen and carbon abundances (N/C) remains unchanged for non-rotating models. However, N/C increases by factors of 10-20 in rotating models at the end of the MS. Cepheids coming from stars with Mini>4-6M_{sun}_ are beyond the core helium burning phase and spend little time in the instability strip. Since they would evolve towards cooler effective temperatures, these Cepheids should show an increase of the pulsation period as a function of age.
- ID:
- ivo://CDS.VizieR/J/A+A/558/A103
- Title:
- Stellar models with rotation. 0.8<M<120, Z=0.002
- Short Name:
- J/A+A/558/A103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the impact of a subsolar metallicity on various properties of non-rotating and rotating stars, such as surface velocities and abundances, lifetimes, evolutionary tracks, and evolutionary scenarios. We provide a grid of single star models covering a mass range of 0.8 to 120M_{sun_} with an initial metallicity Z=0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with models computed with exactly the same physical ingredients but with a metallicity Z=0.014 (solar). We show that the width of the main-sequence (MS) band in the upper part of the Hertzsprung-Russell diagram (HRD), for luminosity above log(L/L_{sun}_)>5.5, is very sensitive to rotational mixing. Strong mixing significantly reduces the MS width. Here for the first time over the whole mass range, we confirm that surface enrichments are stronger at low metallicity provided that comparisons are made for equivalent initial mass, rotation, and evolutionary stage. We show that the enhancement factor due to a lowering of the metallicity (all other factors kept constant) increases when the initial mass decreases. Present models predict an upper luminosity for the red supergiants (RSG) of log (L/L_{sun}_) around 5.5 at Z=0.002 in agreement with the observed upper limit of RSG in the Small Magellanic Cloud. We show that models using shear diffusion coefficient, which is calibrated to reproduce the surface enrichments observed for MS B-type stars at Z=0.014, can also reproduce the stronger enrichments observed at low metallicity. In the framework of the present models, we discuss the factors governing the timescale of the first crossing of the Hertzsprung gap after the MS phase. We show that any process favouring a deep localisation of the H-burning shell (steep gradient at the border of the H-burning convective core, low CNO content), and/or the low opacity of the H-rich envelope favour a blue position in the HRD for the whole, or at least a significant fraction, of the core He-burning phase.
- ID:
- ivo://CDS.VizieR/J/A+A/537/A146
- Title:
- Stellar models with rotation. 0.8<M<120, Z=0.014
- Short Name:
- J/A+A/537/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many topical astrophysical research areas, such as the properties of planet host stars, the nature of the progenitors of different types of supernovae and gamma ray bursts, and the evolution of galaxies, require complete and homogeneous sets of stellar models at different metallicities in order to be studied during the whole of cosmic history. We present here a first set of models for solar metallicity, where the effects of rotation are accounted for in a homogeneous way. We computed a grid of 48 different stellar evolutionary tracks, both rotating and non-rotating, at Z=0.014, spanning a wide mass range from 0.8 to 120M_{sun}_. For each of the stellar masses considered, electronic tables provide data for 400 stages along the evolutionary track and at each stage, a set of 43 physical data are given. These grids thus provide an extensive and detailed data basis for comparisons with the observations. The rotating models start on the ZAMS with a rotation rate v_ini_/v_crit_=0.4. The evolution is computed until the end of the central carbon-burning phase, the early AGB phase, or the core helium-flash for, respectively, the massive, intermediate, and both low and very low mass stars. The initial abundances are those deduced by Asplund et collaborators, which best fit the observed abundances of massive stars in the solar neighbourhood. We update both the opacities and nuclear reaction rates, and introduce new prescriptions for the mass-loss rates as stars approach the Eddington and/or the critical velocity. We account for both atomic diffusion and magnetic braking in our low-mass star models. The present rotating models provide a good description of the average evolution of non-interacting stars. In particular, they reproduce the observed MS width, the positions of the red giant and supergiant stars in the HR diagram, the observed surface compositions and rotational velocities. Very interestingly, the enhancement of the mass loss during the RSG stage, when the luminosity becomes supra-Eddington in some outer layers, help models above 15-20 Msun to lose a significant part of their hydrogen envelope and evolve back into the blue part of the HR diagram. This result has interesting consequences for the blue to red supergiant ratio, the minimum mass for stars to become WR stars, and the maximum initial mass of stars that explode as type II-P supernovae.
- ID:
- ivo://CDS.VizieR/J/AJ/156/126
- Title:
- Stellar parameters & abund. from BACCHUS analysis
- Short Name:
- J/AJ/156/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Data from the SDSS-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13 (DR13) and 14 (DR14). These include high-resolution H-band spectra, radial velocities, and derived stellar parameters and abundances. DR13, released in 2016 August, contained APOGEE data for roughly 150000 stars, and DR14, released in 2017 August, added about 110000 more. Stellar parameters and abundances have been derived with an automated pipeline, the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance of this pipeline by comparing the derived stellar parameters and abundances to those inferred from optical spectra and analysis for several hundred stars. For most elements - C, Na, Mg, Al, Si, S, Ca, Cr, Mn, Ni - the DR14 ASPCAP analyses have systematic differences with the comparisons samples of less than 0.05 dex (median), and random differences of less than 0.15 dex (standard deviation). These differences are a combination of the uncertainties in both the comparison samples as well as the ASPCAP analysis. Compared to the references, magnesium is the most accurate alpha-element derived by ASPCAP, and shows a very clear thin/thick disk separation, while nickel is the most accurate iron-peak element (besides iron itself).
- ID:
- ivo://CDS.VizieR/J/A+A/589/A61
- Title:
- Stellar parameters and abundances for M30
- Short Name:
- J/A+A/589/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The prediction of the PLANCK-constrained primordial lithium abundance in the Universe is in discordance with the observed Li abundances in warm Population II dwarf and subgiant stars. Among the physically best motivated ideas, it has been suggested that this discrepancy can be alleviated if the stars observed today had undergone photospheric depletion of lithium. The cause of this depletion is investigated by accurately tracing the behaviour of the lithium abundances as a function of effective temperature. Globular clusters are ideal laboratories for such an abundance analysis as the relative stellar parameters of their stars can be precisely determined. We performed a homogeneous chemical abundance analysis of 144 stars in the metal-poor globular cluster M30, ranging from the cluster turnoff point to the tip of the red giant branch. Non-local thermal equilibrium (NLTE) abundances for Li, Ca, and Fe were derived where possible by fitting spectra obtained with VLT/FLAMES-GIRAFFE using the quantitative-spectroscopy package SME. Stellar parameters were derived by matching isochrones to the observed V vs V-I colour-magnitude diagram. Independent effective temperatures were obtained from automated profile fitting of the Balmer lines and by applying colour-Teff calibrations to the broadband photometry.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A72
- Title:
- Stellar parameters and abundances in NGC 6752
- Short Name:
- J/A+A/567/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Abundance trends in heavier elements with evolutionary phase have been shown to exist in the globular cluster NGC 6752. These trends are a result of atomic diffusion and additional (non-convective) mixing. Studying such trends can provide us with important constraints on the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. Taking advantage of a larger data sample, we investigate the reality and the size of these abundance trends and address questions and potential biases associated with the various stellar populations that make up NGC 6752. We perform an abundance analysis by combining photometric and spectroscopic data of 194 stars located between the turnoff point and the base of the red giant branch. Stellar parameters are derived from uvby Stromgren photometry. Using the quantitative-spectroscopy package SME, stellar surface abundances for light elements such as Li, Na, Mg, Al, and Si as well as heavier elements such as Ca, Ti, and Fe are derived in an automated way by fitting synthetic spectra to individual lines in the stellar spectra, obtained with the VLT/FLAMES-GIRAFFE spectrograph. Based on uvby Stromgren photometry, we are able to separate three stellar populations in NGC 6752 along the evolutionary sequence from the base of the red giant branch down to the turnoff point. We find weak systematic abundance trends with evolutionary phase for Ca, Ti, and Fe which are best explained by stellar-structure models including atomic diffusion with efficient additional mixing. We derive a new value for the initial lithium abundance of NGC 6752 after correcting for the effect of atomic diffusion and additional mixing which falls slightly below the predicted standard BBN value. We find three stellar populations by combining photometric and spectroscopic data of 194 stars in the globular cluster NGC 6752. Abundance trends for groups of elements, differently affected by atomic diffusion and additional mixing, are identified. Although the statistical significance of the individual trends is weak, they all support the notion that atomic diffusion is operational along the evolutionary sequence of NGC 6752.
- ID:
- ivo://CDS.VizieR/J/A+A/471/795
- Title:
- Stellar population ages and metallicities from colors
- Short Name:
- J/A+A/471/795
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two important stellar-population parameters (age and metallicity) of the dominant stellar populations (DSPs) of galaxies are usually estimated by comparing the observed absorption line indices or colors to predictions of some simple stellar population models. However, some studies show that there is actually recent star formation in galaxies, including early type ones. This suggests that we may not be obtaining accurate the two stellar-population parameters for the DSPs of galaxies. This is obvious when we estimate the two parameters by colors, because the youngest populations dominate the light and make the fitted stellar populations younger and richer in metal. We study how young populations (YSPs) in composite stellar populations (CSPs) affect the colors of star systems and to analyze how the stellar ages and metallicities derived from colors possibly deviate from those of the DSPs. It is found that the age and mass fraction of a YSP affect colors of a mixed star system significantly, but the former is stronger. In addition, our results show that the stellar ages and metallicities derived directly from a pair of colors are about 2.14Gyr younger, while 0.0027 more metal rich on average than those of the DSPs of composite stellar systems. Some possible distributions of the differences between stellar-population parameters determined by colors and those of DSPs of CSPs are presented. The possible distributions of the differences between colors of CSPs and those of their DSPs are also shown. Stellar ages and metallicities measured by colors and line-strength indices are compared in the work, with a sample of 18 galaxies. Furthermore, the YSPs may affect the fundamental plane and Kormendy relation of early type galaxies.
