- ID:
- ivo://CDS.VizieR/J/A+A/646/A30
- Title:
- Evolutionary sequences for ultra-massive CO-core
- Short Name:
- J/A+A/646/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The existence of ultra-massive white dwarf stars, M_WD_>~1.05M_{sun}_, has been reported in several studies. These white dwarfs are relevant for the role they play in type Ia supernova explosions, the occurrence of physical processes in the asymptotic giant-branch phase, the existence of high-field magnetic white dwarfs, and the occurrence of double-white-dwarf mergers. We aim to explore the formation of ultra-massive, carbon-oxygen core white dwarfs resulting from single stellar evolution. We also intend to study their evolutionary and pulsational properties and compare them with those of the ultra-massive white dwarfs with oxygen-neon cores resulting from carbon burning in single progenitor stars, and with binary merger predictions. The aim is to provide a theoretical basis that can eventually help to discern the core composition of ultra-massive white dwarfs and the circumstances of their formation. We considered two single-star evolution scenarios for the formation of ultra-massive carbon-oxygen core white dwarfs, which involve the rotation of the degenerate core after core helium burning and reduced mass-loss rates in massive asymptotic giant-branch stars. We find that reducing standard mass-loss rates by a factor larger than 5-20 yields the formation of carbon-oxygen cores more massive than 1.05M_{sun}_ as a result of the slow growth of carbon-oxygen core mass during the thermal pulses. We also performed a series of evolutionary tests of solar-metallicity models with initial masses between 4 and 9.5M_{sun}_ and with different core rotation rates. We find that ultra-massive carbon-oxygen core white dwarfs are formed even for the lowest rotation rates we analyzed, and that the range of initial masses leading to these white dwarfs widens as the rotation rate of the core increases, whereas the initial mass range for the formation of oxygen-neon core white dwarfs decreases significantly. Finally, we compared our findings with the predictions from ultra-massive white dwarfs resulting from the merger of two equal-mass carbon-oxygen core white dwarfs, by assuming complete mixing between them and a carbon-oxygen core for the merged remnant. These two single-evolution scenarios produce ultra-massive white dwarfs with different carbon-oxygen profiles and different helium contents, thus leading to distinctive signatures in the period spectrum and mode-trapping properties of pulsating hydrogen-rich white dwarfs. The resulting ultra-massive carbon-oxygen core white dwarfs evolve markedly slower than their oxygen-neon counterparts. Our study strongly suggests the formation of ultra-massive white dwarfs with carbon-oxygen cores from a single stellar evolution. We find that both the evolutionary and pulsation properties of these white dwarfs are markedly different from those of their oxygen-neon core counterparts and from those white dwarfs with carbon-oxygen cores that might result from double-degenerate mergers. This can eventually be used to discern the core composition of ultra-massive white dwarfs and their formation scenario.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/103/67
- Title:
- Evolutionary sequences with MC metallicities
- Short Name:
- J/A+AS/103/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Tables of evolutionary sequences for massive stars with metallicities Z=0.002 and Z=0.01 in the mass range 9 to 40 M_{sun}_ and mass ratios 0.9 and 0.6 are presented. The orbital periods are chosen such that mass transfer according to case B occurs, i.e. mass exchange after core hydrogen exhaustion, during semi-detached and contact phases. The evolutionary code used by de Loore & De Greve (1992A&AS...94..453D) for galactic massive close binaries was updated, i.e. new thermodynamic quantities and new opacities were installed. The evolution of both components is followed simultaneously. Stellar wind mass loss rates during the OB phase are scaled according to the radiatively driven wind theory. Wolf-Rayet mass loss rates are assumed to be independent of metallicity. The models presented here may be used to interpret and evaluate the observations of Wolf-Rayet stars and massive binary X-ray sources in the Small and Large Magellanic Clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A113
- Title:
- Evolutionary tracks for pre-main sequence stars
- Short Name:
- J/A+A/541/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The apsidal-motion constants k_j_ and the moment of inertia are often used to study the apsidal-motion and tidal evolution of double-lined eclipsing binaries and planetary systems. On the other hand, the computation of the theoretical light curves of eclipsing binaries, planetary transits, and single rapidly rotating stars requires the knowledge of how the flux is distributed over the distorted stellar surfaces which can derived from the gravity-darkening exponent. Such parameters are available for several masses and chemical compositions covering the main-sequence and giant branch. However, for early phases (pre main-sequence, hereafter PMS) the calculations are scarce or even lacking. We present the calculations of the apsidal-motion constants, the fractional radius of gyration, and the gravity-darkening exponents for an extensive grid of PMS. The code used to generate the PMS models is essentially the same as that described by us in 2004. The apsidal-motion constants, the moment of inertia and the potential energy were computed using a fourth order Runge-Kutta method. The gravity-darkening exponents were computed using a method previously developed by us. The apsidal-motion constants, the moment of inertia, the potential energy, and the gravity-darkening exponents are made available for each point on every evolutionary track for PMS models covering the mass range 0.05-30M_{sun}_. Our calculations are made available for three chemical compositions (X, Z)=(0.757, 0.001), (0.70, 0.02), (0.64, 0.04).
- ID:
- ivo://CDS.VizieR/J/A+A/530/A33
- Title:
- Evolutionary tracks to estimate DLA depletions
- Short Name:
- J/A+A/530/A33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Silicates are an important component of interstellar dust that has been poorly investigated in high redshift galaxies. As a preliminary step to studying silicates at high redshift, we survey silicon depletions in damped Ly{alpha} (DLA) systems. Silicon depletion is mild in the Galactic interstellar medium (ISM) and is expected to be weaker in most DLA systems, so we introduce a method for improving the accuracy of DLA depletion measurements.
- ID:
- ivo://CDS.VizieR/J/A+A/361/1023
- Title:
- Evolution models for {alpha}-enhanced stars
- Short Name:
- J/A+A/361/1023
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present four large sets of evolutionary tracks for stars with initial chemical compositions [Y=0.250, Z=0.008], [Y=0.2773, Z=0.019], [Y=0.320, Z=0.040] and [Y=0.390, Z=0.070] and enhancement of {alpha} elements with respect to the solar pattern. The major improvement with respect to previous similar calculations is that we use consistent opacities - i.e. computed with the same chemical composition as adopted in the stellar models - over the whole relevant range of temperatures. For the same initial chemical compositions [Y, Z] and otherwise identical input physics we present also new evolutionary sequences with solar-scaled mixtures of abundances. Based on these stellar models we calculate the corresponding sets of isochrones both in the Johnson-Cousins UBVRIJHK and HST/WFPC2 photometric systems. Furthermore, we derive integrated magnitudes, colours and mass-to-light ratios for ideal single stellar populations with total mass equal to 1M_{sun}_ Finally, the major changes in the tracks, isochrones, and integrated magnitudes and colours passing from solar-scaled to {alpha}-enhanced mixtures are briefly outlined. Retrieval of the complete data set is possible via the www page http://pleiadi.pd.astro.it .
- ID:
- ivo://CDS.VizieR/J/A+A/311/361
- Title:
- Evolution models of elliptical galaxies. II.
- Short Name:
- J/A+A/311/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present new chemo-spectro-photometric models of elliptical galaxies in which infall of primordial gas is allowed to occur. They aim to simulate the collapse of a galaxy made of two components, i.e. luminous material and dark matter. The mass of the dark component is assumed to be constant in time, whereas that of the luminous material is supposed to accrete at a suitable rate. They also include the effect of galactic winds powered by supernova explosions and stellar winds from massive, early-type stars. The models are constrained to match a number of properties of elliptical galaxies, i.e. the slope and mean colours of the colour-magnitude relation (CMR), V versus (V-K), the UV excess as measured by the colour (1550-V) together with the overall shape of the integrated spectral energy distribution (ISED) in the ultraviolet, the relation between the Mg_2_ index and (1550-V), the mass to blue luminosity ratio M/L_B_ as a function of the B luminosity, and finally the broad-band colours (U-B), (B-V), (V-I), (V-K), etc. The CMR is interpreted as a mass-metallicity sequence of old, nearly coeval objects, whose mean age is 15Gyr. Assuming the law of star formation to be proportional to M_g_^k^(t) with k=1, the rate of star formation as function of time starts small, grows to a maximum, and then declines thus easily avoiding the excess of metal-poor stars found by BCF with the closed-box scheme (the analog of the G-Dwarf Problem in the solar vicinity). Owing to their stellar content, infall models can easily reproduce all the basic data of the galaxies under examination. As far as the UV excess is concerned, the same sources proposed by BCF are found to hold also with the infall scheme. H-HB and AGB manque stars of high metallicity play the dominant role, and provide a robust explanation of the correlation between the (1550-V) colour and the luminosity, mass and metallicity of the galaxies. Furthermore, these models confirm the potential of the (1550-V) colour as an age indicator in cosmology as already suggested by BCF. In the rest frame of a massive and metal-rich elliptical galaxy, this colour suffers from one major variation: at the onset of the so-called H-HB and AGB-manque stars (age about 5.6Gyr). This transition occurs at reasonably small red-shifts and therefore could be detected with the present-day instrumentation.
- ID:
- ivo://CDS.VizieR/J/A+A/335/823
- Title:
- Evolution models of elliptical galaxies. III.
- Short Name:
- J/A+A/335/823
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this study we present a simple model of elliptical galaxies aimed at interpreting the gradients in colours and narrow band indices observed across these systems. Salient features of the model are the gradients in mass density and star formation and infall of primordial gas aimed at simulating the collapse of a galaxy into the potential well of dark matter. Adopting a multi-zone model we follow in detail the history of star formation, gas consumption, and chemical enrichment of the galaxy and also allow for the occurrence of galactic winds according to the classical supernova (and stellar winds) energy deposit. The outline of the model, the time scale of gas accretion and rate of star formation as a function of the galacto-centric distance in particular, seek to closely mimic the results from Tree-SPH dynamical models. Although some specific ingredients of the model can be questioned from many points of view (of which we are well aware), the model has to be considered as a gross tool for exploring the consequences of different recipes of gas accretion and star formation in which the simple one-zone scheme is abandoned. With the aid of this model we discuss the observational data on the gradients in metallicity, colours, and narrow band indices across elliptical galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/501/687
- Title:
- Evolutionnary models for solar twins
- Short Name:
- J/A+A/501/687
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the non-standard mixing history of the solar twins HIP 55459, HIP 79672, HIP 56948, HIP 73815, and HIP 100963, to determine as precisely as possible their mass and age. We computed a grid of evolutionary models with non-standard mixing at several metallicities with the Toulouse-Geneva code for a range of stellar masses assuming an error bar of +/-50K in Teff. We choose the evolutionary model that reproduces accurately the observed low lithium abundances observed in the solar twins. Our best-fit model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. HIP 56 948 is the most likely solar-twin candidate at the present time and our analysis infers a mass of 0.994+/-0.004M_{sun}_ and an age of 4.71+/-1.39Gyr. Non-standard mixing is required to explain the low Li abundances observed in solar twins. Li depletion due to additional mixing in solar twins is strongly mass dependent. An accurate lithium abundance measurement and non-standard models provide more precise information about the age and mass more robustly than determined by classical methods alone.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/651
- Title:
- Evolution of extremely metal-poor stars
- Short Name:
- J/ApJS/155/651
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Intermediate-mass stellar evolution tracks from the main sequence to the tip of the AGB for five initial masses (2-6M_{sun}_) and metallicity Z=0.0001 have been computed. The detailed one-dimensional structure and evolution models include exponential overshooting, mass loss, and a detailed nucleosynthesis network with updated nuclear reaction rates. The network includes a two-particle heavy neutron sink for approximating neutron density in the He-shell flash. It is shown how the neutron-capture nucleosynthesis is important in models of very low metallicity for the formation of light neutron-heavy species, like sodium or the heavy neon and magnesium isotopes. The models have high resolution, as required for modeling the third dredge-up. All sequences have been followed from the pre-main sequence to the end of the AGB when all envelope mass is lost. Detailed structural and chemical model properties as well as yields are presented. This set of stellar models is based on standard assumptions and updated input physics. It can be confronted with observations of extremely metal-poor stars and may be used to assess the role of AGB stars in the origin of abundance anomalies of some globular cluster members of correspondingly low metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A111
- Title:
- Evolution of long-lived globular cluster stars
- Short Name:
- J/A+A/592/A111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Globular clusters host multiple populations of long-lived low-mass stars whose origin remains an open question. Several scenarios have been proposed to explain the associated photometric and spectroscopic peculiarities. They differ, for instance, in the maximum helium enrichment they predict for stars of the second population, which these stars can inherit at birth as the result of the internal pollution of the cluster by different types of stars of the first population. We present the distribution of helium-rich stars in present-day globular clusters as it is expected in the original framework of the fast-rotating massive stars scenario (FRMS) as first-population polluters. We focus on NGC 6752. We completed a grid of 330 stellar evolution models for globular cluster low-mass stars computed with different initial chemical compositions corresponding to the predictions of the original FRMS scenario for [Fe/H]=-1.75. Starting from the initial helium-sodium relation that allows reproducing the currently observed distribution of sodium in NGC 6752, we deduce the helium distribution expected in that cluster at ages equal to 9 and 13Gyr. We distinguish the stars that are moderately enriched in helium from those that are very helium-rich (initial helium mass fraction below and above 0.4, respectively), and compare the predictions of the FRMS framework with other scenarios for globular cluster enrichment.
