Updated BaSTI Stellar Evolution Models and Isochrones. II. α-enhanced Calculations

Abstract

This is the second paper of a series devoted to presenting an updated release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library. Following the publication of the updated solar-scaled library, here we present the library for an α-enhanced heavy element distribution. These new α-enhanced models account for all improvements and updates in the reference solar metal distribution and physics inputs, as in the new solar-scaled library. The models cover a mass range between 0.1 and 15 M ⊙, 18 metallicities between [Fe/H] = −3.20 and +0.06 with [α/Fe] = +0.4, and a He-to-metal enrichment ratio ΔY/ΔZ = 1.31. For each metallicity, He-enhanced stellar models are also provided. The isochrones cover (typically) an age range between 20 Myr and 14.5 Gyr, including consistently the pre-main-sequence phase. The asteroseismic properties of the theoretical models have also been calculated. Models and isochrones have been compared with results from independent calculations, with the previous BaSTI release, and also with selected observations, to test the accuracy/reliability of these new calculations. All stellar evolution tracks, asteroseismic properties, and isochrones are publicly available at http://basti-iac.oa-teramo.inaf.it.

Electron conduction opacities at the transition between moderate and strong degeneracy: Uncertainties and impacts on stellar models

“…Figure 5 displays the run of θ across the structure of the He-core at three selected luminosities during the RGB evolution of a typical low-mass (0.8M ⊙ ), metal poor stellar model (from Pietrinferni et al 2021). In all three cases, T/T F ranges between ∼0.05 at the centre of the He-core, and ∼1 at its outer edge.…”

“…In this section we quantify the effect of using alternatively κ Ioffe c (C07), κ B20 c (B20), κ B20sd c (B20sd), and κ B20wd c (B20wd) opacities on RGB (and the following horizontal branch stage) and WD models. For the RGB computations we rely on the same stellar evolution code, physical assumptions (including atomic diffusion) and input physics adopted by Pietrinferni et al (2021). The calculations by Pietrinferni et al (2021) make use of C07 conductive opacities, hence they are taken as a reference in the following discussion.…”

“…For the RGB computations we rely on the same stellar evolution code, physical assumptions (including atomic diffusion) and input physics adopted by Pietrinferni et al (2021). The calculations by Pietrinferni et al (2021) make use of C07 conductive opacities, hence they are taken as a reference in the following discussion. For the WD models we employ the code and physics inputs described by Salaris et al (2010).…”

“…We have computed models for initial masses in the range 0.8-2.4M ⊙ and various chemical compositions, from the pre-main sequence stage until the He-burning ignition at the tip of the RGB (TRGB), employing the same combinations of metallicity Z and initial helium abundance Y as in Pietrinferni et al (2021). Fig.…”

The updated BaSTI stellar evolution models and isochrones. III. White Dwarfs

“…As part of an ongoing new release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model library (Hidalgo et al 2018;Pietrinferni et al 2021), and given the important role played by evolutionary WD models to address a range of major astrophysics and physics questions, we present here new sets of CO-core WD model computations, that update the Salaris et al (2010) calculationshereafter S10-part of the previous BaSTI release, taking advantage of recent improvements in a number of stellar physics inputs. In these new calculations, that cover the whole relevant mass range, we have included the diffusion of 22 Ne in the liquid phase, which wasn't accounted for by S10, we have updated the electron conduction opacities, the phase diagram for CO compositions, and also the CO stratification in the cores of the models, as described in the next sections.…”