Isochrones for Hydrogen‐burning Globular Cluster Stars. III. From the Sun to the Globular Clusters

Abstract

By comparing the available seismic data for the Sun with the properties of various standard solar models, we can check the reliability of the input physics used to produce low-mass stellar models. The best reproduction of the solar interior is obtained when (1) Coulomb corrections are applied to the EOS, (2) microscopic diffusion of He and heavy elements is taken into account, and (3) internal rotation is neglected. This physics is used to derive new models for H-burning low-mass stars (from the zero-age main sequence to the red giant branch tip) and for central He-burning stars (zero-age horizontal branch models). Isochrones for Galactic globular clusters based on these new models are then presented. Note that since the first paper of this series, we have been systematically using an EOS including Coulomb corrections obtained by means of an accurate Monte Carlo method. When microscopic diffusion is also taken into account, we find that: (1) ages inferred from the turnoff luminosity are reduced by about 10%-15%. In particular, the larger the age and the metallicity, the larger the reduction. (2) Microscopic diffusion has a negligible effect on the horizontal-branch luminosity. (3) As a consequence of points (1) and (2), and at variance with previous findings, the ages inferred by adopting the so-called ΔV method depend on diffusion. (4) Finally, ages inferred from Δ(B-V) are strongly reduced (up to 40%-50%).