On the use of blanketed atmospheres as boundary conditions for stellar evolutionary models
2008 (English)In: Astrophysical Journal, ISSN 0004-637X, Vol. 675, no 1, 746-763 p.Article in journal (Refereed) Published
Stellarmodels have been computed for stars having [Fe/H] = 0.0 (assuming both the Grevesse & Sauval and Asplund et al. heavy-element mixtures) and -2.0 to determine the effects on the predicted T-eff scale of using boundary conditions derived from the latest MARCS model atmospheres. The latter were fitted in a fully consistent way to the interior models at the photosphere and at tau = 100: the resultant evolutionary sequences on the H-R diagram were found to be nearly independent of the chosen fitting point. Tracks were also computed in which the pressure at T = T-eff was obtained by integrating the hydrostatic equation together with either the classical gray T(tau, T-eff) relation or that derived by Krishna Swamy from an empirical solar atmosphere. Due to the effects of differences in the solar-calibrated values of the mixing-length parameter, alpha(MLT), very similar tracks were obtained for the different treatments of the atmosphere, except at solar abundances, where the models based on the Krishna Swamy T(tau, T-eff) relationship predicted similar to 150 K hotter giant branches than the others, in good agreement with the inferred temperatures of giants in the open cluster M67 from recent (V - K) -T-eff relations. Tracks that used new "scaled solar, differentially corrected'' MARCS atmospheres were found to agree well with those that employed the Krishna Swamy T(tau, T-eff) relationship, independently of the assumed metal abundance. (Gray atmospheres are quite different from MARCS models.) Fits of isochrones for [Fe/H] = -2.0 to the CMD of the globular cluster M68, as well as the possibility that alpha(MLT) varies with stellar parameters, are also discussed.
Place, publisher, year, edition, pages
2008. Vol. 675, no 1, 746-763 p.
globular clusters : individual (M68), Hertzsprung-Russell diagram, open clusters and associations : individual (M67), stars : atmospheres, stars : evolution, stars : fundamental parameters (temperatures), Sun : abundances
IdentifiersURN: urn:nbn:se:uu:diva-112413ISI: 000253562000056OAI: oai:DiVA.org:uu-112413DiVA: diva2:286173