Evolution and colors of helium-core white dwarf stars with high-metallicity progenitors

ALTHAUS, L. G.; PANEI, J. A.; ROMERO, A. D.; ROHRMANN, R. D.; CÓRSICO, A. H.; ; GARCÍA-BERRO, E.; MILLER BERTOLAMI, M. M.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Les ulis; Año: 2009 vol. 502 p. 207 - 216

0004-6361

Aims. Motivated by the recent detection of single and binary He-core white dwarfs in metal-rich clusters, we present a full set ofevolutionary calculations and colors appropriate to the study of these white dwarfs. The paper is also aimed at investigating whetherstable hydrogen burning may constitute a major source of energy for massive He-core white dwarfs resulting from high-metallicityprogenitors.Methods. White dwarf sequences are derived by considering the evolutionary history of progenitor stars with supersolar metallicities.We also incorporate a self-consistent, time-dependent treatment of gravitational settling and chemical diffusion, as well as of theresidual nuclear burning.Results. We find that the influence of residual nuclear burning during the late stages of white dwarf evolution is strongly dependent onthe chemical diffusion at the base of the hydrogen-rich envelope. When no diffusion is considered, residual hydrogen burning stronglyinfluences the advanced stages of white dwarf cooling, introducing evolutionary delays of several Gyr. By contrast, when diffusion istaken into account, the role of residual nuclear burning is strongly mitigated, and the evolution is only dictated by the thermal contentstored in the ions. In addition, for all of our sequences, we provide accurate color and magnitudes on the basis of new and improvednon-gray model atmospheres that explicitly include Lyα quasi-molecular opacity.