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

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

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Paris, Francia; Año: 2009 vol. 502 p. 207 - 216

0004-6361

Motivated by the recentdetection of single and binary He-core white dwarfs in metal-rich clusters, we present a fullset of evolutionary calculations and colors appropriate to the study of these white dwarfs. The paper is also aimed at investigating whether stable hydrogen burning may constitute a major source of energy for massive  He-core white dwrafs resulting from high metallicity progenitors. White dwarfs 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 the residual nuclear burning.We find that the influence of residual nuclear burning during the late stages of white dwarf evolution is strongly dependent on the chemical diffusion at the base of the hydrogen-rich envelope. When no diffusion is considered, residual hydrogen burning strongly influences tha advanced stages of white dwarf cooling, introducing evolutionary delays of several Gyr. By contrast, when diffusion is taken into account, the role of residual nuclear burning is strongly mitigated, and the evolution is only dictated by the thermal content stored in the ions. In addition, for all of our sequences, we provide accurate color and magnitudes on the basis of new and improved non-gray model atmospheres that explicitly include Ly_alpha quasi-molecular opacity.