New Evolutionary Sequences for Hot H-Deficient White Dwarfs on the Basis of a Full Account of Progenitor Evolution

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

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Chicago; Año: 2009 vol. 704 p. 1605 - 1615

0004-637X

We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range of stellar masses and helium envelopes on the basis of a complete treatment of the evolutionary history of progenitors stars, including the core hydrogen and helium burning phases, the thermally-pulsing AGB phase, and the born-again episode that is responsible for the hydrogen deficiency. We also provide colors and magnitudes for the new sequences for $T_{ m eff} < 40 000$ K, where the NLTE effects are not dominant. These new calculations provide an homogeneous set of evolutionary tracks appropriate for mass and age determinations for both PG 1159 stars and DO white dwarfs. The calculations are extended down to an effective temperature of 7 000 K. We applied these new tracks to redetermine stellar masses and ages of all known DO white dwarfs with spectroscopically-determined effective temperatures and gravities, and compare them with previous results. We also compare for the first time consistent mass determinations for both DO and PG 1159 stars, and find a considerably higher mean mass for the DO white dwarfs. We discuss as well the chemical profile expected in the envelope of variable DB white dwarfs from the consideration of the evolutionary history of progenitor stars. Finally, we present tentative evidence for a different evolutionary channel, other than that involving the PG 1159 stars, for the formation of hot, hydrogen-deficient white dwarfs.