New evolutionary sequences for hot H-deficient white dwarfs on the basis of a full account of progenitor evolution

TL;DR

This paper provides comprehensive evolutionary models for hot hydrogen-deficient white dwarfs, including new tracks for mass and age determination, and explores different evolutionary channels for their formation.

Contribution

It introduces a complete set of evolutionary calculations for hot H-deficient white dwarfs based on progenitor evolution, extending previous models and analyzing their implications.

Findings

Higher mean mass for DO white dwarfs compared to previous estimates.

New evolutionary tracks improve mass and age determinations for PG 1159 and DO stars.

Evidence suggests alternative formation channels for hot H-deficient white dwarfs.

Abstract

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 $T_{\rm eff} < 40 000$ 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.