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.; MILLER BERTOLAMI, M. M.; GARCIA-BERRO, E.; CÓRSICO, A. H.; ROMERO, A. D.; KEPLER, S.; ROHRMANN, R. D.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

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

0004-637X

We present full evolutionary calculations appropriate for the study of hot hydrogen-deficient DO white dwarfs,PG 1159 stars, and DB white dwarfs. White dwarf sequences are computed for a wide range of stellar masses andhelium envelopes on the basis of a complete treatment of the evolutionary history of progenitors stars, including thecore hydrogen and helium burning phases, the thermally pulsing asymptotic giant branch phase, and the born-againepisode that is responsible for the hydrogen deficiency.We also provide colors and magnitudes for the newsequencesfor Teff < 40,000 K, where the NLTE effects are not dominant. These new calculations provide a homogeneous setof evolutionary tracks appropriate formass and age determinations for both PG1159 stars andDOwhite dwarfs. Thecalculations are extended down to an effective temperature of 7000 K. We applied these new tracks to redeterminestellar masses and ages of all known DO white dwarfs with spectroscopically determined effective temperatures andgravities, and compare them with previous results.We also compare for the first time consistent mass determinationsfor both DO and PG 1159 stars, and find a considerably higher mean mass for the DO white dwarfs. We discussas well the chemical profile expected in the envelope of variable DB white dwarfs from the consideration ofthe evolutionary history of progenitor stars. Finally, we present tentative evidence for a different evolutionarychannel, other than that involving the PG 1159 stars, for the formation of hot, hydrogen-deficient white dwarfs.