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

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

ASTROPHYSICAL JOURNAL

IOP

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 AGBphase, 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 forboth PG 1159 stars and DO white dwarfs.  The calculations are extended down  to an effective  temperature of  7000 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 1159stars,  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.