Hot DQ white dwarfs: a pulsational test of the convective mixing scenario for their formation

ROMERO, A. D.; CÓRSICO, A. H.; ALTHAUS, L. G.; GARCÍA-BERRO, E.

Rio de Janeiro, Brasil

Congreso; XXVII IAU General Assembly; 2009

IAU

Hot  DQ white  dwarfs constitute  a new  class of  white  dwarf stars, uncovered  recently within the  framework of  the SDSS  project. There exist nine of  them  out of a total of  several thousands white dwarfs spectroscopically  identified.  Recently,  three hot  DQ  white dwarfs have  been reported  to exhibit  photometric variability  with periodscompatible with pulsation g-modes.  The pulsation hypothesis has been recently reinforced  by Green et  al. (2009). In this  contribution we present  the results  of  a non-adiabatic  pulsation  analysis of  the C-rich  hot  DQ white  dwarf  stars.  Our  study  relies  on the  full evolutionary  models of  hot  DQ white  dwarfs  recently developed  by Althaus et al. (2009), based on a diffusive/convective mixing scenario first proposed by Dufour  et al.  (2008).  Specifically, the stability analysis was  performed on white  dwarf models from stages  before the blue edge  of the DBV instability  strip ($T_{ m eff}sim$  30 000 K) until  he domain  of the  hot  DQ white  dwarfs ($18000  - 24000$  K), including the DB $rightarrow$  hot DQ white dwarf transition. In our non-adiabatic computations, the frozen convection approximation has been adopted.