New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited

A. H. CÓRSICO; L. G. ALTHAUS; M. M. MILLER BERTOLAMI

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Les Ulis, France; Año: 2006 vol. 458 p. 259 - 267

0004-6361

We reexamine  the theoretical instability domain of pulsating PG1159 stars (GW Vir variables). We performed an extensive  g-mode stability analysis on  PG1159  evolutionary models   with  stellar   masses   ranging  from   0.530  to   0.741 Mo, for which the complete  evolutionary stages  of  their progenitors from the ZAMS, through the thermally pulsing AGB and born-again phases  to the domain of the  PG1159 stars have been considered. We  found that pulsations  in PG1159 stars  are  excited by the kappa-mechanism due to partial ionization of carbon  and oxygen,  and that no  composition gradients  are needed between the surface  layers and the driving region,  much in agreement with previous studies. We show, for the first time, the existence  of  a red edge of the instability strip at high luminosities.  We found that all  of the GW Vir  stars lay within our theoretical  instability strip.  Our results suggest a qualitative  good agreement between the observed and the predicted ranges of unstable periods of  individual stars. Finally, we found that generally the seismic masses  (derived from the period spacing) of GW Vir stars are somewhat different from the masses suggested by evolutionary tracks coupled with spectroscopy. Improvements in the evolution during the thermally pulsing AGB phase and/or during the core  helium burning stage and early  AGB  could help to alleviate the persisting discrepancies.