Asteroseismological modeling of PG1159+035, the prototype of of the GW Vir stars

A. H. CÓRSICO; L. G. ALTHAUS; M. M. MILLER BERTOLAMI; S. O. KEPLER; J. E. S. COSTA

Tübingen, Germany

Conferencia; Hydrogen Deficient stars; 2007

Institut für Astronomie und Astrophysik Tübingen

We present an asteroseismological study on PG 1159-035 —the prototype of the GW Vir variable stars— on the basis of detailed and full PG1159 evolutionary models recently presented by Miller Bertolami & Althaus (2006). We carried out extensive g-mode adiabatic period computations on PG1159 evolutionary modelswith stellar masses spanning the range 0.530 to 0.741M. These models are derived from the complete evolution of progenitor stars, including the thermally pulsing AGB phase and born-again episode. We first constrain the stellar mass of PG 1159−035 by comparing the observed period spacing with the asymptotic period spacing and with the average of the computed period spacings. In this way we derive a stellar mass in the range 0.56 − 0.59M. We also employ the individual observed periods reported recently by Costa et al. (2007) and found a representative seismological model for PG 1159−035 which nicely reproduces the observed period pattern. The model has an effective temperature Teff = 127 680 K, a stellar mass M = 0.565M, a surface gravity log g = 7.42, a stellar luminosity and radius log(L/L) = 2.15 and log(R/R) = −1.62, respectively, and a He-rich envelope thickness Menv = 0.017M. Nonadiabatic calculations predict that this asteroseismological model is pulsationally stable against dipole (` = 1) modes,contradicting the observational evidence. In addition, all of the theoretical pulsation modes are characterized by positive rates of period changes, at odds with the recent measurements by Costa & Kepler (2007).