Asteroseismological measurements on PG 1159-035, the prototype of the GW Vir variable stars

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

ASTRONOMY AND ASTROPHYSICS

EDP Sciences

Lugar: Paris; Año: 2008 vol. 478 p. 869 - 881

0004-6361

Aims: An asteroseismological study on PG 1159-035, the prototype of the GW Vir variable stars, is performed on the basis of detailed and full PG1159 evolutionary models presented by Miller Bertolami & Althaus 2006.Method: We carried out extensive computations of adiabatic g-mode pulsation periods on PG1159 evolutionary models with stellar masses spanning the range 0.530 to 0.741 M. These models are derived from the complete evolution of progenitor stars, including the thermally pulsing AGB phase and born again episode. We constrain the stellar mass of PG 1159-035 by comparing the observed period spacing with the asymptotic period  spacing and with the averange of the computed period spacings. We also employed the individual observed periods reported by Costa et al. 2007 to find representative seismological model for  Pg 1159-035.Results: We derive a stellar mass in the range 0.56-0.59 M from the period spacing data alone. We also find, on the basis of period-fit procedure , an asteroseismological model representative of PG1159-035which reproduces the observed period pattern with an average of the period differences of 0.64-1.03, consistent with the expected model uncertainties. The model has an effective temperature of Teff=128000, a stellar mass of 0.565 M a surface gravity logg=7.42 a stellar luminosity and radius of logL/L=2.15 and LogR/R=-1.62, and a He-rich envelope thickness of Menv=0.017 M. The results of the period-fit analysis carried out in this works suggest that the gravity of PG1159 would be 1 sigma larger than the spectroscopically inferred gravity. For our best fit model of PG1159 -035 all of the pulsation modes are characterized by positive rates of period changes, at odds with the measurements by Costa & Kepler 2007.