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Institut für Astronomie und Astrophysik

Abteilung Astronomie

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Preprint A/07

Asteroseismological constraints on the coolest GW Vir variable star (PG 1159-type) PG 0122+200

A.H. Córsico (1,2), M.M. Miller Bertolami (1,2), L. G. Althaus (1,2), G. Vauclair (3), K. Werner (4)

(1) Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, (1900) La Plata, Argentina.
(2) Instituto de Astrofísica La Plata, IALP, CONICET-UNLP
(3) Universite Paul Sabatier, Observatoire Midi-Pyrenees, CNRS/UMR5572,14 Av. Belin, 31400 Toulouse, France.
(4) Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, 72076 Tübingen, Germany.

To be published in: A&A

Abstract. We present an asteroseismological study on PG 0122+200, the coolest known pulsating PG1159 (GW Vir) star. Our results are based on an augmented set of the full PG1159 evolutionary models recently presented by Miller Bertolami & Althaus (2006). We perform extensive computations of adiabatic g-mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Msun. We derive a stellar mass of 0.626 Msun from a comparison between the observed period spacing and the computed asymptotic period spacing, and a stellar mass of 0.567 Msun by comparing the observed period spacing with the average of the computed period spacing. We also find, on the basis of a period-fit procedure, an asteroseismological model representative of PG 0122+200 which is able to reproduce the observed period pattern with an average of the period differences of 0.88 s. The model has an effective temperature of 81500 K, a stellar mass of 0.556 Msun, a surface gravity log g= 7.6 5, a stellar luminosity and radius of log(L/Lsun)= 1.14 and log(R/Rsun)= -1.73, respectively, and a He-rich envelope thickness of Menv= 0.019 Msun. We derive a seismic distance of about 614 pc and a parallax of about 1.6 mas. The results of the period-fit analysis carried out in this work suggest that the asteroseismological mass of PG 0122+200 could be 6-20 % lower than thought hitherto and in closer agreement (to within 5 %) with the spectroscopic mass. This result suggests that a reasonable consistency between the stellar mass values obtained from spectroscopy and asteroseismology can be expected when detailed PG1159 evolutionary models are considered.

Astrophysics (astro-ph): 0709.0280

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