Third generation stellar models for asteroseismology of hot B subdwarf stars

A test of accuracy with the pulsating eclipsing binary PG 1336–018^⋆

¹ Institut d’Astrophysique et de Géophysique, Université de Liège, 17 Allée du 6 Août, 4000 Liège, Belgium
e-mail: valerie.vangrootel@ulg.ac.be
² Chargé de recherches, Fonds de la Recherche Scientifique, FNRS, 5 rue d’Egmont, 1000 Bruxelles, Belgium
³ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France
⁴ CNRS, IRAP, 14 Av. E. Belin, 31400 Toulouse, France
⁵ Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
⁶ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721, USA

Received: 12 December 2012
Accepted: 12 March 2013

Abstract

Context. Asteroseismic determinations of structural parameters of hot B subdwarfs (sdB) have been carried out for more than a decade now. These analyses rely on stellar models whose reliability for the required task needs to be evaluated critically.

Aims. We present new models of the so-called third generation (3G) dedicated to the asteroseismology of sdB stars, in particular to long-period pulsators observed from space. These parameterized models are complete static structures suitable for analyzing both p- and g-mode pulsators, contrary to the former second generation (2G) models that were limited to p-modes. While the reliability of the 2G models has been successfully verified in the past, this important test still has to be conducted on the 3G structures.

Methods. The close eclipsing binary PG 1336 − 018 provides a unique opportunity to test the reliability of hot B subdwarf models. We compared the structural parameters of the sdB component in PG 1336 − 018 obtained from asteroseismology based on the 3G models, with those derived independently from the modeling of the reflection/irradiation effect and the eclipses observed in the light curve.

Results. The stellar parameters inferred from asteroseismology using the 3G models are found to be remarkably consistent with both the preferred orbital solution obtained from the binary light curve modeling and the updated spectroscopic estimates for the surface gravity of the star. The seismology gives M_∗ = 0.471 ± 0.006  M_⊙, R_∗ = 0.1474 ± 0.0009  R_⊙, and log g = 5.775 ± 0.007, while orbital modeling leads to M_∗ = 0.466 ± 0.006  M_⊙, R_∗ = 0.15 ± 0.01  R_⊙, log g = 5.77 ± 0.06, and spectroscopy yields log g = 5.771 ± 0.015. In comparison, seismology from a former analysis based on the 2G models gave very similar results with M_∗ = 0.459 ± 0.005  M_⊙, R_∗ = 0.151 ± 0.001  R_⊙, and log g = 5.739 ± 0.002. We also show that the uncertainties on the input physics included in stellar models have, at the current level of accuracy, no noticeable impact on the structural parameters derived by asteroseismology.

Conclusions. The stellar models (both of second and third generation) presently used to carry out quantitative seismic analyses of sdB stars are reliable for the task. The stellar parameters inferred by this technique, at least for those that could be tested (M_∗, R, and log g), appear to be both very precise and accurate, as no significant systematic effect has been found.