Testing the forward modeling approach in asteroseismology. II. Structure and internal dynamics of the hot B subdwarf component in the close eclipsing binary system PG 1336-018
Abstract
Aims: We present a stringent test on the forward modeling technique in asteroseismology by confronting the predictions of a detailed seismic analysis of the pulsating subdwarf component in the unique close eclipsing binary system
Methods: We carry out numerical exercises based on the double optimization technique that we developed within the framework of the forward modeling approach in asteroseismology. We use a recently updated version that now incorporates the effects of stellar rotation on the pulsation properties. We thus search in parameter space for the optimal model that objectively leads to the best simultaneous match of the 25 periods (including rotationally-split components) observed in
Results: Our principal result is that our seismic model, which closely reproduces the observed periods, is remarkably consistent with one of the best-fitting possible solutions uncovered independently from the binary light curve analysis, in effect pointing to the correct one. The latter indicates a mass of Mast = 0.466±0.006 M⊙ and a radius of Rast = 0.15±0.01 R⊙ for the sdB star. In comparison, our seismic analysis, combined to high-quality time-averaged spectroscopy, leads to the following estimates of the basic structural parameters of the sdB component: Mast = 0.459±0.005 M⊙, Rast = 0.151±0.001 R⊙, log g = 5.739±0.002, Teff = 32 740 ± 400 K, and log(Menv/Mast) = -4.54±0.07. We also find strong evidence that the sdB star has reached spin-orbit synchronism and rotates as a solid body down to at least r ~ 0.55 Rast. We further estimate that higher-order perturbation effects due to rotation and tidal deformation of the star are insufficient to alter in a significant way the proposed asteroseismic solution itself (i.e., the derived structural parameters and rotation properties). Future efforts to improve further the accuracy of the seismic models will clearly have to incorporate such effects, however.
Conclusions: We conclude that our approach to the asteroseismology of sdB stars has passed a fundamental test with this analysis of PG 1336-018. The structural parameters and inferences about the internal dynamics of this star derived in the present paper through this approach should rest on very solid grounds. More generally, our results underline the power and usefulness of the forward modeling method in asteroseismology, despite historical misgivings about it.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- October 2008
- DOI:
- 10.1051/0004-6361:200809907
- Bibcode:
- 2008A&A...489..377C
- Keywords:
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- stars: binaries: close;
- stars: subdwarfs;
- stars: oscillations;
- stars: interiors;
- stars: rotation;
- stars: individual: PG 1336-018