Issue |
A&A
Volume 488, Number 2, September III 2008
|
|
---|---|---|
Page(s) | 685 - 696 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:200809867 | |
Published online | 09 July 2008 |
Testing the forward modeling approach in asteroseismology*
I. Seismic solutions for the hot B subdwarf Balloon 090100001 with and without a priori mode identification
1
Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 av. E. Belin, 31400 Toulouse, France e-mail: [valerie.vangrootel;stephane,charpinet]@ast.obs-mip.fr
2
Département de Physique, Université de Montréal, CP 6128, Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada e-mail: [fontaine;brassard]@astro.umontreal.ca
3
Steward Observatory, University of Arizona, 933 North Cherry Av., Tucson, AZ 85721, USA e-mail: bgreen@as.arizona.edu
4
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: chayer@stsci.edu
5
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany e-mail: srandall@eso.org
Received:
28
March
2008
Accepted:
1
July
2008
Context. Balloon 090100001, the brightest of the known pulsating hot
B subdwarfs, exhibits simultaneoulsy both short- and long-period
pulsation modes, and shows relatively large amplitudes for its
dominant modes. For these reasons, it has been studied extensively
over the past few years, including a successful experiment carried out
at the Canada-France-Hawaii Telescope to pin down or constrain the
value of the degree index of several pulsation modes through
multicolor photometry.
Aims. The primary goal of this paper is to take advantage of such partial mode identification to test the robustness of our standard approach to the asteroseismology of pulsating subdwarf B stars. The latter is based on the forward approach whereby a model that best matches the observed periods is searched for in parameter space with no a priori assumption about mode identification. When successful, this method leads to the determination of the global structural parameters of the pulsator. As a bonus, it also leads, after the fact, to complete mode identification. For the first time, with the availability of partial mode identification for Balloon 090100001, we are able to evaluate the sensitivity of the inferred seismic model to possible uncertainty in mode identification.
Methods. We carry out a number of exercises based on the double optimization
technique that we developed within the framework of the forward
modeling approach in asteroseismology. We use the set of ten periods
corresponding to the independent pulsation modes for which values of
have been either formally identified or constrained through
multicolor photometry in Balloon 090100001. These exercises differ in
that they assume different a priori mode identification.
Results. Our primary result is that the asteroseismic solution stands very robust,
whether or not external constraints on the values of the degree
are used. Although this may come as a small surprise, the test proves to be
conclusive, and small differences in mode identification among the ten
modes do not affect in any significant way, at the typical accuracy
presently achieved, the final emergent seismic model. This is due to the
structure of the p-mode pulsation spectra
in sdB stars. In all
cases, the inferred structural parameters of Balloon 090100001 remain
practically unchanged. They correspond, and this constitutes our
second important result, to a star beyond the TAEHB with Teff
= 28 000 ± 1 200 K, log g = 5.383 ± 0.004,
= 0.432 ± 0.015, and
=
-4.89 ± 0.14. Other structural parameters are also derived.
Key words: stars: oscillations / stars: interiors / stars: subdwarfs / stars: individual: Balloon 090100001
Based on photometric observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Some of the spectroscopic observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution.
© ESO, 2008
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