Volume 573, January 2015
|Number of page(s)||8|
|Section||Stellar structure and evolution|
|Published online||17 December 2014|
KIC 8302197: a non-rotating or low-inclination pulsating subdwarf B star observed with the Kepler spacecraft
Uniwersytet Pedagogiczny, Obserwatorium na Suhorze, ul. Podchorążych
2 Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, 38711 Breña Baja, Spain
3 Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
4 Dr. Remeis–Sternwarte, Institute for Astronomy, University, Erlangen-Nürnberg, Sternwartstr. 7, 96049 Bamberg, Germany
Received: 28 August 2014
Accepted: 24 October 2014
We present our analysis of Kepler data of a pulsating subdwarf B star, KIC 8302197. We used Q5-17 data and applied a Fourier technique to extract 30 significant pulsation modes. We searched for multiplets and period-spacing sequences to perform a mode identification and to derive a rotation period. To our surprise, KIC 8302197 does not show any multiplets. We explain the lack of multiplets by either a very slow rotation (longer than ~1000 days) or a unique (pole-on) orientation of the pulsation axis. Our mode identification relied solely on period spacing. We were successful in identifying modal degrees of most of the detected modes. An analysis of the period stability did not show any evidence of a companion to the host star. In addition to photometric data, several spectroscopic observations were collected. Our twelve radial-velocity measurements constrain a possible orbital radial-velocity amplitude to be smaller than about 10 km s-1. Furthermore, based on color indices we constrained a possible companion to be an M or later type main sequence, a compact or a substellar object. We found that the atmospheric parameters (Teff = 27 450 ± 200 K, log g = 5.438 ± 0.033 dex, and log (nHe /nH) = −2.56 ± 0.07 dex) of KIC 8302197 are consistent with other slow pulsating subdwarf B stars. From the optical spectra we derived C, N, O, Si and Fe abundances, and set an upper limit for the S abundance.
Key words: asteroseismology / stars: oscillations / subdwarfs / stars: abundances
© ESO, 2014
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