Journal Article

The discovery of two pulsating subdwarf B stars in NGC 6791 using <i>Kepler</i> data

M. D. Reed, A. Baran, R. H. Østensen, J. Telting and S. J. O'Toole

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 427, issue 2, pages 1245-1251
Published in print December 2012 | ISSN: 0035-8711
Published online December 2012 | e-ISSN: 1365-2966 | DOI:
The discovery of two pulsating subdwarf B stars in NGC 6791 using Kepler data

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We report the discovery of two new pulsating subdwarf B (sdB) stars in the open cluster NGC 6791 using data from the Kepler spacecraft. Three sdB stars were observed for one month in short-cadence (1 min) mode and three months in long-cadence (30 min) mode during Quarter 11 (fall 2011). The stars have Kepler Input Catalogue numbers of 2437937, 2569576 and 2569583 with previous designations of B5, B3 and B6, respectively. Another sdB star exists in the cluster and it is also known to be a pulsator. We also obtained Nordic Optical Telescope spectra to update effective temperatures, surface gravities and helium abundances and compare the spectroscopic properties of all four stars on a uniform model grid.

We detect four periodicities between 0.9 and 2.4 h in B3 above a detection limit of 0.53 parts per thousand (ppt) and nine periodicities between 1.1 and 2.2 h in B5 above a detection limit of 0.37 ppt. No pulsations were detected in B6 to the detection threshold of 0.29 ppt. The long-cadence data were less useful as few observations are obtained per pulsation period, yet they do indicate that the pulsations are variable from month to month. The spacings between the pulsation periods are similar to other g-mode pulsating sdB stars observed by Kepler, indicating that the periodicities can be associated witquals; 1 modes. A fit to the periods give spacings of 234.6 ± 0.6 and 242.6 ± 1.5 s for B3 and B5, respectively.

Keywords: stars: oscillations; subdwarfs

Journal Article.  3083 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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