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Title:
A Radial Velocity Study of Hot Subdwarf Stars with Cool Companions
Authors:
Wade, Richard A.; Herrmann, K. A.; Stark, M. A.
Affiliation:
AA(Penn State Univ), AB(Penn State Univ), AC(University of Wyoming)
Publication:
American Astronomical Society, AAS Meeting #211, id.03.33; Bulletin of the American Astronomical Society, Vol. 39, p.728
Publication Date:
12/2007
Origin:
AAS
Bibliographic Code:
2007AAS...211.0333W

Abstract

Many subdwarf B (sdB) stars have composite energy distributions and/or spectra. The companion is a G or K star in most cases. Subdwarf B stars have helium-burning cores typically near 0.5 solar masses, and they have very low mass hydrogen envelopes. How the hydrogen envelopes were lost, very near the time of core helium ignition, is of great interest. Many sdB stars that show a composite nature may have formed by Roche lobe overflow (RLOF). The resulting binaries should have orbital periods of a few years and orbital separations of a few AU. We are observing a sample of fifteen moderately bright sdB stars with composite spectra, to look for radial velocity variations that will indicate their orbital periods. We use the Medium Resolution Spectrograph on the Hobby Eberly Telescope. Since January 2005, we have acquired between 5 and 11 observations of each star (median: N=8) over baselines of six months or longer (median: 12 months). If these systems were formed by RLOF, we expect to see measurable orbital acceleration in many of these systems, barring systematic bad luck with orbital phase or inclination. We will describe the current status of the program and the findings to date.
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