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The VAST Survey - I. Companions and the unexpected X-ray detection of B6-A7 stars

By Robert J. De Rosa, Joanna Bulger, Jenny Patience, Ben Leland, Bruce Macintosh, Adam Schneider, Inseok Song, Christian Marois, James R. Graham, Mike Bessell and René Doyon


With an adaptive optics imaging survey of 148 B6-A7 stars, we have tested the hypothesis that unresolved lower-mass companions are the source of the unexpected X-ray detections of stars in this spectral type range. The sample is composed of 63 stars detected in X-rays within the ROSAT All-Sky Survey and 85 stars that form a control sample; both subsets have the same restricted distribution of spectral type, age, X-ray sensitivity and separation coverage. A total of 68 companion candidates are resolved with separations ranging from 0.3" to 26.2", with 23 new detections. The multiple star frequency of the X-ray sample based on companions resolved within the ROSAT error ellipse is found to be 43 (+6,-6)%. The corresponding control sample multiple star frequency is three times lower at 12 (+4,-3)% -- a difference of 31\pm7%. These results are presented in the first of a series of papers based on our Volume-limited A-Star (VAST) survey -- a comprehensive study of the multiplicity of A-type stars.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Topics: Astrophysics - Solar and Stellar Astrophysics
Year: 2011
DOI identifier: 10.1111/j.1365-2966.2011.18765.x
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