Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.8506s&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #85.06; Bulletin of the American Astronomical Society, Vol. 26, p.1460
Astronomy and Astrophysics
Astronomy
Scientific paper
We have conducted a survey of near-contact binary systems observed during the ROSAT All-Sky Survey (RASS). The near-contact binaries (NCBs) have an A- or F-type primary, with a companion which is one to two spectral types cooler. The systems have periods less than one day and display strong tidal interaction, but are not in contact like the W UMa systems. There are more than 150 such systems known to exist. We have analyzed the RASS data for all of those (58) within 400 pc. We report the detection of 14 systems with X-ray count rates > 0.01 cts s(-1) . The X-ray luminosity function for the NCBs is very similar to that for A-type W UMa systems (derived, admittedly, from only a handful of EINSTEIN observations), but appears to be significantly different from those of W-type W UMa systems and RS CVn binaries. This is consistent with the proposed scenario that the NCBs are evolutionary precursors to the A-type W UMa binaries. The mean X-ray luminosity of the NCBs is log L_x = 29.3+/-0.1 ergs s(-1) , less than that of the RS CVns, but greater than that of normal late-type main sequence star s. The detection of these systems may help to explain why many presumably single A-type stars were detected in the RASS; i.e., the ``single" A-stars may, in fact, be binaries, like the NCBs, with late-type companions. This research was supported in part by NASA Grants NAG 5-1610 and NAG 5-2095 to the University of Georgia.
Caillault Jean-Pierre
Schmitt Juergen H. M. M.
Shaw Scott J.
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