A ROSAT Survey of Near-Contact Binary Systems

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Session 85 -- Binaries
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[85.06] A ROSAT Survey of Near-Contact Binary Systems

J.S. Shaw, J.-P. Caillault (Univ. Georgia), J.H.M.M. Schmitt (MPE-Garching)

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$_{\rm x}$~=~29.3$\pm$0.1~ergs~s$^{-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.

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