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V.V. Makarov (USRA/USNO)
The 100 most luminous in X-ray nearby stars are culled from the ROSAT survey catalogs, within or around a distance of 50 pc. The smallest X-ray luminosity in the sample, given in units of 1029 erg s-1 throughout this paper, is 9.8; the strongest source in the Solar neighborhood is II Peg, a RS CVn star (RS type), at LX=175.8. The sample is divided into 30 RS objects, 4 stars of W UMa type, 5 other kinds of active binaries (e.g., some CABS and \beta Lyr eclipsing variables), 12 BY Dra-type stars (BY), 8 active evolved stars (giants and subgiants), 29 pre-main sequence and T Tauri stars (PMS) and 26 unknown. There is some overlap between these classes, in that a PMS object may also be a BY or RS star. Almost all objects are identified extreme UV sources. The RS objects are significantly stronger in X-ray than the PMS stars. There are 7 objects in the sample with LX>100, all RS type except for one PMS star, BO Mic = Speedy Mic. Only 3 of the 29 PMS objects have LX>25 (10%), and only 7 (24%) have LX>20. At the same time, only 8 RS objects (28%) have LX<20. Thus, the limit of LX=20 appears to be a viable statistical criterion differentiating RS and PMS stars. Almost all objects in the sample are binary or multiple systems; the overall fraction of components (FC) is 0.86. The FC among the PMS objects is 0.77, and among the unknown type 0.82. Surprisingly, 47% of the RS-type objects are parts of wider binary or multiple systems, which makes them hierarchical multiples. The RS stars have fast and apparently random motions with respect to the Local Standard of Rest, while the PMS stars hame moderate velocities and tend to form loose, expanding micro-associations like the Beta Pic and the Horologium.
The author(s) of this abstract have provided an email address for comments about the abstract: makarov@usno.navy.mil
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.