Abstract
The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the
entire sky. While X-ray source counterparts are known to range from distant
quasars to nearby M dwarfs, the RASS data alone are often insufficient to
determine the nature of an X-ray source. As a result, large-scale follow-up
programs are required to construct samples of known X-ray emitters. We use
optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709
stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data
Release 1 footprint. Most of these are bright stars with coronal X-ray emission
unsuitable for SDSS spectroscopy, which is designed for fainter objects (g > 15
mag). Instead, we use SDSS photometry, correlations with the Two Micron All Sky
Survey and other catalogs, and spectroscopy from the Apache Point Observatory
3.5 m telescope to identify these stellar X-ray counterparts. Our sample of 707
X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected
samples of such stars. We derive distances to these stars using photometric
parallax relations appropriate for dwarfs on the main sequence, and use these
distances to calculate LX. We also identify a previously unknown cataclysmic
variable (CV) as a RASS counterpart. Separately, we use correlations of the
RASS and the SDSS spectroscopic catalogs of CVs and white dwarfs (WDs) to study
the properties of these rarer X-ray-emitting stars. We examine the relationship
between (fX/fg) and the equivalent width of the Hbeta emission line for 46
X-ray-emitting CVs and discuss tentative classifications for a subset based on
these quantities. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which
three are newly identified WDs. (abridged)
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