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X-Ray-Emitting Stars Identified from the ROSAT All-Sky Survey and the Sloan Digital Sky Survey
The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey ofthe entire sky. Combining the RASS Bright and Faint Source Catalogsyields an average of about three X-ray sources per square degree.However, while X-ray source counterparts are known to range from distantquasars to nearby M dwarfs, the RASS data alone are often insufficientto determine the nature of an X-ray source. As a result, large-scalefollow-up programs are required to construct samples of known X-rayemitters. We use optical data produced by the Sloan Digital Sky Survey(SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS andfalling within the SDSS Data Release 1 footprint. Most of these arebright stars with coronal X-ray emission unsuitable for SDSSspectroscopy, which is designed for fainter objects (g > 15 [mag]).Instead, we use SDSS photometry, correlations with the Two Micron AllSky Survey and other catalogs, and spectroscopy from the Apache PointObservatory 3.5 m telescope to identify these stellar X-raycounterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars isone of the largest X-ray-selected samples of such stars. We derivedistances to these stars using photometric parallax relationsappropriate for dwarfs on the main sequence, and use these distances tocalculate LX . We also identify a previously unknowncataclysmic variable (CV) as a RASS counterpart. Separately, we usecorrelations of the RASS and the SDSS spectroscopic catalogs of CVs andwhite dwarfs (WDs) to study the properties of these rarer X-ray-emittingstars. We examine the relationship between (fX /fg) and the equivalent width of the Hβ emission line for 46X-ray-emitting CVs and discuss tentative classifications for a subsetbased on these quantities. We identify 17 new X-ray-emitting DA(hydrogen) WDs, of which three are newly identified WDs. We report onfollow-up observations of three candidate cool X-ray-emitting WDs (oneDA and two DB (helium) WDs); we have not confirmed X-ray emission fromthese WDs.Includes observations obtained with the Apache Point Observatory 3.5 mtelescope, which is owned and operated by the Astrophysical ResearchConsortium.
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
| The local interstellar medium and soft local X-ray radiation
The nature of the soft local X-ray radiation is discussed. The questionof whether the radiation originates from a local bubble, a number ofnonlocal bubbles, or the Galactic corona is examined. Attention is givento Rosat findings and to the known characteristics of the Dracomolecular cloud, the Hercules H I shell, and the Hercules field.
| Interstellar NA I D line studies of stars towards the Draco nebula
This study presents new high-dispersion CCD spectra of sodium for eightprogram stars located in the direction of the high-latitude Dracomolecular cloud (DMC). The derived lower distance limit of 180 pc abovethe Galactic plane was evaluated from nondetection of interstellarabsorption lines of sodium at the Draco velocity in sight lines of B8-F0type stars. This result is in agreement with former distance estimatesfrom star counts as well as from UBV photometric extinctionmeasurements. The existence of the most negative velocity components inspectra of the most distant stars suggests a more speculative distanceestimate of 400-600 pc for the DMC. The present determination of a lowerdistance limit to the DMC from an interstellar absorption-line studysupplements the few existing optical determinations of firm (upper)distance limits to other high-latitude molecular clouds.
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