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Description
This catalog contains the results of a complete X-ray survey of the Hyades cluster region using X-ray data from the ROSAT All-Sky Survey (RASS) that was published by Stern, Schmitt and Kahabka in 1995. The Hyades survey covered over 900 square degrees of the sky. Over 185 optically identified Hyades were detected down to a limiting X-ray luminosity of about 1-2x10<sup>28</sup> ergs/s in the 0.1-1.8keV energy band. Among solar-like stars, i.e., main-sequence stars of spectral type G, the RASS detection rate was about 90%. Stern et al. argue that the presence of many binary systems in the cluster is a key factor influencing the Hyades X-ray luminosity function. Short-period (a few days or less) binaries are anomalously X-ray bright, as might have been expected; however, the X-ray luminosity functions of K and possibly M binary stars of all types are significantly different from their single counterparts, confirming the results of Pye et al. (1994, MNRAS, 266, 798) based on a smaller K star sample drawn from deep ROSAT pointings. Comparison with Einstein Observatory studies of a subset of Hyades stars demonstrates a general lack of significant (> a factor of 2) long-term X-ray variability. Stern et al. suggest that this may be the result of the dominance of a small-scale, turbulent dynamo in the younger Hyades stars compared to the large-scale, cyclic dynamo observed in the Sun. The HYADESXRAY database consists of X-ray data for 440 probable and possible Hyades members that were included in the Stern et al. survey and were listed in Table 1 of their published paper. The database contains both stars which were detected as X-ray sources and those which were not: for the latter, upper limits to their X-ray emission are provided. For all listed stars, their X-ray luminosities based on a Hyades distance of 45 pc are provided; for some stars, for which individually determined distances from either the Schwan (1991, A&A, 243, 386) or the Hanson (1975, AJ, 80, 379) proper motion surveys are available, their X-ray luminosities based on these alternate distances are also provided. There were 4 stars detected as RASS sources out of over 180 new Hyades candidates listed in the Reid (1992, MNRAS, 257, 257) proper motion survey which were included in Table 2 (but not Table 1) of the Stern et al. paper. These stars are not included in the current database, but are listed in the help section entitled Reid_Stars (q.v.). Similarly, there were 20 stars detected as RASS sources but which were considered by Stern et al. to be non-members of the Hyades which were included in their Table 3 (but not Table 1). These stars are not included in the current database, but are listed in the help section entitled Rejected_Hyades (q.v.). This HEASARC catalog was created in July 1997, derived from <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/448/683">CDS Catalog J/ApJ/448/683</a> obtained from <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/448/683/">https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJ/448/683/</a>. Additional information provided in the HEASARC documentation was taken from the original published version of the paper containing this catalog. This is a service provided by NASA HEASARC .
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