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Description
The optical identification of large number of X-ray sources such as those from the ROSAT All-Sky Survey is challenging with conventional spectroscopic follow-up observations. The authors have investigated two ROSAT All-Sky Survey fields of size 10 degrees by 10 degrees each, one at a galactic latitude b = 83<sup>o</sup> (26 Com), the other at b = -5<sup>o</sup> (gamma Sge), in order to optically identify the majority of sources. They used optical variability, among other more standard methods, as a means of identifying a large number of ROSAT All- Sky Survey sources. All objects fainter than about 12th magnitude and brighter than about 17th magnitude in or near the error circle of the ROSAT positions were tested for optical variability on hundreds of archival plates of the Sonneberg field patrol. The reference paper contains probable optical identifications of altogether 256 of the 370 ROSAT sources analyzed. In particular, the authors found 126 active galactic nuclei (some of them may be misclassified cataclysmic variables, CVs), 17 likely clusters of galaxies, 16 eruptive double stars (mostly CVs), 43 chromospherically active stars, 65 stars brighter than about 13th magnitude, 7 UV Ceti stars, 3 semi-regular or slow irregular variable stars of late spectral type, 2 DA white dwarfs, 1 Am star, 1 supernova remnant, and 1 planetary nebula. As expected, nearly all active galactic nuclei are found in the high-galactic latitude field, while the majority of CVs is located at low galactic latitudes. The authors identify in total 72 new variable objects. X-ray emission is, not unexpectedly, tightly correlated with optical variability, and thus their new method for optically identifying X-ray sources is demonstrated to be feasible. Given the large number of optical plates used, this method was most likely not more efficient than, for example, optical spectroscopy. However, it required no telescope time, only access to archival data. This table contains the optical spectroscopic and photometric properties of the 722 possible optical counterparts to the 370 ROSAT point sources found by the authors in the 2 examined fields above a maximum likelihood threshold of 8. It is essentially the union of the 314 counterparts which were listed in Table 8 (26 Com field) of the reference paper with the 408 counterparts listed in Table 9 (gamma Sge field) of that paper. We have removed 12 entries from Table 8 for which no optical counterpart was found (1033, 1050, 1060, 1085, 1091, 1103, 1129, 1166, 1177, 1190, 1217 and 1237), 1 additional entry from the same table (1071) where the X-ray emission is more likely associated with galaxy cluster gas emission rather than an individual galaxy in that cluster, and 7 entries from Table 9 (source numbers 2087-2091 and 2093-2094 which are detections of flux enhancements of an extended supernova remnant (SNR 053.6-02.2), for a total of 20 removed, since none of these entries had any positional or optical data given in the original tables. The combined lists of the X-ray sources which were given in Table 1 (26 Com field) of the reference paper and Table 2 (gamma Sge field) of that paper are available in the HEASARC table <a href="/W3Browse/rosat/rass2fxray.html">RASS2FXRAY</a> (to which the present table is linked). This table was created by the HEASARC in April 2015 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/A+A/575/A42">CDS catalog J/A+A/575/A42</a> files table8.dat and table9.dat. This is a service provided by NASA HEASARC .
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