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A. A. Suchkov, R. J. Hanisch (STScI)
ClassX is an automated system for object classification of ROSAT sources (http://heasarc.gsfc.nasa.gov). We used it to classify and compare the X-ray populations in the field of young stellar clusters and regions of star formation. The X-ray sources under study were from the White-Giommi-Angelini catalog (WGACAT; http://wgacat.gfsc.nasa.gov) of ROSAT sources from PSPC pointed observations. The ClassX classifiers distinguish eight object types, including stars O-F5 (blue), F6-G (yellow), and K-M (red). In \rho~Oph and Orion, we find about four to five times more candidate blue and red stars than identified in the WGACAT. For the Pleiades, which is a closer and more advanced SFR, the increase is only a factor of two. For IC 2391, the WGACAT gives 10 blue and 2 red stars. ClassX adds only a couple of red stars but increases the number of blue stars by a factor of four.
The newly identified candidate stars are on average about two times fainter than the sources in the same regions that are classified in the WGACAT. Star candidates in \rho~Oph and Orion have substantially harder X-ray spectra than in the Pleiades and IC~2391, which is also true for sources classified in the WGACAT. This is consistent with the expected stronger absorption effect for sources in the fields of \rho~Oph and Orion. The absorption hypothesis is also supported by much redder colors of the 2MASS counterparts in these two regions.
In comparison with the sources classified in the WGACAT, the 2MASS counterparts of blue candidates in \rho~Oph and Orion are on average redder by about 0.5 mag in J-K and fainter in J by 4 to 5 mag; the candidate red stars have, on the other hand, about the same average J-K color and are fainter in J only by 0.5 to 1 mag.
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Bulletin of the American Astronomical Society, 36 #2
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