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Description
The CMa R1 star-forming region contains several compact clusters as well as many young early-B stars. It is associated with a well-known bright rimmed nebula, the nature of which is unclear (fossil HII region or supernova remnant). To help elucidate the nature of the nebula, the authors' goal was to reconstruct the star-formation history of the CMa R1 region, including the previously unknown older, fainter low-mass stellar population, using X-rays. The authors analyzed images obtained with the ROSAT satellite, covering ~5 square degrees. Complementary VRI photometry was performed with the Gemini South telescope. Color-magnitude and color-color diagrams were used in conjunction with pre-main sequence evolutionary tracks to derive the masses and ages of the X-ray sources. The ROSAT images show two distinct clusters. One is associated with the known optical clusters near Z CMa, to which ~ 40 members are added. The other, which the authors name the "GU CMa" cluster, is new, and contains ~ 60 members. The ROSAT sources are young stars with masses down to M_star ~ 0.5 M_sun, and ages up to 10 Myr. The mass functions of the two clusters are similar, but the GU CMa cluster is older than the cluster around Z CMa by at least a few Myr. Also, the GU CMa cluster is away from any molecular cloud, implying that star formation must have ceased; on the contrary (as already known), star formation is very active in the Z CMa region. The two ROSAT observations that the authors analyzed are the following. By order of increasing RA, the first Field ('Field 1' hereafter), HEASARC ID RP201011 pointing axis RA(J2000} = 7<sup>h</sup> 00<sup>m</sup>, Dec(J2000) = -11<sup>o</sup> 30', has an exposure of 19.7 ks. 'Field 2', HEASARC ID RP201277, pointing axis RA(J2000) = 7<sup>h</sup> 04<sup>m</sup>, Dec(J2000) = -11<sup>o</sup> 33', has a much shorter exposure of 4.6 ks. This table contains the complete list of sources detected in CMa R1 by ROSAT. This online catalog was created by the HEASARC in April 2010 based on machine-readable tables obtained from the CDS (their catalog J/A+A/506/711, file tablea1.dat). This is a service provided by NASA HEASARC .
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