SIMBAD references

We observed a 17'x17' region of the ρ Oph molecular cloud, using the ACIS-I array on board the Chandra X-Ray Observatory. A 100 ks exposure observation revealed ∼100 X-ray sources above the detection limit of ∼10²⁸ ergs.s^–1. About two-thirds of the X-ray sources are identified with an optical and/or IR counterpart, including significant numbers of class I, II, and III sources and a few brown dwarfs. The X-ray detection rate of class I sources is a surprisingly high 70%. Many X-ray flares, possibly because of the magnetic activity, are found from all of the classes. We make systematic spectral studies of the quiescent and flare X-rays for all the X-ray sources. The X-ray temperatures and absorptions of class I sources are generally larger than those of class II and III sources. In addition, X-ray flares from class I sources show slightly higher duty ratio, temperature, and luminosity than those of more evolved classes. We further give brief results on brown dwarfs, sources in a younger phase than class I, unclassified, and unidentified sources. Details for several selected young stellar objects, including the first detection of a neutral iron line (6.4 keV) from a class I source (YLW 16A), are separately addressed.