Erratum: “ChandraObservation of the ρ Ophiuchi Cloud” (ApJ, 557, 747 [2001])

We observed a 17$'\times17'$ region of the $\rho$ Oph molecular cloud, usingthe ACIS-I array onboard the {\it Chandra X-ray Observatory} (CXO). A 100-ksexposure observation revealed $\sim$ hundred X-ray sources above the detectionlimit of $\sim$ 10$^{28}$ ergs s$^{-1}$. About 2/3 of the X-ray sources areidentified to an optical and/or infrared counterpart, including significantnumbers of class I, II and III sources and a few brown dwarfs. The X-raydetection rate of class I sources is surprisingly high of 70 %. Many X-rayflares, possibly due to the magnetic activity, are found from all of theclasses. We make systematic spectral studies on the quiescent and flare X-raysfor all the X-ray sources. The X-ray temperatures and absorptions of class Isources are generally larger than those of class II and III sources. Also X-rayflares from class I sources show a hint of higher duty ratio, temperature andluminosity, than those from more evolved classes. We further give brief resultson brown dwarfs, younger phase than class I, unclassified and unidentifiedsources. Details for several selected young stellar objects, including thefirst detection of a neutral iron line (6.4 keV) from a class I source YLW 16A,are separately addressed.Comment: 16 pages, 14 figures, 4 tables, accepted for publication in ApJ. High resolution image of figure 1 is available at ftp://ftp-cr.scphys.kyoto-u.ac.jp/pub/crmember/kensuke/Chandra/RhoOph/Paper1/ figure1.ep