X-ray Study of Low-mass Young Stellar Objects in the ρ Ophiuchi ...

86 CHAPTER 6. INDIVIDUAL SOURCESthat A-31 is surely associated with KSHK-A. The chance probability to detect a background AGNin the KSHK-A region is only ∼0.2 %. Furthermore, A-31 exhibits variable X-rays typical oflow-mass YSOs. The column density of KSHK-A is ∼10 24 cm −2 (Kamazaki et al., 2001), whichis about twice of the X-ray determined N H of A-31 (∼ 5×10 23 cm −2 ). Thus A-31 would be aYSO embedded near the center of the compact core KSHK-A. KSHK-A is spatially coincidentwith a 6 cm continuum source LFAM6 (Leous et al., 1991), which may be produced by a shockof outflow from a putative protostar (e.g., Rodriguez et al.1989, and references theirin). No NIRcounterpart with K < 15 mag, its close location at the compact core center KSHK-A, the largeabsorption (∼5×10 23 cm −2 ), and the presence of the 6 cm enhancement indicate that A-31 is astrong candidate of X-ray emitting class 0.A northwest part of the CO molecular outflow from the class 0 VLA1623 (designated as E–Hin Yu, & Chernin 1997) is not aligned to the central part (B–D) but is slightly shifted to the northdirection pointing to A-29 and A-31 (Figure 6.21). We speculate that the origin of the outflowE–H is A-29 or A-31 (not from VLA1623), although there is no CO emission at their closer vicinity(Kamazaki et al., 2001).Fig. 6.21.— 12 CO (J=1–0) map aroundVLA1623 (Yu, & Chernin, 1997). Filledsquares represent the positions of A-29 andA-31.BF-36BF-36 is located in the 850 µm clump SMM J16272−2430 with about 30 ′′ separation from its center.It lies in an elongated 1.3 mm core chain with local peaks of B1-MM2, 3, and 4 (Motte et al., 1998).The source is about 30 ′′ south of the peak of B1-MM4 (Figure 6.18). The chance probability ofbackground AGN to be associated within 30 ′′ radius from the core center is ∼20 %. However,BF-36 is among the brightest unidentified sources and is very unique which exhibits a clear flare.We therefore suggest that BF-36 is also a cloud member embedded near the dense core B1-MM4.Since millimeter/sub-millimeter peak fluxes of B1-MM4/SMM J16272−2430 are about ten timesfainter than those harbor A-29 and A-31, although the clump size is comparable (6200 AU), the2–6 times smaller N H of BF-36 (9×10 22 cm −2 ) than those of A-29 and A-31 is consistent with the