红外暗云G79.2+0.38的性质

Properties of Infrared Dark Cloud G79.2+0.38

对MSX红外暗云G79.2+0.38的11'×7'的区域范围进行了12CO(1-0)、13CO(1-0)和C18O(1-0)谱线的同时观测.观测到的两个C18O(1-0)谱线所界定的云核峰值分布分别对应MSX A波段的两块高消光区域.该区域的氢分子柱密度N(H2)-(5-12)×1022 cm-2,平均密度n-(3±1)×104cm-3.两块分子云核的13CO的线尺度分别是1.7和1.2 pc,而C18O的线尺度分别是1.2和0.6 pc,它们包含的质量为2×102-2×103M(?).分子云核的视向平均密度结构可用幂函数(?)(p)-p-0.34±0.02表征. 13CO和C18O的丰度和典型的光学暗云相比低了4至11倍,但是目前还没有证据表明13CO和C18O的相对丰度比X13/18随柱密度有显著变化.

The MSX infrared dark cloud, G79.2+0.38, has been observed over a region of 11'× 7' in the J = 1 - 0 rotational transition lines of 12COand its isotopic molecules, 13COand C18O. Dense molecular cores are found to be associated with the two high extinction patches shown in the band-A MSX image. The two dense cores have column density N(H2) - (5 - 12) × 1022cm-2 and average number density n- (3 ±1)×104cm-3. Their sizes are 1.7 and 1.2pc in 13CO, and 1.2 to 0.6pc in C18O, respectively. The masses of the two cloud cores are estimated to be in the range of 2×102 to 2×103 M(?). The mean density profile fits in a power low distribution of (?)(p) - p-0.34±0.02.CO isotopic molecules, 13CO and C18O, appear to be depleted by a factor of 4 - 11 in the MSX IRDCs compared with the cases of typical optical dark clouds, but, by present data, there is no obvious evidence for the variation of abundance ratio X13/18 of 13CO to C18O over the clouds.