Molecular clouds on the threshold of star formation: the radial density profile of the cores of the RHO ophiuchi and R coronae australis clouds
Molecular clouds on the threshold of star formation: the radial density profile of the cores of the RHO ophiuchi and R coronae australis clouds
复制标题
恒星形成临界点的分子云：蛇夫座 RHO 和澳大利亚日冕云 RHO 核心的径向密度剖面
DOI：
10.1086/161153
复制
发表时间：
1983
期刊：
影响因子：
--
通讯作者：
A. Wootten
中科院分区：
文献类型：
--
作者：
R. Loren;A. Sandqvist;A. Wootten
在缺乏嵌入大质量恒星的寒冷、致密、动态演化的云核中，密度分布应该反映恒星形成门槛处的云演化阶段。根据两次H/SUB_2/CO跃迁的广泛地图，已经确定了位于最近恒星形成的两个邻近区域内的三个这样致密的质量核心的径向密度分布。2厘米谱线发射和吸收图的出现证实了模型对这一跃迁激发的预测。详细的H/SUP2/CO辐射输运模型表明，密度Rho(R)成比例R/sup-3//sup/sup 2/to R/sup-2/，从核心的10/sup 6/cm/sup-3/到包层中的10/sup 4/cm/sup-3/，在0.06到0.60pC的径向距离上发生了快速的径向下降。这些模型要求H/SUB_2/CO丰度随着这些冷核中密度的增加而降低，这可能是气体凝聚到颗粒上的结果。对于核心半径(0.06-0.09 pC)和核心质量(19-110米/次太阳/)的观测值，H/SUB 2/CO谱线宽度表明，由于旋转或湍流引起的速度色散太小，不足以稳定星云免受引力崩塌的影响。更重要的是，观测到的磁场强度似乎也不足以防止星云收缩和最终形成恒星。不寻常的2cmH/sub2/CO向Rho Oph B的发射在空间上被扩展(8‘x 4’)。从这个寒冷致密的(>；10/sup 6/cm/sup-3/)区域缺乏远红外发射表明缺乏嵌入在云层表面或附近的高光度恒星。在一个中央凝聚区的冷的、非常稠密的气体，再加上缺乏内部支持，意味着在Rho Oph B内，已经为可能形成一颗或多颗大质量原恒星奠定了基础。
In a cold, dense, dynamically evolved cloud core that lacks embedded massive stars, the density distribution should reflect a stage of cloud evolution at the threshold of star formation. The radial density distribution in three such dense massive cores, located within two nearby regions of recent star formation, has been determined from extensive maps of two H/sub 2/CO transitions. The appearance of the maps of emission and absorption of the 2 cm line confirms the predictions of models for the excitation of this transition. Detailed models of the H/sub 2/CO radiative transport demonstrate that a rapid radial decline of density, rho(R)proportionalR/sup -3//sup ///sup 2/ to R/sup -2/, from a density of 10/sup 6/ cm/sup -3/ in the core to 10/sup 4/ cm/sup -3/ in the envelope, occurs over radial distances from 0.06 to 0.60 pc. These models require a decline in H/sub 2/CO abundance with increasing density in these cold cores, perhaps a result of condensation of gas onto grains. For the observed values of core radius (0.06-0.09 pc) and core mass (19-110 M/sub sun/), the H/sub 2/CO line widths indicate that the velocity dispersion due to rotation or turbulence is too small to stabilize the cloud against gravitational collapse.more » The observed magnetic field strength also apears to be inadequate to prevent cloud contraction and eventual star formation. The unusual 2 cm H/sub 2/CO emission toward rho Oph B is found to be spatially extended (8' x 4'). The lack of far-infrared emission from this cold dense (>10/sup 6/ cm/sup -3/) region indicates a lack of stars of high luminosity embedded within or near the surface of the cloud. The combination of cold, very dense gas in a centrally condensed region together with a lack of internal support means that within rho Oph B the stage has been set for the possible formation of one or more massive protostars.« less