A statistical study of the evolution of molecular dense cores with high density tracer molecular spect

本研究的目的是基于金牛座暗云复合体致密核心的完整数据集，对恒星形成过程进行统计研究。利用名古屋大学的4米毫米波望远镜，对整个金牛座地区^< 13b> CO和C^< 18b> O光谱的致密核进行了无偏观测。通过调查，我们获得了密度大于10^3cm^<-3>的致密岩心的完整样本（Mizuno et al.1995, Onishi et al.1996）。此外，我们还利用野山射电天文台的45米望远镜在H^<13>CO^+光谱线上对密度更大的核心进行了调查。由H^<13>CO^+观测到的这种致密核的密度大于10 ^4 cm^<-3>，它们是原恒星凝聚的最佳候选者，即处于引力坍缩形成原恒星之前的一个阶段的致密核。因此，我们将H^<13>CO^+核心分类为最年轻的恒星物体，尽管它们还没有被认为是通常意义上的这样的物体。然后我们发现，C^<18>O核与原恒星凝聚，即C^<18>O核与H^<13>CO^+核和冷IRAS源分别具有明显高于其他的分子柱密度。这些C^<18>的核也往往是巨大的，尺寸更大。从统计研究中，我们得到以下结论：(1)恒星无一例外地立即形成，当柱密度达到8.0 * 10^<21> cm^<-2>或更高时，(2)原恒星在- 3 * 10^5 yr内凝结形成原恒星核心，(3)新生恒星周围>=0.1 PC的分子气体在>数* 10^5 yr的时间尺度内耗散。

The aim of this research is to make statistical studies of star formation process based on the complete dataset of dense cores in the Taurus dark cloud complex.We made an unbiased survey for dense cores toward whole the Taurus region in the ^<13>CO and C^<18>O spectra with the 4 meter millimeter-wave telescope at Nagoya University. Through the survey, we obtained a complete sample of dense cores with the density greater than 10^3cm^<-3> (Mizuno et al.1995, Onishi et al.1996). In addition, we made a survey for much denser cores in the H^<13>CO^+ spectral line with the 45 meter telescope at Nobeyama Radio Observatory. Such dense cores detected by the H^<13>CO^+ observations have the density greater than l0^4 cm^<-3>, and they are the best candidates of protostellar condensations, i.e., dense cores that are in a phase just prior to gravitationally collapse forming a protostar. Thus, we classified the H^<13>CO^+ cores as the youngest stellar objects, although they are not yet considered as such objects in a usual sense. Then we found that C^<18>O cores with the protostellar condensations and protostars, i.e., C^<18>O cores with the H^<13>CO^+ cores and cold IRAS sources, respectively, have clearly higher molecular column density than the rest. These C^<18>O cores also tend to be massive and larger in size.From the statistical studies, we obtained the following conclusions ; (1) star formation takes place immediately without exception, when the column density becomes 8.0 * 10^<21> cm^<-2> or higher, (2) protostellar condensation will form a protostellar core in - 3 * 10^5 yr, (3) molecular gas around the new-born star with the size scale of>=0.1 pc is dissipated in a time scale of>several * 10^5 yr.