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

这项研究的目的是基于金牛座暗云复合体致密核的完整数据集，对恒星形成过程进行统计研究。我们使用名古屋大学的4米毫米波望远镜对整个金牛座地区的致密核进行了无偏测量。通过调查，我们获得了密度大于10^3 cm^-3&gt；的致密岩心的完整样本(Mizuno等人，1995，Onishi等人，1996)。此外，我们还用野山射电天文台的45米望远镜对H^&lt；13&gt；CO^+谱线上密度更高的核进行了测量。H^&lt；13&gt；CO^+观测探测到的这种致密核心的密度大于10^4 cm；-3&gt；，它们是原恒星凝聚的最佳候选者，即处于引力塌缩形成原恒星之前的致密核心。因此，我们将H^&lt；13&Gt；CO^+核心归类为最年轻的恒星天体，尽管它们还不被认为是通常意义上的此类天体。然后我们发现，具有原星凝聚和原星的C^&lt；18&gt；O核，即分别具有H^&lt；13&gt；CO^+核和冷IRAs源的C^&lt；18&gt；O核，其分子柱密度明显高于其他核。从统计研究中我们得到以下结论：(1)恒星的形成无一例外地立即发生，当柱密度达到8.0*10^&lt；21&gt；-2&gt；或更高时，(2)原恒星凝聚将在-3*10^5年内形成原恒星核；(3)新生恒星周围尺度为&gt；=0.1pC的分子气体在&gt；几个*10^5年的时间尺度内消失。

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.