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

本研究利用名古屋大学的4米毫米波望远镜对金牛座暗星云复合体致密核的^ CO和C^ O谱进行了无偏观测，并利用完整的数据集对金牛座暗星云复合体致密核的星星形成过程进行了统计研究<13><18>。通过调查，我们获得了密度大于10^3cm^的致密岩心的完整样品<-3>（水野等人，1995;大西等人，1996）。此外，我们还<13>利用野边山射电天文台的45米望远镜对H^ CO^+谱线中密度更大的核心进行了观测。H^ CO^+观测所探测到的这种致密核<13>的密度大于10^4 cm^3<-3>，它们是原恒星凝聚的最佳候选者，即，致密的核心处于重力坍缩形成原恒星之前的阶段。因此，我们将H^<13>CO^+核心归类为最年轻的恒星天体，尽管它们在通常意义上还没有被认为是这样的天体。然后我们发现，C^<18>O核与原恒星凝聚和原恒星，即，C^<18>O核与H^<13>CO^+核和冷红外光谱源的分子柱密度明显高于其他核。通过<18>统计分析，我们得到以下结论：（1）当柱密度达到8.0 × 10^ cm^或更高时，星星的形成无一例外地立即发生<21><-2>;（2）原恒星凝聚在-3 × 10 ^5年内形成原恒星核;（3）新生星星周围的分子气体在大于数 * 10^5年的时间尺度内耗散，其尺度大于0.1 pc。

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.