| Research Abstract |
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.
|
