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A. Mizuno, T. Onishi, Y. Fukui (Nagoya U.), NANTEN Team
We carried out an unbiased survey for dense cores toward the Chamaeleon dark cloud complex in the 13CO and C18O (J=1-0) emission with NANTEN 4m millimeter-wave telescope. In this paper, we discuss the star formation activities in the complex in connection with the physical properties of dense cores. Among the three major clouds of the complex, the star formation efficiencies (SFEs) drastically change, i.e., SFEs of Cha I, II, and III are estimated to be 13%, 1%, and 0%, respectively. The SFE of 13% in Cha I is remarkably higher than typical SFE (~ a few percent) observed in the other nearby star forming regions (e.g., 2% in Taurus, Mizuno et al. 1995) except for Rho-Oph main cloud whose SFE is estimated to be ~ 20% (e.g., Lada & Wilking, 1984).
We identified 23 C18O cores, whose typical mass, radius, peak column density, line-width are 22 M\sun, 0.22 pc, 9.7 \times 1021 cm-2, and 0.82 km s-1, respectively. By comparison between the YSO distribution and molecular column density, we revealed that the surface density of CTTSs immediately increases when the column density becomes greater than 1022 cm-2, while that of WTTSs does not show such a trend. It suggests that star formation takes place in the densest parts where the column density is greater than 1022 cm-2 and that the link between TTSs and dense gas disappears as the TTSs evolve to the weak-line phase.
The average physical properties of the C18O cores in Cha I are characterized by (1) high column density, (2) almost virial equilibrium, and (3) high Mcore/Mcloud ratio. The cores in Cha III show the opposite trend, and those in Cha II are in between. Such trends suggest that Cha I is well-evolved or well gravitationally relaxed cloud-core system, which is probably related to the very high star formation activity in the cloud.
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