Embedded Young Stellar Cluster IRAS 20160+3636 in the Gas Shell of the Expanding HII Region Sh 104

摘要

A young stellar cluster, IRAS 20160+3636, is deeply embedded in the dense molecular cloud in the eastern periphery of the gas ring around the optically visible HII region Sh 104. We investigate the characteristics of the UC HII region, the embedded cluster, and the dense molecular gas containing this young stellar cluster. The star formation in this region has been suggested to be triggered by the "collect and collapse" process. This UC HII region has a greater size, a lower electron density (～ 1.4 x 103 cm-3), and a smaller emission measure (~ 4 x 105 pc cm-6) than the typical UC HII regions. The spectral type of the ionizing star is found to be B0.5. We derive the age of this embedded young cluster ~ 0.5 - 1 Myr and a total mass ~ 175 Mo. The molecular cloud, contaimng IRAS 20160+3636, has a mass ~ 1- 2 x 103 Mo with a mean density ~ 1 - 2 x 103 cm-3. The star formation efficiency ~ 10 - 20％， which is close to the values found in the Galactic molecular clouds. We found the CN to HCN abundance ratio ~ 1 - 2 over the whole molecular cloud, which may suggest that the molecular cloud is under the effect of PDR, resulted from the interaction with expanding HII region.