Expanding Shell and Star Formation in the Infrared Dust Bubble N6
  We have carried out a multi-wavelength study of the infrared dust bubble N6 to extensively investigate the molecular environs and star-forming activities therein. Mapping observations in 12CO J=1-0 and 13CO J=1-0 performed with the Purple Mountain Observatory 13.7-m telescope have revealed four velocity components. Comparison between distributions of each component and the infrared emission suggests that three components are correlated with N6. There are ten molecular clumps detected. Among them, five have reliable detection in both 12CO and 13CO and have similar LTE and non-LTE masses ranging from 200 to higher than 5,000 M_sun. With larger gas masses than virial masses, these five clumps are gravitationally unstable and have potential to collapse to form new stars. The other five clumps are only reliably detected in 12CO and have relatively small masses. Five clumps are located on the border of the ring structure and four of them are elongated along the shell. This is well in agreement with the collect and collapse scenario. The detected velocity gradient reveals that the ring structure is still under expansion due to stellar winds from the exciting star(s). Furthermore, 99 young stellar objects have been identified based on their infrared colors. A group of YSOs reside inside the ring, indicating active star formation in N6. Although no confirmative features of triggered star formation detected, the bubble and the enclosed HII region have profoundly reconstructed the natal could and altered the dynamics therein. 
Jing-Hua Yuan (1), Yuefang Wu (2), Jin Zeng Li (1), and Hongli Liu (1)   ((1) NAOC, (2) PKU)
astro-ph.SR