EPoS Contribution
EPoS Contribution
Different evolutionary stages of Massive star formation

Yuan Wang
U Geneva, Geneva, CH
The formation and early evolution of high-mass stars are still poorly understood. Our SMA observations towards three high-mass star-forming regions in the W3 high-mass star formation complex show these regions, i.e., W3 SMS1 (W3 IRS5), SMS2 (W3 IRS4) and SMS3, are in different evolutionary stages and are located within the same large-scale environment. While we find multiple millimeter continuum sources toward all regions, these three subregions exhibit different dynamical and chemical properties, which indicate that they are in different evolutionary stages. Even within each subregion, massive cores of different ages are found, e.g., in SMS2, sub-sources from the most evolved ultracompact HII region to potential starless cores exist within 30,000 AU of each other. Evidence for interactions between the molecular cloud and the H ii regions is found in the 13CO channel maps, which may indicate triggered star formation. With the similar concept in mind, we also observed high mass complex S255 and S235, try to understand the eraly evolution of high-mass stars better.
Caption: Left: The top left shows the 6 cm VLA continuum image (Tieftrunk et al. 1997), and the rest of the panels show the single-dish 13CO(2--1) channel map with the spectral resolution of 1.2 km/s of the W3 Main complex. The crosses mark the position of the SMA continuum sources SMS1-MM1, SMS2-MM2, SMS3-MM1, and SMS3-MM2.The three circles/ellipses outline the approximate position and size of the three H ii regions, W3 A, H, and D (Tieftrunk et al. 1997). The channel map shows that the molecular cloud forms circle-like structures with velocity gradients around the Hii regions W3 A, H, and D. Furthermore, the young stellar objects (YSOs) and potential starless cores of the SMS1, SMS2, and SMS3 regions are located close to the edge of the H ii regions. These facts together indicate that the H ii regions may have even triggered the star formation in these subregions. Right: We zoom into W3 SMS2 region, the figure shows DCN(3-2) line integrated intensity images and the VLA 22.5 GHz continuum overlaid on the SMA dust continuum emission in the background. Filled triangles mark the millimeter sources detected. MM2 is associated with HCHII region W3 Ca and outflow. MM4, MM5, and MM6 is associated with UCHII region W3 C. MM1, MM3, and MM7 are associated with DCN emissions and are considered to be potential massive starless cores.
Collaborators:
H. Beuther, MPIA, Germany
M. Audard, UniGE, Switzerland
Q. Zhang, CfA, USA
F. Fontani, INAF, Italy
A. Bik, MPIA, Germany
J. Rodon, ESO, Chile
Z. Jiang, PMO, China
C. Fallscheer, U Victoria, Canada
Key publication

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