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The Australia Telescope National Facility Colloquium
11:00-12:00 Fri 09 Sep 2005

ATNF Marsfield Lecture Theatre

Dr Michael Burton

(University of New South Wales)

Uncovering the earliest stages of massive star formation - Dr Michael Burton Colloquium

Rapidity, obscuration, rarity and overlapping evolutionary phenomena
all serve to make the study of the earliest stages of massive star
formation (MSF) both intriguing as well as challenging. We report on a program at UNSW to investigate the earliest stages of the MSF process using a variety of infrared and millimetre-wave techniques. Our study has focussed on prospective sites of massive star formation selected through the signature of methanol maser emission. Millimetre dust emission always accompanies such maser sites and arises from molecualr cores whose mass ranges from a few 100 to a few 1,000 Msun, and likely to represent a massive protostellar cluster. Accompanying these cores are additional cores which are less massive
Whether these represent cores which are forming lower mass stars, or
cores in which star formation is not (yet) occurring, remains to be
determined. A survey for hot core molecular lines from a selection of
the methanol-maser emitting cores shows that ~100K CH3CN emission is
common, indicating internal heating sources when the core is isolated.
CH3CN emission is, however, more prevalent in cores associated with
UCHII regions than those without, suggesting an evolutionary sequence
as the core warms up as a protostellar source switches on in its
interior and begins to evaporate ices from the grains. Examination of selected cores in the mid-IR, at sub-arcsecond resolution in order to identify possible protostellar sources, not only finds such sources, but also shows a multiplicity of sources present, at projected separations of a few thousand AU. These most-luminous members of the proto-clusters also cannot be distributed with a Salpeter-like IMF - there are too many massive sources present in the core.

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Kate Brooks

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