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Colloquium Today:'Methanol masers and millimetre lines: a common origin in protostellar envelopes'

Submitter: Colloquium
Description: The 6.7 GHz methanol maser is only associated with the earliest stages of high-mass star formation and can be used as signposts of these regions. However, it is not clear what physical structures the methanol maser trace and whether they trace a specific mass range and/or evolutionary sequence. We have found that in several sources the methanol maser emission appear to arise equatorial region of the protostar. Moreover, the velocity field of the maser spots suggests that the dominant motion is that of infall rather than rotation.

In an effort to shed more light on this we have mapped the distribution and excitation of the thermal methanol gas by observations of the J=7-6 band at 338 GHz towards a sample of 15 high-mass star-forming regions associated with 6.7 GHz methanol masers. We compare the large scale distribution and velocity field of the thermal methanol gas to that of the maser emission.

Half of the sources have compact thermal methanol gas distributions and linear velocity fields along the major axis suggest that the gas is entrained in outflows. Furthermore, the highest rotation temperatures are found close to the maser position, indicated the location of the high excitation gas. Although the statistics are poor, we find that the large scale velocity gradients seen in the thermal methanol gas is roughly perpendicular to the maser structures.
Copyright: Kalle Torstensson
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