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The hypergiant masers: episodic mass loss, convection and magnetic fields

Published online by Cambridge University Press:  01 March 2007

Roberta M. Humphreys
Roberta M. Humphreys*
Affiliation:
Astronomy Department, University of Minnesota, Minneapolis, MN 55455, USA
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Abstract

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The cool hypergiants are the most luminous known stars in the upper HR Diagram in the apparent temperature range represented by spectral types A to M. Most of the stars in this regime are unstable as evidenced by their high mass loss rates, variability, and in some cases large IR excesses and circumstellar ejecta. We have obtained high resolution multi-wavelength images with HST/WFPC2 of several of the most known evolved cool stars including several well known stellar masers. VX Sgr and S Per were marginally resolved, while NML Cyg has a peculiar asymmetric envelope that has been shaped by its environment. The powerful maser sources IRC+10420 and VY CMa have extensive and complex circumstellar ejecta due to high mass loss episodes apparently driven by large-scale convective activity.

Keywords

supergiantsstars: windsoutflowsstars: activity
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 3 , Symposium S242: Astrophysical Masers and their Environments , March 2007 , pp. 251 - 255
Copyright
Copyright © International Astronomical Union 2008

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