Masers High resolution probes of massive star formation.pdf

a r X i v : a s t r o - p h / 0 3 0 9 7 1 9 v 1 2 6 S e p 2 0 0 3 Star Formation at High Angular Resolution ASP Conference Series, Vol. S-221, 2003 R. Jayawardhana, M.G. Burton, T.L. Bourke Masers : High resolution probes of massive star formation S P Ellingsen School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart 7001, TAS, Australia Abstract. Astrophysical masers are one of the most readily detected signposts of high-mass star formation. Their presence indicates special conditions, probably indicative of a specific evolutionary phase. Masers also represent the ultimate high-resolution probe of star formation with the potential to reveal information on the kinematics and physical con- ditions within the region at milli-arcsecond resolution. To date this po- tential has largely remained unfulfilled, however, recent advances suggest that this will soon change. The key to unlocking the potential of masers lies in identifying where they fit within the star formation jigsaw puzzle. I will review recent high resolution observations of OH, water and methanol maser transitions and what they reveal. I also briefly discuss how multi-transition observations of OH and methanol masers are being used to constrain maser pumping models and through this estimate the physical conditions in the masing region. 1. Introduction Masers are one of the most readily observable signposts of massive star formation and they possess characteristics that mean they have the potential to be very powerful high-resolution probes of these regions. Towards massive star forming regions strong masers are frequently observed from the main-line transitions of OH (Caswell, Haynes Goss 1980), the 22 GHz transition of H2O (Comoretto et al. 1990) and the 6.7 GHz (Menten 1991) and 12.2 GHz (Batrla et al. 1987) transitions of methanol. They are more rarely observed from SiO (see Greenhill et al. these proceedings), H2CO (Hoffman et al. 2003) and NH3 (Mauersberger Wilson Henke