Mon. Not. R. Astron. Soc., 417, 555-566 (2011/October-2)
Flares and proper motions of ground-state OH masers in W75N.
FISH V.L., GRAY M., GOSS W.M. and RICHARDS A.M.S.
Abstract (from CDS):
The star-forming region W75N hosts bright OH masers that are observed to be variable. We present observations taken in 2008 of the ground-state OH maser transitions with the Very Long Baseline Array and the Multi-Element Radio-Linked Interferometer Network and with the Nanay Radio Telescope in 2011. Several of the masers in W75N were observed to be flaring, with the brightest 1720-MHz maser in excess of 400 Jy. The 1720-MHz masers appear to be associated with the continuum source VLA 1, unlike the bright flaring 1665- and 1667-MHz masers, which are associated with VLA 2. The 1720-MHz masers are located in an outflow traced by water masers and are indicative of very dense molecular material near the H II region. The magnetic field strengths are larger in the 1720-MHz maser region than in most regions hosting only main-line OH masers. The density falls off along the outflow, and the order of appearance of different transitions of OH masers is consistent with theoretical models. The 1665- and 1667-MHz VLBA data are compared against previous epochs over a time baseline of over 7 years. The median maser motion is 3.5 km/s with a scatter that is comparable to thermal turbulence. The general pattern of maser proper motions observed in the 1665- and 1667-MHz transitions is consistent with previous observations.
2011 The Authors Monthly Notices of the Royal Astronomical Society2011 RAS
magnetic fields - masers - stars: formation - ISM: individual objects: W75N - ISM: kinematics and dynamics - radio lines: ISM