Journal Article

Flares and proper motions of ground-state OH masers in W75N

Vincent L. Fish, Malcolm Gray, W. M. Goss and A. M. S. Richards

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 1, pages 555-566
Published in print October 2011 | ISSN: 0035-8711
Published online October 2011 | e-ISSN: 1365-2966 | DOI:
Flares and proper motions of ground-state OH masers in W75N

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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 Nançay 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−1 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.

Keywords: magnetic fields; masers; stars: formation; ISM: individual objects: W75N; ISM: kinematics and dynamics; radio lines: ISM

Journal Article.  7071 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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