AAS 199th meeting, Washington, DC, January 2002
Session 134. Formation of Massive Stars
Display, Thursday, January 10, 2002, 9:20am-4:00pm, Exhibit Hall

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[134.19] OH Masers in the High Excitation 6cm Line Observed with the VLBA

K. E. Devine (Carleton College), W. M. Goss (NRAO), P. Palmer (University of Chicago)

Results are presented from VLBA observations of OH 4765-MHz masers in the star-forming regions of W3(OH) and K3-50. OH masers at 4765-MHz appear to be correlated with star forming regions and can be among the strongest masers in a region. Existing models explaining the pumping mechanisms of the excited state maser lines of OH propose that 1720-MHz masers and 4765-MHz masers will arise in the same gas. In W3(OH), three regions of maser emission were detected. In K3-50, one region of maser emission was detected. Results are compared to existing data of nearby maser emission at 1720-MHz when available. These observations seek to improve existing models explaining excited state OH maser emission using the high angular resolution possible with the VLBA. With high angular resolution and phase-referenced data, it is possible to obtain accurate absolute positions for the observed masers in W3(OH) and K3-50. Using MERLIN data obtained by Gray et al. (2001) for 1720-MHz masers in W3(OH), spatial coincidence is shown between observations of 4765-MHz masers and the 1720-MHz masers observed by Gray et al. It appears that no 1720-MHz masers in K3-50 exist near the observed 4765-MHz maser, in contrast to existing models of 4765-MHz maser emission. Angular sizes of 4765-MHz masers are also investigated and, when possible, compared to angular sizes of coincident 1720-MHz masers. Larger angular sizes of 4765-MHz masers suggest unsaturated masers at this frequency. Finally, circular polarization in the observations is examined. Theory indicates that no circular polarization should be observed in OH emission at 4765-MHz; however, existing upper limits on observed circular polarization for this maser line are fairly high. Although the circular polarization of our observations is still currently being investigated, out current upper limit on observed circular polarization from this state is ~ 6 %.

The author(s) of this abstract have provided an email address for comments about the abstract: devinek@carleton.edu

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