Observations of the 6 Centimeter Lines of OH in OH/IR Stars and Star Forming Regions

Details Observations of the 6 Centimeter Lines of OH in OH/IR Stars and Star Forming Regions Observations of the 6 Centimeter Lines of OH in OH/IR Stars and Star Forming Regions

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20910111z&link_type=abstract

2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #101.11; Bulletin of the American Astronomical Society,

Astronomy and Astrophysics

Astronomy

Scientific paper

Recent observational and theoretical advances have given rise to ambiguities regarding the model for OH maser pumping in OH/IR stars. While ground-state OH lines have already been observed, the detection of excited-state OH lines would provide additional constraints on theoretical pumping models. To date, the only positive detections of excited-state OH emission in OH/IR stars have been a 4750 MHz maser in AU Gem and 6035 MHz maser emission in NML Cyg.
We report on Very Large Array observations of the 4750 and 4765 MHz OH lines toward 45 sources, most of which are OH/IR stars. All of the sources have previously exhibited ground-state maser emission. We do not detect excited-state emission in any evolved star at the 100 mJy level (5 σ). However, masers in the 4765 MHz transition are detected toward two star forming regions: Mon R2 and LDN 1084. Masers in each of these sources have been previously detected and have shown significant variability in the past. the 4765 MHz maser in Mon R2, which had exhibited two distinct flares, one of which surpassed 75 Jy before disappearing in 1998 December, appears to be undergoing a new flaring event.
The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. L. K. Z. acknowledges support from the NSF Research Experiences for Undergraduates program.

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