First VLBI synthesis observations of the excited-state OH emission sources at 4765 MHz in W3 (OH).
Abstract
The 2π1/2 J = 1/2, F = 1 - 0 (4765.562 MHz) excited state OH emission from W3(OH) has been observed with four telescopes of the European VLBI network and successfully mapped with a three-element interferometer (Effelsberg-Westerbork Array-Jodrell Bank) having 0arcsec.018 resolution. The maps show three groups of sources with mean separation of the order of 0arcsec.9 to 1arcsec within a region whose total extent is roughly 1arcsec i.e. 0.011 pc at the 2.2 kpc distance of W3(OH). From the observed sizes of the sources the authors derive an apparent brightness temperature ⪆7×108K corresponding to a maser gain exceeding 105. The general properties of the 4765 MHz maser are similar to those of other OH transitions although it is the only OH maser without measurable polarization.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 1988
- Bibcode:
- 1988A&A...201..105B
- Keywords:
-
- Emission Spectra;
- Hydroxyl Emission;
- Interstellar Masers;
- Spatial Distribution;
- Very Long Base Interferometry;
- Ammonia;
- Brightness Temperature;
- O Stars;
- Star Formation;
- Astronomy