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K. B. Marvel (American Astronomical Society), D. Boboltz (USNO)
We present the first VLBI observations of the water masers associated with the evolved star OH12.8-0.9. We suspect that this source is a member of a class of evolved star dubbed ``water fountain" sources due to their unusual H2O maser characteristics. There are three confirmed sources of this type, W43A, IRAS 16342-3814 and IRAS 19134+2131. These objects have both OH and H2O maser emission with a much wider velocity spread than that found in most AGB stars showing maser emission. Typical velocity ranges for the water fountain sources are larger than 100 km s-1 as compared to a spread of rougly 30 km s-1 typically found in evolved stars. Interestingly, VLBI observations of W43A (Imai et al., 2002, Nature 417:289) showed a set of axisymmetric precessing jets of water masers. This jet phenomenon is likely an early stage of the transformation from the spherical symmetry of an evolved star to the axisymmetric structure found in many planetary nebula. OH12.8-0.9 has a wider than normal velocity range, but not as large as the W43A source. We suspect that this source represents the earliest onset of axisymmetric jets in the water fountain sources.
The author(s) of this abstract have provided an email address for comments about the abstract: marvel@aas.org
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.