U Orionis: the evolution and proper motion of the OH maser envelope
Open Access
- 15 March 1991
- journal article
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 249 (2) , 227-240
- https://doi.org/10.1093/mnras/249.2.227
Abstract
The Jodrell Bank MERLIN array was used to map the OH 1665- and 1667-MHz masers in the circumstellar envelope of U Orionis in 1984, 1986 and 1987. The OH masers lie within a region of extent 130 × 180 AU2, and have complex distributions which are different for each line and polarization. The masers show clumpy structures with a typical clump size of ~ 25 AU. The strongest emission is from a ring of radius 60 AU which is interpreted as part of an expanding, tilted torus. The ring has a proper motion of 5.4 ± 1.4 mas yr–1 corresponding to a transverse expansion velocity of ~ 7 km s–1 for the period–luminosity distance to U Orionis of 260 pc. This expansion velocity is also indicated by a compact blueshifted maser spot which lies near the projected stellar position. OH maser emission is also detected from a redshifted filament which appears to project over a considerable radial depth in the envelope and varies in intensity in an erratic fashion.Keywords
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