A search for water and mainline masers in OH/IR star mimics with strong silicate emission features
Abstract
IRAS sources with a strong 9.7-μm silicate emission feature have a low-resolution spectral type of 28 or 29, and appear to be associated with oxygen-rich circumstellar shells. Yet ~=40 per cent of those searched at Arecibo for 1612-MHz emission have none, despite red IR colours, (25-12) mu>-0.55, that point to a thick shell. We report on a water and mainline OH maser search of a complete sample of these OH/IR star colour mimics, where we find seven new water and five new mainline masers. In aggregate, just 10/60 (17 per cent) of this sample are without any kind of detected maser. The frequency of water and mainline masers in these mimics is about half that in OH/IR stars with the same colour, a result that independently confirms that the shells of mimics are in some way different from those of OH/IR stars. Combining these results with other work on the incidence of masers in O-rich shells, we suggest that the percentage of maserless shells increases from ~=11 to ~=25 per cent at (25-12) mum=-0.5.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 1995
- DOI:
- 10.1093/mnras/274.2.439
- Bibcode:
- 1995MNRAS.274..439L
- Keywords:
-
- MASERS;
- STARS: AGB AND POST-AGB;
- CIRCUMSTELLAR MATTER;
- STARS: LATE-TYPE;
- INFRARED: STARS;
- RADIO LINES: STARS