A CIRCUMBINARY RESERVOIR AROUND BM GEMINORUM

We report the detection of both (J = 1-0) and (J = 2-1) CO emission fr om the oxygen-rich circumstellar envelope around a carbon star with an oxygen-rich circumstellar envelope, BM Gem. The line has two distinct components. Unique among mass-losing carbon stars, there is a feature that is much narrower (FWHM similar to 1 km s(-1)) than the ''normal' ' CO emission detected from winds. This narrow feature sits on top of a broader (FWHRM = 15 km s(-1)) line, which is probably the emission f rom the ''normal'' wind. The most plausible interpretation of the narr ow feature is that we are observing emission from a circumbinary reser voir of material, probably in the form of a distorted or puffed-up dis k. We propose that this circumbinary reservoir is composed of oxygen-r ich material left over from a previous phase of mass loss that was tra pped in the system by the action of an as yet undetected companion.