A Circumbinary Reservoir around BM Geminorum?

Abstract

We report the detection of both (J = 1-0) and (J = 2-1) CO emission from 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 ~ 1 km s-1) than the "normal" CO emission detected from winds. This narrow feature sits on top of a broader (FWHM = 15 km s-1) line, which is probably the emission from the "normal" wind. The most plausible interpretation of the narrow feature is that we are observing emission from a circumbinary reservoir of material, probably in the form of a distorted or puffed-up disk. We propose that this circumbinary reservoir is composed of oxygen-rich material left over from a previous phase of mass loss that was trapped in the system by the action of an as yet undetected companion.