Probing the molecular disk in Y Gem: an AGB star with variable UV emission signifying accretion onto a binary companion

We propose to observe CO J65 and 98 line emission from a cool AGBstar, Y Gem, which, in dramatic contrast to most objects in its class,has relatively strong and variable FUV and NUV fluxes evidence ofvariable accretion of matter onto an accretion disk in a binary system.We found Y Gem as a UV source serendipitously, while combing the GALEXarchive as part of a project to look for hot binary companions to coolAGB stars. This object may represent the earliest phases of an AGB starwith a growing accretion disk which will produce collimated jets thatare widely believed to sculpt the round circumstellar envelopes of AGBstars into bipolar planetary nebulae. It may evolve into a member ofthe class of postAGB objects which show no extended outflows, but onlycircumbinary disks. HIFI observations of highJ CO lines are needed to probe the warmest andinnermost circumstellar regions where the hypothesized accretion diskresides and jet launching may occur. Furthermore, the proposed COobservations, together with our existing CO J21 data, will allow usto accurately constrain the CO excitation temperature, and the opticaldepths of the CO lines and thus the total mass of the emitting region.The disk or torus mass will provide an important constraint on itsformation process (e.g., common envelope evolution or BondiHoylewindaccretion/ Roche lobe overflow.) truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]