The circumstellar CO emission of RV bootis - Evidence for a Keplerian disk?

We report on high-resolution CO J=1-0 and J=2-1 interferometric observation s of the oxygen-rich semiregular variable RV Boo supplemented by single-dis h multi-transition data of CO(J=1-0, 2-1, 3-2, 4-3). Detections of the ther mal SiO(v=0, J=2-1, 3-2) transitions as well as the vibrationally excited S iO(v=1, J=2-1) line are also reported. The interferrometric CO J=2-1 observ ations, with a spatial resolution of about 1 ".7, reveal a disk-like struct ure of size 4 ".2 x 3 ".3 around RV Boo. Furthermore, the position-velocity information along a line through the center of the source at a position an gle of about 150 degrees can be interpreted as a sign of Keplerian rotation . Six symmetrically placed features, possibly corresponding to three rings, around a central feature are seen. These observations may therefore, to ou r knowledge, present the first indications of a rotating disk around an AGE star. However, it cannot be fully excluded that the observed kinematical s tructure is caused by a bipolar outflow. From the single-dish CO observatio ns we estimate the molecular mass of the source to be 3 x 10(-5) M-..