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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 observations of the oxygen-rich semiregular variable RV Boo supplemented by single-dish multi-transition data of CO(J=1–0, 2–1, 3–2, 4–3). Detections of the thermal SiO(v=0, J=2–1, 3–2) transitions as well as the vibrationally excited SiO(v=1, J=2–1) line are also reported. The interferometric CO J=2–1 observations, with a spatial resolution of about 1. 7, reveal a disk-like structure of size 4. 2× 3. 3 around RV Boo. Furthermore, the position-velocity information along a line through the center of the source at a position angle of about 150 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 our knowledge, present the first indications of a rotating disk around an AGB star. However, it cannot be fully excluded that the observed kinematical structure is caused by a bipolar outflow. From the single-dish CO observations we estimate the molecular mass of the source to be 3 × 10 M .