Speaker
Description
RV Tauri stars are pulsating post-AGB binaries. In addition to their pulsations, many of them show long-term brightness variations known as the RVb phenomenon. This variability is usually explained as variable obscuration of the central binary by a circumbinary disk, but the required binary–disk geometry has not been directly imaged in detail. I will present high-angular-resolution CHARA interferometric observations of RV Tau, U Mon, and AC Her. These observations resolve the inner binary systems and allow us to combine interferometric astrometry with radial velocities to determine their three-dimensional orbits. For RV Tau, we resolve a circumbinary disk whose orientation is consistent with the binary orbit. This geometry explains the RVb variability: as the post-AGB star moves around the orbit, its light passes through different parts of the inclined disk, producing the observed long-term modulation. For U Mon and AC Her, we also resolve compact emission around the companion stars, which we interpret as circum-companion disks. These disks are likely linked to accretion onto the companions and may be connected to jet launching in these systems. Together, these observations show how long-baseline interferometry can directly test the binary–disk picture for RV Tauri and related post-AGB systems.