Wind Roche-Lobe overflow: a new mass-transfer mode for wide binaries

Most symbiotic binaries consist of an evolved giant star and a hot, accreting companion, typically a white dwarf. In wide symbiotic binaries, the companion may accrete part of the wind emitted by the giant by Bondi-Hoyle accretion. Here we present preliminary simulations of a new mass-transfer mode - wind Roche-lobe overflow (RLOF) - that can occur when the wind acceleration region of the evolved star occurs at several stellar radii (as, e.g., in Mira variables). If this region is relatively close to the Roche-lobe, wind material fills the giant's Roche-lobe and is transferred to the hot component through the inner Lagrangian point (similar to standard RLOF). We show that the accretion rate can be 100 times larger than the rate expected from standard Bondi-Hoyle accretion. Furthermore, mass loss from the system tends to be strongly concentrated towards the binary plane, producing an equatorial outflow. We discuss the implications of this study for the shaping of planetary nebulae, for symbiotic binaries as potential type la supernova progenitors and for the origin of barium stars