Efficient common-envelope ejection through dust-driven winds

Abstract

Common-envelope evolution (CEE) is the short-lived phase in the life of an interacting binary system during which two stars orbit inside a single shared envelope. Such evolution is thought to lead to the inspiral of the binary, the ejection of the extended envelope, and the formation of a remnant short-period binary. However, detailed hydrodynamical models of CEE encounter major difficulties. They show that following the inspiral most of the envelope is not ejected; though it expands to larger separations, it remains bound to the binary. Here we propose that dust-driven winds can be produced following the CEE. These can evaporate the envelope following similar processes operating in the ejection of the envelopes of AGB (Asymptotic Gian Branch) stars. Pulsations in an AGB star drive the expansion of its envelope, allowing the material to cool down to low temperatures thus enabling dust condensation. Radiation pressure on the dust accelerates it, and through its coupling to the gas it drives winds that eventually completely erode the envelope. We show that the inspiral phase in CE binaries can effectively replace the role of stellar pulsation and drive the CE expansion to scales comparable with those of AGB stars, and gives rise to efficient mass-loss through dust-driven winds.