How do red giants respond to mass loss?

Abstract

Many interacting binaries start their mass exchange when a donor overfilling its Roche lobe has evolved to a giant branch. The response of the donor's radius to the mass loss as compared to the response of its Roche lobe determines the fate of the binary system – whether it will proceed with a stable mass transfer, or experience dramatic common envelope event. Recent studies of responses of realistic giant's stellar models to a fast mass loss showed that this response is not purely adiabatic as previously thought but depends on the behavior of giant's superadiabatic surface layer. In this contribution, we explore in further details how an interplay between superadiabatic layer's thermal timescale and the dynamic timescale of the donor affects the donor's mass loss. We also find that the initiation of the mass loss causes mass loss induced pulsations.