Spinning-up the Envelope before Entering a Common Envelope Phase

We calculate the orbital evolution of binary systems where the primary star is an evolved red giant branch (RGB) star, while the secondary star is a low mass main sequence (MS) star or a brown dwarf. The evolution starts when a tidal interaction causes the secondary to spiral-in. Either a common envelope (CE) is formed in a very short time, or the system reaches synchronization and the spiraling-in process substantially slows down. Some of these systems later enter a CE phase. We find that for a large parameters space, binary systems reach stable synchronized orbit before the onset of a CE phase. Such stable synchronized orbits allow the RGB star to lose mass prior to the onset of the CE phase. Even after the secondary enters the giant envelope, the rotation velocity is high enough to cause enhanced mass loss rate. Our results imply that it is crucial to include the pre-CE evolution when studying the outcome of the CE phase. Although we have made the calculations for RGB stars, the results have implications for other evolved stars that interact with close companions.