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Unbinding the envelope in Grazing Envelope Evolution

Presentation #533.09 in the session “Hidden and Active Binaries”.

Published onJan 11, 2021
Unbinding the envelope in Grazing Envelope Evolution

I am conducting three-dimensional hydrodynamic simulations, showing that when a secondary star launches jets while interacting with a primary giant star in a close orbit, the system can avoid entering common envelope evolution (CEE). Instead of a fast in-spiral, the companion slowly enters the envelope as the jets facilitate the unbinding of the giant star envelope outside the companion orbit, in what is termed grazing envelope evolution (GEE). The assumptions are that the secondary star, a main-sequence star, accretes mass via an accretion disk, and that the accretion disk launches the jets. I am running two sets of simulations with and without jets for different companion masses, maintaining a constant jet power in the former case. I am examining which of the simulated systems undergo a GEE rather than a CEE and how efficiently the jets unbind the envelope. The results indicate that systems with lower mass companions are more likely to result in a phase of GEE, when considering a certain jet power. With the smallest companion, a 0.1 solar mass star, the jets unbind 65% of the envelope mass, while almost none of the envelope is unbound if jets are not present. Most of the unbinding occurs while the companion is in a grazing orbit, where it resides on the outskirts of the shrinking giant star. The jets produce a high velocity outflow in the polar directions, which is as massive as the equatorial outflow. These simulations are the first to demonstrate, from beginning to end, a grazing envelope evolution. The results of the simulations show that the GEE can serve as an alternative to the forty-year CEE evolution, in forming short-period binaries that have compact objects and an ejected envelope.

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