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Published May 31, 2022 | Submitted
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On rapid binary mass transfer -- I. Physical model


In some semi-detached binary systems, the donor star may transfer mass to the companion at a very high rate. We propose that, at sufficiently high mass transfer rates such that the accretion disk around the companion becomes geometrically thick (or advection-dominated) near the disk outer radius, a large fraction of the transferred mass will be lost through the outer Lagrangian (L2) point. A physical model is constructed where the L2 mass loss fraction is given by the requirement that the remaining material in the disk has Bernoulli number equal to the L2 potential energy. Our model predicts significant L2 mass loss at mass transfer rates exceeding a few times 10^{-4} Msun/yr -- an equatorial circum-binary outflow (CBO) is formed in these systems. Implications for the orbital evolution and the observational appearance are discussed. In particular, (1) rapid angular momentum loss from the system tends to shrink the orbital separation and hence may increase the formation rate of mergers and gravitational-wave sources; (2) photons from the hot disk wind are reprocessed by the CBO into longer wavelength emission in the infrared bands, consistent with Spitzer observations of some ultra-luminous X-ray sources.

Additional Information

We thank Nadia Zakamska, Jim Stone, Alexey Bobrick and Pablo Marchant for useful conversations. WL was supported by the David and Ellen Lee Fellowship at California Institute of Technology and the Lyman Spitzer, Jr. Fellowship at Princeton University. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 836751. DATA AVAILABILITY. The data underlying this article will be shared on reasonable request to the corresponding author.

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August 22, 2023
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