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Published February 2023 | Published
Journal Article Open

On rapid binary mass transfer - I. Physical model


In some semidetached 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 disc around the companion becomes geometrically thick (or advection-dominated) near the disc outer radius, a large fraction of the transferred mass may be lost through the outer Lagrangian (L2) point, as a result of the excessive energy generated by viscous heating that cannot be efficiently radiated away. A physical model is constructed where the L2 mass-loss fraction is given by the requirement that the remaining material in the disc has Bernoulli number equal to the L2 potential energy. Our model predicts significant L2 mass-loss at mass transfer rates exceeding a few 10⁻⁴ M_⊙ yr⁻¹. An equatorial circumbinary outflow (CBO) is formed in these systems. Implications for the orbital evolution and the observational appearance of the system are discussed. In particular, (1) rapid angular momentum loss from the system tends to shrink the orbit, and hence may increase the formation rate of mergers and gravitational-wave sources; and (2) photons from the hot disc 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

© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) We thank Nadia Zakamska, Jim Stone, Alexey Bobrick, and Pablo Marchant for useful conversations. We are grateful for the careful read and detailed comments made by the referee, Christopher Tout. 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
October 25, 2023