Critically-rotating accretors and non-conservative evolution in Algols

Context. During the mass-transfer phase in Algol systems, a large amount of mass and angular momentum are accreted by the gainer star, which can be accelerated up to its critical Keplerian velocity. The fate of the gainer once it reaches this critical value is unclear. Aims. We investigate the orbital and stellar spin evolution in semi-detached binary systems, specifically for systems with rapidly rotating accretors. Our aims are to better distinguish between the different spin-down mechanisms proposed that can consistently explain the slow rotation observed in Algols’ final states and to assess the degree of non-conservatism due to the formation of a hotspot. Methods. We use our state-of-the-art binary evolution code, Binsta