Mass loss out of close binaries
Case A Roche lobe overflow
Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium e-mail: email@example.com
Accepted: 18 November 2009
Context. Matter leaving the donor during mass transfer spins up the gainer and creates a hot spot in the impact area. If the kinetic energy of the enhanced rotation combined with the radiative energy of the hot spot exceeds the binding energy of the system, matter can escape from the binary.
Aims. We calculate the amount of mass lost during eras of fast mass transfer. We simulate the distribution of mass ratios and orbital periods for interacting binaries with a B-type primary at birth where mass transfer starts during hydrogen core burning of the donor.
Methods. We used the initial distributions of primary mass, mass ratio and orbital period established in a previous paper. The amount of time the binary shows Algol characteristics within different values of mass ratio and orbital period was fixed from conservative and liberal evolutionary calculations. We use these data to simulate the distribution of mass ratios and orbital periods of Algols with the conservative as well as the liberal model.
Results. Rapid rotation and hot spots are frequently observed at the surface of the gainer in a semi-detached binary. The mass transfer rate for low-mass binaries is never sufficiently large to achieve mass loss from the system. Intermediate-mass binaries blow away a large fraction of the transferred mass during short eras of rapid mass transfer.
Conclusions. We compare mass ratios and orbital periods of Algols obtained by conservative evolution with those obtained by our liberal model. We calculate the amount of matter lost according to our model by binaries with an early B-type primary at birth. Since binaries with a late B-type primary evolve almost conservatively, the overall distribution of mass ratios will only yield a few Algols more with high mass ratios than conservative calculations do. Whereas the simulated distribution of orbital periods of Algols fits the observations well, the simulated distribution of mass ratios produces always too few systems with high values.
Key words: binaries: eclipsing / stars: evolution / stars: mass-loss / stars: statistics
© ESO, 2010