Abstract
In earlier papers, we presented a binary evolutionary code for the purpose of reproducing the orbital parameters, masses, radii, and location in the Hertzsprung Russell diagram (abbreviated as HRD) of well-observed Algol systems. In subsequent versions, the effects of mass and angular momentum losses and tidal coupling were included in order to produce the observed distributions of orbital periods and mass ratios of Algol-type binaries. The mass loss includes stellar wind and possible liberal evolution, when the gainer star is not capable to absorb all of the matter during mass transfer from the donor star. We added magnetic braking to our code to better reproduce the observed equatorial velocities. Large equatorial velocities of mass-gaining stars are now lowered by tidal interaction and magnetic braking. Tides are mainly at work at short orbital periods, leaving magnetic braking alone at work during longer orbital periods. The observed values of the equatorial velocities of mass gainers in Algol-type binaries are mostly well reproduced by our code. According to our models, Algols have short periods with a strong magnetic field.
Highlights
The modelling of the evolution of close binaries started with the first papers of a series from Paczynski [1,2,3], soon followed by papers from colleagues in Germany (Kippenhahn & Weigert [4]) and from the USSR (Tutukov & Yungelson [5,6])
Paper [5] explored the loss of matter and angular momentum during the period of mass transfer
The influence of liberal evolution on the distribution of orbital periods and mass ratios of the evolutionary models was compared to the observed distributions for 351 Algols, which were taken from the catalogue of Budding et al [16]
Summary
The modelling of the evolution of close binaries started with the first papers of a series from Paczynski [1,2,3], soon followed by papers from colleagues in Germany (Kippenhahn & Weigert [4]) and from the USSR (Tutukov & Yungelson [5,6]). Equatorial velocities of gainers were modelled in [15] using magnetic braking to keep the equatorial velocity far below critical during the evolution of the binary These successive studies still revealed some remaining discrepancies between theoretical and observed mass ratio and orbital period distributions and raised new questions on the difference between the theoretical rotational velocities (close to the critical one) and the observed values. Our evolution code recognizes a progenitor as plausible when the calculated positions of donor and gainer in the HRD are found to be close to the observations.
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