Aims. We investigate the contribution of different formation scenarios for type Ia supernovae in elliptical galaxies. The singledegenerate scenario (a white dwarf accreting from a late main-sequence or red giant companion) is tested against the doubledegenerate scenario (the spiral-in and merging of two white dwarfs through the emission of gravitational wave radiation). Methods. We use a population-number synthesis code that incorporates the latest physical results in binary evolution and allows us to differentiate between certain physical scenarios (e.g. description of common-envelope evolution) and evolutionary parameters (e.g. mass-transfer efficiency during Roche-lobe overflow). The obtained theoretical distributions of the delay times of type Ia supernovae are compared, both in morphological shape and in absolute number of events, to those which are observed. The critical dependency of these distributions on certain parameters is used to constrain the values of the latter. Results. We find that the single-degenerate scenario alone cannot explain the morphological shape of the observational delay-time distribution, while the double-degenerate scenario (or a combination of both) can. Most of these double-degenerate type Ia supernovae are created through a normal quasi-conservative Roche-lobe overflow followed by a common-envelope phase, not through two successive common-envelope phases. This may cast doubt on the use in other studies of analytical formalisms to determine delay times. In terms of absolute number, theoretical supernova Ia rates in old elliptical galaxies lie a factor of at least three below the observed ones. We propose a solution involving the effect of rotation on the evolution of intermediate mass binaries.

Context. The observed distribution of orbital periods of Algols with a B-type primary at birth agrees fairly well with the prediction from conservative theory. Conservative evolution fails, however, to produce the rather large fraction of Algols observed with a high mass-ratio, especially: q ∈ [0.4-0.6]. Aims. In order to keep Algols for a longer time with a higher mass-ratio without disturbing the distribution of orbital periods too much, interacting binaries have to lose a significant fraction of their total mass without losing much angular momentum before or during Algolism. We propose a mechanism that meets both requirements. Methods. In the case of direct impact the gainer spins up: sometimes up to critical velocity. Equatorial material on the gainer is therefore less bound. A similar statement applies to material located at the edge of an accretion disc. The incoming material moreover creates a hot spot in the area of impact. The sum of the rotational and radiative energy of hot spot material depends on the masstransfer-rate. The sum of both energies overcomes the binding energy at a well defined critical value of the mass-transfer-rate. As long as the transfer-rate is smaller than this critical value RLOF happens conservatively. But as soon as the critical rate is exceeded the gainer will acquire no more than the critical value and RLOF runs into a liberal era. Results. Low-mass binaries never achieve mass-transfer-rates larger than the critical value. Intermediate-mass binaries evolve mainly conservatively but mass will be blown away from the system during the short era of rapid mass-transfer soon after the onset of RLOF. We have calculated the evolution of binaries with a 9 M primary and a 5.4 M companion over a range of initial orbital periods, covering case-A RLOF. Mass-loss from the system is achieved during direct impact only. Conclusions. We find systems that show Algolism for more than ten million years. RLOF occurs almost always conservatively. Only during some 20 000 years the gainer is not capable of grasping all the material that comes from the donor. The mass-ratio q ∈ [0.4-0.6] which was hardly populated by conservative evolution now contains Algols for a significant fraction of their existence.

Context. Several authors have previously introduced liberal evolution of interacting binaries, with the purpose of meeting various observed binary characteristics better than with conservative evolution. Since Algols are eclipsing binaries, the distribution of their orbital periods is known precisely. The distribution of their mass ratios contains, however, more uncertainties. We try to reproduce these two distributions theoretically using a liberal scenario in which the gainer star can lose mass into interstellar space as a consequence of its rapid rotation and the energy of a hot spot. Aims. In a recent paper we calculated the liberal evolution of binaries with a B-type primary at birth where mass transfer starts during core hydrogen burning of the donor. In this paper we include the cases where mass transfer starts during shell hydrogen burning, and it is our aim to reproduce the observed distributions of the system parameters of Algol-type semidetached systems. Methods. Our calculations reveal the amount of time that an Algol binary lives with a well-defined value of mass ratio and orbital period. We used these data to simulate the distribution of mass ratios and orbital periods of Algols. Results. Binaries with a late B-type initial primary hardly lose any mass, whereas those with an early B primary evolve in a nonconservative way. Conservative binary evolution predicts only ∼12% of Algols with a mass ratio q above 0.4. This value is raised up to ∼17% using our scenario of liberal evolution, which is still far below the ∼45% that is observed. Conclusions. Observed orbital periods of Algol binaries longer than one day are faithfully reproduced by our liberal scenario. Mass ratios are reproduced better than with conservative evolution, but the resemblance is still poor.

Context. The chemical processes during the asymptotic giant branch (AGB) evolution of intermediate-mass single stars predict most of the observations of the different populations in globular clusters although some important questions still need to be further clarified. In particular, to reproduce the observed anticorrelations of Na-O and Al-Mg, chemically enriched gas lost during the AGB phase of intermediate-mass single stars must be mixed with matter with a pristine chemical composition. The source of this matter is still debated. Furthermore, observations reveal that a significant fraction of the intermediate-mass and massive stars are born as components of close binaries. Aims. We investigate the effects of binaries on the chemical evolution of globular clusters and on the origin of matter with a pristine chemical composition that is needed for the single-star AGB scenario to work. Methods. We used a population synthesis code that accounts for binary physics to estimate the amount and the composition of the matter returned to the interstellar medium of a population of binaries. Results. We demonstrate that the mass lost by a significant population of intermediate-mass close binaries in combination with the single-star AGB pollution scenario may help to explain the chemical properties of the different populations of stars in globular clusters.

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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 has been 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 large values.

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.

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