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Abstract: Rapid mass transfer in a binary system can drive the accreting star out ofthermal equilibrium, causing it to expand. This can lead to a contact system,strong mass loss from the system and possibly merging of the two stars. In lowmetallicity stars the timescale for heat transport is shorter due to the loweropacity. The accreting star can therefore restore thermal equilibrium morequickly and possibly avoid contact.We investigate the effect of accretion onto main sequence stars withradiative envelopes with different metallicities. We find that a lowmetallicity Z<0.001, 4 solar mass star can endure a 10 to 30 times higheraccretion rate before it reaches a certain radius than a star at solarmetallicity. This could imply that up to two times fewer systems come intocontact during rapid mass transfer when we compare low metallicity. This factoris uncertain due to the unknown distribution of binary parameters and thedependence of the mass transfer timescale on metallicity. In a forthcomingpaper we will present analytic fits to models of accreting stars at variousmetallicities intended for the use in population synthesis models.

Author: S. E. de Mink, M. Cottaar, O. R. Pols


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