When the primary star has strong, outward flowing stellar winds, then as the secondary moves through the ejected material while orbiting the primary, its gravity will accumulate a fraction of that material. This process of wind accretion tends to be found in binaries where the companion is a high mass star, such as those of spectral type O and B.
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To give an idea of how a comprehensive binary evolution algorithm of stars is compiled, the prescription for wind accretion provides a good illustration. In the code, the primary star is set to lose mass by way of its wind at a certain rate according to its evolutionary stage. On the giant branch and beyond for example, Hurley, Pols, & Tout (2000) uses a formula by Kudritzki & Reimers (1978) to model the rate at which the outer layer of material was expelled from the primary. Furthermore, to model the rate at which the secondary star accretes this material, Hurley, Tout, & Pols (2002) use a formula put forth by Bondi & Hoyle (1944).
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For more detailed information on how the code implements wind accretion, please see the aforementioned papers.
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 Diagram Adapted from Dr. Dirk Terrell at Boulder
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