Nucleosynthesis in Binary Systems

Most stars appear to be members of binary or multiple systems. The fraction of massive stars being members of close binaries — i.e. such in which mass overflow is expected to occur — is estimated to be of the order of 20. .. 40% (cf. Garmany et al. 1980, Podsiadlowski 1997, Mason et al. 1998). Thus, it appears necessary to investigate the effect of binary mass transfer on the overall massive star nucleosynthesis yields if the mass transfer would increase the yield of an isotope only by a factor of 3, then massive close binaries might be the dominant source of this isotope. Clearly, most isotopes are not affected by binaries at this level (cf. De Donder Vanbeveren 2002). 

In massive stars, 26Aluminium is produced during core hydrogen burning according to 

The synthesis of 26A1 in secondary components of close binaries was found to deserve special attention. The reason is that for 26 Al, as it is /J-unstable with a mean life time of 1.03 106yr (ti/2 = 7.2 105 yr), not only the amount which is synthesised matters, but also the time of the synthesis. The 7-ray line emission from the decay of 26Al in the Galaxy is observed. However, we can only see the decay of 26 Al nuclei in the interstellar medium the decay inside stars is unobservable. Therefore, the 26Al which is observed 

This would already be sufficient to produce as much as 10-6 Mq 26A1 from this star of initially 18 M0 — two orders of magnitude more than expected from single star calculations at Z0/4 (cf. Langer et al. 1995). However, the H-burning shell source in the secondary component is much more efficient than in corresponding single stars. This 

The thermal time scale mass transfer is initiated by the shrinkage of the orbit as a consequence of angular momentum conservation, as long as Md Mwd- the Roche lobe filling main sequence star is squeezed into a continuously shrinking volume. The stellar radius can fall much below the zero-age main sequence mass-radius relation. Consequently, orbital periods can be achieved which are smaller by a factor / than periods corresponding to unperturbed main sequence stars filling their Roche lobes. For conser- 

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