Institute of Astronomy

Bridging the Gap in Binary Evolution

SpeakerTalk DateTalk Series
Onno Pols26 July 2016Binary Stars Talks

Abstract

Binary mass transfer occurs by Roche-lobe overflow in relatively close systems, and by wind accretion in systems that are too wide for either star to fill its Roche lobe. In the case of red giant primaries, RLOF is often (though not always) unstable and results in a highly non-conservative common envelope event that shrinks the orbit. On the other hand, wind mass loss tends to widen the orbit, and accretion from the wind of an AGB star can leave chemical signatures in the companion star. This divergent orbital evolution is expected to produce a gap in the period distribution of mass-transfer remnant systems. However, observed systems are plentiful in this period range (roughly 100 days to a few years). In this intermediate regime the interaction processes are not well understood; wind interaction, Roche-lobe overflow and even common-envelope evolution are not easily distinguishable here. Remnants of such interaction, which include post-AGB binaries, barium stars and (at low metallicity) carbon-enhanced metal-poor stars, have properties that are at odds with the predictions of standard binary evolution models. In this contribution I will explore some of the processes that may be at work here.

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