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Photograph of Ross Church

Ross Church

Senior lecturer

Photograph of Ross Church

White-dwarf kicks and implications for barium stars

Author

  • R. G. Izzard
  • T. Dermine
  • Ross Church

Summary, in English

The formation mechanism of the barium stars is thought to be well understood. Barium-rich material, lost in a stellar wind from a thermally-pulsing asymptotic-giant branch star in a binary system, is accreted by its companion main-sequence star. Now, many millions of years later, the primary is an unseen white dwarf and the secondary has itself evolved into a giant which displays absorption lines of barium in its spectrum and is what we call a barium star. A similar wind-accretion mechanism is also thought to form the low-metallicity CH and carbon-enhanced metal-poor stars. Qualitatively the picture seems clear but quantitatively it is decidedly murky: several key outstanding problems remain which challenge our basic understanding of binary-star physics. Barium stars with orbital periods less than about 4000 days should - according to theory - be in circular orbits because of tidal dissipation, yet they are often observed to be eccentric. Only one barium-star period longer than 10(4) days has been published although such stars are predicted to exist in large numbers. In this paper we attempt to shed light on these problems. First, we consider the impact of kicking the white dwarf at its birth, a notion which is supported by independent evidence from studies of globular clusters. Second, we increase the amount of orbital angular momentum loss during wind mass transfer, which shrinks barium-star binaries to the required period range. We conclude with a discussion of possible physical mechanisms and implications of a kick, such as the break up of wide barium-star binaries and the limits imposed on our models by observations.

Department/s

  • Lund Observatory

Publishing year

2010

Language

English

Publication/Series

Astronomy & Astrophysics

Volume

523

Document type

Journal article

Publisher

EDP Sciences

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • Galaxy: stellar content
  • stars: AGB and post-AGB
  • stars: chemically peculiar
  • binaries: close
  • abundances
  • nucleosynthesis
  • nuclear reactions

Status

Published

ISBN/ISSN/Other

  • ISSN: 0004-6361