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Photograph of Ross Church

Ross Church

Senior lecturer

Photograph of Ross Church

Thermohaline Mixing in Extremely Metal-poor Stars

Author

  • Kate Henkel
  • Amanda I. Karakas
  • Andrew R. Casey
  • Ross P. Church
  • John C. Lattanzio

Summary, in English

Extremely metal-poor (EMP) stars are an integral piece in the puzzle that is the early universe, and although anomolous subclasses of EMP stars such as carbon-enhanced metal-poor (CEMP) stars are well studied, they make up less than half of all EMP stars with [Fe/H] ∼ -3.0. The amount of carbon depletion occurring on the red giant branch (carbon offset) is used to determine the evolutionary status of EMP stars, and this offset will differ between CEMP and normal EMP stars. The depletion mechanism employed in stellar models (from which carbon offsets are derived) is very important; however, the only widely available carbon offsets in the literature are derived from stellar models using a thermohaline mixing mechanism that cannot simultaneously match carbon and lithium abundances to observations for a single diffusion coefficient. Our stellar evolution models utilize a modified thermohaline mixing model that can match carbon and lithium in the metal-poor globular cluster NGC 6397. We compare our models to the bulk of the EMP star sample at [Fe/H] = -3 and show that our modified models follow the trend of the observations and deplete less carbon compared to the standard thermohaline mixing theory. We conclude that stellar models that employ the standard thermohaline mixing formalism overestimate carbon offsets and hence CEMP star frequencies, particularly at metallicities where carbon-normal stars dominate the EMP star population.

Department/s

  • Lund Observatory
  • eSSENCE: The e-Science Collaboration

Publishing year

2018-08-10

Language

English

Publication/Series

Astrophysical Journal Letters

Volume

863

Issue

1

Document type

Journal article

Publisher

IOP Publishing

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • stars: abundances
  • stars: evolution
  • stars: interiors
  • stars: low-mass

Status

Published

ISBN/ISSN/Other

  • ISSN: 2041-8205