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2 results

  • 20 - Binaries at Very Low Metallicity

  • Edited by Giacomo Beccari, European Southern Observatory, Garching, Henri M. J. Boffin, European Southern Observatory, Garching
  • Book:
    The Impact of Binary Stars on Stellar Evolution
    Published online:
    05 April 2019
    Print publication:
    18 April 2019, pp 298-306

  • Summary

    The binary fraction of metal-poor stars provides important constraints on star formation in the early Galaxy, and is a key piece of information in the understanding the origin of the observed high frequency of C enhanced metal-poor stars. It is now widely accepted that a majority of solar metallicity stars are in binaries; it is not clear, however, if this is the case for metal-poor stars. While state-of-the-art models agree in predicting an increase in the binary fraction and a shift towards lower values for the orbital period distribution at extremely low metallicities, the observational findings paint a patchier picture. This chapter summarises the key motivations for the study of binaries in the very metal-poor regime and reviews the current state of the field and the plans for the future.

  • Formation of the First Stars and Blackholes

  • Naoki Yoshida
  • Journal:
    Proceedings of the International Astronomical Union / Volume 12 / Issue S333 / October 2017
    Published online by Cambridge University Press:
    08 May 2018, pp. 209-215
    Print publication:
    October 2017
    • Article
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  • Cosmic reionization is thought to be initiated by the first generation of stars and blackholes. We review recent progress in theoretical studies of early structure formation. Cosmic structure formation is driven by gravitational instability of primeval density fluctuations left over from Big Bang. At early epochs, there are baryonic streaming motions with significant relative velocity with respect to dark matter. The formation of primordial gas clouds is typically delayed by the streaming motions, but then physical conditions for the so-called direct collapse blackhole formation are realized in proto-galactic halos. We present a promising model in which intermediate mass blackholes are formed as early as z = 30.