Journal Article

Evidence for halo kinematics among cool carbon-rich dwarfs

J Farihi, A R Arendt, H S Machado and L J Whitehouse

in Monthly Notices of the Royal Astronomical Society

Published on behalf of Royal Astronomical Society

Volume 477, issue 3, pages 3801-3806
ISSN: 0035-8711
Published online April 2018 | e-ISSN: 1365-2966 | DOI:

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This paper reports preliminary, yet compelling, kinematical inferences for [math] carbon-rich dwarf stars that demonstrate around 30–60 per cent are members of the Galactic halo. The study uses a spectroscopically and non-kinematically selected sample of stars from the SDSS, and cross-correlates these data with three proper motion catalogues based on Gaia DR1 astrometry to generate estimates of their 3D space velocities. The fraction of stars with halo-like kinematics is roughly 30 per cent for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disc, but close to 60 per cent of the sample lies below an old, metal-poor disc isochrone in reduced proper motion. An ancient population is consistent with an extrinsic origin for C/O >1 in cool dwarfs, where a fixed mass of carbon pollution more readily surmounts lower oxygen abundance and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favours low-mass stars as in the Galactic disc, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

Keywords: proper motions; binaries: general; stars: carbon; stars: chemically peculiar; stars: kinematics and dynamics; Galaxy: halo

Journal Article.  4801 words.  Illustrated.

Subjects: Astronomy and Astrophysics