Farihi, J; Arendt, AR; Machado, HS; Whitehouse, LJ; (2018) Evidence for halo kinematics among cool carbon-rich dwarfs. Monthly Notices of the Royal Astronomical Society , 477 (3) pp. 3801-3806. 10.1093/mnras/sty890. (In press).

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Abstract

This paper reports preliminary, yet compelling, kinematical inferences for N ≳ 600 carbonrich 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.

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