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arXiv · 1804.01989

Evidence for Halo Kinematics among Cool Carbon-Rich Dwarfs

J. Farihi·A. R. Arendt·H. S. Machado·L. J. Whitehouse
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Abstract

This paper reports preliminary yet compelling kinematical inferences for N ~ 600 carbon-rich dwarf stars that demonstrate around 30% to 60% 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 catalogs based on Gaia DR1 astrometry to generate estimates of their 3-D space velocities. The fraction of stars with halo-like kinematics is roughly 30% for distances based on a limited number of parallax measurements, with the remainder dominated by the thick disk, but close to 60% of the sample lie below an old, metal-poor disk 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 abundances, and with a lack of detectable ultraviolet-blue flux from younger white dwarf companions. For an initial stellar mass function that favors low-mass stars as in the Galactic disk, the dC stars are likely to be the dominant source of carbon-enhanced, metal-poor stars in the Galaxy.

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J. Farihi, A. R. Arendt, H. S. Machado, L. J. Whitehouse. 2018-04-05. Evidence for Halo Kinematics among Cool Carbon-Rich Dwarfs. https://doi.org/10.1093/mnras%2Fsty890

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