A method for selecting M dwarfs with an increased likelihood of unresolved ultracool companionship

Neil Cook, D.J. Pinfield, F. Marocco, B. Burningham, H.R.A. Jones, James Frith, J. Zhong, A. Luo, Z. Qi, P.W. Lucas, Mariusz Gromadzki, Avril Day-Jones, Radostin Kurtev, Y. Guo, Y. Wang, Y. Bai, Z. Yi, R. Smart

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Locating ultracool companions to M dwarfs is important for constraining low-mass formation models, the measurement of substellar dynamical masses and radii, and for testing ultracool evolutionary models. We present an optimized method for identifying M dwarfs which may have unresolved ultracool companions. We construct a catalogue of 440 694 M dwarf candidates, from Wide-Field Infrared Survey Explorer, Two Micron All-Sky Survey and Sloan Digital Sky Survey, based on optical- and near-infrared colours and reduced proper motion. With strict reddening, photometric and quality constraints we isolate a subsample of 36 898 M dwarfs and search for possible mid-infrared M dwarf + ultracool dwarf candidates by comparing M dwarfs which have similar optical/near-infrared colours (chosen for their sensitivity to effective temperature and metallicity). We present 1082 M dwarf + ultracool dwarf candidates for follow-up. Using simulated ultracool dwarf companions to M dwarfs, we estimate that the occurrence of unresolved ultracool companions amongst our M dwarf + ultracool dwarf candidates should be at least four times the average for our full M dwarf catalogue. We discuss possible contamination and bias and predict yields of candidates based on our simulations.
Original languageEnglish
Pages (from-to)2192-2208
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date10 Feb 2016
Publication statusPublished - 1 Apr 2016


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