Z. H. Zhang, D. J. Pinfield, B. Burningham, H. R. A. Jones, M. C. Galvez-Ortiz, S. Catalan, R. L. Smart, S. Lepine, J. R. A. Clarke, Ya. V. Pavlenko, D. N. Murray, M. K. Kuznetsov, A. C. Day-Jones, J. Gomes, F. Marocco, B. Sipocz
Red subdwarfs in binary systems are crucial for both model calibration and spectral classification. We search for red subdwarfs in binary systems from a sample of high proper motion objects with SDSS spectroscopy. We present here discoveries from this search, as well as highlighting several additional objects of interest. We find thirty red subdwarfs in wide binary systems including: two with spectral type of esdM5.5, six companions to white dwarfs and three carbon enhanced red subdwarfs with normal red subdwarf companions. Fifteen red subdwarfs in our sample are partially resolved close binary systems. With this binary sample, we estimate the low limit of the red subdwarf binary fraction of ~ 10%. We find that the binary fraction goes down with decreasing masses and metallicities of red subdwarfs. A spectroscopic esdK7 subdwarf + white dwarf binary candidate is also reported. Thirty new M subdwarfs have spectral type of >M6 in our sample. We also derive relationships between spectral types and absolute magnitudes in the optical and near-infrared for M- and L- subdwarfs, and we present an M subdwarf sample with measured U, V, W space velocities.
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http://arxiv.org/abs/1306.3060
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