Sebastien Lepine, Eric J. Hilton, Andrew W. Mann, Matthew Wilde, Barbara Rojas-Ayala, Kelle L. Cruz, Eric Gaidos
We present a spectroscopic catalog of the 1,556 brightest M dwarf candidates in the northern sky, as selected by proper motion and photometry. These bright sources comprise >99% of the known, northern M dwarfs with apparent magnitudes J<9, and most likely include >95% of all such existing objects. Only 679 stars in our sample are listed in the Third Catalog of Nearby Stars (CNS3); most others are relative unknowns and have spectroscopic data presented here for the first time. Observations confirm 1,403 of the candidates to be late-K and M dwarfs with spectral subtypes K7-M6, with subtypes assigned based on spectral index measurements of CaH and TiO molecular bands. We also calculate the Zeta parameter, which measures the ratio of TiO and CaH bandheads, and is correlated with metallicity in M dwarfs/subdwarfs, and for this we present a revised calibration based on corrected values of the CaH and TiO spectral indices. Fits of our spectra to the Phoenix atmospheric model grid are used to estimate effective temperatures. Existing geometric parallax measurements for 624 of the catalog stars are used to recalibrate the subtype/absolute magnitude relationship in M dwarfs; we find that spectroscopic distances are marginally more accurate at earlier (K7-M2) subtypes, but that photometric distances should be preferred for later-type dwarfs (M3-M6). We identify active stars from H$\alpha$ equivalent widths, GALEX UV magnitudes, and ROSAT X-ray fluxes from ROSAT. We combine proper motion data and photometric distances to evaluate the distribution in (U,V,W) velocity space of the entire catalog. The overall velocity-space distribution correlates tightly with the velocity distribution of G dwarfs in the Solar Neighborhood. However, active stars show a smaller dispersion in their space velocities, which is consistent with those stars being younger on average.
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http://arxiv.org/abs/1206.5991
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