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Description
This table contains a spectroscopic catalog of the 1564 brightest (J < 9<sup>m</sup>) M-dwarf candidates in the northern sky, as selected from the SUPERBLINK proper-motion catalog (Lepine and Shara 2005, AJ, 129, 1483). Observations confirm 1408 of the candidates to be late-K and M dwarfs with spectral subtypes K7 - M6. From the low (mu > 40 mas yr<sup>-1</sup>) proper motion limit and high level of completeness of the SUPERBLINK catalog in that magnitude range, the authors estimate that their spectroscopic census most likely includes > 90% of all existing, northern-sky M dwarfs with apparent magnitude J < 9<sup>m</sup>. Only 682 stars in this sample are listed in the Third Catalog of Nearby Stars (CNS3, Gliese and Jahreiss 1991); most others are relative unknowns and have spectroscopic data presented here for the first time. Spectral subtypes are assigned based on spectral index measurements of CaH and TiO molecular bands; a comparison of spectra from the same stars obtained at different observatories, however, reveals that spectral band index measurements are dependent on spectral resolution, spectrophotometric calibration, and other instrumental factors. As a result, the authors find that a consistent classification scheme requires that spectral indices be calibrated and corrected for each observatory/instrument used. After systematic corrections and a recalibration of the subtype-index relationships for the CaH2, CaH3, TiO5, and TiO6 spectral indices, the authors find that they can consistently and reliably classify all the stars to a half-subtype precision. The use of corrected spectral indices further requires them to recalibrate the zeta parameter, a metallicity indicator based on the ratio of TiO and CaH optical bandheads. However, the authors find that their zeta values are not sensitive enough to diagnose metallicity variations in dwarfs of subtypes M2 and earlier (+/- 0.5 dex accuracy) and are only marginally useful at later M3-M5 subtypes (+/- 0.2 dex accuracy). Fits of their spectra to the Phoenix atmospheric model grid are used to estimate effective temperatures. These suggest the existence of a plateau in the M1-M3 subtype range, in agreement with model fits of infrared spectra but at odds with photometric determinations of T<sub>eff</sub>. Existing geometric parallax measurements are extracted from the literature for 624 stars, and are used to determine spectroscopic and photometric distances for all the other stars. Active dwarfs are identified from measurements of H-alpha equivalent widths, and the authors find a strong correlation between H-alpha emission in M dwarfs and detected X-ray emission from ROSAT and/or a large UV excess in the GALEX point source catalog. Proper motion data and photometric distances are combined in order to evaluate the (U, V, W) distribution in velocity space, which is found to correlate 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. The authors state that this catalog will be very useful for guiding the selection of the best M dwarf targets for exoplanet searches, in particular those using high-precision radial velocity measurements. This online catalog was created by the HEASARC in June 2013 based on a machine-readable version of Tables 1, 3 and 7 from the paper which were obtained from the AJ website (Tables 1 and 3) or from the first author (Table 7). This is a service provided by NASA HEASARC .
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