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Description
This table contains the results from a spectroscopic study of 1080 nearby active M dwarfs, selected by correlating the Two Micron All Sky Survey (2MASS) and ROSAT catalogs at galactic latitudes greater than 15 degrees above or below the Galactic Plane and using a matching radius of 20 arcseconds, as well as color cuts (J-H < 0.75, H-K > 0.15 and 0.8 < J-K < 1.1) designed to select M dwarfs. The authors have derived the spectral types and estimated distances for all of their stars. The spectral types range between K5 and M6. Nearly half of the stars lie within 50 pc. The authors have measured the equivalent width of the H-alpha emission line. Their targets show an increase in chromospheric activity from early to mid-spectral types, with a peak in activity around M5. Using the count rate and hardness ratios obtained from the ROSAT catalog,the authors have derived the stellar X-ray luminosities. Their stars display a "saturation-type" relation between the chromospheric and coronal activity. The relation is such that log L<sub>X</sub>/L<sub>bol</sub> remains "saturated" at a value of approximately -3 for varying H-alpha equivalent width. The authors have found 568 matches in the USNO-B catalog and have derived the tangential velocities v<sub>tan</sub> for these stars. There is a slight trend of decreasing chromospheric activity with age, such that the stars with higher v<sub>tan</sub> values have lower H-alpha equivalent widths. The coronal emission, however, remains saturated at a value of log L<sub>X</sub>/L<sub>bol</sub> ~ -3 for varying tangential velocities, suggesting that the coronal activity remains saturated with age. The authors do not find any break in the saturation-type relation at the spectral type at which stars become fully convective (~M3.5). Most of the stars in their sample show more coronal emission than the dMe stars in the Hyades and Praesepe clusters and have v<sub>tan</sub> < 40 km s<sup>-1</sup>, suggesting that they belong to a young population. This table was created by the HEASARC in March 2010 based on the (corrected) electronic version of Table 1 from the reference paper which was obtained from the Astronomical Journal web site. This is a service provided by NASA HEASARC .
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