Meeting the cool neighbors. XI. Beyond the NLTT catalog

We have combined near-infrared data from the Two Micron All Sky Survey with ancillary optical data to identify previously unrecognized proper-motion stars that have colors and magnitudes consistent with nearby M dwarfs. We present follow-up observations of 392 stars from that sample, including similar to 200 stars discussed here for the first time. Our distance estimates, based primarily on spectroscopic parallaxes, place 123 stars within 20 pc of the Sun. One hundred and seventy-six stars exhibit H alpha emission, and 82 stars have plausible X-ray counterparts from ROSAT observations. The distribution of chromospheric and coronal activity is broadly consistent with data for other nearby late-type stars, with similar to 30 stars having activity levels comparable to Pleiades M dwarfs. We have identified several M dwarfs that are probably wide ( > 1000 AU) companions of F and G stars. We have recomputed the 20 pc luminosity function, adding the 123 new candidates found in the present survey. The revised luminosity function is in closer agreement with the 8 pc data set for stars with M-J > 8 but probably remains incomplete at the similar to 20% level.