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 ~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 Hα 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 ~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 ~20% level.