The Solar Neighborhood XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc

We present results of the largest, most comprehensive study ever done of the stellarmultiplicity of the most common stars in the Galaxy, the red dwarfs. We have conducted an all-sky, volume-limited survey for stellarcompanions to 1120 M dwarfprimaries known to lie within 25 pc of the Sun via trigonometric parallaxes. In addition to a comprehensive literature search, stars were explored in new surveys for companions at separations of 2" to 300". A reconnaissance of wide companions to separations of 300" was done via blinking archival images. I-bandimages were used to search our sample for companions at separations of 2" to 180". Various astrometric and photometric methods were used to probe the inner 2" to reveal close companions. We report the discovery of 20 new companions and identify 56 candidate multiple systems. We find a stellarmultiplicity rate of 26.8 +/- 1.4% and a stellarcompanion rate of 32.4 +/- 1.4% for M dwarfs. There is a broad peak in the separation distribution of the companions at 4 -- 20 AU, with a weak trend of smaller projected linear separationsfor lower mass primaries. A hint that M dwarfmultiplicity may be a function of tangential velocity is found, with faster moving, presumably older, stars found to be multiple somewhat less often. We calculate that stellarcompanions make up at least 17% of mass attributed to M dwarfsin the solar neighborhood, with roughly 11% of M dwarfmass hidden as unresolved companions. Finally, when considering all M dwarfprimaries and companions, we find that the mass distribution for M dwarfsincreases to the end of the stellarmain sequence.