Two nearby M dwarf binaries from the Two Micron All Sky Survey

We report the discovery of two binary M dwarf systems in the immediate sola r neighbourhood using the Two Micron All Sky Survey (2MASS). The first is a n M6.5 companion to the nearby G star HD 86728 (Gl 376). The known properti es of HD 86728 indicate that the M dwarf (Gl 376B) is old, metal-rich and o nly 14.9 parsec away. The M dwarf is highly active, with both H alpha and X -ray emission. Thus, Gl 376B offers the opportunity to study an old, bright , active M dwarf with known metallicity, age and luminosity. We show that i t is probable that Gl 376B is itself an unresolved pair. The other system c onsists of an M6.5 and an M8 dwarf with 14.5 arcsec separation. We estimate a distance of similar to 16 parsec for this very low-mass pair. Stronger a ctivity is observed in the M6.5 dwarf, supporting evidence that chromospher ic activity is weakening near the hydrogen-burning limit.