A search for companions to nearby southern M dwarfs with near-infrared speckle interferometry

We searched the 9 M-dwarf primaries nearer than 5 pc and south of declination δ = −30◦ for companions with separations 1-10AU and found none. Taken togetherwith the 25 northern primaries studied by Henry and McCarthy (1990) the fraction of binaries and triples within the now complete sample of all M dwarfs within 5 pc is 9/34 = 26± 9%, and the average number of companions per system is 0.32± 0.10. This is lower by 2σ than the observed multiplicity fraction of 43 ± 5%, and companions per system of 0.49 ± 0.05 in the sample of nearby solar-type main sequence stars. It is also much lower than the extrapolated binary fraction among young stars in Taurus. We discuss the implications of this finding.