Binaries at the Bottom of the Main Sequence and below

International audienceLong-term radial-velocity surveys of G, K and M dwarfs of the solar neighbourhood are presented. The inferred orbital elements are discussed, focusing on the (e log P) diagram, the mass-ratio and secondary mass distributions, and on the binary frequency of the studied samples. The proportion of companions to M dwarfs is found to be not significantly different from the binary frequency among G- and K-dwarf primaries. The mass function of stellar and planetary companions to solar-type stars strongly suggests different formation and evolution mechanisms for the two populations. Finally, beautiful mass-luminosity relations are obtained from low-mass binaries with high-precision radial-velocity measurements and adaptive optics visual data