Poster abstract

We have carried out the largest high angular resolution M-dwarf binary survey to date. 800 young M dwarfs within ~50 pc of the Sun, and with spectral types in the range M0 to M6 were surveyed for visual companions in the i- and z-band with a typical angular resolution of 100 mas. The study was carried out using the two Lucky Imaging cameras AstraLux and AstraLux Sur at the Calar Alto 2.2m telescope in Spain and the ESO 3.5 New Technologt Telescope in Chile, respectively. The primary goals of the survey are i) identify short-period binaries suitable to improve the mass-luminosity relation for stars of MK type later than M3V, which is still poorly calibrated, ii) study binary properties as a function of primary mass, and compare the observed properties with model predictions, and binary properties of more massive stars and of brown dwarfs, and iii) identify binaries suitable for high-precision astrometric monitoring for future exoplanet surveys using interferometry. We report on the how binary properties change with primary mass, and investigate how the early- to mid-M dwarf binary sample with primary masses in the range ~0.15 to 0.5 solar masses compare to the binary properties of very-low-mass stars and brown dwarfs on the one hand, and those of solar type star on the other hand. We discuss the findings in the framework of recent theoretical investigations on the formation of low-mass stars and brown dwarfs.