Poster Abstracts

Name/Affiliation:  Carolina Bergfors (University College London)

Title:  The AstraLux M dwarf survey part 2: The multiplicity of mid- to late-type M dwarfs

The multiplicity properties of M dwarfs provide key constraints on the formation of very low mass stars and brown dwarfs. Identification and orbital monitoring of individual close and nearby young low mass binaries can in addition provide fundamental physical parameters, such as dynamical mass, that are crucial for constraining the mass-luminosity relation and evolutionary models. Multiplicity surveys also provide essential information for target selection in exoplanet surveys. In the AstraLux M dwarf multiplicity survey, we used high resolution Lucky Imaging to statistically investigate the multiplicity of a large sample (~700) early- to mid-type M dwarfs. Here we extend the survey to include 286 M5-M8 dwarfs in the solar neighbourhood to further explore the multiplicity properties in the mass range between solar type stars and brown dwarfs. Among these mid- to late-M dwarfs, we confirm 68 common proper motion binaries/multiples, using astrometric measurements in several epochs and colour criteria. 43 of these are new discoveries. The multiplicity fraction in this mass range is found to be 26-31% and the results are consistent with a continuous trend in multiplicity fraction and semi-major axis distribution from more massive stars to very low mass stars and brown dwarfs, supporting a common formation scenario for stars and brown dwarfs.