The very low mass multiple system LHS\,1070 -- a testbed for model atmospheres for the lower end of the main sequence

Abstract : LHS1070 is a nearby multiple system of low mass stars. It is an important source of information for probing the low mass end of the main sequence, down to the hydrogen-burning limit. The primary of the system is a mid-M dwarf and two components are late-M to early L dwarfs, at the star-brown dwarf transition. Hence LHS1070 is a valuable object to understand the onset of dust formation in cool stellar atmospheres.This work aims at determining the fundamental stellar parameters of LHS1070 and to test recent model atmospheres: BT-Dusty,BT-Settl, DRIFT, and MARCS models.Unlike in previous studies, we have performed a chi^2-minimization comparing well calibrated optical and infrared spectra with recent cool star synthetic spectra leading to the determination of the physical stellar parameters Teff, radius, and log g for each of the three components of LHS1070.