Precision Masses of the low-mass binary system GJ 623

We have used Aperture Masking Interferometry and Adaptive Optics (AO) at the Palomar 200'' to obtain precise mass measurements of the binary M dwarf GJ 623. AO observations spread over 3 years combined with a decade of radial velocity measurements constrain all orbital parameters of the GJ 623 binary system accurately enough to critically challenge the models. The dynamical masses measured are $m_{1}=0.371\pm0.015 M_{\sun}$ (4%) and $m_{2}=0.115\pm0.0023 M_{\sun}$ (2%) for the primary and the secondary respectively. Models are not consistent with color and mass, requiring very low metallicities.