Precision masses of the low-mass binary system GJ 623

We have used aperture masking interferometry and adaptive optics (AO) at the Palomar 200 inch telescope to obtain precise mass measurements of the binary M dwarf GJ 623. AO observations spread over 3 yr 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 m₁ = 0.371 ± 0.015 M _⊙ (4%) and m₂ = 0.115 ± 0.0023 M _⊙ (2%) for the primary and the secondary, respectively. Models are not consistent with color and mass, requiring very low metallicities.