Accurate masses of low mass stars GJ 765.2AB (0.83 M_⊙ + 0.76 M_⊙)

Abstract

Context: Because of the lack of precise masses, the coverage of the main-sequence empirical mass-luminosity relation for stars in the mass range from 0.6 M_⊙ to 0.9 M_⊙ is incomplete. The nearby K-type visual and spectroscopic binary GJ 765.2 = MLR 224 is a good candidate for new reliable points in this significant part of the relation.
Aims: We have found a combined orbital solution for the pair and derived physical properties of the components using interferometric and spectroscopic data.
Methods: The diffraction-limited speckle observations were mostly collected at the 6 m BTA telescope, and the velocities of the components were obtained using the CORAVEL radial velocity scanner on the Swiss 1 m telescope.
Results: In a combined solution, the orbital period is found to be 11.919 yr. The masses of the GJ 765.2 components are M_A=0.831± 0.020 M_⊙ and M_B=0.763± 0.019 M_⊙. The obtained orbital parallax of the system, π_orb=31.0±0.5 mas, is 7 percent lower than the Hipparcos value. The absolute V magnitudes of the stars, derived from the measured speckle magnitude differences, are: M_V^A=5.99±0.04 and M_V^B=6.64±0.05. The effective temperatures of the components, T_eff^A=5060±130 K and T_eff^B=4690±160 K, follow from the V-K and J-K color indices. The star metallicity value, estimated from the 6 m telescope spectrum, is [M/H]=-0.35±0.15 dex.
Conclusions: .The presented individual masses have 2.4% and 2.5% relative accuracies. Therefore, the components of GJ 765.2 rank among a dozen stars with masses accurate to within a few percent in the mass range 0.6-0.9 M_⊙. The existing data on the kinematics of GJ 765.2 and its chromospheric activity indicate that the binary belongs to the middle age (3-4× 10⁹ yr) thin disk population of the galaxy.

Based on observations made with the 6 m BTA telescope, which is operated by the Special Astrophysical Observatory, Russia, and the Observatoire de Haute-Provence, operated by the Centre National de la Recherche Scientifique de France. Tables 1 and 2 are only available in electronic form at http://www.aanda.org