Special Astrophysical Observatory, N. Arkhyz, Karachai-Cherkesia 369167, Russia e-mail: email@example.com
2 Laboratoire d'Astrophysique de Grenoble, BP 53X, 38041 Grenoble Cedex, France
3 Observatoire de Genève, 1290 Sauverny, Switzerland
4 Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
5 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Accepted: 8 November 2006
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 to 0.9 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 and . The obtained orbital parallax of the system, mas, is 7 percent lower than the Hipparcos value. The absolute V magnitudes of the stars, derived from the measured speckle magnitude differences, are: and . The effective temperatures of the components, K and K, follow from the and color indices. The star metallicity value, estimated from the 6 m telescope spectrum, is [M/H] 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 . The existing data on the kinematics of GJ 765.2 and its chromospheric activity indicate that the binary belongs to the middle age ( yr) thin disk population of the galaxy.
Key words: stars: binaries: visual / stars: fundamental parameters / stars: late-type
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.
© ESO, 2007