Ultra-precise Masses and Magnitudes for the Gliese 268 M-dwarf Binary

Recent advances in astrometry using interferometry and precision radial velocity techniques combined allow for a significant improvement in the precision of masses of M‐dwarf stars in visual systems. We report recent astrometric observations of Gliese 268, an M‐dwarf binary with a 10.4 day orbital period, with the IOTA interferometer and radial velocity observations with the ELODIE instrument. Combining these measurements leads to preliminary masses of the constituent stars with uncertainties of 0.4%. The masses of the components are 0.22596±0.00084 M_⊙ for the primary and 0.19230±0.00071 M_⊙ for the secondary. The system parallax is determined by these observations to be 0.1560±.0030 arcsec (2.0% uncertainty) and is within Hipparcos error bars (0.1572±.0033). We tested these physical parameters, along with the near‐infrared luminosities of the stars, against stellar evolution models for low‐mass stars. Discrepancies between the measured and theoretical values point toward a low‐level departure from the predictions. These results are among the most precise masses measured for visual binaries.