A new detached K7 dwarf eclipsing binary system

We present an analysis of a new, detached, double-lined eclipsing binary system with K7 Ve components, discovered as part of the University of New South Wales (UNSW) Extrasolar Planet Search. The object is significant in that only six other binary systems are known with comparable or lower mass. Such systems offer important tests of mass-radius theoretical models. Follow-up photometry and spectroscopy were obtained with the 40-inch and 2.3-m telescopes at Siding Spring Observatory (SSO), respectively. An estimate of the radial velocity amplitude from spectral absorption features, combined with the orbital inclination (83.5°) estimated from light-curve fitting, yielded a total mass of M total= 1.041 ± 0.06 M⊙ and component masses of M A= 0.529 ± 0.035 M⊙ and M B= 0.512 ± 0.035 M⊙. The radial velocity amplitude estimated from absorption features (167 ± 3 km s−1) was found to be less than the estimate from the Hα emission lines (175 ± 1.5 km s−1). The light-curve fit produced radii of R A= 0.641 ± 0.05 R⊙ and R B= 0.608 ± 0.06 R⊙, and a temperature ratio of T B/T A= 0.980 ± 0.015. The apparent magnitude of the binary was estimated to be V= 13.9 ± 0.2. Combined with the spectral type, this gave the distance to the binary as 169 ± 14 pc. The timing of the secondary eclipse gave a lower limit on the eccentricity of the binary system of e≥ 0.0025 ± 0.0005. This is the most statistically significant non-zero eccentricity found for such a system, possibly suggesting the presence of a third companion.