* Astronomy

Title: A new detached K7 dwarf eclipsing binary system
Authors: T.B. Young, M.G. Hidas, J.K. Webb, M.C.B. Ashley, J.L. Christiansen, A. Derekas, C. Nutto

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 Extrasolar Planet Search. The object is significant in that only 6 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 2.3m telescopes at SSO respectively. An estimate of the radial velocity amplitude from spectral absorption features, combined with the orbital inclination (83.5 deg) estimated from lightcurve fitting, yielded a total mass of M=(1.041 ±0.06)M_sun and component masses of M_A=(0.529 ±0.035)M_sun and M_B=(0.512 ±0.035)M_sun. The radial velocity amplitude estimated from absorption features (167 ±3)kmps was found to be less than the estimate from the H_alpha emission lines (175 ±1.5)kmps. The lightcurve fit produced radii of R_A=(0.641 ±0.05)R_sun and R_B=(0.608 ±0.06)R_sun, 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 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.

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