A new detached K7 dwarf eclipsing binary system

August 2006 • 2006MNRAS.370.1529Y

Authors • Young, T. B. • Hidas, M. G. • Webb, J. K. • Ashley, M. C. B. • Christiansen, J. L. • Derekas, A. • Nutto, C.

Abstract • 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 +/- 0.06M_solar and component masses of M_A = 0.529 +/- 0.035M_solar and M_B = 0.512 +/- 0.035M_solar. The radial velocity amplitude estimated from absorption features (167 +/- 3kms^-1) was found to be less than the estimate from the Hα emission lines (175 +/- 1.5kms^-1). The light-curve fit produced radii of R_A = 0.641 +/- 0.05R_solar and R_B = 0.608 +/- 0.06R_solar, 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 +/- 14pc. 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.

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Jessie Christiansen

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