Accurate Orbital Solution for the New and Metal-poor Eclipsing Binary Tycho 5227-1023-1

Abstract

The orbit and physical parameters of the previously unsolved double-lined eclipsing binary Tyc 5227-1023-1, discovered during the search for RR Lyr variable candidate members of the Aquarius stream, are derived using high-resolution échelle spectroscopy and V,{I}^\prime photometry. A synthetic spectral analysis of both components has been performed, yielding metallicity [M/H] = -0.63 ± 0.11 for both stars and a temperature for the secondary that is in close agreement with the one from the orbital solution, while the temperature of the primary is determined from photometry ({T}₁=6350 {{K}}). The masses and radii ({M}₁=0.96+/- 0.02,{M}₂=0.84+/- 0.01 {M}_⊙ , {R}₁=1.39+/- 0.01,{R}₂=0.98+/- 0.01 {R}_⊙ ) reveal that both stars have already slightly evolved away from the main-sequence band, having an age of about 7 Gyr, and the results of the synthetic spectral analysis support the claim of corotation with the orbital motion. The radial velocity of the system is -60+/- 2 {km} {{{s}}}^-1, while its distance, computed from orbital parameters and the derived reddening {E}_B-V=0.053, is 496 ± 35 pc. Even though Tyc 5227-1023-1 was initially treated as a possible member of the Aquarius stream, the results presented here disagree with reported values for this ancient structure and suggest a likely membership of the thick disk.