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

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 ($T_1=6350K$). The masses and radii ($M_1=0.96\pm 0.02,M_2=0.84\pm 0.01M_{\odot },$ $R_1=1.39\pm 0.01,R_2=0.98\pm 0.01R_{\odot }$) 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 $-60\pm 2km{s}^{-1}$, 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.