# Accurate orbital solution for the new and metal poor eclipsing binary Tycho~5227-1023-1

## TL;DR

This study precisely determines the orbital and physical parameters of the metal-poor eclipsing binary Tyc 5227-1023-1, revealing its evolutionary state and likely membership in the Galactic thick disk rather than the Aquarius stream.

## Contribution

The paper provides the first detailed orbital solution and physical characterization of Tyc 5227-1023-1, a metal-poor eclipsing binary, using high-resolution spectroscopy and photometry.

## Key findings

- Both stars are slightly evolved, about 7 Gyr old.
- The system's metallicity is [M/H] = -0.63.
- The binary is likely part of the thick disk, not the Aquarius stream.

## 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 variables candidate members of the Aquarius stream, are derived using high resolution \'echelle spectroscopy and $V$, $i^\prime$ photometry. Synthetic spectral analysis of both components has been performed, yielding metallicity [M/H] = $-0.63 \pm 0.11$ for both stars and the temperature of the secondary which 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 ($M_1 = 0.96 \pm 0.02, M_2 = 0.84 \pm 0.01$ M$_{\odot}$, $R_1 = 1.39 \pm 0.01, R_2 = 0.98 \pm 0.01$ R$_{\odot}$) 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 synthetic spectral analysis support the claim of co-rotation with the orbital motion. The radial velocity of the system is $-60 \pm 2$ km sec$^{-1}$ while its distance, computed from orbital parameters and the derived reddening $E_{B-V}$ = 0.053, is $496 \pm 35$ 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.