Stellar spectroscopic parameters (T_eff and log g) of our programme stars. The open circle, open rectangles, and open triangles correspond to our targets: solar twin Y1194, turn-off stars, and subgiant stars, respectively. The solar value is indicated by a red star. A set of MIST isochrones with initial metallicities of [Fe/H] between 0 and 0.1, and age of 4 and 4.5 Gyr (Dotter 2016; Choi et al. 2016) are shown as solid lines.