Distribution of vsin i. Top left: histogram of vsin i for the overall sample in this work. Only results from stars with S /N > 50 and log g < 5 are shown. Top right: histogram of vsin i for stars in different T_eff ranges, as marked in the figure. Bottom left: stellar number density distribution in the T_eff-vsin i plane. The solid line delineates the critical rotation velocity, V_c, as a function of T_eff, derived based on the ZAMS MIST isochrones (Choi et al. 2016). Bottom right: stellar number density distribution in the [Fe/H]–vsin i plane. Since we do not impose a prior limit on vsin i, our fit allows for negative vsin i values. A negative vsin i simply means that the star has a small rotation velocity, and the distribution at the negative tail serves as a proxy for the measurement uncertainties.