Investigated stars compared with the evolutionary tracks of M = 0.8 M_⊙ and [Fe/H] = − 2 (dash-dotted curve), − 3 (dashed curve), and − 4 (dotted curve). The crosses on the [Fe/H] = − 2 and [Fe/H] = − 4 evolutionary tracks mark stellar age of 13.4 Gyr. Symbols as in Fig. 2. For the five MW stars with the Gaia parallax available, the vertical lines connect the star’s positions corresponding to log g_sp (small black circles) and log g_Gaia (small black circles inside larger size circles). The cross in the right part indicates log g and T_eff error bars of 0.2 dex and 100 K, respectively.