Hertzsprung-Russel diagram of the observed sources. Overlaid are the PARSEC 1.2S isochrones and mass tracks from Bressan et al. (2012). The dots represent the mean bolometric luminosity for each star as a function of T_eff. The vertical bars indicate the minimum and maximum range of L_* for each star. The cross at the bottom shows the typical uncertainty. In our analysis, we only regarded sources with 0.2 M_⊙ ≤ M ≤ 2.0 M_⊙ and 5.5 ≤ log(τ[yr]) ≤ 7.3 in order to exclude outliers in the Hertzsprung-Russel diagram.