HRD of NGC 6819 showing RC and RGB member stars. Except for standard single stars, some are members of binary systems, some are overmassive stars, and one star (KIC4937011) is undermassive. The solid lines show evolutionary tracks from the RGB phase until the first thermal pulse in the AGB phase for a 1.60 M_⊙ and a 2.50 M_⊙ star with solar metallicity, and the dotted line represents a 0.70 M_⊙ star with solar metallicity from the beginning of the CHeB stage until the first thermal pulse in the AGB phase. KIC4937011 is dimmer and cooler than other member stars at the same evolutionary stage, and it would be compatible with a 1.60 M_⊙ RGB star if we had no information about its evolutionary state and mass. For a full description of the models used in the figure, see Handberg et al. (2017).