Location of stars belonging to C2 star cluster (< 2.5″). Left panel: Location of stars in CMD. The white cross corresponds to the brightest star. The white squares are those stars with 23 < F814W <  24. Stars with F814W >  24 are shown as white dots. Theoretical PARSEC isochrones of 10 Myr, 100 Myr, 250 Myr, 500 Myr, 1 Gyr, and 5 Gyr are shown as colour-coded curves according to their stellar masses given by the theoretical isochrones. K1 and K2 O-type stars from Gull et al. (2022) are shown as the cyan triangle and the cyan diamond, respectively. Those massive stars are capable of ionising individually two Leo A H II regions. Right panel: Location of stars of the C2 star cluster in Leo A H II region (grey contours), superimposed with the HST/ACS F814W frame.