Color–magnitude diagram of the field of LH 91. All magnitudes are already corrected for the extinction contribution of our Galaxy and LH 91. The small black dots are the targets of the whole sample (9423 stars). Small gray-filled dots are the stars with photometric uncertainties < 0.05 mag in each band. The large red dots represent the PMS star candidates with Hα excess emission at the 3σ level. Solid green and dashed light-blue lines show the theoretical isochrones from Bressan et al. (2012) for ages 8 Myr and 1.5 Gyr, respectively, metallicity Z = 0.007, and a distance modulus (m_V − M_V)₀ = 18.55.