Redshift of formation as a function of stellar mass for a sample of VIPERS passive red galaxies. The error bars correspond to different burst duration (τ = 0.1 and 0.3 Gyr). Both calculations were based on the BC03 model assuming stellar metallicity evolving with mass (0.1 log (Z/Z_⊙) for the highest stellar mass bin). The cyan areas correspond to the 1σ weighted distribution of redshift of formation obtained for individual spectra for redshift bin 0.7 <z< 0.8 and different stellar mass bins.