Location of NGC 4523 on the main sequence relation (filled cyan square) defined by star-forming galaxies in the Virgo cluster (adapted from Boselli et al. 2023). Late-type galaxies (≥Sa) are indicated by black symbols, early-type galaxies by red symbols. Filled dots are for H I gas rich objects (HI-def ≤ 0.4), while H I deficient objects (HI-def > 0.4) by empty circles. Star formation rates have been derived assuming stationary conditions. The Y-axis on the right side gives the corresponding Hα luminosities corrected for dust attenuation. The black solid line shows the best fit obtained for gas-rich star-forming systems. The horizontal dotted and dashed lines indicate the corresponding SFR derived using the number of ionising photons produced by an O3 class III and a B0 class III star as derived using the model atmospheres of Sternberg et al. (2003). The typical uncertainty in the data is shown at the lower left corner.