Lighting up stars in chemical evolution models: the CMD of Sculptor

We present a novel approach to draw the synthetic colour–magnitude diagram (CMD) of
galaxies, which can provide – in principle – a deeper insight in the interpretation and understanding
of current observations. In particular, we ‘light up’ the stars of chemical evolution
models, according to their initial mass, metallicity and age, to eventually understand how the
assumed underlying galaxy formation and evolution scenario affects the final configuration of
the synthetic CMD. In this way, we obtain a new set of observational constraints for chemical
evolution models beyond the usual photospheric chemical abundances. The strength of our
method resides in the very fine grid of metallicities and ages of the assumed data base of stellar
isochrones. In this work, we apply our photochemical model to reproduce the observed CMD
of the Sculptor dSph and find that we can reproduce the main features of the observed CMD.
The main discrepancies are found at fainter magnitudes in the main sequence turn-off and
sub-giant branch, where the observed CMD extends towards bluer colours than the synthetic
one; we suggest that this is a signature of metal-poor stellar populations in the data, which
cannot be captured by our assumed one-zone chemical evolution model.