Colour–magnitude diagram of Trumpler 20 from the photometric study of Carraro et al. (2010). Only stars within 6 arcmin from the cluster centre are considered. Over-imposed are three isochrones displaced using as reddening 0.34 mag and as apparent distance modulus 13.6 mag. The solid dashed isochrone is the best fit, for an age of 1.5 Gyr. To illustrate uncertainties in the age, we display two additional isochrones (solid red symbols) for an age of 1.4 and 1.7 Gyr. See text for details.