We present a semi-analytical approach that, applied to the Hess diagram of
a young star cluster, is able to retrieve the values of mass, age, star-formation
spread, distance modulus, foreground and differential reddening, and binary fraction.
The global optimisation method known as adaptive simulated annealing (ASA) is used
to minimise the residuals between the observed and simulated Hess diagrams of a star
cluster. The simulations are realistic and take the most relevant parameters of young
clusters into account. Important features of the simulations are: a normal (Gaussian)
differential reddening distribution, a time-decreasing star-formation rate, the unresolved
binaries, and the smearing effect produced by photometric uncertainties on Hess diagrams.
Free parameters are: cluster mass, age, distance modulus, star-formation spread, foreground
and differential reddening, and binary fraction.
Even for low-mass star clusters, our approach is sensitive to the values of cluster mass, age,
distance modulus, star-formation spread, foreground and differential reddening and, to a
lesser degree, binary fraction. Compared with simpler approaches, the inclusion of binaries,
a decaying star-formation rate and a normally distributed differential reddening, appear
to yield more constrained parameters, especially the mass, age and distance from the Sun.