  Context: The calibration of binary systems with accurately known masses
and/or radii provides powerful tools to test stellar structure and evolution
theory and to determine the age and helium content of stars. We study the
eclipsing double-lined spectroscopic binary system RS Cha, for which we have
accurate observations of the parameters of both stars (masses, radii,
luminosities, effective temperatures and metallicity). Aims: We have calculated
several sets of stellar models for the components of the RS Cha system, with
the aim of reproducing simultaneously the available observational constraints
and to estimate the age and initial helium abundance of the system. Methods:
Using the CESAM stellar evolution code, we model both components starting from
the initial mass and metallicity and adjusting the input parameters and physics
in order to satisfy the observational constraints. Results: We find that the
observations cannot be reproduced if we assume that the abundance ratios are
solar but they are satisfied if carbon and nitrogen are depleted in the RS Cha
system with respect to the Sun. This is in accordance with the abundances
observed in other young stars. The RS Cha system is in an evolutionary stage at
the end of the PMS phase where models are not strongly sensitive to various
physical uncertainties. However we show that the oscillations of these two
stars, which have been detected, would be able to discriminate between
different options in the physical description of this evolutionary phase.
