  Early release science observations of the cluster NGC3603 with the WFC3 on
the refurbished HST allow us to study its recent star formation history. Our
analysis focuses on stars with Halpha excess emission, a robust indicator of
their pre-main sequence (PMS) accreting status. The comparison with theoretical
PMS isochrones shows that 2/3 of the objects with Halpha excess emission have
ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of
them are older than 10 Myr. The study of the spatial distribution of these PMS
stars allows us to confirm their cluster membership and to statistically
separate them from field stars. This result establishes unambiguously for the
first time that star formation in and around the cluster has been ongoing for
at least 10-20 Myr, at an apparently increasing rate.

Solar and Stellar Astrophysics