  We derive stellar masses, ages and star formation histories of massive
early-type galaxies in the z=1.237 RDCS1252.9-2927 cluster and compare them
with those measured in a similarly mass-selected sample of field contemporaries
drawn from the GOODS South Field. Robust estimates of these parameters are
obtained by comparing a large grid of composite stellar population models with
8-9 band photometry in the rest-frame NUV, optical and IR, thus sampling the
entire relevant domain of emission of the different stellar populations.
Additionally, we present new, deep $U$-band photometry of both fields, giving
access to the critical FUV rest-frame, in order to constrain empirically the
dependence on the environment of the most recent star formation processes. We
find that early-type galaxies, both in the cluster and in the field, show
analogous optical morphologies, follow comparable mass vs. size relation, have
congruent average surface stellar mass densities and lie on the same Kormendy
relation. We also that a fraction of early-type galaxies in the field employ
longer timescales, $\tau$, to assemble their mass than their cluster
contemporaries. Hence we conclude that, while the formation epoch of early-type
only depends on their mass, the environment does regulate the timescales of
their star formation histories. Our deep $U$-band imaging strongly supports
this conclusions. It shows that cluster galaxies are at least 0.5 mag fainter
than their field contemporaries of similar mass and optical-to-infrared colors,
implying that the last episode of star formation must have happened more
recently in the field than in the cluster.
