  We present the results of a Near-Infrared deep photometric survey of a sample
of six embedded star clusters in the Vela-D molecular cloud, all associated
with luminous (~10^3 Lsun) IRAS sources. The clusters are unlikely to be older
than a few 10^6 yrs, since all are still associated with molecular gas. We
employed the fact that all clusters lie at the same distance and were observed
with the same instrumental setting to derive their properties in a consistent
way, being affected by the same instrumental and observational biases. We
extracted the clusters' K Luminosity Functions (KLF) and developed a simple
method to correct them for extinction, based on colour-magnitude diagrams. The
reliability of the method has been tested by constructing synthetic clusters
from theoretical tracks for pre-main sequence stars and a standard Initial Mass
Function (IMF). The clusters' IMFs have been derived from the dereddened KLFs
by adopting a set of pre-main sequence evolutionary tracks and assuming coeval
star formation. All clusters are small (~100 members) and compact (radius
\~0.1-0.2 pc); their most massive stars are intermediate-mass (~2-10 Msun)
ones. The dereddened KLFs are likely to arise from the same distribution,
suggesting that the selected clusters have quite similar IMFs and star
formation histories. The IMFs are consistent with those derived for field stars
and clusters. Adding them together we found that the ``global'' IMF appears
steeper at the high-mass end and exhibits a drop-off at ~10 Msun. In fact, a
standard IMF would predict a star with M>22.5 Msun within one of the clusters,
which is not found. Hence, either high-mass stars need larger clusters to be
formed, or the IMF of the single clusters is steeper at the high-mass end
because of the physical conditions in the parental gas.

Astrophysics