  Eta Chamaeleontis is a unique young (~9 Myr) association with 18 systems
concentrated in a radius of ~35 arcmin, i.e. 1pc at the cluster distance of
97pc. No other members have been found up to 1.5 degrees from the cluster
centre. The cluster mass function is consistent with the IMF of other rich
young open clusters in the higher mass range but shows a clear deficit of low
mass stars and brown dwarfs with no objects below 0.1Msun. The aim of this
paper is to test whether this peculiar mass function could result from
dynamical evolution despite the young age of the cluster. We performed N-body
numerical calculations starting with a log-normal IMF and different initial
conditions in terms of number of systems and cluster radius using the code
NBODY3. We simulated the cluster dynamical evolution over 10 Myr and compared
the results to the observations. We found that it is possible to reproduce eta
Cha when starting with a very compact configuration (with Ninit=40 and
R0=0.005pc) which suggests that the IMF of the association might not be
abnormal. The high initial density might also explain the deficit of wide
binaries that is observed in the cluster.
