The fate of the pre-main sequence-rich clusters Collinder197 and vdB92:
  dissolution?
  We investigate the nature and possible evolution of the young Galactic star
clusters Collinder 197 (Cr 197) and vdB 92. The colour-magnitude diagrams
(CMDs) are basically characterised by a poorly-populated MS and a dominant
fraction ($\ga75%$) of PMS stars, and the combined MS and PMS CMD morphology in
both clusters consistently constrains the age to within $5\pm4$ Myr, with a
$\sim10$ Myr spread in the star formation process. The MS$ + $PMS stellar
masses are $\approx660^{+102}_{-59} \ms$ (Cr 197) and $\approx750^{+101}_{-51}
\ms$ (vdB 92). Cr 197 and vdB 92 appear to be abnormally large, when compared
to clusters within the same age range. They have irregular stellar radial
density distributions (RDPs) with a marked excess in the innermost region, a
feature that, at less than 10 Myr, is more likely related to the star formation
and/or molecular cloud fragmentation than to age-dependent dynamical effects.
The velocity dispersion of both clusters, derived from proper motions, is in
the range $\sim15 - 22 \kms$. Both clusters appear to be in a super-virial
state, with velocity dispersions higher than those expected of
nearly-virialised clusters of similar mass and size. A possible interpretation
is that Cr 197 and vdB 92 deviate critically from dynamical equilibrium, and
may dissolve into the field. We also conclude that early cluster dissolution
leaves detectable imprints on RDPs of clusters as massive as several $10^2
\ms$. Cr 197 and vdB 92 may be the link between embedded clusters and young
stellar associations.
