  Star clusters projected onto dense stellar fields require field star
decontamination to confirm their nature and derive intrinsic photometric and
structural fundamental parameters. The present work focusses on the OCs or
candidates NGC5715, Lynga4,9, Trumpler23,26 and Czernik37 which are projected
against crowded bulge and/or disc fields. We develop a CMD field star
decontamination algorithm based on 2MASS data, and respective uncertainties, to
detect cluster star excesses over the background. On the other hand,
colour-magnitude filters are used to build stellar radial density profiles and
mass functions. The results convey compelling evidence that Ly9 and Cz37 are
intermediate-age open clusters, and their fundamental parameters are measured
for the first time. Tr23 is a particularly challenging object, since besides
high background level, its field presents variable absorption in near-IR bands.
We confirm it to be an intermediate-age open cluster. These OCs are located 0.9
- 1.6kpc within the Solar Circle, with ages similar to that of the Hyades.
Structurally, they are well described by King profiles. In all cases, core and
limiting radii are significantly smaller than those of nearby OCs outside the
Solar circle. We test the effect of background levels on cluster radii
determinations by means of simulations. They indicate that for central
clusters, radii may be underestimated by about 10--20%, which suggests that the
small sizes measured for the present sample reflect as well intrinsic
properties related to dynamical evolution effects. The objects probably have
been suffering important tidal effects that may have accelerated dynamical
evolution, especially in Cz37, the innermost object.
