40 and 30 seconds respectively. The night was not photometric and the observing conditions improved as we moved from the outer fields to the internal ones. Information on the various fields and on all the technicalities of the reduction and analysis are reported in the appendix of the paper.

The $V$ *vs.* $(V-I)$ color magnitude diagram for a total of 33615 stars of M55 is shown in Figures \[M55tot\] and \[cmdradial\]. In total we detected 36800 objects of the cluster$+$field; $\simeq9\%$ of them were eliminated after having applied a selection in the [DAOPHOT II]{} PSF interpolation parameters as in [@Piotto90a]. Although the exposure time was relatively short, the brightest stars of the red giant branch and of the asymptotic giant branch are saturated, though they can be still used for the radial star counts. We have omitted them from the final CMD.

In the following we will analyze the data using a division into three radial subsamples: inner ($r\le r_c$), intermediate ($r_c<r\le 2r_c$), and outer ($2r_c<r\le r_t$). The core radius is $r_c=143\arcsec$, as found from the radial density profile analysis ( Section 5). In Figure \[cmdradial\] we show the brightest part of the CMD of M55, divided in the three 