noteworthy. Indeed, there is a growing body of evidence that the radial distribution of BS stars in GCs might be bimodal, as shown by [@Ferraro97] for or [@Ivo97] and [@Piotto97] for . What makes our result for M55 of some interest is that this distribution has been interpreted in terms of environmental effects on the production of BS stars. However, the fact that M55 has a very low concentration (c=0.8), while M3 and NGC 1851 are high concentration clusters (c=1.85 and c=2.24 respectively, Djorgovski 1993), might make this conclusion at least questionable.

Luminosity and mass function \[M55lf\]
======================================

From the CMD we have derived a luminosity function (LF) for the stars of M55. Figure \[M55fdl\] shows the LFs in the different annuli defined in the previous Section (inner, intermediate and outer).

The three LFs have been normalized to the star counts of the SGB region in the magnitude interval $15.90<V<17.40$, after subtracting the contribution of the background/foreground stars scaled to the area of each annulus. In the lower part of Figure \[M55fdl\], we show also the LF of the background/foreground stars estimated from the star counts at $r>1.3~r_t$ vertically shifted for clarity. In order to reduce contamination by those stars, 