  We have fitted the surface brightness of a sample of 79 elliptical galaxies
pertaining to the Coma cluster of galaxies using the Sersic profile. This model
is defined through three primary parameters: scale length (a), intensity
(\Sigma_0), and a shape parameter (\nu); physical and astrophysical quantities
may be computed from these parameters. We show that correlations are stronger
among primary parameters than the classical astrophysical ones. In particular,
the galaxies follow a high correlation in \nu and a parameters. We show that
the \nu and a correlation satisfies a constant specific entropy condition. We
propose to use this entropy relation as distance indicator for clusters.
