M55 is a low central concentration, $c=0.8$ [@Trager95], low metallicity, ${\rm [Fe/H]}=-1.89$ [@Zinn80], cluster located at $\simeq4.9$ kpc from the Sun [@Mand96]. Although it is a nearby object, it has received little or sporadic attention until very recently. The works of [@Mateo96] and [@Fahlman96] presented photometric datasets of M55 that have been used principally to establish the age and the tidal extension of the Sagittarius dwarf galaxy. [@Mand96] published the first deep (down to $V\simeq24.5$) photometry of the cluster (other previous studies of the stellar population of M55 are in Lee, 1977; Shade, VandenBerg, and Hartwick, 1988; and Alcaino , 1992). From the data of a field at $\simeq2$ core radii from the center, [@Mand96] estimated a new apparent distance modulus for M55, $(m-M)_V=13.90\pm0.09$, and from the luminosity function they found that the high-mass end of the mass function ($0.5<M/M_{\odot}<0.8$) is well fitted by a power law with $x=0.5\pm0.2$, whereas at the low-mass end ($M/M_{\odot}<0.4$) the mass function has a slope of $x=1.6\pm0.1$.

From the dynamical point of view, M55 has been previously studied by [@Pryor91] in their papers on the mass-to-light ratio of globular clusters. Their principal conclusion is that this cluster might have a power law mass function 