  The study of satellite galaxies can provide information on the merging and
aggregation processes which, according to the hierarchical clustering models,
form the larger spiral galaxies we observe. With the aim of testing
hierarchical models of galaxy formation, we have conducted an observational
program which comprises H$\alpha$ imaging for both the parent and the satellite
galaxies, taken from the compilation by Zaritsky et al. (1997) that contains
115 galaxies orbiting 69 primary isolated spiral galaxies. We have observed a
subsample of 37 spiral and irregular galaxies taken from the compilation
mentioned above. The aim of this study is to determine star formation
properties of the sample galaxies. In this work we present the preliminary
results of this program that we have carried out with the 1.8-m Vatican
Telescope (VATT).
