In 1993/1994 we started a long-range photometry program on clusters of galaxies in order to estimate in detail the cluster Luminosity Function (LF) and the morphology of the brightest cluster galaxies. Our aim was to gain more accurate knowledge on this topic both to better understand formation and evolution, and to improve the comparison with numerical simulations. Straightforward scientific drivers are at the basis of this investigation: the Luminosity Function of cluster galaxies at present time is the result of cluster initial formation and subsequent evolution - taking into account internal phenomena and external interactions.
It is reasonable, and to some extent expected, that at formation the galaxy mass function is a universal constant. In this case, assuming that every evolutionary process keeps a constant M/L ratio, it would be reasonable to expect a universal LF, even if it cannot be excluded that evolution and richness might play a role on this stage. Present day observing evidence is, however, that the mass is organised into differently shaped and differently luminous galaxies - the galaxy population depending strongly on the cluster density and morphology. It would be strange if Nature, in the unfolding of this multivariate process, could set to work such a fine-tuning as to maintain the exact proportionality between mass and luminosity, even assuming a universal initial mass function.
The assumption of a universal LF for all the clusters (Colless 1989 and, more recently, Threntham 1997, 1998) might therefore be too coarse of a tool for characterizing the cluster population. Infall and ICM-galaxies interaction might further perturb the shape of the LF during the evolution of the cluster. In this respect it seemed of fundamental importance to evaluate the faint end of the LF. Meanwhile, important work has been published on this topic following the excellent papers on the Virgo Cluster by Binggeli et al. (1988). Biviano et al. (1995) approached the study by selecting a catalogue of bright galaxies in the Coma cluster. Undoubtedly, this direct method is a sound way to proceed, but the construction of a spectrophotometric catalogue of a large number of rich clusters demands an unaffordable amount of time with a 4 meter class telescope.
Another very interesting photometric approach is that of Bernstein et al. (1995), for the same Coma cluster, where particular attention has been given to the faint end of LF. In that work, however, the bright part remains ill-defined.
A general consideration of the different studies is the limited application of their results, often making it impossible to compare directly the catalogue and Lfs. This led us to build our consistent photometric catalogues.
In this paper we outline at first the selected sample: other authors might be interested in this bookkeeping (avoiding or comparing duplications) and it will help the reader to follow our work to its the completion.
Secondly, we detail our observational strategy and methods of data reduction, particularly in those points where they differ from the standard analysis used in the literature. They will then form a basic reference for other papers in preparation. The observing strategies are strongly related and tuned to the data analysis methods. These procedures have first been applied to the cluster Abell 496 (see also Molinari et al. 1998, Paper I, for discussion on LF), for which we publish here the photometry.
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