In the last ten years, two comprehensive studies of dwarf galaxy populations
in galaxy clusters have been carried out based on photographic plate material
taken at the Las Campanas du Pont 100-inch telescope. This telescope had a unique
imaging capability, being equipped with a wide field (
)
camera for 50 cm 
50 cm high resolution (10.9 arcsecs mm
) photographic
glass plates (Bowen & Vaughan Jr. 1973). Because it was the only telescope worldwide
offering such a facility, it became of great importance for the early
exploration of dwarf populations in galaxy aggregations like clusters and groups.
The first surveyed cluster was the nearest cluster in Virgo, which also is the dominating structure of the Local Supercluster. Based on the Virgo Cluster Catalogue (VCC, Binggeli et al. 1985), Binggeli, Sandage and collaborators presented a series of papers on different aspects of this cluster and its member galaxies (Binggeli et al. 1984, 1987; Sandage & Binggeli 1984; Sandage et al. 1985a,b) which significantly improved the knowledge in several fields of research, e.g. morphological classification of dwarf galaxies, their photometric and physical properties, type-specific luminosity functions of galaxies, variation of galaxy type mixture in dependence of the environmental density, substructure in clusters of galaxies.
Ferguson (1989), in collaboration with Sandage, carried out a dwarf galaxy study in the Fornax cluster a few years later. This less rich cluster lies roughly at the same distance to the Local Group as the Virgo cluster. Ferguson & Sandage (1988) investigated the cluster luminosity function (LF) and compared it with the LFs of Virgo and five nearby groups of galaxies (Ferguson & Sandage 1991). The analysis of the morphological type distributions revealed the extension of the morphology-density relation for cluster galaxies (Dressler 1980a; Binggeli et al. 1987) to group environments.
Many interesting results have been found for the different galaxy types, in particular for the dwarf galaxies, based on the data of the two cluster populations in Virgo and Fornax. However due to the small number of only two cluster studies, it is still debated whether the observations reflect "cosmic'' properties or they are characteristic for only a specific cluster population. To follow up this question, it was planned to carry out a further dwarf population study in a more distant cluster which would be as extensive and detailed as the previous two cluster studies. Our intention was to take photographic plates with the du Pont telescope but the wide-field camera was no longer available. We therefore worked with existing du Pont plates which were part of the material used to establish the morphology-density relation for classical Hubble types (Dressler 1980b).
Upon a visual examination of high quality film copies of ten du Pont plates each
covering one galaxy cluster with a redshift between 0.01<z<0.03, the
Centaurus cluster at 
kms
appeared as the most promising cluster
for our project. An excellent photographic exposure, taken under good seeing conditions,
was available. Additionally, there are several scientific reasons in favour of this cluster.
The giant galaxies in Centaurus show a pronounced bimodal distribution in the sky, pointing to
a prominent substructure feature. This brings up the question about the distribution of the
dwarf galaxies. Moreover, a remarkable bimodal velocity distribution, known as Cen30
and Cen45, has been reported by Lucey et al. (1980) and Lucey et al. (1986). Is it caused
by the dynamics of an infalling group of galaxies (Cen45) into the main cluster component (Cen30)
both belonging to the same young cluster which is still in the stage of
formation, or is the gravitational force of a nearby "Great Attractor" (Lynden-Bell et al. 1988)
responsible for the unusual velocities? Amongst others, these questions will be of special
interest within our study.
All results of our Centaurus cluster survey are collected in a series of five papers. The present PaperI describes the technical aspects we used to establish the sample galaxies of the Centaurus Cluster Catalogue and to acquire structure parameters for each galaxy. The subsequent papers of the series will appear in the main journal of A&A:
In PaperII we discuss the distributions of the individual Hubble types within the surveyed cluster region. We report the detection of a prominent zone of very low galaxy density and explore the galaxy type mixture. After deriving the clusterspecific parameters, the Centaurus galaxy population is compared to those of the Virgo and the Fornax cluster. Recent results of the Cen30/45 puzzle have been taken into account to infer consequences on the real spatial distribution of the Centaurus cluster galaxies. This leads to a new distance of Centaurus relative to Virgo which is discuss within a cosmological context.
In PaperIII the luminosity functions are presented for the complete
cluster population as well as for many individual Hubble types. Their
properties are discussed and compared to the corresponding LFs in Virgo.
It is suggested that the individual LFs of S0's, spirals, and dE&dS0's are
good distance indicators. Furthermore, we give new reasons which definitively
call into question the reliability of the Schechter parameter 
to measure
cluster distances.
PaperIV is dedicated to the systematic photometric properties of the early-type dwarf galaxies. Moreover, we use two relations to establish a new distance for Centaurus and Fornax relative to Virgo, respectively.
Finally, in PaperV a 2D-substructure analysis is carried out on the three cluster populations of Centaurus, Virgo, and Fornax. For the first time dwarf galaxies are taken into account for this purpose.