1 Introduction

The Pleiades star cluster is an ideal hunting ground for substellar objects mainly due to its richness of members, young age, proximity and scarce interstellar absorption. Taking advantage of these properties, several photometric searches aimed at finding brown dwarfs (BDs) have been performed during the last decade (see Hambly 1998 for a review). The recent spectroscopic confirmations of Pleiades objects at the stellar-substellar boundary and genuine substellar members (Basri et al. 1996; Rebolo et al. 1996; Martín et al. 1998; Stauffer et al. 1998) previously discovered as a result of optical photometric surveys in small areas suggest that a numerous population of very low-mass objects may be found in this cluster. This encourages future surveys to discover BDs cooler and less massive than those ($0.075-0.05\,M_{\odot}$) previously detected by these surveys. The Pleiades offers a unique opportunity to establish the observational properties of these rather elusive objects and to characterize the initial mass function in the substellar mass regime.

1.1 The survey

As part of an on-going search for BDs in the Pleiades, we have conducted a deep CCD-based IZ survey using the 2.5m Isaac Newton Telescope (INT) located on the Observatorio del Roque de los Muchachos (ORM, island of La Palma). The area covered was 1.05deg² within the central region of the cluster (a small fraction of the total area was also observed using the R filter). More than 40 faint ($I\ge 17.5$), very red ($I-Z \ge 0.5$) objects have been detected down to $I\,\sim\,22$. Their location in the colour-magnitude diagram suggests cluster membership. In this paper we report on the details of this survey along with the selection criteria. We provide IZ magnitudes, coordinates and finder charts for all candidates. Preliminary results of this survey were presented in Zapatero Osorio et al. (1997a, 1998a). An extensive discussion on the membership of the candidates and derivation of the initial mass function will be given in a forthcoming paper (Zapatero Osorio et al. 1998b).