1 Introduction

Planetary nebulae (PNe) represent one of the final stages in the evolution of low and intermediate mass stars. They have been used to trace the chemical evolution of galaxies, not only in the Milky Way (see Esteban & Peimbert 1995 and references therein) but also in close neighbours such as the LMC (Dopita et al. 1997), M 31 (Richer et al. 1999; Jacoby & Ciardullo 1999) and M 32 (Richer et al. 1999). Extragalactic PNe have also been used as secondary distance indicators by means of the so-called planetary nebulae luminosity function (PNLF, see Jacoby 1997, and references therein). For this technique, complete samples of PNe up to a given magnitude are an important requirement, not the least of these being for defining the actual form of the PNLF (see Méndez 2000). Recently Magrini et al. (2000) announced the detection of 134 candidate planetary nebulae (PNc) in M33. This galaxy has received recent attention because, as stated by Magrini et al. (2000), it is one of the important members of the Local Group for which the PN population was poorly known. In that paper the objects were detected in H$\alpha$, [O III] and continuum images. Since we have acquired similar images in a deeper search made by us for LBV candidates in a restricted region of M33, we report on the PNc we have found and compare the PNc reported by Magrini et al. (2000) with the sources detected by us. While our search is limited to a smaller spatial area, we should detect fainter PNc.

We find that we recover all of the PNc reported by Magrini et al. (2000) in the region observed by us, but also find new objects with similar characteristics, i.e. strong emission in H$\alpha$ or [O III] and lack of emission in the continuum filter images. In order to contribute to the study of these objects in M33 we present here the results of the search.