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Astron. Astrophys. 355, 713-719 (2000)

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1. Introduction

Extragalactic planetary nebulae (PNe) are known in almost all galaxies of the Local Group. Most of them were discovered in the last decade by means of continuum-subtracted images in the bright nebular line of [O III] at 5007 Å (Ciardullo et al. 1989; Jacoby 1989). M33, one of the two other large spiral galaxies of the Local Group besides the Milky Way, is to our knowledge the only major nearby galaxy which has not been searched for PNe yet. We aimed to fill up this gap taking advantage of new observational capabilities offered by a wide field camera which has recently become operational at the Isaac Newton telescope of La Palma. [O III], H[FORMULA] and continuum images, following the procedure described in Jacoby (1989), allowed us to detect 134 candidate PNe in M33 and a large number of other emission line objects (mostly HII regions). In this paper we report on the discovery of these PNe, describe the selection criteria and the properties of these objects. Future work is planned to study spectroscopically the individual candidates, confirm their nature and determine their physical properties. In Sect. 2 we present the observation and data reduction. Sect. 3 contains the analysis of data. The classification of the detected emission line objects according to their size and line ratios is done in Sect. 4. With the candidates PNe we construct their luminosity function and determine the distance of M33 (Sect. 4). Conclusions are given in Sect. 5.

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© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000