A search for planetary nebulae in M33

We searched for planetary nebulae (PNe) in the nearby spiral galaxy M33 using the Wide Field Camera at the 2.54 m Isaac Newton Telescope of La Palma (Spain). Images in the [O III] nebular line at lambda 5007 Angstrom, in the H alpha+[N II] lines around 6560 Angstrom, and in the continuum around 5550 Angstrom allowed us to detect a large number of emission line objects. Among them, 134 candidate PNe have been selected. In addition, we found 63 emission-line objects which have a non-negligible continuum emission, and for this reason they have been conservatively discarded from the group of candidate PNe. We have derived the PN luminosity function. It agrees very well with that of galaxies in the Local Group. The resulting distance to M33 is 840 +/- 90 kpc, in excellent agreement with the value obtained using Cepheids.