5 Conclusions

We use the method of subtracted images to identify PNc candidates as those objects with emission in H$\alpha$ or [O III] lines, but with a lack of emission in the continuum filter images. We find that the uncritical use of a single scale factor may introduce errors comparable to those of other error sources even when using continuum filters close to the on-line filters and that these errors increase with the separation in wavelength between on-line and continuum filters.

We find 48 sources that fulfill the criteria given above and comparing our results with those of a previous search by Magrini et al. (2000, 2001) we found good agreement in the objects detected, but we derive smaller fluxes.

Following the criterion that those objects with an [OIII]/H$\alpha$ ratio greater that 1.0 are bona fide PNe, we find 14 such objects in the area searched, 4 of them had not been reported before. The rest are probably either low excitation PNe or small H II regions. A spectroscopic follow-up study is needed to find the true nature of the sources.

Acknowledgements

LC acknowledges a CONACyT (México) posdoctoral grant at the IAC. AH acknowledges support for this work from the Spanish DGES under project PB97-1438-C02-01 and from the Gobierno Autonómico de Canarias under project PI1999/008. The data presented here have been taken using ALFOSC, which is owned by the Instituto de Astrofísica de Andalucía (IAA) and operated at the Nordic Optical Telescope under agreement between IAA and the NBIfA of the Astronomical Observatory of Copenhagen.