Planetary nebulae in the outer disk and halo of M31

We developed a method to identify planetary nebula (PN) candidates in imaging data of the Sloan Digital Sky Survey (SDSS). This method exploits the SDSS' five-band sampling of emission lines in PN spectra, which results in a color signature distinct from that of other sources and can be applied to galaxies where PNe appear as point sources. We tested this method with SDSS data of M31. In areas searched by previous authors, we were able to recover more than 3/4 of the earlier known PNe, with incompleteness caused largely by crowding effects. We then extended this search to the full area of M31's halo and disk sampled by the SDSS. We will present the method and early results from this project