Infrared planetary nebulae in the NRAO VLA sky survey

In order to construct a sample of planetary nebulae (PNe) unbiased by dust extinction, we first selected the 1358 sources in the IRAS Point Source Cat alog north of J2000 declination delta = -40 degrees having measured S(25 mu m) greater than or equal to 1 Jy and colors characteristic of PNe: detecti ons or upper limits consistent with both S(12 mu m) less than or equal to 0 .35S(25 mu m) and S(25 mu m) greater than or equal to 0.35S(60 mu m). The m ajority are radio-quiet contaminating sources such as asymptotic giant bran ch stars. Free-free emission from genuine PNe should make them radio source s. The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog were us ed to reject radio-quiet mid-infrared sources. We identified 454 IRAS sourc es with radio sources brighter than S approximate to 2.5 mJy beam(-1) (equi valent to T approximate to 0.8 K in the 45 " FHWM NVSS beam) by positional coincidence. They comprise 332 known PNe in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae and 122 candidate PNe, most of which lie at ver y low Galactic latitudes. Exploratory optical spectroscopic observations su ggest that most of these candidates are indeed PNe optically dimmed by dust extinction, although some contamination remains from H II regions, Seyfert galaxies, etc. Furthermore, the NVSS failed to detect only 4% of the known PNe in our infrared sample. Thus it appears that radio selection can great ly improve the reliability of PN candidate samples without sacrificing comp leteness.