RADIO-CONTINUUM OBSERVATIONS OF PLANETARY-NEBULA CANDIDATES FROM THE NORTHERN-HEMISPHERE

We analyzed radio continuum observations of unidentified IRAS point sources with far IR colors that are typical of planetary nebulae. These IRAS-selected planetary nebula candidates are located outside the galactic bulge and were observed with the Westerbork Radio Synthesis Telescope, We have detected 20 new planetary nebulae out of 82 observed candidates. The detected sources are very close to the galactic plane. The detection rate is highest in that part of the color-color diagram, where planetary nebulae are expected to spend most time during their evolution. The radio and IR properties are compared with PN detected in the same way in the galactic bulge and with optical planetary nebulae which fulfill the same selection criteria On average, the IR excess of the IRAS-selected and radio detected planetary nebula candidates is higher than for the optical planetary nebulae.