Observations of 23 Planetary Nebulae at 408 MHz

Abstract

Various observers (e.g. Slee and Orchiston 1965; Davies et al. 1967; Hughes 1967; Thompson and Colvin 1967; Thompson, Colvin, and Stanley 1967; Kaftan-Kassim 1968) have so far detected nearly 100 planetary nebulae a.t high radiofrequencies (~3 GHz). In this range, the nebulae have been shown to be optically thin, their spectra being almost flat. Wherever possible, the radio flux densities have been compared with hydrogen recombination line observations.