OBSERVATIONS OF THE 2-MU-M UNIDENTIFIED LINES IN PLANETARY-NEBULAE

Medium resolution spectra in the K window have been obtained for thirteen planetary nebulae and one compact H II region in order to study the behaviour of the unidentified line at 2.287-mu-m. The wavelengths of this line and the unidentified 2.199-mu-m line have been measured in NGC 7027 at high spectral resolution using a Fabry-Perot interferometer. Based on the interferometric measurements and the lack of correlation of the 2.287-mu-m line with emission in H-2 lines, the unidentified lines are not lines of molecular hydrogen. The 2.287-mu-m line is strongest in medium-high excitation nebulae, and is absent in nebulae of very low and very high excitation, implying that the ionization potential of the parent atom or ion is about 30-40 eV and that the ion itself has an ionization potential of perhaps 40-60 eV.