Abundances of Planetary Nebula NGC2392
  The spectra of the planetary nebula NGC2392 is reanalysed using spectral measurements made in the mid-infrared with the Spitzer Space Telescope. The aim is to determine the chemical composition of this object. We also make use of IUE and ground based spectra. Abundances determined from the mid-infrared lines, which are insensitive to electron temperature, are used as the basis for the determination of the composition, which are found to differ somewhat from earlier results. The abundances found, especially the low value of helium and oxygen, indicate that the central star was originally of rather low mass. Abundances of phosphorus, iron, silicon and chlorine have been determined for the first time in this nebula. The variation of electron temperature in this nebula is very clear reaching quite high values close to the center. The temperature of the central star is discussed in the light of the high observed stages of ionization. The nebular information indicates the spectrum of the star deviates considerably from a blackbody. 
S.R. Pottasch, J. Bernard-Salas, T.L. Roellig