TheSpitzerIRS Infrared Spectrum and Abundances of the Planetary Nebula IC 2448

We present the mid-infrared spectrum of the planetary nebula IC 2448. Inorder to determine the chemical composition of the nebula, we use the infraredline fluxes from the Spitzer spectrum along with optical line fluxes from theliterature and ultraviolet line fluxes from archival IUE spectra. We determinean extinction of C(H-beta) = 0.27 from hydrogen recombination lines and theradio to H-beta ratio. Forbidden line ratios give an electron density of 1860cm-3 and an average electron temperature of 12700 K. The use of infrared linesallows us to determine more accurate abundances than previously possiblebecause abundances derived from infrared lines do not vary greatly with theadopted electron temperature and extinction, and additional ionization stagesare observed. Elements left mostly unchanged by stellar evolution (Ar, Ne, S,and O) all have subsolar values in IC 2448, indicating that the progenitor starformed out of moderately metal deficient material. Evidence from the Spitzerspectrum of IC 2448 supports previous claims that IC 2448 is an old nebulaformed from a low mass progenitor star.Comment: 7 pages, 2 figures, accepted for publication in The Astrophysical Journa