Irs Observations of Lmc Planetary Nebula Smp 83

The first observations of the infrared spectrum of the LMC planetary nebula SMP 83 as observed by the recently launched Spitzer Space Telescope are presented. The high resolution (R ∼ 600) spectrum shows strong emission lines but no significant continuum. The infrared fine structure lines are used, together with published optical spectra, to derive the electron temperature of the ionized gas for several ions. A correlation between the electron temperature with ionization potential is found. Ionic abundances for the observed infrared ions have been derived and the total neon and sulfur abundances have been determined. These abundances are compared to average LMC abundances of H II regions to better understand the chemical evolution of these elements. The nature of the progenitor star is also discussed. Stars of low and intermediate mass evolve through the planetary nebula phase. By the ejection of their outer layers the Planetary Nebulae (PNe) contribute to the enrichment of the interstellar medium. Spectroscopic studies of PNe are essential to better understand and quantify this enrichment. Until the launch of the Spitzer Space Telescope it was impossible to fully study PNe in the in-frared outside the galaxy's chemical environment because of the faintness of extragalactic targets. Reaching targets in the Large and Small Magellanic Clouds (LMC, SMC) is particularly appealing because they have known distances and arise in a lower metallicity environment than galactic targets. Since the distance is known the enrichment of expelled nebular material can be combined with accurate knowledge of the central star's luminosity. In this letter, the infrared spectrum of the LMC planetary nebula SMP 83, taken with the IRS 4 spectrograph on board the Spitzer Space Telescope, is presented. The nature of the central star of SMP 83 is not yet well known and has been the subject of several studies. Dopita et al. (1993), using HST imagery, conclude that SMP 83 is a type I PN with a very massive progenitor star of 6 M ⊙ , close to the progenitor mass limit for a PN. Torres-Peimbert et al. (1993) reported the sudden development of Wolf-Rayet (WR) features in the He II line at λ4686 in the nebula. During 1993 and 1994 the central star experienced an increase in luminosity which was studied by Vassiliadis (1996) and more recently by Hamann et al. (2003). The latter showed that the chemical composition of the atmosphere is that of incompletely processed CNO material. …