Utraviolet observations of the planetary nebula NGC 2242

Abstract

We present IUE observations of the high-ionization planetary nebula NGC 2242. The ultraviolet spectrum exhibits strong emission lines of C IV, He il, C III], and [Ne iv], plus weaker emission from O IV and N IV. We have also obtained narrow-band imaging of NGC 2242 in the He II 4686 Â emission line; comparison of the \4686 flux from this image with the \1640 flux from the UV spectrum gives a reddening coefficient c(Hß) = 0.37, consistent with that derived from our optical spectrum. From the UV data and previously published optical spectra, we estimate abundances for He, C, O, Ne, and Ar. The oxygen abundance is approximately one-sixth the solar value for T e = 25,000 K; Ne/H and Ar/H are down by a factor of two to three from typical disk PN values. C/O is probably not greater than unity. Helium is not enhanced, arguing against classification as a Type I PN. The observed abundance pattern in NGC 2242 resembles that seen in the halo planetary DDDM-1, except for the strikingly low C/O ratio in the latter object. We suggest that a proper-motion study be done to determine whether NGC 2242 is a member of the disk or of the halo population.

Space Telescope Imaging Spectrograph Slitless Observations of Small Magellanic Cloud Planetary Nebulae: A Study on Morphology, Emission‐Line Intensity, and Evolution

“…The model values of [Oiii] /Hβ are shown as a function of stellar temperature over the range of temperatures encountered by a star of mass = 2 M ⊙ , as it evolves from the AGB tip to its maximum post-AGB temperature. At stellar temperatures in excess of ∼ 10 5 K the [Oiii] /Hβ ratio is in rough agreement with the present observations (see also Garnett & Dinerstein (1989, 1988). It is worth noting that the Galactic models presented here are not to be compared directly with the known observed [Oiii] /Hβ distribution, without accounting for selection effects that hamper Galactic PN statistics.…”

Comparative Absorption and Emission Abundance Analyses of Nebulae: Ion Emission Densities for IC 418

“…Some objects exhibit the problem, while others do not, and its manifestation is the variation in the intensities of an ion's recombination lines as a whole relative to the forbidden lines of that ion among different objects. No convincing explanation has emerged that accounts for this phenomenon (Garnett & Dinerstein 2001b;Liu 2002aLiu , 2002b. Analyses of optical and IR spectra of various PNe have now extended the problem generally to CNO ions and to H II regions (Peimbert, Storey, & Torres-Peimbert 1993;Esteban et al 1999;Tsamis et al 2002), and the discrepancies between the predicted and observed intensities of forbidden lines relative to the recombination lines from the same ion in selected nebulae can exceed an order of magnitude.…”