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ELEMENTAL ABUNDANCES IN 16 PLANETARY NEBULAE FROM DEEP, HIGH-RESOLUTION OPTICAL SPECTROSCOPY

Abstract

We present elemental abundances of 16 planetary nebulae (PN) derived from deep, high-resolution (λ/Δλ = 36,700) optical spectra. A PN is the ionized ejected envelope of a low-mass star (1-8 solar masses) at the end of its nuclear fusion lifetime. The spectra cover the wavelength range 3600—10,400 Å, and were obtained with the 2D-coudé spectrograph on the 2.7-m Harlan J. Smith Telescope at McDonald Observatory (TX). Between 100 and 600 distinct emission lines were detected in the observed PN, making these the deepest spectra ever obtained for most objects in our sample. Using the PyNeb package, as well as newly-developed Python and IDL routines that partially automate the data analysis, we have determined electron temperatures and densities, as well as ionic and elemental abundances in each PN. Specifically, we utilize both permitted (recombination) and forbidden (collisionally-excited) emission lines to compute abundances. Our abundances agree well with previous studies of these PN. The deep spectra have allowed us to study the abundances of many elements (including P, K, Ca, Fe, and “neutron-capture” elements heavier than Zn) for the first time in these PN, as well as abundances from permitted C, N, O, and Ne lines. These results will provide new details of nucleosynthesis in the progenitor stars of PN, the composition of nebular dust grains, and the “abundance discrepancy problem,” in which abundances from permitted lines are systematically higher than those from forbidden lines. Numerical simulations of these PN, conducted with the widely-used Cloudy photoionization modeling code, are underway to study the ionization equilibria of the detected elements and to apply corrections for unobserved ionization states.

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