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SA: Chemical Abundances in Planetary Nebulae: Collisionally Excited Lines vs. Recombination Lines – Peña
April 18 @ 9:30 am – 10:15 am CMT
Chemical abundances of planetary nebulae (PNe) help us to understand several processes of the nucleosynthesis of the progenitor star. Elements such as He, C, and N can be processed in the stellar nucleus and partially brought up to the stellar surface through dredge-up processes. Other elements such as O, Ne, Ar, S (the alpha-elements) are supposedly not perturbed by stellar nucleosynthesis, therefore they provide information of the chemistry at the stellar formation time. Although there are some well documented cases where O and Ne abundances seem altered by nucleosynthesis and some of these elements have been transported to the surface, and have been ejected in the nebular material. Chemical abundances are generally determined by analyzing the collisionally excited lines and also can be determined from some recombination lines (RLs). CELs and RLs line intensities allow to obtain nebular physical parameters (temperature and density), and ionic abundances of several elements, Total abundances are obtained by using Ionization Correction Factors (ICFs) from the literature. It is known that there exists a discrepancy in the abundances (ADF) derived from both types of lines. Usually the abundances derived from RLs is larger than the one derived from CELs This occurs in HII regions as well as in PNe. ADFs determined for PNe are usually larger than in HII regions. In same cases the value is as large as 100 or more. In this work we analyze the chemistry of some PNe, determined from CELs and RLs. Some possible causes for such a discrepancy will be presented.