Dr. Donald Garnett, at the University of Arizona, will study the problem of why recombination lines (RLs) from twice-ionized oxygen (O), carbon (C), nitrogen (N), and other heavy elements yield much higher abundances than the corresponding collisionally-excited forbidden lines (FLs) from the same species. This problem challenges our confidence in abundances derived from planetary nebulae and ionized hydrogen (HII) regions in the Milky Way and other galaxies and their interpretation for stellar nucleosynthesis and chemical evolution studies. In this project, Dr. Garnett will (1) map the spatial distribution of RLs and FLs in a variety of planetary nebulae and giant HII regions to determine how physical structures affect their distribution, (2) study the hot gas content using data from FUSE and X-ray satellite missions to see if the presence of hot gas is a contributing factor, and (3) examine the spatial variation of electron temperature using a variety of diagnostics to determine if large observed differences between the temperature derived from the Balmer line/continuum ratio and the temperature derived from forbidden line ratios are related to physical structures. This project will use already existing and scheduled ground-based spectroscopy, FUSE spectra and Chandra/XMM imaging, as well as new ground-based spectroscopy of RLs in HII regions. ***
