January 1, 2013.
Planetary nebulae (PNe) form around low to intermediate mass stars transitioning from the giant branch to white dwarf phase. The outer layer of the star is ejected during the transition and this gas, ionized by the central star, emits a line-spectrum. This spectrum traces the chemical abundances that were characteristic of the interstellar medium in which the star formed (e.g. oxygen) as well as of the elements created by these progenitor stars (e.g. nitrogen) aiding our understanding of chemical evolution of galaxies. In this project, we use modeling of the emission lines of PNe to determine the accuracy of direct methods of measuring abundances, which rely on using the observed emission line ratios. By generating a large number of models with varying temperature and luminosity of the central star, we estimate how much uncertainty to expect due to these parameters alone. We investigate the possibility of determining PNe chemical abundances by comparing observed line ratios to the predictions of a grid of models with known chemical abundances as an alternative to the direct methods. We also report the model predictions for line strengths in the mid and far-infrared that could be observed by SOFIA.
Stars, Interstellar Medium and the Galaxy
NASA Ames Research Center (ARC)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).