Chemical Enrichment in Planetary Nebulae from A to Z (alpha to zinc)

University Of Texas At Austin, Austin TX

Investigators

Abstract

A planetary nebula carries a record of the internal nuclear processes and enrichment in its asymptotic giant branch star progenitor, as well as of the initial composition of the star. Planetary nebulae are also particularly important contributors to Galactic chemical enrichment for nuclei synthesized by slow neutron captures (the 's-process'). In a previous NSF-supported project, Dr. Dinerstein conducted a near-ir spectroscopic survey of Galactic planetary nebulae, and found substantial self-enrichment of the s-process products Se and Kr in about 40% of the detected sources. This study established the demographics of enrichment for the 'light-s' peak, traced by Sr - Zr (Z = 38-40) in stars. Building on this earlier work, Dr Dinerstein will extend the Se and Kr study to planetary nebulae in other Local Group galaxies, moving into a new, lower-metallicity regime. She will also search for elements of the 'heavy-s' peak, Ba, Xe, etc. via high-resolution optical and infrared spectroscopy. A third part of this project will be an investigation of Fe-peak elements in planetary nebulae. Although Fe itself suffers depletion into dust in planetary nebulae, the nearby element Zn undergoes little to no depletion yet closely tracks Fe in stars (except at extremely low metallicities). Therefore, Zn/H abundances will be derived as a surrogate to make the first Fe/H determinations of local group planetary nebulae to compare with abundances of alpha elements such as O and Ar. Finally, gas phase Fe will be investigated to search for point-to-point variations within individual nebulae to address the question of how uniformly dust condenses and survives in planetary nebula ejecta. This last study is particularly important as variations in the dust-to-gas ratio may lead to other inhomogeneities and affect the thermal balance which in turn may explain long standing abundance discrepancies from optical recombination lines versus collisionally excited lines. The work here is multidisciplinary by nature and will foster a close connection to laboratory spectroscopists for line identifications, oscillator strengths, etc., and the results of this work may help constrain nuclear cross sections and stellar evolution calculations. There also is growing interest in using planetary nebulae as distance indicators and probes of dark matter in their parent galaxies, making it important to understand the nature of their progenitors. These projects will enable the training of both graduate and undergraduate students (who will be supported) and materials developed here will be part of an education/outreach program to 'academic magnet' public schools in the Austin Independent School District.