Further Measurements of Thermal Energy Charge Transfer in Support of Ground-Based Astronomy

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AWARD NO: AST-0606960PI: Daniel SavinINSTITUTION: Columbia UniversityTITLE: Further Measurements of Thermal Energy ChargeTransfer in Support of Ground-Based AstronomyABSTRACTThis research is a continuation of an ongoing laboratory study of thermal energycharge transfer among atoms and ions of astrophysical interest. It has long been knownthat thermal energy charge transfer plays an important role in determining the ionizationstructure, thermal structure, emission spectrum and absorption spectrum for a range ofcosmic plasmas. These include photoionized gas found in planetary nebulae, H II regions,Wolf-Rayet nebulae, luminous blue variable nebulae, Lyman alpha clouds, and theintergalactic medium; shocks in supernova remnants and Herbig-Haro objects; andprimordial gas clouds during the epoch of protogalaxy and first star formation.Unfortunately, many theoretical calculations carried out during the past 25 years inresponse to the demand for reliable thermal energy charge transfer data are reliable toonly a factor of 3-10. And while the latest state-of-the-art calculations are expected to bemore reliable, such efforts are less common and can still be off by a factor of 3 when notbenchmarked against experiments. However, few laboratory measurements exist despitethe demand from the community.To address this need, an ongoing series of laboratory measurements of thermal energycharge transfer will be continued using the Oak Ridge National Laboratory ion-atommerged-beams apparatus. Here, measurements will be made of the thermal energy chargetransfer of C2+, O+, O2+, Se3+, and Kr2+. Reliable charge transfer data for thecosmically abundant C2+, O+, and O2+ are needed for modeling planetary nebulae and HII regions as well as shocks in supernovae remnants and Herbig-Harrow objects. Data forSe3+ and Kr2+ are needed to analyze planetary nebula spectra in order to study bothnucleosynthesis via the slow neutron capture process and convective dredge-up in theplanetary nebula progenitor stars. These results will be used to produce rate coefficientswith an estimated accuracy of * 20% and will provide fits for plasma modeling. Moderncharge transfer theory will also be benchmarked against these results. Finally, thelaboratory apparatus will be modified so that the metastable fraction in the ion beams canbe measured and controlled. For beams with a significant metastable fraction, this willallow the extraction of absolute cross sections for both the ground state and metastableions in the beam. This new capability will further increase the uniqueness of the OakRidge National Laboratory ion-atom merged-beams apparatus.The training and professional preparation of a graduate student will be supported. Thisstudent will carry out a large portion of the project in partial fulfillment of therequirements for the degree of Doctor of Philosophy. The results of this research will bepresented via seminars and colloquia to colleagues in academia, government, andindustry. Reports at national and international conferences will be given and published inthe appropriate journals. In addition, this work will further enhance the Columbia/OakRidge National Laboratory infrastructure for research and education. Prof. Gary Ferlandat the University of Kentucky will input the new rate coefficients into CLOUDY which isone of the most commonly used codes for modeling photoionized gas.