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Topic

Calcium Excess in Novae: Beyond Nuclear Physics Uncertainties

Department of Physics and Astronomy

Date & location

• Friday, November 29, 2024
• 2:00 P.M.
• Clearihue Building, Room B007

Examining Committee

Supervisory Committee

• Dr. Falk Herwig, Department of Physics and Astronomy, University of Victoria (Co-Supervisor)
• Dr. Chris Ruiz, Department of Physics and Astronomy, UVic (Co-Supervisor)

External Examiner

• Dr. Ryan Budney, Department of Mathematics and Statistics, UVic

Chair of Oral Examination

• Dr. Ashery Mbilinyi, Department of Computer Science, UVic

Abstract

We examine Ca abundances in classical novae from spectroscopic observations spanning 65 years and investigate whether they are systematically high compared to those predicted by nova models. For the first time, we perform Monte Carlo simulations assessing the impact of nuclear reaction rate uncertainties on abundances predicted by multi-zone nova models. We compare these results with similar simulations using one-zone nova models. While the Ca abundances in the models are sensitive to variations of rates of the reactions ³⁷Ar(p, γ)³⁸K and ³⁸K(p, γ)³⁹Ca, the nuclear physics uncertainties of these reactions cannot account for the discrepancy between the observed and predicted Ca abundances in novae. We also investigate the impact of the ¹⁹F(p, γ)/¹⁹F(p, α) branching ratio that controls hot CNO cycle breakout on Ca production by increasing this ratio by factors of 10 and 100, finding no increase in the Ca abundance. To explain the peculiar abundances observed in novae with high Ca abundances, alternative mixing scenarios with different pre-mixed material are explored. The dust fractionation hypothesis, which suggests that the Ca overabundance could be explained by Ca being trapped in dust, is ruled out due to the simultaneous overabundance of Ar, which would not be expected to be trapped in dust. Furthermore, the overabundance of Ca has important implications for measuring 7Be in nova ejecta, as Ca lines are used to estimate 7Be abundances. If the Ca abundance is incorrectly determined, it could lead to inaccurate 7Be abundance estimates. Possible alternative explanations for the observed Ca overabundance are discussed.