2025ApJ...993..156L

We examine Ca abundances in classical novae from spectroscopic observations spanning 65 yr 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 multizone 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. 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.