Uncertainties in the ¹⁸F(p, α)¹⁵O reaction rate in classical novae

¹ School of Physics & Astronomy, James Clerk Maxwell Building, University of Edinburgh, Edinburgh EH9 3FD, UK
² Extreme Light Infrastructure – Nuclear Physics, Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), 077125 Bucharest-Măgurele, Romania
e-mail: david.kahl@eli-np.ro
³ Departament de Física, Universitat Politècnica de Catalunya, EEBE, 08019 Barcelona, Spain
⁴ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain

Received: 13 January 2021
Accepted: 3 June 2021

Abstract

Context. Direct observation of γ-ray emission from the decay of ¹⁸F ejected in classical nova outbursts remains a major focus of the nuclear astrophysics community. However, modeling the abundance of ejected ¹⁸F, and thus the predicted detectability distance of a γ-ray signal near 511 keV emitted from these transient thermonuclear episodes, is hampered by significant uncertainties in our knowledge of the key ¹⁸F(p, α) reaction rate.

Aims. We analyze uncertainties in the most recent nuclear physics experimental results employed to calculate the ¹⁸F(p, α) reaction rate. Our goal is to determine which uncertainties have the most profound influence on the predicted abundance of ¹⁸F ejected from novae in order to guide future experimental works.

Methods. We calculated a wide range of ¹⁸F(p, α) reaction rates using the R-Matrix formalism, which allowed us to take all interference effects into account. Using a selection of 16 evenly spaced rates over the full range, we performed 16 new hydrodynamic nova simulations.

Results. We have performed one of the most thorough theoretical studies of the impact of the ¹⁸F(p, α) reaction in classical novae to date. The ¹⁸F(p, α) rate remains highly uncertain at nova temperatures, resulting in a factor of ∼10 uncertainty in the predicted abundance of ¹⁸F ejected from nova explosions. We also found that the abundance of ¹⁸F may be strongly correlated with that of ¹⁹F.

Conclusions. Despite numerous nuclear physics uncertainties affecting the determination of the ¹⁸F(p, α) reaction rate, dominated by unknown interference signs between 1/2⁺ and 3/2⁺ resonances, future experimental work should focus on firmly and precisely determining the directly measurable quantum properties of the subthreshold states in the compound nucleus ¹⁹Ne near 6.13 and 6.29 MeV.