Thermonuclear 28P(p, γ)29S reaction rate and astrophysical implication in ONe nova explosion

Abstract

Context. An accurate 28P(p, γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of 29S, together with a shell model and a direct capture calculation, we reanalyzed the 28P(p, γ)29S thermonuclear reaction rate and its astrophysical implication. Aims. We focus on improving the astrophysical rate for 28P(p, γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods. We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results. The contribution from the capture on the first excited state at 105.64 keV in 28P is taken into account for the first time. We find that the capture rate on the first excited state in28 P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107 K to 4 × 108 K, resulting in the total 28P(p, γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109 K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of 28P(p, γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present 28P(p, γ)29S uncertainty are 28Si, 33,34S, 35,37Cl, and 36Ar, with relative abundance changes at the level of only 3% to 4%.