Improved thermonuclear rate of ⁴²Ti(p,γ)⁴³V and its astrophysical implication in the rp process

¹ Key Laboratory of High Precision Nuclear Spectroscopy, Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Rd, Lanzhou, 730000 PR China
e-mail: sqhou@impcas.ac.cn
² School of Nuclear Science and Technology, University of Chinese Academy of Sciences, 19A Yuquan Rd, Shijingshan District, Beijing, 100049 PR China
³ Department of Physics & Astronomy, 120 E. Cameron Ave., University of North Carolina at Chapel Hill, NC, 27599-3255 USA
⁴ Triangle Universities Nuclear Laboratory (TUNL), 116 Science Drive, Duke University, Durham, NC, 27708-0308 USA
⁵ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), Konkoly Thege M. út 15-17, 1121 Budapest, Hungary
⁶ CSFK, MTA Centre of Excellence, Konkoly Thege Miklós út 15-17, Budapest, 1121 Hungary
⁷ E. A. Milne Centre for Astrophysics, University of Hull, Cottingham Rd, Kingston upon Hull, HU6 7RX UK
⁸ Joint Institute for Nuclear Astrophysics, Center for the Evolution of the Elements, 640 S Shaw Lane, East Lansing, MI, 48824 USA

Received: 30 May 2023
Accepted: 10 July 2023

Abstract

Context. Accurate ⁴²Ti(p,γ)⁴³V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rp process) that occurs in X-ray bursts.

Aims. We aim to improve the thermonuclear rates of ⁴²Ti(p,γ)⁴³V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on the rp process.

Methods. We reevaluated the reaction rate of ⁴²Ti(p,γ)⁴³V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn.

Results. The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus ⁴³V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region of rp-process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 10⁸ K. Using a trajectory with a peak temperature of 1.95×10⁹ K, we performed the rp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that the rp-process path does not bypass the isotope ⁴³V.

Conclusions. Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for ⁴²Ti(p,γ)⁴³V. The adoption of the new rates confirms that the reaction path of ⁴²Ti(p,γ)⁴³V(p,γ)⁴⁴Cr(β⁺)⁴⁴V is a key branch of the rp process in X-ray bursts.