New 34Cl proton-threshold states and the thermonuclear 33S(p,gamma)34Cl rate in ONe novae

TL;DR

This study measures nuclear states in 34Cl to better understand the 33S(p,gamma)34Cl reaction rate, which influences sulfur isotope predictions in ONe novae and aids in identifying presolar grains of nova origin.

Contribution

First measurement of 34Cl states near the proton threshold, identifying new resonances that refine the 33S(p,gamma)34Cl reaction rate relevant to nova nucleosynthesis.

Findings

Confirmed known states and discovered 15 new states in 34Cl.

Identified potential dominant resonances at specific energies affecting the reaction rate.

Results may alter sulfur isotope ratio predictions in nova ejecta.

Abstract

Analysis of presolar grains in primitive meteorites has shown isotopic ratios largely characteristic of the conditions thought to prevail in various astrophysical environments. A possible indicator for a grain of ONe nova origin is a large 33S abundance: nucleosynthesis calculations predict as much as 150 times the solar abundance of 33S in the ejecta of nova explosions on massive ONe white dwarfs. This overproduction factor may, however, vary by factors of at least 0.01 - 3 because of uncertainties of several orders of magnitude in the 33S(p,gamma)34Cl reaction rate at nova peak temperatures (Tpeak ~ 0.1 - 0.4 GK). These uncertainties arise due to the lack of nuclear physics information for states within ~ 600 keV of the 33S+p threshold in 34Cl (Sp(34Cl) = 5143 keV). To better constrain this rate we have measured, for the first time, the 34S(3He,t)34Cl reaction over the region Ex(34Cl) = 4.9 - 6 MeV. We confirm previous states and find 15 new states in this energy region. New 33S(p,gamma)34Cl resonances at ER = 281(2), 301(2) and 342(2) keV may dominate this rate at relevant nova temperatures. Our results could affect predictions of sulphur isotopic ratios in nova ejecta (e.g., 32S/33S) that may be used as diagnostic tools for the nova paternity of grains.