Improving the 33S(p,γ)34Cl reaction rate for models of classical nova explosions

Reduced uncertainty in the thermonuclear rate of the S-33(p, gamma) Cl-34 reaction would help to improve our understanding of nucleosynthesis in classical nova explosions. At present, models are generally in concordance with observations that nuclei up to roughly the calcium region may be produced in these explosive phenomena; better knowledge of this rate would help with the quantitative interpretation of nova observations over the S-Ca mass region, and contribute towards the firm establishment of a nucleosynthetic endpoint. As well, models find that the ejecta of nova explosions on massive oxygen-neon white dwarfs may contain as much as 150 times the solar abundance of S-33. This characteristic isotopic signature of a nova explosion could possibly be observed through the analysis of microscopic grains formed in the environment surrounding a nova and later embedded within primitive meteorites. An improved S-33(p, gamma)Cl-34 rate (the principal destruction mechanism for S-33 in novae) would help to ensure a robust model prediction for the amount of S-33 that may be produced. Finally, constraining this rate could confirm or rule out the decay of an isomeric state of Cl-34 (E-x = 146 keV, t(1/2) = 32 m) as a source for observable gamma-rays from novae. We have performed several complementary experiments dedicated to improving our knowledge of the S-33(p, gamma)Cl-34 rate, using both indirect methods (measurement of the S-34(He-3, t)Cl-34 and S-33(He-3, d)Cl-34 reactions with the Munich Q3D spectrograph) and direct methods (in normal kinematics at CENPA, University of Washington, and in inverse kinematics with the DRAGON recoil mass separator at TRIUMF). Our results will be used with nova models to facilitate comparisons of model predictions with present and future nova observables.