Search for nova presolar grains: gamma-ray Spectroscopy of Ar-34 and its relevance for the astrophysical Cl-33(p,gamma) reaction

The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical 33Cl(p,gamma)34Ar reaction is expected to play a decisive role. As such, we have performed a detailed gamma-ray spectroscopy study of 34Ar. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in 34Ar, have been made for the first time. Uncertainties in the 33Cl(p,gamma) reaction have been dramatically reduced and the results indicate that a newly identified l=0 resonance at Er=396.9(13) keV dominates the entire rate for T=0.25–0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected 32S/33S abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain.Postprint (published version