NewCl34proton-threshold states and the thermonuclearS33(p,γ)Cl34rate in ONe novae
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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 $^{33}\mathrm{S}$ abundance: nucleosynthesis calculations predict as much as 150 times the solar abundance of $^{33}\mathrm{S}$ 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 $^{33}\mathrm{S}$$(p,\ensuremath{\gamma})$$^{34}\mathrm{Cl}$ reaction rate at nova peak temperatures (${T}_{\mathrm{peak}}~0.1\text{\ensuremath{-}}0.4$ GK). These uncertainties arise due to the lack of nuclear physics information for states within $~600$ keV of the $^{33}\mathrm{S}$$+p$ threshold in $^{34}\mathrm{Cl}$ (S${}_{p}$($^{34}\mathrm{Cl}$) = 5143 keV). To better constrain this rate we have measured, for the first time, the $^{34}\mathrm{S}$($^{3}\mathrm{He}$,$t$)$^{34}\mathrm{Cl}$ reaction over the region ${E}_{x}$($^{34}\mathrm{Cl}$) = 4.9--6 MeV. We confirm previous states and find 15 new states in this energy region. New $^{33}\mathrm{S}$$(p,\ensuremath{\gamma})$$^{34}\mathrm{Cl}$ resonances at ${E}_{R}=281(2)$, 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., $^{32}\mathrm{S}$/$^{33}\mathrm{S}$) that may be used as diagnostic tools for the nova paternity of grains.