Spectroscopy of P30 and the abundance of Si29 in presolar grains

Abstract

The astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction is expected to play a key role in determining the final $^{29}\mathrm{Si}$ yields ejected in nova explosions. Such yields are used to accurately identify the stellar origins of meteoritic stardust and recently, distinctive silicon isotopic ratios have been extracted from a number of presolar grains. Here, the light-ion $^{28}\mathrm{Si}(^{3}\mathrm{He},p$) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus $^{30}\mathrm{P}$ that govern the rate of the astrophysical $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction. In particular, $\ensuremath{\gamma}$ decays were observed from resonances up to ${E}_{r}=500\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$, and key resonances at 217 and 315 keV have now been identified as ${2}^{+}$ and ${2}^{\ensuremath{-}}$ levels, respectively. The present paper provides the first estimate of the 217-keV resonance strength and indicates that the strength of the 315-keV resonance, which dominates the rate of the $^{29}\mathrm{Si}(p,\ensuremath{\gamma}$) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of $^{29}\mathrm{Si}$ ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.