Spectroscopy of P 30 and the abundance of Si 29 in presolar grains

The astrophysical 29Si(p,¿) reaction is expected to play a key role in determining the final 29Si 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 28Si(3He,p) fusion-evaporation reaction was used to populate low-spin proton-unbound excited states in the nucleus 30P that govern the rate of the astrophysical 29Si(p,¿) reaction. In particular, ¿ decays were observed from resonances up to Er=500keV, and key resonances at 217 and 315 keV have now been identified as 2+ and 2- 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 29Si(p,¿) reaction over the entire peak temperature range of oxygen-neon novae, is higher than previously expected. As such, the abundance of 29Si ejected during nova explosions is likely to be less than that predicted by the most recent theoretical models.
Postprint (published version)