Hydrogen Burning of Si-29 and Its Impact on Presolar Stardust Grains from Classical Novae

Presolar stardust grains found in primitive meteorites are believed to retain the isotopic composition of stellar outflows at the time of grain condensation. Therefore, laboratory measurements of their isotopic ratios represent sensitive probes for investigating open questions related to stellar evolution, stellar explosions, nucleosynthesis, mixing mechanisms, dust formation, and galactic chemical evolution. For a few selected presolar grains, classical novae have been discussed as a potential source. For SiC, silicate, and graphite presolar grains, the association is based on the observation of small N(C-12)/N(C-13) and N(N-14)/N(N-15) number abundance ratios compared to solar values, and abundance excesses in Si-30 relative to Si-29, as previously predicted by models of classical novae. We report on a direct measurement of the Si-29(p,gamma)P-30 reaction, which strongly impacts simulated delta Si-29 values from classical novae. Our new experimental Si-29(p,gamma)P-30 thermonuclear reaction rate differs from previous results by up to 50% in the classical nova temperature range (T = 100-400 MK), while the rate uncertainty is reduced by up to a factor of 3. Using our new reaction rate in Monte Carlo reaction network and hydrodynamic simulations of classical novae, we estimate delta Si-29 values with much reduced uncertainties. Our results establish delta Si-29 values measured in presolar grains as a sensitive probe for assessing their classical nova paternity. We also demonstrate that delta Si-30 values from nova simulations are currently not a useful diagnostic tool unless the large uncertainty of the P-30(p,gamma)S-31 reaction rate can be significantly reduced.