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We investigate the effects of thermonuclear reaction rate variations on 26Alproduction in massive stars. The dominant production sites in such events wererecently investigated by using stellar model calculations: explosiveneon-carbon burning, convective shell carbon burning, and convective corehydrogen burning. Post-processing nucleosynthesis calculations are performedfor each of these sites by adopting temperature-density-time profiles fromrecent stellar evolution models. For each profile, we individually multipliedthe rates of all relevant reactions by factors of 10, 2, 0.5 and 0.1, andanalyzed the resulting abundance changes of 26Al. Our simulations are based ona next-generation nuclear physics library, called STARLIB, which contains arecent evaluation of Monte Carlo reaction rates. Particular attention is paidto quantifying the rate uncertainties of those reactions that most sensitivelyinfluence 26Al production. For stellar modelers our results indicate to whatdegree predictions of 26Al nucleosynthesis depend on currently uncertainnuclear physics input, while for nuclear experimentalists our results representa guide for future measurements. We tabulate the results of our reaction ratesensitivity study for each of the three distinct massive star sites referred toabove. It is found that several current reaction rate uncertainties influencethe production of 26Al. Particularly important reactions are 26Al(n,p)26Mg,25Mg(alpha,n)28Si, 24Mg(n,gamma)25Mg and 23Na(alpha,p)26Mg. These reactionsshould be prime targets for future measurements. Overall, we estimate that thenuclear physics uncertainty of the 26Al yield predicted by the massive starmodels explored here amounts to about a factor of 3.

The Effects of Thermonuclear Reaction-Rate Variations on 26Al Production in Massive Stars: a Sensitivity Study