Nuclear Reaction Rates and Carbon Star Formation

Abstract

We have studied how the third dredge-up and the carbon star formation in low-mass Asymptotic Giant Branch stars depends on certain key nuclear reaction rates. We find from a set of complete stellar evolution calculations of a 2Msun model with Z=0.01 including mass loss, that varying either the N14(p,g)O15 or the 3-alpha reaction rate within their uncertainties as given in the NACRE compilation results in dredge-up and yields that differ by a factor of 2. Model tracks with a higher rate for the 3-alpha rate and a lower rate for the N14(p,g)O15 reaction both show more efficient third dredge-up. New experimental results for the N14(p,g)O15 reaction rates are surveyed, yielding a rate which is about 40% lower than the tabulated NACRE rate, and smaller than NACRE's lower limit. We discuss the possible implications of the revised nuclear reaction stellar evolution calculations that aim to reproduce the observed carbon star formation at low mass, which requires efficient third dredge-up.