The 12C + 12C reaction and the impact on nucleosynthesis in massive stars

M. Pignatari, R. Hirschi, M. Wiescher, R. Gallino, M. Bennett, M. Beard, C. Fryer, F. Herwig, G. Rockefeller, Francis Timmes

Research output: Contribution to journalArticlepeer-review

80 Scopus citations


Despite much effort in the past decades, the C-burning reaction rate is uncertain by several orders of magnitude, and the relative strength between the different channels 12C(12C, α)20Ne, 12C(12C, p)23Na, and 12C( 12C, n)23Mg is poorly determined. Additionally, in C-burning conditions a high 12C+12C rate may lead to lower central C-burning temperatures and to 13C(α, n)16O emerging as a more dominant neutron source than 22Ne(α, n) 25Mg, increasing significantly the s-process production. This is due to the chain 12C(p, γ)13N followed by 13N(β +)13C, where the photodisintegration reverse channel 13N(γ, p)12C is strongly decreasing with increasing temperature. Presented here is the impact of the 12C+ 12C reaction uncertainties on the s-process and on explosive p-process nucleosynthesis in massive stars, including also fast rotating massive stars at low metallicity. Using various 12C+12C rates, in particular an upper and lower rate limit of ∼50,000 higher and ∼20 lower than the standard rate at 5 × 108 K, five 25 M stellar models are calculated. The enhanced s-process signature due to 13C(α, n)16O activation is considered, taking into account the impact of the uncertainty of all three C-burning reaction branches. Consequently, we show that the p-process abundances have an average production factor increased up to about a factor of eight compared with the standard case, efficiently producing the elusive Mo and Ru proton-rich isotopes. We also show that an s-process being driven by 13C(α, n)16O is a secondary process, even though the abundance of 13C does not depend on the initial metal content. Finally, implications for the Sr-peak elements inventory in the solar system and at low metallicity are discussed.

Original languageEnglish (US)
Article number31
JournalAstrophysical Journal
Issue number1
StatePublished - Jan 1 2013


  • stars: abundances
  • stars: evolution
  • stars: interiors

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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