Abstract:

Background: Type Ia supernovae contribute significantly to the nucleosynthesis of many Fegroup and
intermediatemass elements. However, the robustness of nucleosynthesis obtained via models of this class of
explosions has not been studied in depth until now.
Purpose: We explore the sensitivity of the nucleosynthesis resulting from thermonuclear explosions of massive
white dwarfs with respect to uncertainties in nuclear reaction rates. We put particular emphasis on indentifying
the individual reactions rates that most strongly affect the isotopic products of these supernovae.
Method: We have adopted a standard onedimensional delayed detonation model of the explosion of a
Chandrasekharmass white dwarf and have postprocessed the thermodynamic trajectories of every mass shellwith
a nucleosynthetic code to obtain the chemical composition of the ejected matter. We have considered increases
(decreases) by a factor of 10 on the rates of 1196 nuclear reactions (simultaneously with their inverse reactions),
repeating the nucleosynthesis calculations after modification of each reaction rate pair. We have computed as
well hydrodynamic models for different rates of the fusion reactions of 12C and of 16O. From the calculations we
have selected the reactions that have the largest impact on the supernova yields, and we have computed again
the nucleosynthesis using two or three alternative prescriptions for their rates, taken from the JINA REACLIB
database. For the three reactions with the largest sensitivity we have analyzed as well the temperature ranges
where a modification of their rates has the strongest effect on nucleosynthesis.
Results: The nucleosynthesis resulting from the type Ia supernova models is quite robust with respect to variations
of nuclear reaction rates,with the exception of the reaction of fusion of two 12C nuclei. The energy of the explosion
changes by less than ∼4% when the rates of the reactions 12C + 12C or 16O + 16O are multiplied by a factor of
×10 or ×0.1. The changes in the nucleosynthesis owing to the modification of the rates of these fusion reactions
are also quite modest; for instance, no species with a mass fraction larger than 0.02 experiences a variation of
its yield larger than a factor of 2. We provide the sensitivity of the yields of the most abundant species with
respect to the rates of the most intense reactions with protons, neutrons, and α. In general, the yields of Fegroup
nuclei are more robust than the yields of intermediatemass elements. Among the species with yields larger than
10−8M , 35S has the largest sensitivity to the nuclear reaction rates. It is remarkable that the reactions involving
elements with Z > 22 have a tiny influence on the supernova nucleosynthesis. Among the chargedparticle
reactions, the most influential on supernova nucleosynthesis are 30Si + p 31P + γ , 20Ne + α 24Mg + γ ,
and 24Mg + α 27Al + p. The temperatures at which a modification of their rate has a larger impact are in the
range 2 T 4 GK. 