Carla Baldovin Saavedra
Nucleosynthesis of 26Al and 60Fe in a 25 solar masses star
Abstract. Since before they were actually observed in the interstellar medium, the radioactive isotopes 26Al and 60Fe were predicted to be produced in different astrophysical sites, one of them being the presupernova evolution of massive stars.
The nucleosynthesis of both isotopes is studied during the post main sequence evolutionary stage of convective shell carbon burning, following a model of a 25 solar masses star and solar metallicity.
26Al is produced exclusively via 25Mg(p,γ)26Al reaction and its abundance is closely related to the proton density, which depends on temperature through 12C(12C,p)23Na reaction. A thermal instability developed in the final phase of the carbon burning stage rises the temperature of the shell and gives extra protons injection, increasing the final 26Al abundance. The effects of nuclear uncertainties were also analysed by different tests, showing that the final abundance of 26Al depends linearly on the uncertainties in the cross sections of the reactions 25Mg(p,γ)26Al and 26Al(β+)26Mg.
60Fe is produced by a chain of neutron capture reactions starting from 56Fe during the first phase of the shell carbon burning when the neutron density is higher than 1011 n cm-3. The final temperature rising in the shell does not affect the final 60Fe abundance, because of its large decay time. The tests performed showed that the final 60Fe abundance is linearly dependent on the cross section uncertainties of 59Fe(n,γ)60Fe, therefore a measure of this cross section is needed.