Wednesday,
10 January 2007
at 11:00
Carla Baldovin Saavedra
Universita degli Studi di Torino
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.
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