RT info:eu-repo/semantics/doctoralThesis
T1 S-process nucleosynthesis in AGB stars with the full spectrum of turbulence scheme for convection
A1 Yagüe López, Andrés
A2 Programa de Doctorado en Astrofísica
K1 ASTRONOMIA Y ASTROFISICA
K1 ANALISIS NUMERICO
K1 ESTRELLAS
AB Abstract. This thesis describes SNUPPAT (s-process nucleosynthesis post processingcode for Aton), a post-processing slow neutron-capture process (s-process) codedeveloped by us for the stellar evolutionary code ATON. The aim is to provideATON, which shows distinct key physical characteristics to other evolutionarycodes, with the capability of following heavy element nucleosynthesis in lowto intermediate-mass stars. Meaning that we have to increase the number ofspecies followed from 30 (ATON follows 30 species from hydrogen to 31P) toaround 320 (from hydrogen to 210Po) at the very least. In the long term wehope that, through ATON nucleosynthesis predictions, we may open the wayto a deeper understanding of the physics and evolution during the thermallypulsing asymptotic giant branch (TP-AGB) phase.This objective is realized by the creation from scratch of a nucleosynthesiscode, explained at the beginning of this thesis, along with possible optimizationsto some of the traditional numerical methods used for these kind of astrophysicalproblems. We also tackle the issue of mixing, which includes both the convective mixing as well as the convective overshooting responsible of, among otherthings, the formation of an effective 13C pocket, essential for nucleosynthesis inTP-AGB stars.Following the code description, we present SNUPPAT solar metallicity results in the form of final stellar surface abundances. We explore different stellarinitial masses as well as variations of the extra-mixing parameter, which governsthe convective overshooting behavior. These results are analyzed to connectthem with the different physical processes taking place in the deeper layers ofthe AGB stars.Finally, we compare our results with those from other known s-processingnumerical codes, finding a reasonably good agreement with at least one of them(specifically, the MONASH version of the Mount Stromlo Stellar Structure Program), which coincidentally is the nucleosynthesis code that better explains the currently limited observational information (Rb, Zr abundances) about thesestars. We note the fact that ATON-SNUPPAT appears to generate hottermodels with a low third dredge-up efficiency that forces us to increase the nucleosynthesis output in the helium intershell, in order to obtain comparablesurface abundances. The consequence is that SNUPPAT predictions present,generally, the signs of a higher overall neutron exposure (a measure of the totalneutron captures) in the final stellar surface abundances.
YR 2018
FD 2018
LK http://riull.ull.es/xmlui/handle/915/23872
UL http://riull.ull.es/xmlui/handle/915/23872
LA en
DS Repositorio institucional de la Universidad de La Laguna
RD 27-nov-2024