Presolar grains and AGB stars Maria Lugaro Sterrenkundig Instituut University of Utrecht

Outline of the talk 1.Intro to asymptotic giant branch (AGB) stars 2.Information from presolar grains on AGB stars 3.Examples: A. The s process B. Presolar grains from massive AGB stars? C. The “isotopic evolution” of the Galaxy 4.Summary and future opportunities

Courtesy of Richard Powell AGB stars Theoretical evolutionary track of a star of 2 M  All stars with masses M  go through the AGB phase Core H exhaustion Core He burning starts Core He exhaustion 1. Intro to AGB stars

Schematic out-of-scale picture of the structure of AGB stars. 1. Introduction to AGB stars is activated most of the time triggers convection in the He intershell

1. Introduction to AGB stars 4 He, 12 C, 22 Ne, elements heavier than Fe produced by slow neutron captures (the s process): Zr, Ba,... At the stellar surface: C>O, s- process enhance ments Time evolution of the structure of AGB stars.

Consider the main ingredient to constructing theoretical AGB stars: Consider presolar grains: Silicon Carbide grains: 95% show the signature of AGB star origin Oxide and Silicate grains: a large fraction of them are believed to be from AGB stars The vast majority of presolar grains analyzed to date come from AGB stars! 2. Information from presolar grains on AGB stars

Light elements, e.g.: C, N, O, Ne, Mg, Al Intermediate- mass elements, e.g.: Si, Ca, Ti, Cr, Fe, Ni Heavy elements, e.g.: Sr, Zr, Mo, Ba Very precise isotopic ratios 2. Information from presolar grains on AGB stars

Light elements, e.g.: C, N, O, Ne, Al Intermediate- mass elements, e.g.: Si, Ca, Ti, Cr, Fe, Ni Heavy elements, e.g.: Sr, Zr, Mo, Ba Nuclear reactions + mixing in AGB stars Chemical evolution of the Galaxy Processes in binary systems 2. Information from presolar grains on AGB stars 3. Examples A. The s process

proton diffusion 13 C  n) 16 O 22 Ne  n) 25 Mg Where are the neutrons in the AGB intershell?

3. Examples A. The s process Single star models showed that a large spread of 13 C amounts at any given [Fe/H] was needed to cover spectroscopic observations: Busso et al. (2001) use a spread of a factor of ~ 50. Stellar population synthesis including the s process shows that a small spread is needed. Bonacic-Marinovic et al. (2006) use a spread of 2  See poster.

3. Examples A. The s process From analysis of more than one element in the same presolar SiC grain, Barzyk et al. (2006) independently find the same spread of 2 as population synthesis models. Lugaro et al. (2003) used a spread of a factor of 24 to cover single presolar SiC grain data.

Light elements, e.g.: C, N, O, Ne, Mg, Al Intermediate- mass elements, e.g.: Si, Ca, Ti, Cr, Fe, Ni Heavy elements, e.g.: Sr, Zr, Mo, Ba Nuclear reactions + mixing in AGB stars Chemical evolution of the Galaxy Processes in binary systems 3. Examples B. Presolar grains from massive AGBs?

Presolar spinel grain OC2 is unique in that it shows large excesses in the heavy Mg isotopes......and very low 18 O/ 16 O. The origin of grain OC2 has been tentatively attributed to a massive AGB star ≈ M  +117% of solar +43% of solar 3.3  solar solar/26 3. Examples B. Presolar grains from massive AGBs?

Examples B. Presolar grains from massive AGBs? Lugaro et al. (2006) compare OC2 to detailed models of massive AGBs. Proton captures occur at the base of the convective envelope: hot bottom burning. Within this solution we predict: a 17 O(p,  ) 14 N rate close to its current upper limit (+25%) and a 16 O(p,  ) 17 F rate close to its current lower limit (-43%)

Light elements, e.g.: C, N, O, Ne, Mg, Al Intermediate- mass elements, e.g.: Si, Ca, Ti, Cr, Fe, Ni Heavy elements, e.g.: Sr, Zr, Mo, Ba Nuclear reactions + mixing in AGB stars Chemical evolution of the Galaxy Processes in binary systems 3. Examples C. The “isotopic evolution” of the Galaxy

The Si composition of different SiC populations is determined by: 2. Neutron captures in the AGB parent star. 1. The initial composition of the parent star produced by Galactic chemical evolution effects, which are still very uncertaint. 3. Examples C. The “isotopic evolution” of the Galaxy Zinner et al. (2006) combine SiC data and theoretical predictions for nucleosynthesis in AGB stars to obtain information on the Galactic evolution of the Si isotopes.

3. Examples C. The “isotopic evolution” of the Galaxy “At Z < 0.01 the 29 Si/ 28 Si ratio rises much faster than predicted by the model of Timmes & Clayton (1996). The grain data suggest a low-metallicity source of 29 Si and 30 Si not cosidered in the present Galactic chemical evolution models.”... or something wrong with the models???

Light elements, e.g.: C, N, O, Ne, Mg, Al Intermediate- mass elements, e.g.: Si, Ca, Ti, Cr, Fe, Ni Heavy elements, e.g.: Sr, Zr, Mo, Ba Nuclear reactions + mixing in AGB stars Chemical evolution of the Galaxy Perform detailed computations of the “isotopic evolution” of the Galaxy. Test the modelling of AGB stars. Test nuclear reaction rates. There are not yet models of the composition of AGB stars with a compact binary companion. Processes in binary systems 4. Summary and future opportunities