Does the main component of the s process in AGB stars constrain the neutron source in the 13C pocket?

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Nuclei in the Cosmos Debrecen, Hungary 7-11 July, 2014 Does the main

1 Nuclei in the Cosmos Debrecen, Hungary 7-11 July, 2014 Does the main component of the s process in AGB stars constrain the neutron source in the 13C pocket? Oscar Trippella, Maurizio Busso, Enrico Maiorca, Franz Käppeler, Sara Palmerini 1. Department of Physics, University of Perugia, and INFN, Section of Perugia. 2. INAF, Observatory of Arcetri, Florence and INFN, Section of Perugia. 3. Karlsruhe Institute of Technology, Campus North, Institute of Nuclear Physics, Karlsruhe. 4. INFN, Laboratori Nazionali del Sud, Catania. 7th July,

2 Introduction: s-process in AGB-LMS. s-process Thermally Pulsing (TP) Asymptotic Giant Branch (AGB) low mass stars (LMS) 22 Ne(α,n)25Mg < Old Nuclear Physics classifications: Weak component A<90 - massive stars Main component from Sr to Bi Strong component for 208Pb - unnecessary 13 C(α,n)16O 2

3 13 C-pocket formation: the standard idea. An amount of protons is injected into the He-rich region below the envelope at each dredge-up phenomenon and the 13C reservoir is formed by: C(p,γ)13N(β+ ν)13c 12 DANGER: Too efficient proton captures produce 14N that is an efficient absorber for most of the neutrons, inhibiting the captures on heavier nuclei. Gallino et al.(1998) and Bisterzo et al.(2014) suggested a proton-mixing typically of about (0.5-2) 10-3 M and showed how this choice allows the buildup of the s-process main component. Cristallo et al.( ) provided a more quantitative approach, assuming that convective velocities at the envelope border do not drop abruptly to zero, but decrease exponentially. Gallino et al.(1998) 3

4 Open issues of the standard scenario. Spectroscopic measurements (D Orazi et al.,2009; Maiorca et al.,2011; Jacobson et al.,2013) in open clusters younger than the Sun showed that the abundances of neutron-rich elements have continued to increase. Other indications of an increasing s-process production came from McWilliams et al.(2013) in the Sagittarius Dwarf Galaxy and for Ba by Mishenina et al.(2013). (See also Karakas's talk) Maiorca et al.(2011) Mishenina et al.(2013) More extended 13 C pocket Theoretically speaking, Piersanti et al.(2013) showed that in models with stellar rotation, instabilities at the shear layer induce more effective mixing, leading mainly to 14N. (See also Hirschi's talk!!!) 16 The 13and C(α,n) O reaction as a neutron Nuclei source in the forcosmos the s-process Debrecen in LMS Hungary St. Tecla 07/07/ /09/2013 Oscar Oscar Trippella Trippella - UNIPG University INFN of Perugia 11 4

5 13 C-pocket formation: a forced mechanism. m ' r e k r Pa m s i an h ec Magnetic buoyancy Convective envelope During TDU Turbolent regime Helium Shell Differential rotation 2. Magnetic structures can reach the envelope 1. Rotational shears can promote magnetic fields C-O degenerate core Rigid body rotation 3. An amount of protons can be injested into the He-rich region. 16 Oscar Oscar Trippella Trippella - UNIPG University The 13and C(α,n) INFN O reaction of Perugia as a neutron Nuclei source in the forcosmos the s-process Debrecen in LMS Hungary St. Tecla 07/07/ /09/

6 The extended 13C-pocket. The 13C-pocket is more extended than in the common assumptions mad so far. The average value is 4-6 x 10-3 solar masses, covering a large part of the intershell region. The profile of proton penetration is roughtly EXPONENTIAL. The 13C-pocket is where the green line overcomes the red one. There is only a limited neutron production in the 14N-rich region, because 14N is the main neutron absorber. 6

7 MagnetoHydroDinamics MHD model by Nucci & Busso (2014) No numerical approximations (exact analytic solution). Simple geometry: toroidal magnetic flux tubes. Equations: Solutions: e Se so' s Bu er t s o sp ( )!! 0 P1! where k is the exponent of the density distribution: 7

8 Code improvements: nuclear inputs. o C La ta a gn e (. l ta ) d n a gl n Lo e l. a t 3) 1 0 (2 See La Cognata's talk!!! Recent n-captures cross sections. Recent beta-decays. 8

9 Results for the chemical evolution of the 13 Galaxy with the new C -pocket. Extended 13C pocket Standard 13C pocket 9

10 The s-process main component: case A. Production factors normalized to unity Standard 13C pocket 1 x 10-3 Low metallicity [Fe/H]=-0.5 Main component starting from A=90 (BUT: Problems in chemical evolution. Need of an extra unknown process in the range A = ) High number of Thermal Pulses 10

11 The s-process main component: case B. Sr Production factors normalized to unity Extended 13C pocket 6 x Zr 89 Y Ba, 140 Ce Higher metallicity [Fe/H]=-0.15 Main component starting from A=86 Small number of Thermal Pulses C-star Luminosity Function respected 10

12 The ratio among s-only nuclei in the 2 cases. Similar results for A>90 Using simply an unique stellar generation at a suitable metallicity it is not possible to distinguish between the two cases 86 Sr 87 Sr Ex re ten su d Bi lts d ed p (2 ster ivid ock 01 zo e e 4) et d b t 's on al. y es In our model with a large pocket: Larger contributions to the weak-s elements 86 Sr, 87Sr are full members of main component In standard scenario the solar LEEP (Light Element Primary production) must be invoked to explain Galactic (and even solar) enrichment of s-process elements in the range 90<A<130 11

13 Age Metallicity Relation. Case A Standard pocket Case B Extended pocket Short time interval Small contribution to the Galaxy Solar LEPP integration Long time interval Main contribution to the Galaxy Solar LEPP isn't necessary 12

14 Conclusions. A summary: recent observational and theoretical issues on the s-process; an extended 13C pocket as a consequence of magnetic bouyancy; the main component for A>90 can be reproduced in both cases by single-population models, but at rather different metallicities; nuclei for A<90 are fed more efficiently in the case of an extended pocket; no solar LEPP contribution is needed using a deeper 13C pocket. Several tests could be performed to discriminate between the two cases: s/c ratio of post-agb stars; SiC grains and meteorites; chemical evolution of the Galaxy; a quantitative model for the 13C pocket. Thanks for your attention!!! 13

Impact of Nuclear Reaction Uncertainties on AGB Nucleosynthesis Models

Impact of Nuclear Reaction Uncertainties on AGB Nucleosynthesis Models, ab R. Gallino, b F. Käppeler, c M. Wiescher, d and C. Travaglio a a INAF - Astronomical Observatory Turin, Turin, Italy b University