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Li (and CNO) abundances due to non-convective mixing in RGB and AGB stars

The Giant Branches Workshop - Lorentz Center, Leiden , Netherland 11-15 May 2009. Li (and CNO) abundances due to non-convective mixing in RGB and AGB stars. Sara Palmerini Maurizio Busso, Roald Guandalini, Enrico Maiorca Dip. di Fisica Università degli Studi di Perugia

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Li (and CNO) abundances due to non-convective mixing in RGB and AGB stars

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  1. The GiantBranches Workshop - Lorentz Center, Leiden, Netherland 11-15 May 2009 Li (and CNO) abundances due to non-convective mixing in RGB and AGB stars Sara Palmerini Maurizio Busso, Roald Guandalini, Enrico Maiorca Dip. di Fisica Università degli Studi di Perugia INFN sez. di Perugia - Italy

  2. Abundanceanomaliesafterthe Luminositybumpof the RGB H-burningShell ConvectiveEnvelope • Evolved stars: unexpected isotopic ratios for light nuclei: • 12C/13C (FDU 25-30 but 10- 15 shown by popI RGB stars) • Li abundances in Red Giants: wide dispersion • Presolar grains: also 26Al/27Al, 17O/16O, 18O/16 O The Giant Branches - Leiden 11-15 May 2009

  3. Models of extra-mixing PARAMETRIC Boothroyd, Sackmann, Wasserbug 1994-1995: ‘CBP’ circulation like transport of matter. Subsequentshown to beequivalent to a diffusive mixing (Nollett et al. 2003)  12C/13C, 26Al and O isotopic ratios in presolar grains Sackmann & Boothroyd 1999Creation/ destruction of Li due to deepmixing in red-giants • Charbonnel 1994; Charbonnel & Do Nascimiento 1998, Denissenkov & Van den Berg 2003 andPalacios et al. 2003 Processes induced by rotation (shear instabilities and diffusion, meridionalcirculation)  12C/13C, Li + 3He depletion. • BUT Rotation would not yield sufficiently extended extra-mixing processes to account for the observations.(Palacios et al. 2006) • + more……….(e.g. gravitational waves….) PHYSICAL The Giant Branches - Leiden 11-15 May 2009

  4. New ideasforphysicalcauses: density unbalances Thermohaline mixing diffution due to the molecular weight inversion induced by 3He+3He4He + 2p (Eggleton, Dearborn & Lattanzio 2006 and Charbonnel et Zahn 2007) Importance on the Main Sequence Slow mixing V~ cm/sec. Nuclear source. Magnetizedmatter has a lower gas pressure: Pge = Pgi + B2/8p dPg(i-e)(<0)= -B2/8p Itisthereforelighter (and cooler) & MovesOutward! Magnetic buoyancy dynamo mechanism might persist in red giant stars (Busso et al. 2007; Wasserburg & Busso 2008; Nordhaus et al. 2008) The Giant Branches - Leiden 11-15 May 2009

  5. FAST & SLOW magnetic mixing: CASE 1 SLOW: Cool Bottom Processes? MIXING VELOCITY  SLOW(cm/sec):aswellasFAST(km/sec) mixing are possiblebymagneticmodels Bubblegeometry Mixing velocity HEAT EXCHANGE  CASE 2 FAST: Detached bubbles ‘BUBBLE’ SURFACE The Giant Branches - Leiden 11-15 May 2009

  6. 3He+4He→7Be+γ ↓ 7Be (p, γ) 8B→ 4He+4He 7Be (e-, ν) 7Li →7Li(p,a)4He T ≥ 3−4 × 106 K T>2∙107K→7Be* What do we mean by ‘fast’? Fast enough to produce Li, saving Be to the envelope against p and having e- captures (t~53 days) A Cameron & Fowler’s mixing mechanism (1971) carries7Be rapidly out of the high-temperature zone The Giant Branches - Leiden 11-15 May 2009

  7. RGB & AGB - Radiative Layers Above the H shell • IF WE MIX INFINITELY & FAST, AND CARRY ALL 7Be TO THE SURFACE • X(Li) = 2-3X10-9 Y(LI) = 3-4X10-10  Log (e(Li)) = Log(Y(Li))+12 = 2-3. If the velcity is high but non infinity more Li can be produce along the path up to Log(e(Li)) =4 The Giant Branches - Leiden 11-15 May 2009

  8. No direct correlation between Li and CNO in C-stars sample CNO  Lambert et al. 1986 Li  Boffin et al. 1993: Li depends on the mixing velocity, CNO nuclei do not. Only from Li-CNO comparisons  better information on the physical model UsingbolometriccorrectionsforOxygen and CarbonRichstars byGuandaliniet al. (2006), Guandalini & Busso (2008) The Giant Branches - Leiden 11-15 May 2009

  9. FAST Mixing SLOW Mixing Guandalini et al. IN PRESS The Giant Branches - Leiden 11-15 May 2009

  10. Also C, N,O and Al are affectedby the mixing FAST Mixing So Li increasing is accompanied by other chemical modifications, with effects due to Ṁ (0.1-1 10-6M8/yr) The Giant Branches - Leiden 11-15 May 2009

  11. Slow mixing effectsduring the AGB: CBP + TDU ΔTP = Log TH –Log TP = 0.1-0.4 Ṁ mixing rate in unit of 10-6M8/yr The Giant Branches - Leiden 11-15 May 2009

  12. CNO: fromanoxygento a carbonrich AGB star Star sample by Smith & Lambert 1990, Lambert et al.1986 The Giant Branches - Leiden 11-15 May 2009

  13. Grains…. Zinner et al 2007, Nittler et al 1997, Choi et al.2000, Amari et al. 2001 Contamination (?!) Duprat private comunication The Giant Branches - Leiden 11-15 May 2009

  14. Conclusions:Magnetic (M) & Thermoaline (T) T M • Different mixing velocities • Li production • Li destruction • Occurence during MS • Occurence during late evolutionary stages • Very Deep mixing ? Magneticbuoyances and thermoaline mixing are complementaryprocessworkingtodetermine the chemicalevolutionof low mass stars The Giant Branches - Leiden 11-15 May 2009

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