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 INFN sez. di Perugia - Italy
Abundance anomalies after the Luminosity bump of the RGB H-burning Shell Convective Envelope 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 Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
Models of extra-mixing PARAMETRIC Boothroyd, Sackmann, Wasserbug 1994-1995: ‘CBP’ circulation like transport of matter. Subsequent shown to be equivalent to a diffusive mixing (Nollett et al. 2003) 12C/13C, 26Al and O isotopic ratios in presolar grains Sackmann & Boothroyd 1999Creation/ destruction of Li due to deep mixing in red-giants Charbonnel 1994; Charbonnel & Do Nascimiento 1998, Denissenkov & Van den Berg 2003 and Palacios et al. 2003 Processes induced by rotation (shear instabilities and diffusion, meridional circulation) 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 Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
New ideas for physical causes: 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. Magnetized matter has a lower gas pressure: Pge = Pgi + B2/8p dPg(i-e) (<0) = -B2/8p It is therefore lighter (and cooler) & Moves Outward! Magnetic buoyancy dynamo mechanism might persist in red giant stars (Busso et al. 2007; Wasserburg & Busso 2008; Nordhaus et al. 2008) Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
FAST & SLOW magnetic mixing: CASE 1 SLOW: Cool Bottom Processes? MIXING VELOCITY SLOW (cm/sec):as well as FAST (km/sec) mixing are possible by magnetic models Bubble geometry Mixing velocity HEAT EXCHANGE CASE 2 FAST: Detached bubbles ‘BUBBLE’ SURFACE Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
What do we mean by ‘fast’? Fast enough to 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) carries 7Be rapidly out of the high-temperature zone Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
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 Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
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 Using bolometric corrections for Oxygen and Carbon Rich stars by Guandalini et al. (2006), Guandalini & Busso (2008) Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
The Giant Branches - Leiden 11-15 May 2009 FAST Mixing SLOW Mixing Guandalini et al. IN PRESS Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
Also C, N,O and Al are affected by the mixing FAST Mixing So Li increasing is accompanied by other chemical modifications, with effects due to Ṁ (0.1-1 10-6M8/yr) Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
Slow mixing effects during the AGB: CBP + TDU ΔTP = Log TH –Log TP = 0.1-0.4 Ṁ mixing rate in unit of 10-6M8/yr Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
CNO: from an oxygen to a carbon rich AGB star Star sample by Smith & Lambert 1990, Lambert et al.1986 Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
Duprat private comunication Grains…. Zinner et al 2007, Nittler et al 1997, Choi et al.2000, Amari et al. 2001 Contamination (?!) Duprat private comunication Sara Palmerini The Giant Branches - Leiden 11-15 May 2009
Conclusions: Magnetic (M) & Thermoaline (T) Different mixing velocities Li production Li destruction Occurence during MS Occurence during late evolutionary stages Very Deep mixing ? Magnetic buoyances and thermoaline mixing are complementary process working to determine the chemical evolution of low mass stars Sara Palmerini The Giant Branches - Leiden 11-15 May 2009