1. The Giant Branches Workshop - Lorentz Center,
Leiden, Netherland 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. 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 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 May 2009

3. Models of extra-mixing
PARAMETRIC
Boothroyd, Sackmann, Wasserbug : ‘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 1999Creation/ destruction of Li due to deep mixing in red-giants
Charbonnel 1994; Charbonnel & Do Nascimiento 1998, Denissenkov & Van den Berg and Palacios et al 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 May 2009

4. 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 May 2009

5. 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 May 2009

6. 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 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
Sara Palmerini
The Giant Branches Leiden 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
Using bolometric corrections for Oxygen and Carbon Rich stars
by Guandalini et al. (2006), Guandalini & Busso (2008)
Sara Palmerini
The Giant Branches Leiden May 2009

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

10. 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 ( M8/yr)
Sara Palmerini
The Giant Branches Leiden May 2009

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

12. 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 May 2009

13. 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 May 2009

14. 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 May 2009