Giants reveal what dwarfs conceal: Li abundance in lower RGB stars as diagnostic of the primordial Li Alessio Mucciarelli (Department of Astronomy, University of Bologna, Italy) Mucciarelli, Salaris & Bonifacio, 2012, MNRAS, 410,2195

The Li problem … LITHIUM WMAP Dwarf stars 2.2-2.4 2.72

Pietrinferni et al.(2006) RGB Bump FDU The FDU ends when the convective envelope attains its maximum depth Deepening of the convective envelope

Another plateau … Mucciarelli et al.(2011) Gratton et al.(2000) Spite et al.(2006) Palacios et al.(2006) Lind et al.(2008)

Why lower RGB stars? - They are sensitive to the total amount of Li left in the star after the MS - They are very weakly affected by atomic diffusion The surface Li abundance at the end of FDU is only 0.07 dex lower when diffusion is fully efficient. NO DIFFUSION DIFFUSION Depletion starting from A(Li)=2.72

Why lower RGB stars? - They are sensitive to the total amount of Li left in the star after the MS - They are very weakly affected by atomic diffusion Depletion starting from A(Li)=2.72 In MS stars the effect of diffusion reaches several tenths of dex The (uncertain) effect of diffusion is minimized !!!

A very robust constraint for the efficiency of the turbulent mixing Why lower RGB stars? - They are sensitive to the total amount of Li left in the star after the MS - They are very weakly affected by atomic diffusion SPITE PLATEAU Lower RGB PLATEAU A very robust constraint for the efficiency of the turbulent mixing Mucciarelli et al.(2011) M4

17 lower RGB Halo stars … (UVES + ELODIE spectra) Li @ 6708 A We employed 3 Teff scales: - 2 IRFM using (J-K) colours (Alonso et al. 1999, Gonzalez Hernandez & Bonifacio 2009) - Excitation equilibrium FDU FDU-0.01 dex FDU-0.10 dex Mucciarelli et al.(2012)

Primordial Li abundance from lower RGB … Mucciarelli et al.(2012) Field Halo stars NGC 6397 (GIRAFFE) Standard 2.33 2.42 ---- Diffusion 2.40 2.49 ---- NGC 6752 (UVES) Standard 2.26 2.37 2.27 Diffusion 2.32 2.41 2.33 M4 (GIRAFFE) Standard ---- ---- 2.35 Diffusion ---- ---- 2.40

Lower RGB stars: some advantages … The lower RGB are the only possibility to infer the initial A(Li) in stars more distant than those usually observed to investigate the Spite Plateau To enlarge the sample of field and GC stars within our Galaxy To assess whether the Li problem exists also in extragalactic systems (but see also Monaco et al. 2010)

to observe the lower RGB stars in Lower RGB stars: some advantages … The lower RGB are the only possibility to infer the initial A(Li) in stars more distant than those usually observed to investigate the Spite Plateau 30 hours with FLAMES to observe the lower RGB stars in M54 + Sgr (PI: Mucciarelli, 089.D-0341 )

Conclusions… The lower RGB stars are significantly less sensitive to the efficiency of atomic diffusion (compared with the dwarf stars) (2) The unique route to derive A(Li) in distant stellar systems (alternative to the Spite Plateau) (3) A robust constraint for the efficiency of turbulent mixing (complementary to the Spite Plateau)