Atomic dif Atomic diffusion and lithium usion and lithium pr - PowerPoint PPT Presentation

Atomic dif Atomic diffusion and lithium usion and lithium pr processing in ocessing in old metal poor star old metal poor stars Olivier Richard LUPM UMR5299, Université Montpellier II, Montpellier, France Main collaborators: Georges Michaud, Jacques Richer (Montréal, Canada) Andreas Korn (Uppsala, Sweden)

Plan Plan • atomic diffusion in stellar modeling, • atomic diffusion at work in population II stars: Effects in the center, on surface abundances, and the effect of initial metallicity,

Transport in the radiative zone: chemical composition variations in the radiative zone due to particles transport processes • Competition between g and Mass g rad approx. determines Loss movement of elements • Competing transport processes can hinder diffusion G. Alecian, 2002

Burger’s equations Expr Expression used ession used in e in evolution olution calcula calculations tions          m r m r P             j i i j  ra d i m N g g N Z eE K w w z   i i i i i ij j i ij    r m m   j i j        m z 5 T 5        j ij  N k K w w a r b r    i ij j i ij i ij j   2 r 2 m m    j i j • 2 equations for each species (28 in the code) • Solved for each mesh points (~1500) • and at each time step (~1000)

Radiative accelerations Expr Expression used ession used in e in evolution olution calcula calculations tions  Dimensionless h    u frequency rad  ( ) i 1 L  kT  rad r R u g P u du ( )   i 2 4 (total) r c X Normalised 0 4 u i u 15 u e black body  P u ( )   Flux  2 4  4 u e 1 distribution  (Li) u • 1.5 GigaBytes of  data ; OPAL u i ( )  (Fe) (1996) u – Integration over fraction of photons  given to i at each (total) u frequency

Mixing parametrization Expression used Expr ession used in e in evolution olution calcula calculations tions 0.77 M סֽ , [Fe/H]=-2.31 Convective Zone  3       D 400 D ( T )  T He 0   ( ) T 0 Notation T6.0 => log( T 0 )=6.0 D T D He Surface Center

Abundance variations in metal poor stars: 0.8 M סֽ , [Fe/H]=-2.31 Surface r Log( ∆ M/M * ) Center

0.8 M סֽ , [Fe/H]=-2.31 Surface r Log( ∆ M/M * ) Center

0.8 M סֽ , [Fe/H]=-2.31 Close to turn-of Close to turn-off Surface Diffusion affects the r upper 40 % of R * Log( ∆ M/M * ) Most of the star affected by abundance anomalies Center

0.8 M סֽ , [Fe/H]=-2.31 Surface r Log( ∆ M/M * ) Center

Effect of diffusion in the center of the star 0.8 M סֽ , [Fe/H]=-2.31 13.5 Gyr Center Richard et al., 2002a

Globular cluster age: M92 case Age reduction: ~10% 15 Gyr 13.5 Gyr VandenBerg et al., 2002

Predicted surface abundances 0.8 M סֽ , [Fe/H]=-2.31 Factor of actor of ~1000 in ~1000 in the pr the predicted surf edicted surface ace Richard et al., 2002a Fe a abundance undance

Lithium abundance and radiative acceleration in a 0.77 M סֽ , [Fe/H]=-3.31 Bottom of the surface CZ Li Log g g rad > g Center Center Li a Li abun undance decr dance decreas ease due to due to atomic dif omic diffusion and n usion and nuclear b lear burning rning

0.77 M סֽ , [Fe/H]=-3.31 Bottom of the surface CZ Center Lithium d thium dredg edge-up a -up after T r TO

Lithium in models for [Fe/H]=-2.31 13.5Gyr 0.77 M סֽ Center 13.5Gyr isochrones for main- Richard et al., 2005 sequence models

Primordial Lithium and the spite plateau Diffusive models Blue triangles: Thorburn 94 Red triangles (GC): Bonifacio 2002 Pink crosses: Bonifacio et al. 2003 Green squares (GC): Bonifacio et al. 2002 Diffusive models with additional mixing Blue triangles: spite et al. 84 Red squares: Ryan et al. 99 Richard et al., 2005

Abundance variation with Teff for [Fe/H]=-2.11 12.5Gyr isochrones for TO and past TO models Li bump at SGB stage

Globular cluster NGC6397 Korn et al., 2006, Korn et al., 2007

Effect of metallicity on Fe surface abundance 0.8 M סֽ at 12Gyr 13.5Gyr isochrones g rad >g for models with [Fe/H] init < -1.31

Li and Fe surface abundances evolution at different metallicity 0.8 M סֽ Strong effect of radiative acceleration on Fe for very metal poor stars => thermohaline convection ?

Conclusion Atomic diffusion have also to be taken into account in population II stars. It’s lead to better agreement between cosmology and stellar physics (Lithium problem, globular cluster age) Lithium abundances at subgiant branch stage gives constraints on competing processes Atomic diffusion is need in models to better understand the physics of these competing processes Radiative acceleration could have strong effects on very metal poor stars Even if atomic diffusion is reduced by competing processes in the superficial zones effects remain in the center