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

• cessing in old metal poor star
• ld 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

Mass Loss

• Competition between g and

grad approx. determines movement of elements

• Competing transport

processes can hinder diffusion

• G. Alecian, 2002

Burger’s equations

• 2 equations for each species (28 in the code)
• Solved for each mesh points (~1500)
• and at each time step (~1000)

 

 

   

5 5 2 2

j i i j i i i i i ij ij j i j j ij i ij ij i ij j j i j ra j i d i j i

m r m r P m N g N Z eE K z r m m m z T w w w N k K a r g b r m w r m                                          

 

Expr Expression used ession used in e in evolution

• lution calcula

calculations tions

 

4 2 4

15 ( ) 4 1

u u

u e P u e   

Radiative accelerations

• 1.5 GigaBytes of

data ; OPAL (1996)

– Integration over fraction of photons given to i at each frequency

2

1 ( ) 4 ( ) (total)

u rad i i R u rad r

L P u du r c g i X    







Expr Expression used ession used in e in evolution

• lution calcula

calculations tions

h u kT  

( )

u i



(total)

u

 (Fe)

u

 (Li)

u



Dimensionless frequency Normalised black body Flux distribution

3 He

400 ( ) ( )

T

D D T T  



      

DT DHe

Center Surface Convective Zone

0.77Mסֽ, [Fe/H]=-2.31 Expr Expression used ession used in e in evolution

• lution calcula

calculations tions

Notation T6.0 => log(T0)=6.0

Mixing parametrization

r Surface Center

Abundance variations in metal poor stars: 0.8Mסֽ, [Fe/H]=-2.31

Log(∆M/M*)

0.8Mסֽ, [Fe/H]=-2.31

Log(∆M/M*) r Surface Center

0.8Mסֽ, [Fe/H]=-2.31

Log(∆M/M*) r Surface Center

Close to turn-of Close to turn-off

Diffusion affects the upper 40 % of R* Most of the star affected by abundance anomalies

0.8Mסֽ, [Fe/H]=-2.31

Log(∆M/M*) r Surface Center

Effect of diffusion in the center of the star

Center

13.5 Gyr

0.8Mסֽ, [Fe/H]=-2.31

Richard et al., 2002a

Globular cluster age: M92 case

Age reduction: ~10%

VandenBerg et al., 2002

13.5 Gyr 15 Gyr

Predicted surface abundances

0.8Mסֽ, [Fe/H]=-2.31

Richard et al., 2002a

Factor of actor of ~1000 in ~1000 in the pr the predicted surf edicted surface ace Fe a abundance undance

Lithium abundance and radiative acceleration in a 0.77 Mסֽ, [Fe/H]=-3.31

Log g Bottom of the surface CZ Center Center grad>g Li a Li abun undance decr dance decreas ease due to due to atomic dif

• mic diffusion and n

usion and nuclear b lear burning rning

Li

0.77 Mסֽ, [Fe/H]=-3.31

Bottom of the surface CZ Center Lithium d thium dredg edge-up a

• up after T

r TO

0.77 Mסֽ

Lithium in models for [Fe/H]=-2.31

13.5Gyr isochrones for main- sequence models

Richard et al., 2005

13.5Gyr

Center

Blue triangles: spite et al. 84 Red squares: Ryan et al. 99

Primordial Lithium and the spite plateau

Richard et al., 2005 Diffusive models Diffusive models with additional mixing

Blue triangles: Thorburn 94 Red triangles (GC): Bonifacio 2002 Pink crosses: Bonifacio et al. 2003 Green squares (GC): Bonifacio et al. 2002

Abundance variation with Teff for [Fe/H]=-2.11

12.5Gyr isochrones for TO and past TO models Li bump at SGB stage

Korn et al., 2006, Korn et al., 2007

Globular cluster NGC6397

0.8 Mסֽ at 12Gyr

13.5Gyr isochrones

Effect of metallicity on Fe surface abundance

grad>g for models with [Fe/H]init< -1.31

0.8 Mסֽ

Li and Fe surface abundances evolution at different metallicity

=> thermohaline convection ? Strong effect of radiative acceleration

• n Fe for very metal poor stars

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