Surface abundances of Am Surface abundances of Am stars stars

as a constraint on rotational as a constraint on rotational mixingmixing

Olivier Richard1,2, Suzanne Talon2, Georges Michaud2

1 GRAAL UMR5024, Université Montpellier II, Montpellier, France

2 Département de physique, Université de Montréal, Montréal, Canada

• Am stars

• Montréal Models

• Results

Surface abundances of Am Surface abundances of Am stars stars

as a constraint on rotational as a constraint on rotational mixingmixing

• Statistics suggest all non-magnetic stars with V<80 km/s• Recent observations in open clusters

Mg~ normal Al, Si, S: ~normal or slight overabundance Ca ~ normal or underabundant Ni and Fe overabundant

Am StarsAm Stars

Burger’s equationsBurger’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 jii i i i

j i j

ji ij i

ij ij

ijij ij j

j i

j

r di

j i

a

ij

m r m rPm N g N Z eE

r m m

mTN k a r b

w wg

rr m m

K

w

z

zK w

Radiative accelerationsRadiative accelerations

• 1.5 GigaBytes of data ; OPAL (1996)– Integration over

fraction of photons given to i at each frequency

2 0

1 ( )

(to( ) )

l)(

t4 a

ru

adr

ia

Rr

ud

LP u d

ig u

r c Xi

Expression used in evolution calculations

hu

kT

4

24

15( )

4 1

u

u

u eP u

e

( )u i

(total)u

(Fe)u

(Li)u

Mixing modelMixing model

• Simplest version of the turbulent diffusion coefficient obtained from self-consistent treatment of the meridional circulation following Zahn (1992)

• Mixing added to the code as a diffusion process with a parametric mixing diffusion coefficient:

TnD

Mixing modelMixing model

• Simplest version of the turbulent diffusion coefficient obtained from self-consistent treatment of the meridional circulation following Zahn (1992)

• Mixing added to the code as a diffusion process with a parametric mixing diffusion coefficient:

TnD

Computed modelsComputed models

• Models of 1.7 and 1.9 solar masses

• With mixing coefficient corresponding to surface velocity of 50 km/s (V50), 15 km/s (V15), and 5 km/s (V5, V5N)

Richer et al. (2000) 1.9R300-2 and 1.9R1k-2 models

Effective temperature and surface gravity evolution

1.9

1.7

Radiative acceleration in the 1.9 solar masses models

Abundance profiles at 800 Myr

Model 1.9V5

r

1

0

Abundance evolution in the 1.9 solar masses models

The Praesepe star HD73045

The Praesepe star HD73045

Conclusion

• In the mixing model the turbulence seems to be too strong to allow the Am phenomenon to occur at a reasonable velocity

• Need of self-consistent abundance determination for a lot of chemical species in stars of different ages and metallicity