Am/Fm

STARS

General properties

Teff > 6100 K (o Leo)

Teff < about 10000 K (transition area to HgMn stars)

Main sequence stars

Slow rotation: vsini < 90 km/s

Often in binary systems: about 80 % of Am stars are in binary systems.

Peculiarities

Underabundant:

C, N, O, Ca, Sc

Overabundant:

Fe-peak elements, Y, Ba, rare earths.

The slow rotation switches on the diffusion processes that lead to the peculiar abundances.

What do we observe?

The observed abundances reproduce quite well the predictions of diffusion models

More on diffusion…

When the rotational velocity goes below 90 km/s the Helium goes deep into the atmosphere.

It goes down in a time dependent on the inverse of the rotational velocity.

It settles at a depth dependent on the rotational velocity.

The limit is 90 km/s.

More on diffusion…

More on diffusion…

More on diffusion…

Peculiarities are dependent on rotational velocity!!

2.5P1:Vsurf=50km/s with anisotropy

2.5P2:Vsurf=15km/s with anisotropy

2.5P3:Vsurf=50km/s without anisotropy

What do we observe?

Elements underabundant in Am stars increase their abundance with increasing of vsini, till the cluster mean.

Apparently it does not work with Sc, but it should.

Why?

What do we observe?

Elements not peculiar do not show any trend with vsini, as expected.

What do we observe?

Elements overabundant in Am stars decrease their abundance with increasing of vsini, till the cluster mean.

What do we observe?

Same properties as seen before:

Fe is an indicator of peculiarity, that is vsini dependent, so we find the same structure as before.

What do we observe?

No clear trend with mass and fractional age

Velocity fields

Line profiles and bisectors

• Weak lines: reproduced reasonably well

• Strong lines: line cores agree with observations, but wide wings and strong asymmetry are not predicted by the model

• Bisectors: small span, weak blue asymmetry

3-D non-grey3-D grey HR 4750 (Teff=8100 K)

1-D ATLAS9, t=4 km/s

Velocity fields

High microturbulence velocity to compensate the increase of equivalenth width due to the distorted blue wing. The distortion is increasing with the depth of the line.

Velocity fieldsWe have taken 1371 HARPS spectra of 32 Aqr from the ESO archive (Carrier et al. 2007)

R about 120000

SNR each spectrum between 100 and 300 at 5300Å

We have radial velocity shifted all the spectra according to the orbital elements of the binary system

We have add all these spectra to obtain one single spectrum with a SNR about 1000 with this result:

Velocity fields

32Aqr: R=120000, 65000, 45000, 30000

Velocity fields

32Aqr: vsini=1, 5, 10, 15 km/s

Two open questions

What is happening at the transition region with HgMn stars

alpha Andromedae: Kochukhov et al. 2007

Line profile in cool slow rotating Am stars