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Beryllium and the formation of the Thick Disk and of the Halo

Published online by Cambridge University Press:  01 June 2008

Luca Pasquini ,
R. Smiljanic ,
P. Bonifacio ,
R. Gratton ,
D. Galli  and
S. Randich
Luca Pasquini
Affiliation:
ESOGarching bei München, Germany email: lpasquin@eso.org
R. Smiljanic
Affiliation:
ESOGarching bei München, Germany email: lpasquin@eso.org Universidade de São Paolo, IAG, S. Paulo, Brazil
P. Bonifacio
Affiliation:
GEPI Observatoire de Paris - Meudon, France INAF, Osservatorio di Trieste, Trieste, Italy CIFIST Marie Curie Excellence Team
R. Gratton
Affiliation:
INAF-Osservatorio di Padova, Padova, Italy
D. Galli
Affiliation:
INAF-Osservatorio di Arcetri, Firenze, Italy
S. Randich
Affiliation:
INAF-Osservatorio di Arcetri, Firenze, Italy
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Abstract

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We use Beryllium to investigate star formation in the early Galaxy. Be has been demonstrated to be a good indicator of time in these early epochs. By analyzing the so-far largest sample of halo and thick disk metal poor stars, we find a clear scatter in Be for a given value of [Fe/H] and [O/H]. The scatter is very pronounced for Halo stars, while it is marginal for thick disk stars. Our halo stars separate in the [α/Fe] - Be diagram, showing two main branches: one indistinguishable from the thick disk stars, and one with lower [α/Fe] ratio. The stars belonging to this branch are characterized by highly eccentric orbits and small perigalactic radius (Rmin). Their kinematics are consistent with an accreted component.

Keywords

Stars: AbundancesGalaxy: HaloGalaxy: Disk

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