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Beryllium abundances and the formation of the halo and the thick disk

Published online by Cambridge University Press:  23 April 2010

Rodolfo Smiljanic ,
L. Pasquini ,
P. Bonifacio ,
D. Galli ,
B. Barbuy ,
R. Gratton  and
S. Randich
Rodolfo Smiljanic
Affiliation:
IAG, University of São Paulo, São Paulo, Brazil ESO, Garching bei München, Germany email: rsmiljan@eso.org
L. Pasquini
Affiliation:
ESO, Garching bei München, Germany email: rsmiljan@eso.org
P. Bonifacio
Affiliation:
GEPI Observatoire de Paris - Meudon, France INAF, Osservatorio di Trieste, Trieste, Italy CIFIST Marie Curie Excellence Team
D. Galli
Affiliation:
INAF-Osservatorio di Arcetri, Firenze, Italy
B. Barbuy
Affiliation:
IAG, University of São Paulo, São Paulo, Brazil
R. Gratton
Affiliation:
INAF-Osservatorio di Padova, Padova, Italy
S. Randich
Affiliation:
INAF-Osservatorio di Arcetri, Firenze, Italy
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Abstract

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The single stable isotope of beryllium is a pure product of cosmic-ray spallation in the ISM. Assuming that the cosmic-rays are globally transported across the Galaxy, the beryllium production should be a widespread process and its abundance should be roughly homogeneous in the early-Galaxy at a given time. Thus, it could be useful as a tracer of time. In an investigation of the use of Be as a cosmochronometer and of its evolution in the Galaxy, we found evidence that in a log(Be/H) vs. [α/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined. We also found evidence that the star formation rate was lower in the outer regions of the thick disk, pointing towards an inside-out formation.

Keywords

Stars: abundanceslate-type – Galaxy: halothick disk
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S268: Light Elements in the Universe , November 2009 , pp. 483 - 488
Copyright
Copyright © International Astronomical Union 2010

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