Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-01-12
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
6 pages, 5 figures, To appear in the Proceedings of IAU Symp. 268 - Light Elements in the Universe (C. Charbonnel, M. Tosi, F.
Scientific paper
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. [alpha/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.
Barbuy Batriz
Bonifacio Piercarlo
Galli Daniele
Gratton Raffaele
Pasquini Luca
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