Volume 553, May 2013
|Number of page(s)||13|
|Section||Galactic structure, stellar clusters and populations|
|Published online||30 April 2013|
The s-process in the Galactic halo: the fifth signature of spinstars in the early Universe? ⋆
1 Leibniz–Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2 Astrophysics Group, Lennard–Jones Laboratories, EPSAM, Keele University, ST5 5BG, Staffordshire, UK
3 Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, 5-1-5 Kashiwanoha, 277-8583 Kashiwa, Japan
4 Geneva Observatory, Geneva University, 1290 Sauverny, Switzerland
5 Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
Received: 28 November 2012
Accepted: 18 February 2013
Context. Very old halo stars have previously been found to show at least four different abundance anomalies, which models of fast-rotating massive stars (spinstars) can successfully account for: rise of N/O and C/O, low 12C/13C, and a primary-like evolution of Be and B. Here we show the impact of these same stars in the enrichment of Sr and Ba in the early Universe.
Aims. We study whether the s-process production of fast-rotating massive stars can offer an explanation for the observed spread in [Sr/Ba] ratio in halo stars with metallicity [Fe/H] < −2.5.
Methods. By means of a chemical inhomogeneous model, we computed the enrichment of Sr and Ba by massive stars in the Galactic halo. Our model takes, for the first time, the contribution of spinstars into account.
Results. The model (combining an r-process contribution with an s-process from fast-rotating massive stars) is able to reproduce the observed scatter in the [Sr/Ba] ratio at [Fe/H] < −2.5. Toward higher metallicities, the stochasticity of the star formation fades away owing to the increasing number of exploding and enriching stars, and as a consequence the predicted scatter decreases.
Conclusions. Our scenario is again based on the existence of spinstars in the early Universe. Very old halo stars have previously been found to show at least four other abundance anomalies, which rotating models of massive stars can successfully account for. Our results provide a fifth independent signature of fast-rotating massive stars: an early enrichment of the Universe in s-process elements.
Key words: Galaxy: evolution / Galaxy: halo / stars: rotation / nuclear reactions, nucleosynthesis, abundances / stars: massive / stars: abundances
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.