IAG, Universidade de São Paulo, Rua do Matão 1226, Cidade Universitária,
2 Université de Sophia-Antipolis, Observatoire de la Côte d’Azur, CNRS UMR 6202, BP 4229, 06304 Nice Cedex 4, France
3 GEPI, Observatoire de Paris, CNRS, UMR 8111, 92195 Meudon Cedex, France
4 National Optical Astronomy Observatory, Tucson, Arizona 85719, USA and JINA: Joint Institute for Nuclear Physics
5 GEPI, Observatoire de Paris, CNRS, UMR 8111, 61 Av. de l’Observatoire, 75014 Paris, France
6 National Superconducting Cyclotron Laboratory, Department of Physics and Astronomy and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824, USA
7 National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo, Japan
8 RIKEN, iTHES Research Group, 2-1 Hirosawa, Wako, 351-0198 Saitama, Japan
Received: 17 March 2014
Accepted: 28 March 2014
Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak.
Aims. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with −3.4 ≤ [Fe/H] ≤ −2.4 classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is (are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars.
Methods. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph, using spectra in the wavelength ranges 3400–4500 Å, 6800–8200 Å, and 8700–10 000 Å, with resolving power R ~ 40 000 (blue arm) and R ~ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum.
Results. We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and “normal” very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented. Although the abundance ratios of the second r-process peak elements (usually associated with the main r-process) are nearly identical for r-I and r-II stars, the first r-process peak abundance ratios (probably associated with the weak r-process) are more enhanced in r-I stars than in r-II stars, suggesting that differing nucleosynthesis pathways were followed by stars belonging to these two different classifications.
Key words: Galaxy: halo / stars: abundances
Observations obtained with the VLT, at the European Southern Observatory, Paranal, Chile, under proposal 080.D-0194(A) (PI:V. Hill).
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2014