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The Hamburg/ESO R-process Enhanced Star survey (HERES): Project Overview, and New r-II Stars

Published online by Cambridge University Press:  23 December 2005

N. Christlieb ,
T.C. Beers ,
P.S. Barklem ,
M.S. Bessell ,
V. Hill ,
J. Holmberg ,
A.J. Korn ,
B. Marsteller ,
L. Mashonkina  and
S. Rossi
...Show all authors
N. Christlieb
Affiliation:
Hamburger Sternwarte, Universität Hamburg, Germany email: nchristlieb@hs.uni-hamburg.de Department of Astronomy and Space Physics, Uppsala University, Sweden
T.C. Beers
Affiliation:
Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, USA
P.S. Barklem
Affiliation:
Department of Astronomy and Space Physics, Uppsala University, Sweden
M.S. Bessell
Affiliation:
Research School of Astronomy & Astrophysics, Australian National University, Australia
V. Hill
Affiliation:
Observatoire de Paris, GEPI and URA 8111 du CNRS, France
J. Holmberg
Affiliation:
Niels Bohr Institute, Copenhagen University, Denmark Nordic Optical Telescope Scientific Association, Spain
A.J. Korn
Affiliation:
Department of Astronomy and Space Physics, Uppsala University, Sweden Universitäts-Sternwarte München, Germany
B. Marsteller
Affiliation:
Department of Physics and Astronomy and JINA: Joint Institute for Nuclear Astrophysics, Michigan State University, USA
L. Mashonkina
Affiliation:
Universitäts-Sternwarte München, Germany Institute of Astronomy, Russian Academy of Sciences, Russia
S. Rossi
Affiliation:
Departamento de Astronomia Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Brazil
F.-J. Zickgraf
Affiliation:
Hamburger Sternwarte, Universität Hamburg, Germany email: nchristlieb@hs.uni-hamburg.de
K.-L. Kratz
Affiliation:
VISTARS HGF – Virtual Institute for Nuclear Structure and Nuclear Astrophysics, Mainz Institut für Kernchemie, Universität Mainz, Germany
B. Nordström
Affiliation:
Niels Bohr Institute, Copenhagen University, Denmark Lund Observatory, Lund University, Sweden
B. Pfeiffer
Affiliation:
VISTARS HGF – Virtual Institute for Nuclear Structure and Nuclear Astrophysics, Mainz Institut für Kernchemie, Universität Mainz, Germany
J. Rhee
Affiliation:
Center for Space Astrophysics, Yonsei University, Korea Space Astrophysics Laboratory, California Institute of Technology, USA
S.G. Ryan
Affiliation:
Department of Physics and Astronomy, Open University, UK
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Abstract

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We report on a dedicated effort to identify and study metal-poor stars that are strongly enhanced in r-process elements ($\mbox{[r/Fe]}>+1.0$dex; hereafter r-II stars), the Hamburg/ESO R-process Enhanced Star survey (HERES). In a sample of 253 confirmed metal-poor stars for which “snapshot” spectra ($R\sim 20,000$; $S/N \sim 50/1$ per pixel) were obtained with VLT/UVES, and abundances were determined in an automated fashion using the methods of Barklem et al. (2005), we identified eight new r-II stars. They are now being studied in detail by means of higher resolution and S/N spectroscopy. The new r-II stars have metallicities in the range $-3.2<\mbox{[Fe/H]}<-2.6$. Future searches for r-II stars should therefore focus on stars in this [Fe/H] range. Moderately r-process enhanced stars (i.e., $+0.3\,\mbox{dex}<\mbox{[r/Fe]}<+1.0\,\mbox{dex}$; r-I stars) were found at metallicities as high as $\mbox{[Fe/H]} = -1.5$. The [Fe/H] ranges in which r-I and r-II stars can be found may provide an important constraint for the identification of the site(s) of the r-process(es).

Keywords

stars: abundances – stars: Population II – Galaxy: abundances – Galaxy: evolution – Galaxy: halo
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 1 , Symposium S228: From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution , May 2005 , pp. 439 - 443
Copyright
© 2005 International Astronomical Union

Footnotes

Based in large part on observations collected at the European Southern Observatory, Paranal, Chile (proposals number 68.B-0320 and 170.D-0010).