EDP Sciences
Free Access
Volume 428, Number 3, December IV 2004
Page(s) 1027 - 1037
Section Instruments, observational techniques, and data processing
DOI https://doi.org/10.1051/0004-6361:20041536

A&A 428, 1027-1037 (2004)
DOI: 10.1051/0004-6361:20041536

The Hamburg/ESO R-process Enhanced Star survey (HERES)

I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements
N. Christlieb1, 2, T. C. Beers3, P. S. Barklem2, M. Bessell4, V. Hill5, J. Holmberg6, 7, A. J. Korn2, 8, B. Marsteller3, L. Mashonkina9, 8, Y.-Z. Qian10, S. Rossi11, G. J. Wasserburg12, F.-J. Zickgraf1, K.-L. Kratz13, 14, B. Nordström6, 15, B. Pfeiffer13, 14, J. Rhee16, 17 and S. G. Ryan18

1  Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
    e-mail: nchristlieb@hs.uni-hamburg.de
2  Department of Astronomy and Space Physics, Uppsala University, Box 515, 75120 Uppsala, Sweden
3  Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
4  Research School of Astronomy & Astrophysics, Australian National University, Cotter Road, Weston, ACT 2611, Australia
5  Observatoire de Paris, GEPI and URA 8111 du CNRS, 92195 Meudon Cedex, France
6  Astronomical Observatory, NBIfAFG, Juliane Meries Vej 30, 2100 Copenhagen, Denmark
7  Nordic Optical Telescope Scientific Association, Apartado 474, 38 700 Santa Cruz de La Palma, Spain
8  Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany
9  Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia
10  School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
11  Departamento de Astronomia Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05508-900 São Paulo SP, Brazil
12  Division of Geophysics and Planetary Sciences, California Institute of Technology, Pasadena, CA91125, USA
13  Institut für Kernchemie, Universität Mainz, 55128 Mainz, Germany
14  VISTARS HGF - Virtual Institute for Nuclear Structure and Nuclear Astrophysics, Mainz, Germany
15  Lund University Box 43, 22100 Lund, Sweden
16  Center for Space Astrophysics, Yonsei University, Seoul 120-749, Korea
17  Space Astrophysics Laboratory, California Institute of Technology, MC 405-47, Pasadena, CA 91125, USA
18  Department of Physics and Astronomy, Open University, Walton Hall, Milton Keynes, MK7 6AA, UK

(Received 25 June 2004 / Accepted 11 August 2004 )

We report on a dedicated effort to identify and study metal-poor stars strongly enhanced in  r-process elements ( $\mbox{[r/Fe]}>1$ dex; hereafter r-II stars), the Hamburg/ESO R-process Enhanced Star survey (HERES). Moderate-resolution (~ 2 Å) follow-up spectroscopy has been obtained for metal-poor giant candidates selected from the Hamburg/ESO objective-prism survey (HES) as well as the HK survey to identify sharp-lined stars with  $\mbox{[Fe/H]}<-2.5$ dex. For several hundred confirmed metal-poor giants brighter than  $B\sim 16.5$ mag (most of them from the HES), "snapshot" spectra ( $R\sim 20\,000$ $S/N \sim 30$ per pixel) are being obtained with VLT/UVES, with the main aim of finding the  2-3% r-II stars expected to be among them. These are studied in detail by means of higher resolution and higher  S/N spectra. In this paper we describe a pilot study based on a set of 35 stars, including 23 from the HK survey, eight from the HES, and four comparison stars. We discovered two new r-II stars, CS 29497-004 ( $\mbox{[Eu/Fe]}=1.64\pm 0.22$) and CS 29491-069 ( $\mbox{[Eu/Fe]}=1.08\pm
0.23$ ). A first abundance analysis of CS 29497-004 yields that its abundances of Ba to Dy are on average enhanced by  1.5 dex with respect to iron and the Sun and match a scaled solar  r-process pattern well, while Th is underabundant relative to that pattern by 0.3 dex, which we attribute to radioactive decay. That is, CS 29497-004 seems not to belong to the class of  r-process enhanced stars displaying an "actinide boost", like CS 31082-001 (Hill et al. 2002), or CS 30306-132 (Honda et al. 2004b). The abundance pattern agrees well with predictions of the phenomenological model of Qian & Wasserburg.

Key words: surveys -- stars: abundances -- stars: population II -- Galaxy: abundances -- Galaxy: halo

SIMBAD Objects

© ESO 2004

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