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The Hamburg/ESO R-process Enhanced Star survey (HERES). I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements

Christlieb, N. and Beers, T. C. and Barklem, P. S. and Bessell, M. and Hill, V. and Holmberg, J. and Korn, A. J. and Marsteller, B. and Mashonkina, L. and Qian, Y.-Z. and Rossi, S. and Wasserburg, G. J. and Zickgraf, F.-J. and Kratz, K.-L and Nordström, B. and Pfeiffer, B. and Rhee, J. and Ryan, S. G. (2004) The Hamburg/ESO R-process Enhanced Star survey (HERES). I. Project description, and discovery of two stars with strong enhancements of neutron-capture elements. Astronomy and Astrophysics, 428 (3). pp. 1027-1037. ISSN 0004-6361. doi:10.1051/0004-6361:20041536.

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We report on a dedicated effort to identify and study metal-poor stars strongly enhanced in r-process elements ([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 ([Fe/H]<-2.5 dex. For several hundred confirmed metal-poor giants brighter than B ~ 16.5 mag (most of them from the HES), "snapshot" spectra (R ~ 20,000; S/N ~ 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 ([Eu/Fe] = 1.64 ± 0.22) and CS 29491-069 ([Eu/Fe] = 1.08 ± 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.

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URLURL TypeDescription Paper
Christlieb, N.0000-0002-4043-2727
Beers, T. C.0000-0003-4573-6233
Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 2004 ESO. Article published by EDP Sciences. Received 25 June 2004. Accepted 11 August 2004. Based in large part on observations collected at the European Southern Observatory, Paranal, Chile (proposal number 68.B-0320). We are grateful to the ESO staff at Paranal and Garching for obtaining the VLT/UVES observations and reducing the data, respectively. Computations of tailored MARCS models by M. Mizuno-Wiedner, B. Edvardsson and B. Gustafsson are acknowledged. We are grateful to K. Eriksson and B. Edvardsson for technical help with the abundance analysis programs, and B. Gustafsson for many valuable comments. J. Cohen kindly derived an effective temperature for CS 29497−004 from broad-band photometry for us. We are indebted to A. Frebel for careful proofreading of an earlier version of the manuscript. N.C. acknowledges financial support through a Henri Chretien International Research Grant administered by the American Astronomical Society, from Deutsche Forschungsgemeinschaft under grants Re 353/44-1 and CH 214/3-1, and a Marie Curie Fellowship of the European Community program Improving Human Research Potential and the Socio-Economic Knowledge under contract number HPMF-CT-2002-01437. T.C.B. acknowledges partial funding for this work from grants AST 00-98508 and AST 00-98549 awarded by the US National Science Foundation and from award PHY 02-16783, Physics Frontiers Center/Joint Institute for Nuclear Astrophysics (JINA). P.B. acknowledges the support of the Swedish Research Council. A.J.K. acknowledges support from the Studienstiftung des deutschen Volkes and the Akademie Leopoldina under grant BMBF-LPD 9901/8-87. S.R. thanks the Brazilian Institutions FAPESP and CNPq for partial financial support. The work by G.J.W. was supported by DOE DE-FG03-88ER 13851, Caltech Division Contribution No. 9011(1116).
Funding AgencyGrant Number
American Astronomical SocietyUNSPECIFIED
Deutsche Forschungsgemeinschaft (DFG)Re 353/44-1
Deutsche Forschungsgemeinschaft (DFG)CH 214/3-1
European Community Marie Curie FellowshipHPMF-CT-2002-01437
NSFAST 00-98508
NSFAST 00-98549
NSFPHY 02-16783
Swedish Research CouncilUNSPECIFIED
Studienstiftung des deutschen Volkes and the Akademie LeopoldinaBMBF-LPD 9901/8-87
Department of Energy (DOE)DE-FG03-88ER 13851
Subject Keywords:surveys; stars : abundances; stars : population II; Galaxy : abundances; Galaxy : halo
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences9011
Lunatic Asylum Lab1116
Issue or Number:3
Record Number:CaltechAUTHORS:20131219-102017506
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Official Citation: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. Christlieb, T. C. Beers, P. S. Barklem, M. Bessell, V. Hill, J. Holmberg, A. J. Korn, B. Marsteller, L. Mashonkina, Y.-Z. Qian, S. Rossi, G. J. Wasserburg, F.-J. Zickgraf, K.-L. Kratz, B. Nordström, B. Pfeiffer, J. Rhee and S. G. Ryan A&A 428 (3) 1027-1037 (2004) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43092
Deposited By: Ruth Sustaita
Deposited On:19 Dec 2013 19:00
Last Modified:10 Nov 2021 16:32

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