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

被引:128
作者
Christlieb, N
Beers, TC
Barklem, PS
Bessell, M
Hill, V
Holmberg, J
Korn, AJ
Marsteller, B
Mashonkina, L
Qian, YZ
Rossi, S
Wasserburg, GJ
Zickgraf, FJ
Kratz, KL
Nordström, B
Pfeiffer, B
Rhee, J
Ryan, SG
机构
[1] Univ Hamburg, Hamburger Sternwarte, D-20129 Hamburg, Germany
[2] Michigan State Univ, Dept Phys & Astron, E Lansing, MI 48824 USA
[3] Uppsala Univ, Dept Space Phys & Astron, S-75120 Uppsala, Sweden
[4] Australian Natl Univ, Res Sch Astron & Astrophys, Weston, ACT 2611, Australia
[5] Observ Paris, GEPI, F-92195 Meudon, France
[6] CNRS, URA 8111, F-92195 Meudon, France
[7] NBIfAFG, Astron Observ, DK-2100 Copenhagen, Denmark
[8] Nord Opt Telescope Sci Assoc, Santa Cruz De La Palma 38700, Spain
[9] Univ Sternwarte Munchen, D-81679 Munich, Germany
[10] Russian Acad Sci, Inst Astron, Moscow 109017, Russia
[11] Univ Minnesota, Sch Phys & Astron, Minneapolis, MN 55455 USA
[12] Univ Sao Paulo, Dept Astron, Inst Astron Geofis & Ciencias Atmosfer, BR-05508900 Sao Paulo, Brazil
[13] CALTECH, Div Geophys & Planetary Sci, Pasadena, CA 91125 USA
[14] Johannes Gutenberg Univ Mainz, Inst Kernchem, D-55128 Mainz, Germany
[15] VISTARS HGF, Virtual Inst Nucl Struct & Nucl Astrophys, Mainz, Germany
[16] Lund Univ, S-22100 Lund, Sweden
[17] Yonsei Univ, Ctr Space Astrophys, Seoul 120749, South Korea
[18] CALTECH, Space Astrophys Lab, Pasadena, CA 91125 USA
[19] Open Univ, Dept Phys & Astron, Milton Keynes MK7 6AA, Bucks, England
基金
巴西圣保罗研究基金会;
关键词
surveys; stars : abundances; stars : population II; Galaxy : abundances; Galaxy : halo;
D O I
10.1051/0004-6361:20041536
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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 (similar to2 Angstrom) 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 similar to 16.5 mag (most of them from the HES), "snapshot" spectra (R similar to 20 000; S/N similar to 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.
引用
收藏
页码:1027 / 1037
页数:11
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