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Issue A&A
Volume 428, Number 1, December II 2004
Page(s) L9 - L12
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:200400094



A&A 428, L9-L12 (2004)
DOI: 10.1051/0004-6361:200400094

Letter

Lead abundance in the uranium star CS 31082-001

B. Plez1, V. Hill2, R. Cayrel3, M. Spite2, B. Barbuy4, T. C. Beers5, P. Bonifacio6, F. Primas7 and B. Nordström8, 9

1  GRAAL, CNRS UMR 5024, Université de Montpellier 2, 34095 Montpellier Cedex 5, France
2  Observatoire de Paris, GEPI, CNRS UMR 8111, 5 place Jules Janssen, 92195 Meudon Cedex, France
3  Observatoire de Paris, GEPI, CNRS UMR 8111, 61 av. de l'Observatoire, 75014 Paris, France
    e-mail: roger.cayrel@obspm.fr
4  IAG Universidade de São Paolo, Dep. de Astronomia CP 3386, Rua do Matão 1226, São Paolo 05508-900, Brazil
5  Department of Physics & Astronomy and JINA, Michigan State University, East Lansing, MI 48824, USA
6  Istituto Nazionale per l'Astrofisica - Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
7  ESO, Karl-Schwarzschild-Str. 2, 85749 Garching bei München, Germany
8  Lund Observatory, Box 43, 22100 Lund, Sweden
9  Niels Bohr Institute, Juliane Maries Vej 30, 2100 Copenhagen, Denmark

(Received 21 July 2004 / Accepted 21 October 2004 )

Abstract
In a previous paper we were able to measure the abundance of uranium and thorium in the very-metal poor halo giant BPS  CS 31082-001 , but only obtained an upper limit for the abundance of lead (Pb). We have got from ESO 17 h of additional exposure on this star in order to secure a detection of the minimum amount of lead expected to be present in CS 31082-001 , the amount arising from the decay of the original content of Th and U in the star. We report here this successful detection. We find an LTE abundance $\log\mathrm{(Pb/H)}+12=-0.55 \pm 0.15$ dex, one dex below the upper limits given by other authors for the similar stars  CS 22892-052 and BD +17° 3248 , also enhanced in r-process elements. From the observed present abundances of Th and U in the star, the expected amount of Pb produced by the decay of 232Th, and 238U alone, over 12-15 Gyr is $-0.73\pm 0.17$  dex. The decay of 235U is more difficult to estimate, but is probably slightly below the contribution of 238U, making the contribution of the 3 actinides only slightly below, or even equal to, the measured abundance. The contribution from the decay of 234U has was not included, for lack of published data. In this sense our determination is a lower limit to the contribution of actinides to lead production. We comment this result, and we note that if a NLTE analysis, not yet possible, doubles our observed abundance, the decay of the 3 actinides will still represent 50 per cent of the total lead, a proportion higher than the values considered so far in the literature.


Key words: stars: abundances -- physical data and processes: nuclear reactions, nucleosynthesis, abundances -- atomic data

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