C.D.S. - SIMBAD4 rel 1.7 - 2021.05.16CEST10:30:54

2002ApJ...579..626S - Astrophys. J., 579, 626-638 (2002/November-2)

Thorium and uranium chronometers applied to CS 31082-001.


Abstract (from CDS):

We use the classical r-process model to explore the implications of the recently reported first observation of U in the extremely metal-poor, r-process element-enriched halo star CS 31082-001 for U and Th cosmochronometry. Using updated nuclear physics input and performing a new, conservative, analysis of the remaining uncertainties in the classical r-process model, we confirm that U (together with Th) abundance observations in metal-poor stars are a promising tool for dating r-process events in the early Galaxy, independent of assumptions on Galactic chemical evolution. We show that nuclear physics uncertainties limit the present accuracy of estimated U/Th ages to about 2 Gyr. Critical nuclear data that are required to lower this uncertainty include β-delayed fission branchings and reliable predictions of the onset of deformation in the vicinity of the N=184 shell closure around 244Tl, as both directly affect predicted U/Th ratios in r-process models. In this paper we apply, for the first time, the new HFBCS-1 mass model within the framework of the classical r-process model. We find that the predicted U and Th abundances are incompatible with the solar U and Th abundances and trace this back to a different prediction of the onset of deformation around 244Tl. In the case of CS 31082-001, we find it likely that the zero-age U and Th abundances were enhanced by about a factor of 2.5 compared to both (1) a theoretical extrapolation from the observed stable elements using the classical r-process model and (2) the zero-age abundances of Th and U in other r-process-enhanced, metal-poor halo stars. Although presently ad hoc, this ``actinide boost'' assumption solves the apparent problem of the relative age difference compared with other metal-poor halo stars and, at the same time, the problem of the inconsistency of ages based on U/(stable nucleus), Th/(stable nucleus) and U/Th ratios. There clearly exist differences, among some r-process-enhanced, metal-poor stars, in the level of the elemental abundances of actinides beyond the third r-process peak. Whether CS 31082-001 is a relatively rare case or commonplace awaits the identification of larger numbers of r-process-enhanced, metal-poor stars in which both U and Th can be measured. Using the U/Th ratio, we obtain a best age estimate for the r-process elements in CS 31082-001 of 15.5±3.2 Gyr. Future observations of Pb and Bi and a better determination of the r-process contribution to solar Pb are needed to put the age estimates for this and other stars on a more solid basis. For our most likely scenario, we provide predictions of the expected upper and lower limits on the abundances of the elements Pb and Bi in CS 31082-001.

Abstract Copyright:

Journal keyword(s): Galaxy: Abundances - Galaxy: Evolution - Nuclear Reactions, Nucleosynthesis, Abundances - Stars: Abundances - Stars: Population II

Simbad objects: 8

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Number of rows : 8

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
1 BPS CS 31082-0001 Pe* 01 29 31.1311330115 -16 00 45.496485322 12.527 12.427 11.642 11.189 10.713 CEMP 251 0
2 HD 103113 * 11 52 24.3741285162 +07 32 41.363286698   11.17 9.71     K5 5 0
3 HD 108577 PM* 12 28 16.8615508146 +12 20 41.090259163   10.18 9.55 9.8   KIIvw 69 0
4 HD 115444 Pe* 13 16 42.4591800169 +36 22 52.695481224   9.77 8.97 8.3 7.88 G9V 230 0
5 HD 126238 Pe* 14 25 29.9570911985 -43 38 36.947126248   8.44 7.68 7.44   G3/8wF0/2 105 1
6 BD+17 3248 HB* 17 28 14.4691668039 +17 30 35.848406966   10.02 9.34     KIIvw 205 0
7 HD 186478 Pe* 19 45 14.1410795461 -17 29 27.071420634   10.116 9.302 8.527 7.961 K2III 135 0
8 BPS CS 22892-0052 Pe* 22 17 01.6558480594 -16 39 27.051900047   14.03 13.20 13.06 12.19 KIIvw 420 0

    Equat.    Gal    SGal    Ecl

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