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Roughly half of the heavy elements (atomic mass greater than that of iron) are believed to be synthesized in the late evolutionary stages of stars with masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly iron) capture neutrons and progressively build up (through the slow-neutron-capture process (1,2), or s-process) heavier elements that are subsequently brought to the stellar surface by convection. Two neutron sources, activated at distinct temperatures, have been proposed: [sup.13]C and [sup.22]Ne, each releasing one neutron per α-particle ([sup.4]He) captured (1-4). To explain the measured stellar abundances (1-7), stellar evolution models invoking the [sup.13]C neutron source (which operates at temperatures of about one hundred million kelvin) are favoured. Isotopic ratios in primitive meteorites, however, reflecting nucleosynthesis in the previous generations of stars that contributed material to the Solar System, point to higher temperatures (more than three hundred million kelvin), requiring at least a late activation of [sup.22]Ne (ref. 1). Here we report a determination of the s-process temperature directly in evolved low-mass giant stars, using zirconium and niobium abundances, independently of stellar evolution models. The derived temperature supports [sup.13]C as the s-process neutron source. The radioactive pair [sup.93]Zr-[sup.93]Nb used to estimate the s-process temperature also provides, together with the pair [sup.99]Tc- [sup.99]Ru, chronometric information on the time elapsed since the start of the s-process, which we determine to be one million to three million years., We obtained high-resolution spectra of 17 S-type stars and 6 M-type stars using the high-resolution (resolving power, λ/Δλ = 85,000) HERMES spectrograph (8) (Extended Data Table 1 and Extended Data [...]

The abundance of heavy r-elements may provide a better understanding of the r- process, and the determination of several reference r-elements should allow a better determination of a star's age. The space UV region (λ < 3000 Å) presents a large number of lines of the heavy elements, and in the case of some elements, such as Bi, Pt, Au, detectable lines are not available elsewhere. The extreme 'r-process star' CS 31082-001 ([Fe/H] = -2.9) was observed in the space UV to determine abundances of the heaviest stable elements, using STIS on board Hubble Space Telescope. PACS Nos: 32.30.Rj, 39.30.+w, 31.50.+w L'abondance des elements lourds peut aider a comprendre le processus r. La determination de l'abondance de plusieurs elements de reference devrait permettre de mieux cerner l'age de l'etoile. La region de l'UV spatial (λ < 300 nm) presente un grand nombre de lignes d'elements lourds. En particulier, dans le cas des elements Bi, Pt et Au, ces raies ne sont detectables que dans l' UV. Le telescope spatial Hubble nous a permis d'observer, dans ce domaine de longueurs d'onde, l'etoile CS 31082-001 qui est riche en elements r. [Traduit par la Redaction], 1. Introduction The European Southern Observatory (ESO) large programme FIRST STARS was devoted to an accurate determination of abundances in very metal-poor stars, by means of optical and near-UV spectra [...]

Author(s): S. Van Eck (corresponding author) [1]; S. Goriely [1]; A. Jorissen [1]; B. Plez [2] About half of the stable nuclei heavier than iron are believed to be synthesized [...]

Author(s): R. Cayrel (corresponding author) [1]; V. Hill [2]; T. C. Beers [3]; B. Barbuy [4]; M. Spite [5]; F. Spite [5]; B. Plez [6]; J. Andersen [1, 7]; P. [...]