Cosmic abundances: The impact of stellar duplicity

The mass-transfer scenario links chemical peculiarities with stellar duplicity for an increasing number of stellar classes (classical and dwarf barium stars, subgiant and giant CH stars, S stars without technetium, yellow symbiotic stars, WIRRING stars, Abell-35-like nuclei of planetary nebulae...). Despite these successes, the mass-transfer scenario still faces several problems: What is the mass-transfer mode? Why orbital elements of dwarf barium stars do not fully match those of the classical barium stars? What is the origin of the few non-binary stars among dwarf barium stars? The paper reviews these open questions.Comment: 14 pages, 4 figures, to appear in `Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis', edited by F.N. Bash, T.G. Barnes, ASP Conf. Ser., in pres

A CORAVEL radial-velocity monitoring of giant Ba and S stars: spectroscopic orbits and intrinsic variations

This paper provides orbital parameters for 38 barium stars and 10 extrinsic S stars derived from a decade-long CORAVEL monitoring. Lower bounds on the orbital period (generally exceeding 10 y) have been obtained for 10 more systems. Mira S, SC and (Tc-poor) C stars have also been monitored and show intrinsic radial-velocity variations due to atmospheric phenomena. Tentative orbital solutions are proposed for 3 stars (S UMa, X Cnc, BD-08:1900) where the velocity and photometric periods are different. Three stars (RZ Peg, SS Vir and R CMi) exhibit radial-velocity variations synchronous with the light variations. Pseudo-orbital solutions have been derived for those stars. In the case of RZ Peg, a line-doubling phenomenon is observed near maximum light, and probably reflects the shock wave propagating through the photosphere.Comment: Astronomy & Astrophysics Supplements, 20 pages, 8 figures, 8 tables (LaTeX). Also available at: http://obswww.unige.ch/~udry/cine/barium/barium.htm

Spectroscopic binaries among AGB stars from HERMES/Mercator: the case of V Hya

We report on our search for spectroscopic binaries among a sample of AGB stars. Observations were carried out in the framework of the monitoring of radial velocities of (candidate) binary stars performed at the Mercator 1.2m telescope, using the HERMES spectrograph. We found evidence for duplicity in UV Cam, TU Tau, BL Ori, VZ Per, T Dra, and V Hya. This short communication focus on V Hya, found to behave like RV Tau of the b subtype, which are binaries surrounded by a disc.Comment: Poster presented at IAU Symp. 343 "Why Galaxies Care About AGB Stars", Vienna, august 201

Some modifications to the SNIP journal impact indicator

The SNIP (source normalized impact per paper) indicator is an indicator of the citation impact of scientific journals. The indicator, introduced by Henk Moed in 2010, is included in Elsevier's Scopus database. The SNIP indicator uses a source normalized approach to correct for differences in citation practices between scientific fields. The strength of this approach is that it does not require a field classification system in which the boundaries of fields are explicitly defined. In this paper, a number of modifications that will be made to the SNIP indicator are explained, and the advantages of the resulting revised SNIP indicator are pointed out. It is argued that the original SNIP indicator has some counterintuitive properties, and it is shown mathematically that the revised SNIP indicator does not have these properties. Empirically, the differences between the original SNIP indicator and the revised one turn out to be relatively small, although some systematic differences can be observed. Relations with other source normalized indicators proposed in the literature are discussed as well

The temperature and chronology of heavy-element synthesis in low-mass stars

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, 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: 13C and 22Ne, each releasing one neutron per alpha-particle (4He) captured. To explain the measured stellar abundances, stellar evolution models invoking the 13C 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 22Ne. 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 13C as the s-process neutron source. The radioactive pair 93Zr-93Nb used to estimate the s-process temperature also provides, together with the pair 99Tc-99Ru, chronometric information on the time elapsed since the start of the s-process, which we determine to be one million to three million years.Comment: 30 pages, 10 figure

Rivals for the crown: Reply to Opthof and Leydesdorff

We reply to the criticism of Opthof and Leydesdorff [arXiv:1002.2769] on the way in which our institute applies journal and field normalizations to citation counts. We point out why we believe most of the criticism is unjustified, but we also indicate where we think Opthof and Leydesdorff raise a valid point