429 research outputs found
First Stars: Abundance Patterns from O to Zn and Derived SNe Yields in the Early Galaxy
No full textInternational audienceMost of the work reported here has been conducted within the ESO Large Programme 165.N-0276 "Galaxy Formation, Early Nucleosynthesis, and the First Stars", which has covered 4 periods 65-68, from April 2000 to November 2001, with a total of 38 nights in visitor mode. The team had R. Cayrel as PI, and 13 CoIs
The evolution of the milky way from its earliest phases: constraints on stellar nucleosynthesis
No full textWe computed the evolution of the abundances of O, Mg, Si, Ca, K, Ti, Sc, Ni, Mn, Co, Fe and Zn in the Milky Way. We made use of the most widely adopted nucleosynthesis calculations and compared the model results with observational data with the aim of imposing constraints upon stellar yields. To best fit the data in the solar neighborhood, when adopting the Woosley & Weaver (1995, ApJS, 101, 181) yields for massive stars and the Iwamoto et al. (\cite{Iwamoto99}, ApJS, 125, 439) ones for type Ia SNe, it is required that: i) the Mg yields should be increased in stars with masses from 11 to 20 Msun and decreased in masses larger than 20 Msun. The Mg yield should be also increased in SNe Ia. ii) The Si yields should be slightly increased in stars above 40 Msun, whereas those of Ti should be increased between 11 and 20 Msun and above 30 Msun. iii) The Cr and Mn yields should be increased in stars with masses in the range 11-20 Msun; iv) the Co yields in SNe Ia should be larger and smaller in stars in the range 11-20 Msun; v) the Ni yield from type Ia SNe should be decreased; vi) the Zn yield from type Ia SNe should be increased. vii) The yields of O (metallicity dependent SN models), Ca, Fe, Ni, and Zn (the solar abundance case) in massive stars from Woosley & Weaver (\cite{Woosley95}) are the best to fit the abundance patterns of these elements since they do not need any changes. We also adopted the yields by Nomoto et al. (\cite{Nomoto97}, Nucl. Phys. A, 621, 467) and Limongi & Chieffi (\cite{Limongi03}, ApJ, 592, 404) for massive stars and discuss the corrections required in these yields in order to fit the observations. Finally, the small spread in the [el/Fe] ratios in the metallicity range from [Fe/H] = -4.0 up to -3.0 dex (Cayrel et al. \cite{Cayrel03}, A&A, 416, 1117) is a clear sign that the halo of the Milky Way was well mixed even in the earliest phases of its evolution
Observational Evidence for Atmospheric Physical Characteristics Relevant to Stellar Evolution
No full textPrecision Engineering behind European Astronomy Programmes
No full textThe fields of astronomy science have presented significant precision engineering challenges. Numerous solutions for these fields of science have achieved unprecedented levels of accuracy, sensitivity and sheer scale. Notwithstanding of their importance to science understanding, many of these precision engineering developments have become key enabling technologies for wealth generation and other human well-being issues. This paper provides a brief historical overview of astronomy instruments. Later, details of critical precision engineering developments that supported the establishment of leading European astronomical instruments are illustrated. Finally, significant precision engineering demands to enable future sciences programmes are introduced
Abundances in the Uranium-rich Star CS 31082-001
No full textThe recent discovery by Cayrel et al. of U in CS 31082-001 along with Os and Ir at greatly enhanced abundances but with [Fe/H] = -2.9 strongly reinforces the argument that there are at least two kinds of Type II supernova (SN II) sources for r-nuclei. One source is the high-frequency H events responsible for heavy r-nuclei (A > 135) but not Fe. The H-yields calculated from data on other ultra-metal-poor stars and the Sun provide a template for quantitatively predicting the abundances of all other r-elements. In CS 31082-001 these should show a significant deficiency at A < 135 relative to the solar r-pattern. It is proposed that CS 31082-001 should have had a companion that exploded as an SN II H event. If the binary survived the explosion, this star should now have a compact companion, most likely a stellar-mass black hole. Comparison of abundance data with predicted values and a search for a compact companion should provide a stringent test of the proposed r-process model. The U-Th age determined by Cayrel et al. for CS 31082-001 is, to within substantial uncertainties, in accord with the r-process age determined from solar system data. The time gap between the big bang and the onset of normal star formation allows r-process chronometers to provide only a lower limit on the age of the universe
Piégeage par implantation d'hélium : Interactions dopants/défauts
No full textThèse sous la direction de R. Jérisian et D. Mathiot soutenue le 10 décembre 2003 - Université Louis Pasteur (Strasbourg I) - Laboratoire PHASE (PHysique et Applications des SEmi-conducteurs, UPR 292
Lithium in NGC 6397 (Gonzalez Hernandez+, 2009)
No full textPhotometric data of the dwarf and subgiant stars of the globular cluster NGC 6397. We also provide the signal-to-noise of the spectra, the 3D and 1D Halpha-based effective temperatures, 3D Li abundances, and the equivalent widths and errors: dEWa: Error of the equivalent width measurements estimated from a fitting routine that uses as free parameters the velocity shift, the continuum location, and the equivalent width of the Li line. dEWb: Error of the equivalent width associated to the signal-to-noise ratio and the wavelength dispersion of the spectra, derived using Cayrel's formula (Cayrel, 1988, IAU Symp. 132: The Impact of Very High S/N Spectroscopy on Stellar Physics, 132, 345).VizieR On-line Data Catalog: J/A+A/505/L13info:eu-repo/semantics/publishe
Post-quantum Cryptography: Lattice Identification Schemes
No full textThis survey presents an overview and a comparative analysis of the state of art in post-quantum identification schemes based on lattices. Furthermore, we propose an adaptation of the HB family of identification in a lattice context. The aspects taken into account in such comparison are performance, security, communication costs, underlying hard-problem, completeness, soundness, and key sizes.7903/04/15729748Blum, A., Kalai, A., Wasserman, H., Noise-tolerant learning, the parity problem, and the statistical query model (2003) J. 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