Analysis and Calibration of Natural Guide Star Adaptive Optics Data

From natural guide star adaptive optics data taken with the Come-On Plus and with the Starfire Optical Range Generation II instruments in the JHK bands and in the I band respectively, we describe and analyse the point spread function. The ultimate exploitation of adaptive optics images requires the deconvolution and therefore the calibration of the point spread function which is commonly made by observing a point source close to the astronomical target. In the partial correction regime, the calibration mismatch which is the main source of noise or bias in the deconvolution process is induced by the varying seeing conditions. We therefore stress the procedure enable to increase the quality of the calibration and discuss the typical performances in term of astrometry, photometry and dynamic range to be possibly extracted from current adaptive optics images as a function of the Strehl ratio achieved and the stability of the point spread function. Alternative techniques to the point spread function calibration and other problems like anisoplanaticism are briefly reviewed.Comment: 16 pages latex file using psfig with 11 postscript figures in uuencoded compressed tar-file. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

La délicate articulation des cultures scolaire et jeune. Les usages de Twilight de quelques professeurs d'un lycée de ZEP

Actes consultables sur Internet : http://www.enfanceetcultures.culture.gouv.fr/actes/dagiral_tessier.pdfInternational audienc

Téléchargement et culture potentielle: Du changement des modes d'accès au changement des pratiques

Certaines pratiques culturelles sont actuellement reconfigurées en profondeur par l'apparition des technologies liées à internet. La pratique du téléchargement de musique en ligne dit "peer-to-peer" (P2P) constitue une manifestation particulièrement visible de ces transformations. Nous souhaitons montrer ici comment, au de l'étiquette de "piratage", ces nouveaux outils peuvent constituer pour leurs usagers de nouvelles manières de connaître la musique ; l'usage de logiciels P2P, associé à d'autres outils du web, pouvant à la fois susciter de nouvelles pratiques de découverte et de nouvelles manières de consommer la musique. Ces hypothèses seront testées ici à travers la reconstruction d'un parcours typique d'utilisateur de deux de ces outils : Soulseek et All Music Guide

Low-mass star formation in CG1: a diffraction limited search for pre-main sequence stars next to NX Puppis

Using adaptive optics at the ESO 3.6m telescope, we obtained diffraction limited JHK-images of the region around the Herbig AeBe star NX Pup. We clearly resolved the close companion (sep. 0.128") to NX Pup -- originally discovered by HST -- and measured its JHK magnitudes. A third object at a separation of 7.0" from NX Pup was identified as a classical T Tauri star so that NX Pup may in fact form a hierarchical triple system. We discuss the evolutionary status of these stars and derive estimates for their spectral types, luminosities, masses and ages.Comment: Latex using l-aa-ps.sty with links to 5 postscript figures. Complete postscript version also available at http://lucky.astro.uni-wuerzburg.de/ Accepted for publication in A&

Ethylenediamine- and propylenediaminediacetic acid derivatives as ligands for the "fac-[M(CO)3]+" core (M = Re, 99mTc)

The reaction of Re(CO)5Cl with o- or p-N-(nitrophenyl)ethylenediaminediacetic acid (H2L1, H2L2) and o- or p-N-(nitrophenyl)propylenediaminediacetic acid (H2L3, H2L4) in methanol leads to the formation of stable anionic [Et3NH][Re(CO)3(L)]·H2O complexes 1-4. These compounds have been characterized by means of IR, mass spectrometry, elemental analysis, NMR and conductimetry, as well as X-ray crystallography for 2 and 3. The [Re(CO)3]+ moiety is coordinated via the nitrogen of the iminodiacetic acid unit and two oxygens of monodentate carboxylate groups. In each case, the nitro group of the aromatic ring remains uncoordinated. The analogous technetium-99m complexes 1' and 3' were also prepared quantitatively by the reaction of H2L1 and H2L3, respectively, with the fac-[99mTc(CO)3(H2O)3]+ precursor in ethanol. The corresponding Re and 99mTc compounds were shown to possess the same structure by means of HPLC studies. The high affinity of these ligands for the Tc(I) or Re(I) core, coupled with the easiness of their derivatization (by reduction of the nitro group in amino group), implies that the utilization of this ligand system to develop target-specific radiopharmaceuticals for diagnosis and therapy is promising

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

International audienceNitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO2 substrate from a ZnO colloidal solution. Zinc peroxide (ZnO2) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H2O2 solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250°C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV-Visible transmittance spectroscopy

Nondestructive measurement of the roughness of the inner surface of hollow core-photonic bandgap fibers

We present optical and atomic force microscopy measurements of the roughness of the core wall surface within a hollow core photonic bandgap fiber (HC-PBGF) over the [3×10-2 µm-1 to 30 µm-1] spatial frequency range. A recently developed immersion optical profilometry technique with picometer-scale sensitivity was used to measure the roughness of air-glass surfaces inside the fiber at unprecedentedly low spatial frequencies, which are known to have the highest impact on HC-PBGF scattering loss and, thus, determine their loss limit. Optical access to the inner surface of the core was obtained by the selective filling of the cladding holes with index matching liquid using techniques borrowed from micro-fluidics. Both measurement techniques reveal ultralow roughness levels exhibiting a 1/f spectral power density dependency characteristic of frozen surface capillary waves over a broad spatial frequency range. However, a deviation from this behavior at low spatial frequencies was observed for the first time, to the best of our knowledge

Star formation triggered by non-head-on cloud-cloud collisions, and clouds with pre-collision sub-structure

In an earlier paper, we used smoothed particle hydrodynamics (SPH) simulations to explore star formation triggered by head-on collisions between uniform-density 500 M clouds, and showed that there is a critical collision velocity, vCRIT. At collision velocities below vCRIT, a hub-and-spoke mode operates and delivers a monolithic cluster with a broad mass function, including massive stars (M 10 M) formed by competitive accretion. At collision velocities above vCRIT, a spider’s-web mode operates and delivers a loose distribution of small sub-clusters with a relatively narrow mass function and no massive stars. Here we show that,if the head-on assumption is relaxed, vCRIT is reduced. However, if the uniform-density assumption is also relaxed, the collision velocity becomes somewhat less critical: a low collision velocity is still needed to produce a global hub-and-spoke system and a monolithic cluster, but, even at high velocities, large cores – capable of supporting competitive accretion and thereby producing massive stars – can be produced. We conclude that cloud–cloud collisions may be a viable mechanism for forming massive stars – and we show that this might even be the major channel for forming massive stars in the Galaxy