Web-Based Visualization of Very Large Scientific Astronomy Imagery

Visualizing and navigating through large astronomy images from a remote location with current astronomy display tools can be a frustrating experience in terms of speed and ergonomics, especially on mobile devices. In this paper, we present a high performance, versatile and robust client-server system for remote visualization and analysis of extremely large scientific images. Applications of this work include survey image quality control, interactive data query and exploration, citizen science, as well as public outreach. The proposed software is entirely open source and is designed to be generic and applicable to a variety of datasets. It provides access to floating point data at terabyte scales, with the ability to precisely adjust image settings in real-time. The proposed clients are light-weight, platform-independent web applications built on standard HTML5 web technologies and compatible with both touch and mouse-based devices. We put the system to the test and assess the performance of the system and show that a single server can comfortably handle more than a hundred simultaneous users accessing full precision 32 bit astronomy data.Comment: Published in Astronomy & Computing. IIPImage server available from http://iipimage.sourceforge.net . Visiomatic code and demos available from http://www.visiomatic.org

Detection and Removal of Artifacts in Astronomical Images

Astronomical images from optical photometric surveys are typically contaminated with transient artifacts such as cosmic rays, satellite trails and scattered light. We have developed and tested an algorithm that removes these artifacts using a deep, artifact free, static sky coadd image built up through the median combination of point spread function (PSF) homogenized, overlapping single epoch images. Transient artifacts are detected and masked in each single epoch image through comparison with an artifact free, PSF-matched simulated image that is constructed using the PSF-corrected, model fitting catalog from the artifact free coadd image together with the position variable PSF model of the single epoch image. This approach works well not only for cleaning single epoch images with worse seeing than the PSF homogenized coadd, but also the traditionally much more challenging problem of cleaning single epoch images with better seeing. In addition to masking transient artifacts, we have developed an interpolation approach that uses the local PSF and performs well in removing artifacts whose widths are smaller than the PSF full width at half maximum, including cosmic rays, the peaks of saturated stars and bleed trails. We have tested this algorithm on Dark Energy Survey Science Verification data and present performance metrics. More generally, our algorithm can be applied to any survey which images the same part of the sky multiple times.Comment: 17 pages, 6 figures. Accepted for publication in Astronomy and Computin

Collaboration sociale d'entreprise : Le réveil du courrier électronique ?

National audienceThis article studies the persistence of email while enterprise social collaborative tools are more and more promoted within firms: Can this be purely explained by the fear of change, or should other factors be considered? We claim here first that some important capabilities of messaging are lacking in enterprise social tools and second that email could be enhanced by adding new social capabilities. The first point is studied by a theoretical comparison of the different tools; the second point by a prototype followed by experimentation. This work leads to the conclusion that there are still some distinctive capabilities of messaging, which could explain its persistence, and also that email can remain a foundation to implement new social capabilities. These results open new research perspectives, and provide learnings to practitioners for the deployment of collaborative features for enterprises.Cet article part du constat de la persistance des usages de la messagerie électronique à l'heure des outils sociaux collaboratifs d'entreprise : est-elle uniquement explicable par des résistances au changement, ou d'autres facteurs doivent-ils être considérés ? Nous formulons ici les hypothèses que certaines capacités importantes de la messagerie manquent aux outils sociaux, puis que la messagerie peut être améliorée par l'ajout de nouvelles capacités sociales. La première hypothèse est étudiée par une comparaison théorique des différentes capacités des outils en présence ; la seconde par un prototypage suivi d'une expérimentation. Ces travaux concluent d'une part à l'existence de capacités distinctives de la messagerie susceptibles d'expliquer la persistance de son usage, et d'autre part à la possibilité de partir de l'email pour mettre en oeuvre de nouvelles capacités sociales, ouvrant ainsi des perspectives de recherche sur ce sujet, mais fournissant également des indications aux praticiens pour le déploiement de fonctions collaboratives dans les entreprises

Inferring the photometric and size evolution of galaxies from image simulations

Current constraints on models of galaxy evolution rely on morphometric catalogs extracted from multi-band photometric surveys. However, these catalogs are altered by selection effects that are difficult to model, that correlate in non trivial ways, and that can lead to contradictory predictions if not taken into account carefully. To address this issue, we have developed a new approach combining parametric Bayesian indirect likelihood (pBIL) techniques and empirical modeling with realistic image simulations that reproduce a large fraction of these selection effects. This allows us to perform a direct comparison between observed and simulated images and to infer robust constraints on model parameters. We use a semi-empirical forward model to generate a distribution of mock galaxies from a set of physical parameters. These galaxies are passed through an image simulator reproducing the instrumental characteristics of any survey and are then extracted in the same way as the observed data. The discrepancy between the simulated and observed data is quantified, and minimized with a custom sampling process based on adaptive Monte Carlo Markov Chain methods. Using synthetic data matching most of the properties of a CFHTLS Deep field, we demonstrate the robustness and internal consistency of our approach by inferring the parameters governing the size and luminosity functions and their evolutions for different realistic populations of galaxies. We also compare the results of our approach with those obtained from the classical spectral energy distribution fitting and photometric redshift approach.Our pipeline infers efficiently the luminosity and size distribution and evolution parameters with a very limited number of observables (3 photometric bands). When compared to SED fitting based on the same set of observables, our method yields results that are more accurate and free from systematic biases.Comment: 24 pages, 12 figures, accepted for publication in A&

New Security Protocols for Offline Point-of-Sale Machines

EMV (Europay MasterCard Visa) is the protocol implement-ed to secure the communication between a client’s payment device and a Point-of-Sale machine during a contact or an NFC (Near Field Communication) purchase transaction. In several studies, researchers have analyzed the operation of this protocol in order to verify its safety: unfortunately, they have identified two security vulnerabilities that lead to multiple attacks and dangerous risks threatening both clients and merchants. In this paper, we are interested in proposing new security solutions that aim to overcome the two dangerous EMV vulnerabilities. Our solutions address the case of Point-of-Sale machines that do not have access to the banking network and are therefore in the “offline” connectivity mode. We verify the accuracy of our proposals by using the Scyther security verification tool

ALBUM: a tool for the analysis of slitless spectra and its application to ESO WFI data

ALBUM is a general-purpose tool to visualize and screen large amounts of slitless spectra. It was developed for a search for emission-line stars in SMC and LMC clusters. The observations were obtained with ESO's Wide Field Imager (WFI) and comprise ~8 million low-resolution spectra. The tool as well as the results of its application to the SMC part of the database are presented. The inferred frequency of Be stars is compared to the one in the higher-metallicity environment of the Milky Way.Comment: The 2007 ESO instrument calibration workshop, Garching bei Muenchen : Allemagne (2007); 4 page

L'analyse des images dans les grands relevés d'astronomie visible/proche -infrarouge

- Le volume et la nature des données issues des grands relevés d'imagerie astronomique posent des problèmes spécifiques en matière de traitement et d'analyse. Je présente les réponses actuelles, mais aussi les questions en suspens concernant la détection et l'analyse morphologique des sources dans le domaine visible / proche-infrarouge

The merging cluster of galaxies Abell 3376: an optical view

Abell 3376 is a merging cluster of galaxies at redshift z=0.046, famous mostly for its giant radio arcs, and shows an elongated and highly substructured X-ray emission, but has not been analysed in detail at optical wavelengths. We have obtained wide field images of Abell 3376 in the B band and derive the GLF applying a statistical subtraction of the background in three regions: a circle of 0.29 deg radius (1.5 Mpc) encompassing the whole cluster, and two circles centered on each of the two brightest galaxies (BCG2, northeast, coinciding with the peak of X-ray emission, and BCG1, southwest) of radii 0.15 deg (0.775 Mpc). We also compute the GLF in the zone around BCG1, which is covered by the WINGS survey in the B and V bands, by selecting cluster members in the red sequence in a (B-V) versus V diagram. Finally, we discuss the dynamical characteristics of the cluster implied by a Serna & Gerbal analysis. The GLFs are not well fit by a single Schechter function, but satisfactory fits are obtained by summing a Gaussian and a Schechter function. The GLF computed by selecting galaxies in the red sequence in the region surrounding BCG1 can also be fit by a Gaussian plus a Schechter function. An excess of galaxies in the brightest bins is detected in the BCG1 and BCG2 regions. The dynamical analysis based on the Serna & Gerbal method shows the existence of a main structure of 82 galaxies which can be subdivided into two main substructures of 25 and 6 galaxies. A smaller structure of 6 galaxies is also detected. The B band GLFs of Abell 3376 are clearly perturbed, as already found in other merging clusters. The dynamical properties are consistent with the existence of several substructures, in agreement with a previously published X-ray analysis.Comment: 11 pages, 12 figures, accepted for publication in A&