Impact of micro-telluric lines on precise radial velocities and its correction

Context: In the near future, new instruments such as ESPRESSO will arrive, allowing us to reach a precision in radial-velocity measurements on the order of 10 cm/s. At this level of precision, several noise sources that until now have been outweighed by photon noise will start to contribute significantly to the error budget. The telluric lines that are not neglected by the masks for the radial velocity computation, here called micro-telluric lines, are one such noise source. Aims: In this work we investigate the impact of micro-telluric lines in the radial velocities calculations. We also investigate how to correct the effect of these atmospheric lines on radial velocities. Methods: The work presented here follows two parallel lines. First, we calculated the impact of the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum by synthetic atmospheric spectra and evaluated the effect created by the presence of the telluric lines. Then, we divided HARPS spectra by synthetic atmospheric spectra to correct for its presence on real data and calculated the radial velocity on the corrected spectra. When doing so, one considers two atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS. Results: We find that the micro-telluric lines can induce an impact on the radial velocities calculation that can already be close to the current precision achieved with HARPS, and so its effect should not be neglected, especially for future instruments such as ESPRESSO. Moreover, we find that the micro-telluric lines' impact depends on factors, such as the radial velocity of the star, airmass, relative humidity, and the barycentric Earth radial velocity projected along the line of sight at the time of the observation.Comment: Accepted in A&

Io: IUE observations of its atmosphere and the plasma torus

Two of the main components of the atmosphere of Io, neutral oxygen and sulfur, were detected with the IUE. Four observations yield brightnesses that are similar, regardless of whether the upstream or the downstream sides of the torus plasma flow around Io is observed. A simple model requires the emissions to be produced by the interaction of O and S columns in the exospheric range with 2 eV electrons. Cooling of the 5 eV torus electrons is required prior to their interaction with the atmosphere of Io. Inconsistencies in the characteristics of the spectra that cannot be accounted for in this model require further analysis with improved atomic data. The Io plasma torus was monitored with the IUE. The long-term stability of the warm torus is established. The observed brightnesses were analyzed using a model of the torus, and variations of less than 30 percent in the composition are observed, the quantitative results being model dependent

Alice: The Rosetta Ultraviolet Imaging Spectrograph

We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700-2050 A spectral band with a spectral resolution between 8 A and 12 A for extended sources that fill its ~0.05 deg x 6.0 deg field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a concave holographic reflection grating. The imaging microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a 2 D delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and the nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating normally in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet Linear T7 in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaignComment: 11 pages, 7 figure

Occurrence and diversity of bacterial communities in Tuber magnatum during truffle maturation

none9Tuber magnatum, an ascomycetous fungus and obligate ectomycorrhizal symbiont, forms hypogeous fruit bodies, commonly called Italian white truffles. The diversity of bacterial communities associated with T. magnatum truffles was investigated using culture-independent and -dependent 16S rRNA genebased approaches. Eighteen truffles were classified in three groups, representing different degrees of ascocarp maturation, based on the percentage of asci containing mature spores. The culturable bacterial fraction was 4.17 (+/- 1.61) x 10.000.000, 2.60 (+/- 1.22) x 10.000.000 and 1.86 (+/-1.32) x 1.000.000 cfu g-1 for immature, intermediate and mature ascocarps respectively. The total of bacteria count was two orders of magnitude higher than the cfu g-1 count. Sequencing results from the clone library showed a significant presence of alpha-Proteobacteria (634 of the 771 total clones screened, c. 82%) affiliated with Sinorhizobium, Rhizobium and Bradyrhizobium spp. The bacterial culturable fraction was generally represented by gamma-Proteobacteria (210 of the 384 total strains isolated, c. 55%), which were mostly fluorescent pseudomonads. Fluorescent in situ hybridization confirmed that alpha-Proteobacteria (85.8%) were the predominant components of truffle bacterial communities with beta-Proteobacteria (1.5%), gamma-Proteobacteria (1.9%), Bacteroidetes (2.1%), Firmicutes (2.4%) and Actinobacteria (3%) only poorly represented. Molecular approaches made it possible to identify alpha-Proteobacteria as major constituents of a bacterial component associated with T. magnatum ascoma, independently from the degree of maturation.openE. BARBIERI; C. GUIDI; J. BERTAUX; P. FREY-KLETT; J. GARBAYE; P. CECCAROLI; R. SALTARELLI; A. ZAMBONELLI; V. STOCCHIBarbieri, Elena; C., Guidi; J., Bertaux; P., FREY KLETT; J., Garbaye; Ceccaroli, Paola; Saltarelli, Roberta; A., Zambonelli; Stocchi, Vilbert

Parameterized maximum likelihood method (PML): application to space-time radar localization

We present a maximum likelihood method for the localization of sources with known waveforms . It's a joint space time radar localization which is a generalisation of recent methods to coherent signal . The obtained results are usefull in wireless communications for the identification of propagation channel with a pilot signal . An exact maximum likelihood method is presented . Variances of estimation and related Cramer Rao Bound are established . Simulations results illustrate the behaviour of the algorithm.Nous présentons une technique du maximum de vraisemblance qui localise des sources dont les formes d'ondes sont identiques et connues. Il s'agit d'une localisation radar conjointe direction-retard qui est une extension aux cas de signaux cohérents des méthodes actuellement utilisées et exploitant la connaissance des signaux émis. Les résultats obtenus s'appliquent de la même manière aux cas des communications mobiles pour lesquelles on veut identifier le canal de propagation à l'aide d'un signal connu. Un estimateur exact du maximum de vraisemblance est présenté. Les variances d'estimation ainsi que les bornes de Cramer-Rao sont établies. Des résultats de simulations viennent illustrer le comportement des algorithmes pour lesquels les performances sont comparées à la borne de Cramer-Rao

Localisation 2D à l'aide d'un réseau phasé très perturbé.

Dans cet article nous proposons d'améliorer la robustesse des algorithmes d'autocalibration en 2D (gisement et site) à l'aide d'une régularisation. Nous avons introduit un a priori sur le module des gains des capteurs. En effet, lorsque l'on utilise une antenne omnidirectionnelle, nous montrons que l'estimée des gains des obtenue à l'aide des éléments diagonaux de la matrice de corrélation est une information très précieuse. Nous proposons alors deux techniques de régularisation qui exploitent ces résultats. La première, gràce à une contrainte sur la somme des modules exhibe une vitesse de convergence élevée. La seconde exploite chaque contrainte de gain simultanément et nécessite la mise en oeuvre d'une optimisation itérative. De nombreuses simulations viennent confirmer les résultats attendus et montrent les améliorations apportées