Analysis of astrometric catalogues with vector spherical harmonics

Comparison of stellar catalogues with position and proper motion components using a decomposition on a set of orthogonal vector spherical harmonics. We show the theoretical and practical advantages of this technique as a result of invariance properties and the independence of the decomposition from a prior model. We describe the mathematical principles used to perform the spectral decomposition, evaluate the level of significance of the multipolar components and examine the transformation properties under space rotation. The principles are illustrated with a characterisation of the systematic effects in the FK5 catalogue compared to Hipparcos and with an application to the extraction of the rotation and dipole acceleration in the astrometric solution of QSOs expected from Gaia.Comment: accepted for publication in Astronomy & Astrophysic

Analyse spectrale des résidus de la télémétrie laser sur la lune

L'observation des signaux en astronomie conduit très souvent à un échantillonnage irrégulier dû à de nombreux effets instrumentaux, atmosphériques ou astronomiques. C'est par exemple le cas des mesures de distance Terre-Lune par télémétrie laser. Ainsi l'observatoire de la Côte d'Azur, où s'effectuent ces tirs, fournit des résidus correspondant à la différence entre la distance observée et celle prédite par la théorie tenant compte de tous les effets connus. Les observations ont un bruit variable et sont irrégulièrement échantillonnées dans le temps avec la présence de trous d'observations. Si la transformée de Fourier discrète est bien adaptée à l'étude des phénomènes stationnaires échantillonnés régulièrement, elle est inopérante en présence d'un échantillonnage irrégulier, d'autant plus que des phénomènes non stationnaires peuvent être à l'origine des écarts entre l'observation et la théorie. Nous avons donc été amenés à développer une méthode d'analyse spectrale associée aux résidus de la télémétrie laser-lune afin mettre en évidence des phénomènes périodiques non pris en compte dans la théorie actuelle

Ground Based Optical Tracking of Gaia

International audienceGaia's unprecedented ambitions regarding astrometric accuracy and precision require a level of knowledge of the position and velocity vector of the satellite itself not required in other satellite mission. Thus the usual methods of determining these quantities do not suffice and new approaches must be invoked. One of these is the Ground Based Optical Tracking (GBOT) campaign

Utilisation d'images de référence pour la compression d'images: Application à la misssion GAIA

La mission GAIA de l'Agence Spatiale Européenne devra mesurer tous les astres jusqu'à la magnitude 20 avec une précision de plusieurs ordres de grandeur meilleure que celle obtenue avec le satellite Hipparcos. Le débit d'information étant totalement incompatible une transmission complète des données au sol, un taux de compression très élevé est nécessaire. La compression des images sans a priori à l'aide de la transformation de Haar conduit à un taux de compression très insuffisant. La compression à partir des images de synthèse formées par les objets connus permet un facteur de compression adéquat. Cela devrait permettre la réalisation d'une carte du ciel avec une résolution d'au moins un ordre de grandeur meilleure que celle des cartes disponibles aujourd'hui

Synthèse et caractérisations de nouveaux copolymères en étoile à coeur de Fullerène comportant des séquences de Poly(1,4-Phénylène

PAU-BU Sciences (644452103) / SudocSudocFranceF

TOM20-mediated transfer of Bcl2 from ER to MAM and mitochondria upon induction of apoptosis

International audienceIn this work, we have explored the subcellular localization of Bcl2, a major antiapoptotic protein. In U251 glioma cells, we found that Bcl2 is localized mainly in the ER and is translocated to MAM and mitochondria upon induction of apoptosis; this mitochondrial transfer was not restricted to the demonstrator cell line, even if cell-specific modulations exist. We found that the Bcl2/mitochondria interaction is controlled by TOM20, a protein that belongs to the protein import machinery of the mitochondrial outer membrane. The expression of a small domain of interaction of TOM20 with Bcl2 potentiates its anti-apoptotic properties, which suggests that the Bcl2-TOM20 interaction is proapoptotic. The role of MAM and TOM20 in Bcl2 apoptotic mitochondrial localization and function has been confirmed in a yeast model in which the ER-mitochondria encounter structure (ERMES) complex (required for MAM stability in yeast) has been disrupted. Bcl2-TOM20 interaction is thus an additional player in the control of apoptosis

Optimizing asteroid orbit computation for Gaia with normal points

Context. In addition to the systematic observations of known solar-system objects (SSOs), a continuous processing of new discoveries requiring fast responses is implemented as the short-term processing of Gaia SSO observations, providing alerts for ground-based follow-up observers. The common independent observation approach for the purposes of orbit computation has led to unrealistically large ephemeris prediction uncertainties when processing real Gaia data. Aims. We aim to provide ground-based observers with a cloud of sky positions that is shrunk to a fraction of the previously expected search area by making use of the characteristic features of Gaia astrometry. This enhances the efficiency of Gaia SSO follow-up network and leads to an increased rate of asteroid discoveries with reasonably constrained orbits with the help of ground-based follow-up observations of Gaia asteroids. Methods. We took advantage of the separation of positional errors of Gaia S SO observations into a random and systematic component. We treated the Gaia observations in an alternative way by collapsing up to ten observations that correspond to a single transit into a single so-called normal point. We implemented this input procedure in the Gaia S SO short-term processing pipeline and the OpenOrb software. Results. We validate our approach by performing extensive comparisons between the independent observation and normal point input methods and compare them to the observed positions of previously known asteroids. The new approach reduces the ephemeris uncertainty by a factor of between three and ten compared to the situation where each point is treated as a separate observation. Conclusions. Our new data treatment improves the sky prediction for the Gaia SSO observations by removing low-weight orbital solutions. These solutions originate from excessive curvature of observations, introduced by short-term variations of Gaia attitude on the one hand, and, as a main effect, shrinking of systematic error bars in the independent observation case on the other hand. We anticipate that a similar approach may also be utilized in a situation where observations from a single observatory dominate.Peer reviewe