Prévisions (titres à définir)
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En 2012, le site du VLT au Chili accueillera un spectrographe à intégrale de champ de dernière génération dénommé MUSE (Multi Unit Spectroscopic Explorer). Cet instrument permettra l'acquisition de cubes hyperspectraux massifs (environ 1.2Go par cube) de résolutions spectrale et spatiale inégalées et dont l'analyse et le traitement nécessitent le développement de méthodes novatrices dédiées. L'ANR DAHLIA (Dedicated Algorithms for HyperspectraL Imaging in Astronomy) fédère ainsi quatre laboratoires (le CRAL à Lyon, l'OCA à Nice, le LATT à Toulouse et le LSIIT à Strasbourg) autour de la problématique du traitement des observations hyperspectrales qui seront prochainement acquises par l'instrument MUSE.
Dans le cadre de ce projet de recherche, je présenterai les travaux réalisés par l'équipe PASEO au LSIIT portant sur le développement d'une nouvelle méthode de fusion des observations brutes capteurs. En effet, l'étude des galaxies lointaines requérant l'acquisition d'un grand nombre d'observations (jusqu'à 80 poses) réalisée chacune dans des conditions d'observation différentes (PSF, décalages spectraux et spatiaux, bruits, grilles d'échantillonnage, rayons cosmiques...) et l'analyse scientifique, le stockage et la manipulation de ce jeu de données volumineux (jusqu'à 80x1.2Go) étant problématique, il est primordial de proposer une fusion intelligente de l'ensemble des observations hyperspectrales. L'image fusionnée résultante synthétise alors toute l'information présente dans le jeu de données initial.
La méthode originale proposée s'appuie sur un cadre bayésien rigoureux et prend l'ensemble des paramètres de chacune des observations capteurs en compte lors du processus de fusion. De plus, l'approche statistique bayésienne offre la possibilité d'estimer les incertitudes liées à l'image fusionnée et de les utiliser comme a priori pour des traitements ultérieurs (débruitage, déconvolution...). Enfin, l'algorithme présenté permet également la détection et la suppression conjointe des rayons cosmiques polluant les observations brutes.
Max-Planck Institut, Garching, Munich
The massive black hole in the centre of the Milky Way is a key laboratory to study the interactions between stars, gas and the central object that are at play in galactic nuclei. Sgr A* is characterized by an overall extremely low accretion rate. Nevertheless, a few times per day the source brightens by up to two orders of magnitude in the infrared and even more in the X-ray domain. These flare events are extremely interesting since they happen in the innermost accretion zone, and hence can act as unique probes for the accretion process and the strong gravitational field close to the event horizon. This talk focuses on the observational status of flares in Sgr A*, arguing that despite the great level of observational details available, many aspects of accretion onto Sgr A* are still open.
Ada Nebot Gomez-Moran
Observatoire de Strasbourg
The evolution of all close binaries depends crucially on the rate at which angular momentum is extracted from the binary orbit. The two most important sources of angular momentum loss are the common envelope and magnetic braking. Both processes are poorly understood. White dwarf plus main sequence binaries (WDMS) are ideal systems to constrain current theories of binary star evolution. In current samples old binaries containing cold white dwarf are significantly underrepresented. A dedicated survey carried out to identify and characterize WDMS binaries is presented. From spectroscopic and photometric observations those binaries that have gone through a common envelope phase are identified and their binary parameters are measured, providing the observational input for theories of common envelope and angular momentum loss.
Close compact binaries are among the most fascinating objects in the Galaxy. Two stars orbit around their centre of mass within a few hours in a binary system that well fits into the sun. These small systems contain big physics: close white dwarf binaries are the progenitors of supernova Ia that are used as standard candles to constrain dark energy and close double degenerates are among the most promising candidates to directly measure gravitational radiation with missions such as LISA.
Despite their importance for modern astrophysics, our understanding of the formation and evolution of close compact binaries remained very limited for decades. Since Paczinsky (1976) outlined the first sketches of the puzzle little progress was made primarily because the two most important angular momentum loss mechanisms that drive the formation and evolution of close compact binaries, common envelope evolution and magnetic braking, remained observationally and theoretically unconstrained.
In continuation of the recent seminar by my former PhD student Ada Nebot, I will present and discuss the results of a project especially designed to progress with our understanding of close binary evolution. Based on large samples of white dwarf/main sequence binaries identified by SDSS we obtained new clear constraints on common envelope evolution and magnetic braking that may well represent a breakthrough in the field.
I started this project in 2002/2003 as a post-doc at the Observatoire Astronomique de Strasbourg and it's a pleasure for me to present the (almost) final results at this very nice place.
Thomas Boch , Brice Gassmann, Françoix-Xavier Pineau, Pierre Fernique
CDS, Obs. Strasbourg
Nous présenterons et démontrerons les nouveaux outils suivants :
Astronomical Institute, Utrecht, Pays-bas
Supernova remnants have long been suspected to be the main source of the cosmic rays. The main reason is that they have enough power to maintain the energy density of cosmic rays, and early evidence for acceleration consisted of radio synchrotron radiation, proving the existence of accelerated electrons with GeV energies. Over the last decade, however, much more evidence has accumulated that supernova remnants are active particle accelerators. This evidence consists of X-ray synchrotron radiation from shock fronts, TeV emission from supernova remnants, and optical evidence. In this talk I will review the current status with introducing both the theoretical background and discussing the observational evidence with an emphasis on X-ray and optical studies that I have been involved in myself. Although the progress has been rapid over the last decade there are still problems accounting for cosmic ray acceleration due to supernova remnants. I will discuss these problems as well and discuss possible future tests of various cosmic ray acceleration scenarios.
From various independent observations, it has been established that most of our Universe lies invisible. According to standard physical laws, ordinary matter only accounts for 4% of the total energy content of the Universe. The remaining 96% is made of dark matter, and of the even more puzzling dark energy. In this talk, I will review some of the main evidence in favour of dark energy and I will present how its various proposed interpretations all seem to point to new physics, from the vanilla cosmological constant to modifications of gravity. I will then focus on the Abnormally Weighting Hypothesis, a unified dark matter-dark energy approach in which particular dark matter is the source of modified gravity. I will present several impacts of this framework on cosmic acceleration, galactic dynamics and solar systems constraints on general relativity.
Observatoire de Strasbourg
Galaxy clusters are gravitationally bound structures inhabited by several thousands of galaxies in a very small region in the sky. The central megaparsec of clusters is dominated by early type galaxies, which are observed to obey tight empirical scaling relations as the Fundamental plane and the Red-sequence. In this work, we present deep Js and Ks-band imaging of 15 galaxy clusters at z=1, which were discovered in the Red-Sequence Cluster Survey (RCS-1) and followed up using the VLT/ISAAC instrument. We built the Ks-band luminosity function for the composite cluster down to M*≃+2.5 through the application of a background subtraction method, and we found that it can be described by a Schechter function with Ks*=18.82 and α=-0.42. Furthermore, we built the background subtracted color-magnitude diagram for the composite cluster, and measured for the first time the ratio of luminous-to-faint red-sequence galaxies at z=1 from a large ensemble of clusters. We found a decrease by about 50% in this ratio from z=1.05 to 0.45, that can be explained by a simple evolutionary model developed in this work consisting in an early truncation of the star formation for bright cluster galaxies and a delayed truncation for faint cluster galaxies. Our results suggest that bright cluster galaxies formed most of their stellar content at z=3, that faint cluster galaxies are still forming stars at z=1, and that the red-sequence is not yet fully in place at z=1.
SRON Netherlands Institute for Space Research, Pays-Bas
The growth and evolution of supermassive black holes is tightly linked to the evolution of the surrounding host galaxy and further environments. It has become evident that the black holes in Active Galactic Nuclei are not only accreting, but also show significant outflows of photoionised gas. High-resolution X-ray and UV spectroscopy has allowed to study these outflows in detail. One of the most important questions is constraining the location of the outflow, which allows to assess the full impact on its environment. Here I will describe a big monitoring campaign on one of the brightest AGN, the Seyfert 1 galaxy Markarian 509. During a period of three months this source has been monitored by five satellites (XMM-Newton, Integral, Hubble, Chandra and Swift). I will present some of the latest results from this campaign, that cover a range of topics such as the high-resolution X-ray spectrum, the continuum variability and the interstellar medium of our Galaxy.
Institut d'Astrophysique & Géophysique, Université de Liège
Depuis le lancement des observatoires XMM-Newton et Chandra, notre compréhension de l'émission X des étoiles massives de type O, B ou Wolf-Rayet a été considérablement changée. Dans ce séminaire, je montrerai comment la spectroscopie à haute résolution et la sensibilité sans précédent de ces deux observatoires ont apporté une multitude d'informations nouvelles tant sur les étoiles massives isolées que sur les systèmes binaires où les vents stellaires des étoiles massives interagissent. En parallèle, de nouvelles questions sont apparues qui nécessitent une augmentation importante de la sensibilité des observations que seul un observatoire X de nouvelle génération, tel qu'IXO, pourra apporter.
Observatoire de Strasbourg
We discuss the details of the mass discrepancy phenomenon in galaxies usually accounted by postulating the presence of a non-luminous component. In the theoretical framework of Newtonian gravity and dark matter (DM) halos we start by recalling the properties of the latter as emerging from the state-of-the-art of numerical simulations performed in the current LCDM scenario of cosmological structure formation. We then report the complex phenomenology of the observed distribution of DM in galaxies. In particular, we list six outstanding challenges that these observations pose to the current paradigm of galaxy formation: the history-independent link of this distribution of DM with baryons, the observed absence of DM cusps, the phase-space correlation and sharp mass function of luminous subhalos of the Milky Way, the presence of large galaxies in underdense regions of the local Universe, and the prevalence of low bulge-to-disk ratios.
Observatoire de Strasbourg
Nous profiterons du séminaire pour vous montrer en avant premiere la nouvelle interface de VizieR. Celle-ci actuellement disponible en version beta (http://viz-beta.u-strasbg.fr) devrait remplacer l'existante courant janvier 2011. Je vous montrerai en quoi, cette version, constituée d'un formulaire en entrée plus concis, vous permettra une navigation plus aisée à l'intérieur de la base de données. Ensuite, en partant d'un constat d'utilisation des critères de recherche dans VizieR, j'expliquerai leurs évolutions, en terminant par vous présenter l'ajout d'une recherche basée sur le contenu des catalogues et reposant sur la technologie UCD. Enfin, d'autres nouveautés vous seront présentées, comme des nouveaux formats de sorties qui aboutissent aussi à la possibilité de crossmatch entre données VizieR.
Max-Planck-Institute for extraterrestrial Physics, Garching
GRAVITY is the second generation VLTI instrument for precision narrow-angle astrometry and interferometric imaging. It will bring the most advanced vision of optical interferometry to the VLT: with its fiber-fed integrated optics, its wavefront sensors and fringe tracker, and a novel metrology concept, GRAVITY will push the sensitivity and accuracy far beyond what is offered today. Providing ten microarcsecond precision astrometry and four milliarcsecond resolution imaging, GRAVITY will directly probe physics close to the event horizon of the Galactic Center black hole. The observations of hot gas moving on the last stable orbit will directly proof the existence of the supermassive black hole without resorting to theoretical assumptions. The detection of General Relativistic effects in stellar orbits will probe General Relativity in the so far unexplored regime of strong gravity. GRAVITY observations will potentially even allow to test Wheeler's no-hair theorem of black holes. My talk will cover both instrumental and astrophysical aspects of GRAVITY with special focus on the Galactic Center supermassive black hole.
GEPI, Observatoire de Paris
Although the Milky Way bulge is our closest opportunity to study in detail such a complex chemo-dynamical system, its formation and evolution is still poorly understood. The high extinction, the crowding, and the superposition of multiple structures along the line-of-sight make studies of the inner Galactic regions challenging. Two main scenarios have been invoked for the bulge formation: gravitational collapse or hierarchical merging of subclumps, and secular evolution of the disc through a bar forming a pseudo-bulge. I will present evidences that both scenarios have taken place in the Galactic bulge.
MPE, Garching, Allemagne
The enigmatic source Sgr A*, coincident with the massive black hole at the center of the Milky Way, exhibits energetic near-infrared and X-ray flares roughly once a day. Since their discovery ten years ago, much effort has been put in to try to uncover the physical origin of these flares. In a multiwavelength campaign carried out in April 2007, a particularly bright flare was caught at both near-infrared and X-ray wavelengths. The high quality simultaneous lightcurves exhibited a number of curious properties. In this talk I will present our (i) spectral analysis of this flare, which implies a synchrotron emission mechanism, and (ii) time-dependent models which show that the curious properties of the simultaneous lightcurves can be explained by a sudden magnetic field decrease during the flare, consistent with a scenario in which the flares are produced by a sudden magnetic reconnection in the inner regions of the accretion flow.
Institut d'Astrophysique de Paris
Euclid is one of the ESA Cosmic Vision M-mission that was pre-selected last year for a Phase A study. The science driver of Euclid is the understanding of the origin of the accelerated expansion of the Universe using two cosmological probes: weak lensing tomography and baryon acoustic oscillations. In this seminar, I will present the scientific motivations, the scientific objectives and the current baseline of the Euclid space mission.
Observatoire de Genève
Globular clusters are among the oldest objects in the Universe at which an age can be given. As such they are unique tools to constrain the physics of stellar evolution models. In this presentation I will focus on the information we can mainly retrieve based on recent abundance determinations in globular clusters stars. Li and C shows abundance variations along the RGB which can be explained by thermohaline mixing occurring in stars. Besides light elements from C to Al shows large abundance variations which can only be explained by an intra-cluster self-pollution during the birth of the clusters. I will also look if dynamical models which reproduce globular clusters with several populations of low-mass stars.
MPE, Garching, Allemagne
Using the XMM-Newton observatory, we performed X-ray surveys of several Local Group Galaxies. This comprises the spiral galaxies M31 and M33 and most recently the Small Magellanic Cloud, a dwarf irregular galaxy. The X-ray source populations in each of these galaxies differ in their composition of the various source classes like supernova remnants, high and low mass X-ray binaries and supersoft X-ray sources. In M31 an X-ray monitoring of the central part revealed that classical novae represent the major class of supersoft X-ray sources. The Small Magellanic Cloud (SMC) is remarkable with respect to its large number of more than 80 known Be/X-ray binaries, almost as many as in the Milky Way, although its mass is 50-100 times smaller than that of the Milky Way. The large samples allow to investigate their statistical properties, but also to find interesting cases.
Observatoire de Strasbourg
Reionisation is a powerful probe of high-z galaxy formation. It is also an important feedback mechanism: photo-heating of the gas in low mass galaxies results in its evaporation, thereby preventing further star formation. This process has been proposed as the cause of the very low luminosity of the satellite population of the Milky Way, potentially solving the missing satellites problem. Despite the importance of this process, it is poorly understood: the nature of the sources responsible for reionising the universe and their distribution still eludes us. Locally, we do not know if the reionisation of our Galaxy and especially of its satellites was externally-driven by distant massive sources, or internally-driven by sources within the progenitor of the Milky Way. In order to address this question, I will present a semi-analytical model of the population of satellite galaxies of the Milky Way capturing the basic properties of photo-evaporation, and compare its outcome with the observed population. I will then discuss the numerical simulations planned to improve the model and their diffusion using tools designed at the Observatoire.
Observatoire de Paris, GEPI
I will summarize results obtained in the frame of the IMAGES large programme at VLT. Using 3D spectroscopy (with GIRAFFE), multi-slit spectroscopy (with FORS2), as well as other public data in the CDFS field (HST/ACS, Spitzer, etc.) we have studied in detail the morpho-kinematic properties of a representative sample of intermediate-mass galaxies at z=0.6. These results suggest an important role of major mergers in the formation of local spiral galaxies. I will discuss how these results can be interpreted in the frame of the Lambda-CDM model, and how they compare with results obtained at higher redshifts with other integral field spectrographs.
University of Illinois
A valuable source of information on the distribution of dark matter and the growth of structures lies in the peculiar velocity field of the galaxies. I present here a short review of peculiar velocity field reconstruction methods and in particular the more recently Monge-Ampere-Kantorovitch reconstruction method of galaxy trajectories. I then illustrate the use of orbit reconstruction in three contexts. First, I apply this method to recover peculiar velocities of galaxies to a real galaxy sample: the 2MASS Redshift survey. I compare the predicted peculiar velocities predicted from the distribution of galaxies to the observed peculiar velocities in our neighborhood of 30 Mpc/h. I study the origin of the motion of the Local Group relative to the Cosmic Microwave Background dipole. I discuss how these two studies may help at putting additional constraints on the Lambda CDM models. Second, I study the peculiar velocities as a tracer of the evolution of cosmic voids and how they can be used to constrain the physical properties of Dark Energy at different redshifts. Finally, I use the reconstructed peculiar velocities to produce a precise re-simulation of the dark matter distribution in the Local Universe. I discuss some of the applications of this simulation.
Observatoire de Paris-Meudon
Université de Bâle
La poussière cosmique est produite dans les environments chauds et denses caractérisant les vents stellaires et les explosions de supernovae. Ces environnements sont très differents les uns des autres mais les conditions nécessaires a la condensation des grains sont souvent similaires. Je présenterai les différents types de grains, les mécanismes responsables de leur formation, ainsi que les milieux circumstellaires les plus efficaces à former la poussière cosmique dans l'univers proche et lointain.
CEA, Irfu, SAp
Situés au croisement des grands filaments cosmiques, les amas de galaxies sont les produits les plus massifs, et les plus récents, de la formation hiérarchique des structures. Comme l'Univers dans son ensemble, ils sont constitués de 85% de matière noire et de 15% de matière visible, essentiellement du gaz chaud intergalactique piégé dans le potentiel de la matière noire et observable en rayons X. Leur étude permet de mieux comprendre la physique de la formation des structures, de l'effondrement gravitationnel de la matière noire aux processus complexes qui régissent l'histoire thermo-dynamique des baryons. Je ferai le bilan des avancées faites dans ces domaines grâce aux observatoires X modernes, particulièrement XMM-Newton et Chandra, ainsi que plus récemment grâce à la montée en puissance d'autres techniques d'observation du milieu intra-amas (effet SZ, observation radio). En particulier je resumerai les principaux résultats sur les amas obtenus récemment avec le satellite Planck. Je présenterai aussi brièvement les récents progrès sur la détermination des paramètres cosmologiques à partir des amas, rendus possibles par ces observations.
LAOG Grenoble & Observatoire de Strasbourg
It has been known since the 1950s that no gas, or only tentative traces, has been observed in Galactic globular clusters (GCs) despite a continuous supply from evolved stars. Naive theory suggests that this stellar gas should sink to the centre of the GC potential, resulting in the accumulation of tens to hundreds of solar masses of gas between Galactic disk crossings. In this talk I will present the results from new 3D hydrodynamic simulations of RGB and AGB stellar wind material forming an intra-cluster medium (ICM) within King-model and multi-mass model GCs moving through the Galactic halo. I will discuss the influence that modelling the GC structure and stellar mass-loss has on the ICM content and its implications for future work on studying the role of gas within GCs.
GEPI, Observatoire de Paris
The way we perceive constraints on the chemical evolution of the galactic disk has evolved significantly in the last years, as a consequence of both observational (chemical abundances, ages, etc) and theoretical advances (radial mixing). I'll review some of these constraints and advances, and their impact on the standard chemical evolution description of the disk. I'll discuss also how the radial migration process offers a possible new interpretation of the well known stellar metallicity - giant extrasolar planet correlation.
LESIA, Observatoire de Paris
Jets, brief collimated structures, are extremely common dynamical events of the solar atmosphere. They occur over a broad range of spatial and temporal scales. Recent solar missions (e.g. STEREO, Hinode, SDO) have provided ground breaking observations of these events which has pushed forward the efforts to model these events.A large part of this seminar will be devoted to the presentation of the events and the description of their main properties. I will then present the results a recent numerical experiment of the trigger of this coronal jets. I will show that magnetic reconnection is the key process and I will discuss how 3D simulations are modifying our previous understanding of the driving process of solar jets.
Fullerenes are large molecules made of carbon arranged in a spherical or ellipsoidal configuration. These molecules were discovered in laboratory experiments aimed at understanding the formation of long carbon chains in the circumstellar environment of carbon stars. Because of their remarkable stability, fullerenes have been predicted to survive the harsh conditions of the insterstellar medium, where they could contribute to the interstellar extinction, charge exchange with ions, and provide active surfaces for complex chemical reactions. Targeted searches for the presence of fullerenes in various astrophysical environments were unsuccessful or not conclusive, until now. We have recently made the first conclusive detection of fullerenes (C60 and C70) on Tc1, a young Planetary Nebula. The molecules amount to a few percent of the available carbon in this region. Fullerenes could therefore lock up a significant fraction of the cosmic carbon. C60 has now been detected in several astronomical environments. These findings suggest that the circumstellar envelope of evolve stars could be the birthplace of fullerenes, but the formation and excitation mechanisms are however not yet understood. In this talk I will review our current knowledge on fullerene detection and formation, their relevance in space, and the potential contribution of future follow up studies.
Observatoire de Strasbourg
Understanding the evolution of galaxies remains one of the challenges of the modern astrophysics. Despite the significant progress achieved in this field during last 20 years, still no single scenario is able to explain all the observed properties of early-type galaxies, in particular of ubiquitous low luminosity objects. Stellar populations and internal kinematics contain a fossil record of a galaxy life, and studying them provides an opportunity for better understanding of mechanisms responsible for the galaxy evolution. I will discuss the evolution of early-type galaxies with the emphasis on low-luminosity systems. This will be based on the analysis of optical spectroscopic observations obtained with modern instruments on large telescopes, using state-of-the-art numerical simulations and the unprecedented power of the Virtual Observatory. The traditional discovery paradigm in astronomy implies the construction of new instruments and development of new observational or computational techniques. The VO breaks this paradigm because new discoveries are made using existing data from archives and catalogues and publicly available tools. Among the results that I will present are: (1) first 3D spectroscopic observations of dwarf elliptical galaxies that led to the discovery of evolutionary decoupled dE nuclei; (2) VO-powered discovery of 70% of known compact elliptical galaxies in the Universe and modelling their evolution by numerical simulations; (3) the GalMer database containing the results of TreeSPH modelling of major and minor galaxy mergers and their application to the interpretation of observations, ``a virtual telescope''; (4) 3D spectroscopic studies of nearby poststarburst and giant lenticular galaxies made in order to understand the role of environment. At the end I will discuss the importance of various galaxy evolution mechanisms (internal vs external, mergers, tidal stripping etc.) for early-type galaxies of different masses located in different environments.
Université de Bâle
La poussière cosmique est produite dans les environments chauds et denses caractérisant les vents stellaires et les explosions de supernovae. Ces environnements sont très différents les un des autres mais les conditions nécessaires à la condensation des grains sont souvent similaires. Je présenterai les différents types de grains, les mécanismes responsables de leur formation, ainsi que les milieux circumstellaires les plus efficaces à former la poussière cosmique dans l'univers proche et lointain.
Observatoire Astronomique de Strasbourg Benoît Famey