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Accueil > Le Laboratoire > Séminaires et conférences > Archives > Résumés 2011-2012

 Résumés 2011-2012

13 July 2012 - 14h

  • Edwin Henneken (Smithsonian Astrophysical Observatory, Cambridge, Massachusetts, USA)
  • The Astrophysics Data System - Two Decades of Internet Librarianship

The SAO/NASA Astrophysics Data System (ADS) has been heavily used by astronomers since its inception, almost 20 years ago. In the past seven years its use has expanded to include substantially more scientists than the world’s approximately 10,000 research astronomers. Currently there are about 55,000 frequent users, and up to 10 million infrequent users per year. Access by the general public now accounts for about half of all ADS use, demonstrating the vast reach of the content in our databases. Increased demand and running into limitations of our infrastructure prompted the ADS team to start thinking about to migrate to a more flexible, scalable service without compromising the high standards our users have come to expect of our service. That is why we introduced the ADS Labs platform ( ADS Labs is a platform that ADS is introducing in order to test and receive feedback from the community on new technologies and prototype services. Currently, ADS Labs features a new interface for abstract searches, faceted filtering of results, visualization of co-authorship networks, article-level recommendations, and a full-text search service. In this presentation I’ll talk about ADS in general and highlight some of the unique aspects of ADS Labs.

15 June 2012 - 14h

  • Mark McCaughrean (Head of Research, European Space Agency, ESTEC, The Netherlands)
  • Astrophysics in the ESA space science programme

The European Space Agency operates missions covering the electromagnetic spectrum from radio wavelengths to gamma rays, including Planck, Herschel, HST, XMM-Newton, and INTEGRAL. I shall present some recent scientific results from these missions and link them into the broader context of ESA’s space science programme. New astrophysics missions under development include Gaia, Euclid, and JWST, with others currently under study. I will discuss their scientific potential and complementarity with ground-based facilities, with a focus on my own research into the formation and evolution of stars and their planetary systems.

14 June 2012 - 11h

  • Fabio Gastaldello (INAF-IASF Milano)
  • Xray follow up of Strong lensing detected structures : from Galaxy Groups to Galaxy Clusters

Strong Gravitational Lensing is a well recognized powerful probe of the Dark Matter distribution in the Universe, giving unbiased constraints on the two dimensional mass distribution.
Yet, in order to gain further insights in the properties of galaxy groups and clusters, a multi wavelength approach is needed.
In particular, Xray observations provides a complementary probe of the gravitational potential.
I will present results of the XMM snapshot program to detect and characterize luminosity and temperature of strong lensing groups of the SL2S (Strong Lensing Legacy Survey) sample. Increasing in mass and size, I will report on the X-ray and optical spectroscopy follow-up of the spectacular lensing cluster Abell 1703.

1 June 2012 - 14h

  • Ruben Salvaterra (INAF Milan)
  • High-z Gamma-Ray Bursts

The detection of GRB 090423 at z=8.2 has strengthened the idea that GRBs can be used as a powerful tool to study the Universe during and beyond the reionization epoch. I will review the current status and the future prospects of the observations of very high redshift (i.e. z>6) GRBs and discuss how high-z GRBs can help us to shed light on the early stages of galaxy formation and on the reionization process.

25 May 2012 - 14h

  • Danilo Marchesini (Tufts, US)
  • Massive Galaxies at z=2-4 : New Insights into Galaxy Formation and Evolution

In the past five years, our understanding of the galaxy population at redshift z=2-4 has improved significantly, thanks to the increasing ability to construct comprehensive snapshots (in time) from z=4 (when the universe was 1.5 billion years old) to z=2 (when it was 3.5 billion years old). As these 2 billion years of the cosmic history represent a key epoch in the buildup and evolution of galaxies, studies of the properties of galaxies at these redshifts provide important clues on the physical processes at work during galaxy formation and
evolution. I will summarize our current knowledge of the massive galaxy population at z=2-4, with an emphasis on the new results from the NEWFIRM Medium-Band Survey, a large NOAO/Yale program which uses medium band-width filters in the near-infrared to obtain well-sampled spectral energy distributions and high-quality photometric redshifts at z>1.5 over 0.5 square degree. I will conclude by outlining on-going experiments/surveys which will take our understanding of galaxy formation and evolution to the next level.

11 May 2012 - 14h

  • Sara M. Petty, UCLA
  • The origin of the ultraviolet excess in early type galaxies : evidence for a multi-stage formation history

In the local Universe, massive elliptical galaxies are often observed to exhibit a peculiar property : a substantial excess of ultraviolet emission (UVX) over what is expected from their (presumed) old, red stellar populations. Several origins for the UVX have been proposed, including a population of hot young stars, or a population of old, horizontal branch stars that have undergone substantial mass loss from their outer atmospheres, allowing the hot UV radiation to escape. Even with many decades of observations, the origin of the UV excess in local ellipticals remains controversial today. In this paper we present new results on UVX from combining WISE and GALEX data. I will show that at least a substantial part of the UV excess must come from a population of `extreme’ horizontal branch (EHB) stars, and that the fraction of EHB stars changes with galactocentric radius. This population of EHB stars can plausibly be used to understand the formation history of massive ellipticals, suggesting that a substantial fraction of stars at large radii assembled via a different mechanism to the stars in the central regions.

26 Mar 2012 - 15h30

  • Benoit Neichel (Gemini Observatory)
  • Premieres images de GeMS (the Gemini MCAO system)

GeMS, pour "Gemini Multi-conjugate Adaptive Optics System" est le premier instrument d’Optique Adaptative à grand champ dédié à la communauté astronomique à utiliser plusieurs étoiles lasers, et ainsi offrir un champ de correction 10 fois supérieurs aux autres systèmes d’OA actuels. Depuis Janvier 2011 GeMS est en "commissioning" au telescope Gemini au Chili, et depuis Decembre de la même année il produit ses premières images corrigées grand champ. Les premiers résultats sont très encourageant avec des Rapport de Strehl de 30% en bande H sur l’integralité du champ de 85x85 arcsec, et démontrent du fort potentiel de cet instrument, et des futurs générations d’OA pour les ELTs. Dans cette présentation, je reviendrais sur le principe de l’Optique Adaptative Multi-conjuguée, de son implementation au sein de GeMS, et je decrirais les résultats obtenus sur le ciel.

23 Mar 2012 - 14h

  • Eric Fossat (Observatoire de la Côte d’Azur)
  • Le Dome C, meilleur site astronomique du monde ?

Le point d’interrogation est évidemment plein de sous-entendus.
Une dizaine d’année d’efforts de qualification du site ont prouvé que le Dôme C, au même titre que les autres points hauts du plateau Antarctique, offre un certain nombre de propriétés uniques au monde aux astronomes observateurs. Ciel coronal en été, transparence infra-rouge imbattable, avec des fenêtres spectrales qui s’ouvrent ou s’entrouvrent là et pas ailleurs ; refroidissement passif des récepteurs infra-rouge jusqu’à -70°C au moins, statistique de beau temps comparable à celle de l’Atacama, seeing moyen record de 0,3 arc-sec au dessus de la couche limite.
Les points durs sont d’une part cette fin de phrase, "au dessus de la couche limite" qui fait une trentaine de mètres d’épaisseur en moyenne (très mince météorologiquement parlant, mais au dessus, c’est quand même à 40 ou 50 mètres !), et d’autre part le givre qui prend un malin plaisir à s’installer partout malgré l’air le plus sec du monde. L’avenir ambitieux du développement instrumental là-bas va passer par une lutte difficile, qui sera gagnée un jour, pas forcément tout de suite.
Je présenterai quelques résultats de la qualification, on fera un peu de physique au passage, et je montrerai pas mal de belles images.

16 Mar 2012 - 14h

  • David Ehrenreich (IPAG, Grenoble)
  • Escaping atmospheres of exoplanets : towards hot neptunes, super-earths, and Earth-like planets

Nearly 700 extrasolar planets have been detected so far and an intense characterisation effort has been undertaken to unveil the atmospheric properties of some of these distant worlds seen in transit accross their stars. A large number of transiting exoplanets are found in extreme irradiation environments, very close to their stars, and the question arise of whether the atmospheres of these planets remain stable or get blown away. Atmospheric evaporation was observed in some hot giant exoplanets or "hot jupiters", but does not significantly alter the fate of these massive objects ( 300 Earth masses). Hot neptunes, on the other hand, are a class of exoplanets with typical masses around 20x Earth. They are the link between hot jupiters and super-earths (1 to 10 Earth masses). It is surmised that the latters can be evaporation remnants, with atmospheres completely eroded by the extreme stellar irradiation. In this case, could hot neptunes be the progenitors of the hot rocky planets detected by the Corot and Kepler missions ? Detecting their extended atmospheres and measuring their mass loss rates and atmospheric heating efficiencies are key steps towards the understanding of the atmospheric dynamics and properties of low-mass exoplanets. After an introduction about planetary transits, I will review the results we have obtained with HST on the atmospheric evaporation of transiting exoplanets, on both observational and theoretical sides. I will finally discuss the prospects about atmospheric characterisation for Earth-size planets in more temperate - habitable - environments, and how the upcoming transit of Venus in June 2012 could be a Rosetta stone to interpret the future transmission spectra of Earth-like exoplanets that could be obtained with JWST.

17 Feb 2012 - 14h

  • Jean Eisenstaedt, Directeur de recherches émérite. SYRTE, Observatoire de Paris, CNRS, UPMC.
  • L’histoire des sciences : à quoi bon ?

À quoi bon travailler la science et son histoire ? À mon sens, il n’y a que de bonnes raisons de s’y mettre : essentiellement pour mieux comprendre. Pour mieux comprendre la science face à ceux qui la font, à ceux qui l’utilisent. Pour mieux comprendre ce qui fut fait et ce que nous faisons. Pour mieux comprendre "comment ça marche", la structure de la science, son impact, son emprise sur les techniques, sur la société, sur chacun d’entre nous.
Je n’ai pas l’intention de théoriser mais simplement, à travers des questions, essentiellement les miennes (car contrairement à la science, c’est au singulier que ce fait l’histoire), de dire ce que m’apporte l’histoire des sciences et en particulier celle des relativités sur lesquelles j’ai longtemps travaillé. Avant tout, beaucoup de travail et de plaisir, celui de comprendre, un peu moins mal...

10 Feb 2012 - 14h

  • Simona Mei (GEPI, Obs. de Paris)
  • The Evolution of the Galaxy Mass-Size Relation in Different Environments

We present our recent results on the evolution of the galaxy mass-size relation in different environments up to z 1.3. We find that results on the evolution of the mass-size relation depend on how galaxies are morphologically selected (visually or by their sersic indices). When we select early-type galaxies (ETG) by visual morphology, the field mass-size relation does not show significant evolution from z 1.3 to the present in the mass range we probe. Interestingly, this is in contrast from what is observed at higher masses. In denser environments, the ETG mass-size relation at z 1.3 is shifted towards smaller sizes. We compare with results in the COSMOS field.

20 Jan 2012 - 14h

  • Alessandro Morbidelli (Laboratoire Lagrange, Nice)
  • Solar System evolution and the diversity of planetary systems

Extrasolar planetary systems provide evidence for extensive migration of giant planets. However, it is usually assumed that Jupiter and Saturn did not migrate significantly. Hydrodynamical simulations show that Jupiter should have migrated inwards in the solar nebula when Saturn was not yet formed. Then Saturn, once close to its final mass, could have migrated faster than Jupiter until being caught in their mutual 2:3 mean motion resonance. Once in resonance, the two planets could have migrated outwards. We find that the inward-then-outward migration of Jupiter, with a migration reversal at 1.5AU, explains the current structure of the Solar System at an unprecedented level. It would have truncated the disk of planetesimals at about 1AU, explaining the large Earth/Mars mass-ratio. It would have also depleted, then re-populated the asteroid belt region, with inner-belt bodies originating between 1 and 3AU and outer belt bodies originating between and beyond the giant planets, thus explaining the significant compositional differences across the belt. Finally, the orbits of the giant planets when the gas is removed would correspond to the initial conditions of the "Nice model", which explains the current configuration of the outer Solar System. Therefore, we conclude that there is substantial evidence for a wide-range migration of Jupiter and Saturn in the solar nebula. Assuming that giant planets form in sequence at increasing distances from the central star, most of the observed diversity of planetary systems could stem from the occurrence or avoidance of two events : (i) the capture in resonance of the first, inner planet by the second, initially smaller one, which triggers outward migration and (ii) the growth of the outer planet beyond the mass of the inner one, which causes inward migration of both planets to resume. The Solar System structure results from the occurrence of (i) and avoidance of (ii).

17 Jan 2012 - 14h

  • David Valls-Gabaud (LERMA, Observatoire de Paris)
  • MESSIER : Opening the low surface brightness universe

Astronomy has traditionally been interested in exploring the faintest and farthest objects, which require large apertures, and large focal ratios for resolving extended objects. In this talk I will argue that the last niche in classical instrumentation lies in fast optics, small f number, to explore the ultra faint, low surface brightness regime which remains largely to be studied, and is one of the keys for the understanding of galaxy formation. The main limiting factors in these studies are the sky brightness and its variability, the flat fields and the wings of the PSF, which all point to a space instrument. I will present the science and technical case for MESSIER, a microsatellite proposed to CNES for a detailed design study.

6 Jan 2012 - 14h

  • Laurent Pueyo (John Hopkins University / STScI)
  • Towards a more exhaustive understanding of exo-planetary worlds with direct imaging

Upcoming direct imaging surveys will mitigate selection effects inherent to the currently known exo-planetary population since they are sensitive to objects in an orbital space orthogonal to the one available with indirect methods. In as such, they are a critical component of comparative exo-planetology since they will help refine a statistical distribution of planetary mass objects less sensitive to observational biases. I will first discuss the how upcoming imaging surveys improve this completeness problem, and how solutions for instrumentation on future observatories will further address it. In particular I will review concepts underlying current coronagraphs aimed at imaging exo-planets and discuss their applicability to Extremely Large Telescopes and potential future space missions. In a second part I will delve into the details of planning efforts for upcoming large scale ground based imaging surveys. Extracting well-constrained astrometric and spectro-photometric signal will be critical to the full scientific fruition of such campaigns aimed at constraining the bulk physical properties and atmospheric chemistry of giant gaseous planets. I will illustrate progress made in this domain using two recent examples. I will introduce a solution to the problem of IFS spectro-photometry in the high speckle noise regime using learnings from the Palomar P1640 phase I survey. I will finally present our recent result regarding the astrometic characterization of a multiple planetary system ``pre-covered’’ in the HST-NICMOS archive.

9 Dec 2011 - 14h

  • Claudia Maraston (Portsmouth)
  • Stellar population modelling and clues to galaxy evolution

Understanding the formation and evolution of galaxies is a central topic in modern cosmology and astrophysics. It has been recognised early on that the study of stellar populations in galaxies is a powerful tool to address galaxy formation, because stellar evolution acts on timescales that are well understood and are independent of the cosmological model. The modelling of stellar populations allows to derive key quantities such as galaxy formation epochs, stellar masses, and the history of star formation. In this talk I will review our current knowledge on the theoretical modelling of stellar populations, highlighting the areas where progress could be made. I will then provide some key examples from current work where the study of stellar populations allowed to get important insights on the formation and evolution of galaxies.

25 Nov 2011 - 14h

  • Emmanuel Lellouch (LESIA)
  • Herschel observe le Système Solaire

Lancé en mai 2009, le satellite Herschel explore l’Univers dans le domaine submillimétrique, au moyen de trois instruments (spectrmètres et photomètres) couvrant le domaine 55-700 microns. Les observations du système solaire sont principalement organisées au travers de 2 Key Programmes. Le programme "Water and related chemistry in the Solar System" consiste essentiellement en une étude des atmosphères planétaires et cométaires — avec un accent particulier sur l’eau. On en présentera les résultats principaux notamment sur (i) l’origine de l’eau dans les planètes extérieures (ii) l’exploration du spectre de Titan (iii) le rapport D/H dans les comètes et l’activité des comètes distantes. On présentera ensuite le programme "TNOs are cool : a survey of the transneptunian region" qui consiste à mesurer la taille, l’albédo, et les propriétés thermophysiques d’un grand échantillon d’objets transneptuniens.

18 Nov 2011

  • Geoff Marcy (Berkeley)
  • Planets as small as Twice the Size of Earth : Orbits, Radii, and Occurrence

The talk will report the observed distribution of planet radii, orbital distances, and occurrence around stars for planets with orbital periods less than 50 days around Solar-type stars. We draw from extensive Kepler spaceborne telescope measurements that offer good detectability of planets with radii as small as 2.0 Earth-radii.
The occurrence of planets as a function of planet radius and orbital period increases strongly toward the smallest radii (2 Earth-radii) and toward longer orbital periods (up to 50 days, 0.25 AU). The detection of rocky planets between 0-100C is in reach, but we may be farther than we think from answering it.

10 Nov 2011

  • Thierry Fouchet (LESIA)
  • Climatologie et météorologie de la stratosphère de Saturne

Depuis 2005, l’instrument CIRS à bord de la sonde Cassini mesure la structure thermique et l’abondance des hydrocarbures dans la stratosphère de Saturne. Ces observations ont permis de découvrir l’oscillation équatoriale de température et de mesurer pour la première fois les variations saisonnières de température. L’oscillation équatoriale sur Saturne est analogue à l’oscillation quasi-biennale terrestre. C’est une structure verticale formée de deux courants-jets superposés et de sens opposés qui se propage vers le bas au cours di temps. Ainsi, à une altitude donnée, le vent alterne en rétrograde et prograde au cours d’une période. Il semble que sur Saturne, la période soit d’environ 15 ans, soit une demi-année kronienne. Je montrerai comment cette oscillation équatoriale résulte de l’interaction entre les ondes atmosphériques (ondes de gravité, etc...) et le vent zonal moyen.
Grâce aux observations des variations saisonnières de température, je montrerai également comment nous avons pu mettre en évidence l’importance de la circulation interhémisphérique pour transporter la chaleur depuis l’hémisphère d’été vers l’hémisphère d’hiver. Je montrerai également comment la grande tempête de 2010, qui complètement perturbé les couches nuageuses des moyennes latitudes de l’hémisphère nord a également a fortement affecté la structure thermique de la stratosphère.

8 Nov 2011 à 15h

  • Yael Nazé (Liège)
  • X-ray emission from massive stars

The X-ray emission from massive stars was serendipitously discovered 30 years ago. With the advent of XMM and Chandra, many new facets of this high-energy phenomenon have been revealed, leading to many changes in (and challenges to !) "common wisdom". In this seminar, we will explore how and why O, B, WR, and LBV stars emit X-rays, including the peculiar processes linked to colliding winds in binaries and magnetically confined winds. We will see how X-rays can provide useful constraints on the stellar properties, thereby offering a complementary diagnostics to the info obtained in the UV-visible-IR domains.

4 Nov 2011

  • Keith Shortridge (AAO)
  • AAOGlimpse and other AAO software

The Anglo-Australian Observatory (recently renamed the Australian Astronomical Observatory) has a long history of producing interesting software, starting with the original control system for the Anglo-Australian Telescope (AAT) which set the standard for telescope control systems for years to come. I will discuss some aspects of the software effort at AAO, such as the way we have used software simulation of hardware in recent projects, for example the recent replacement of the original AAT control system. In particular I will look at a new experimental image display program, written partly as a learning exercise and partly just for fun. AAOGlimpse ( uses OpenGL to display FITS data (and even JPEG images) as 3D surfaces that can be rotated and viewed from different angles, all in real-time. It is WCS-compliant and designed to handle three-dimensional data. The resulting display can provide new insights into the data - mainly by encouraging people to look at it closely - but it also produces some nice graphical effects.

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