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Institut d'Astrophysique et
de Géophysique (Bât. B5c)

Quartier Agora
Allée du 6 août, 19C
B-4000 Liège 1 (Sart-Tilman)

Tel.: 04.366.9774
Fax: 04.366.9729
Recul rapide Année précédente Séminaires : Archives 2012 Année suivante Avance rapide
Jan Fév Mar Avr Mai Jun Jul Aoû Sep Oct Nov Déc
Mois précédent Mois suivant Février 2012
Séminaire suivant  1er séminaire : jeudi 16 février, 15h45
Electromagnetic turbulence and particle acceleration in space
Martin Pohl (Universitat Potsdam, Germany)

Astrophysical plasmas are collisionless, meaning the momentum exchange between particles is provided by self-excited electromagnetic turbulence. In many objects we observe particle acceleration to very high energies, and at the same time see evidence of strong magnetic turbulence. I review recent advances in our understanding of wave-particle interactions in non-thermal sources and describe future lines of research.
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 23 février, 15h45
Constraints on dark matter from its capture in compact stars
Peter Tinyakov (ULB)

We argue that observations of neutron stars and white dwarfs can impose constraints on dark matter candidates even with very small elastic and/or inelastic cross section, thus probing regions of parameters which are inaccessible for direct searches. In particular, current neutron star observations exclude asymmetric bosonic non-interacting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT.
Mois précédent Mois suivant Mars 2012
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 08 mars, 16h00
Les anneaux planétaires, un modèle pour les disques astrophysiques ?
Quelques dernières nouvelles de la sonde Cassini

André Brahic (CEA Saclay et Université Paris-Diderot)

Séminaire organisé conjointement par le Centre Spatial de Liège (CSL) et le Département Astrophysique, Géophysique et Océanologie (AGO)
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 15 mars, 15h45
The Theory for R-parity and the LHC
Sogee Spinner (SISSA, Trieste, Italy)

Studies in the MSSM usually assume the existence of an ad hoc discrete symmetry, R-parity, which stabilizes the proton and eliminates many unknown SUSY parameters. It furthermore has consequences for the most well known SUSY predictions: missing energy and stable dark matter. I will discuss the simplest framework for determining the fate of R-parity (B-L symmetries) and show that even in cases where R-parity is violated, realistic models exist. Such models hold further consequences for the neutrino sector and collider phenomenology.
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 22 mars, 11h00
Extragalactic observations using GMRT
Amitesh OMAR (ARIES, India)

I shall summarize the Giant Meterwave Radio Telescope (GMRT) operating at frequencies lower than 1450 MHz, in India. This is currently the most sensitive radio telescope in the world at the low frequencies. The telescope is routinely used for galactic and extragalactic observations. I will describe results on nearby galaxies using this telescope. The radio continuum mainly due to synchrotron emission from galaxies can be detected at a level of sub-mJy. The HI 21 cm-line, tracer of atomic Hydrogen is widely used to image gas distribution in galaxies. Some results on HI imaging of Wolf Rayet galaxies will be presented.
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 22 mars, 15h45
QCD analysis of Lambda leptoproduction in the DIS target fragmentation region
Federico Ceccopieri (IFPA, ULg)

Lambda leptoproduction in the DIS target fragmentation region is described with the aid of fracture functions which are extracted from a simultaneous fit to a number of muon and neutrino DIS experiments. The fragmentation properties of the left-over spectator system into Lambda hyperon are discussed within the proposed model for fracture functions.
Séminaire précédant Séminaire suivant 7ème séminaire : mercredi 28 mars, 14h00
Les techniques d'Eddy Covariance atmosphérique et aquatique:
des outils adaptés à l'étude des flux métaboliques en zone côtière

Pierre Polsenaere (Royal Netherlands Institute for Sea Research (NIOZ Yerseke))

Mois précédent Mois suivant Avril 2012
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 05 avril, 15h30
Caractérisation des effets du réchauffement climatique sur l'océan superficiel au cours des 50 dernières années
Mathieu Hamon (IFREMER)

Séminaire précédant Séminaire suivant 9ème séminaire : lundi 23 avril, 14h00
Soft collinear gravity
Grigory Kirilin (Technische Universität München)

We study the problem of collinear and soft singularities in the perturbative quantum gravity by constructing an effective field theory similar to the soft-collinear effective theory for QCD. We have found that the collinear sector of the effective theory is trivial to the leading ``multipole'' order which corresponds to the well known fact that there are no collinear singularities in the perturbative quantum gravity, while the soft sector shows the factorization property similar to those for SCET. We also discuss the connection of our approach to the recent study performed by Akhoury et al. [Phys. Rev. D84 (2011) 104040] as well as to the original paper by Weinberg [Phys. Rev. 140 (1965) B516] where cancellation of the collinear singularities was demonstrated for the first time.
Séminaire précédant Séminaire suivant 10ème séminaire : mercredi 25 avril, 14h00
Holographic methods for nonperturbative QCD
Oscar Cata (Munich University)

I will discuss some applications of the gauge-gravity duality as applied to the strong interactions. In particular, I will show how the holographic recipe on a gravity 5-dimensional action naturally leads at low energies to the chiral Lagrangian, with concrete predictions for the low-energy coefficients. I will also discuss how to evaluate quantities that depend on the whole (Euclidean) range of energies, such as the hadronic contributions to the anomalous magnetic moment of the muon.
Séminaire précédant Séminaire suivant 11ème séminaire : jeudi 26 avril, 15h45
Signatures photométrique et spectroscopique des pulsations d'étoiles en rotation rapide
Daniel Reese (AGO)

Une part importante des étoiles plus massives que le Soleil sont en rotation rapide. La rotation engendre de nombreux phénomènes complexes, ce qui rend difficile la modélisation de telles étoiles et nécessite l'apport de contraintes observationnelles. L'astérosismologie, l'étude des oscillations stellaires, est actuellement la celle façon de sonder directement la structure interne des étoiles. Or, la rotation rapide complique énormément l'étude des oscillations stellaires, à la fois sur le plan théorique et sur le plan observationnel. Dans cet exposé, j'expliquerai les effets de la rotation rapide sur la classification et la géométrie des modes acoustiques. Ensuite, je décrirai des travaux en cours sur les signatures photométriques et spectroscopiques de ces oscillations, lesquelles permettront de contraindre la correspondance entre les modes calculés théoriquement et ceux qu'on observe.
Mois précédent Mois suivant Mai 2012
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 03 mai, 15h45
Habitabilité et biosignatures, de la Terre à l'espace
Emmanuelle Javaux (Département de Géologie)

Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 10 mai, 15h45

Aurélie Violette (UMCCB)

Séminaire précédant Séminaire suivant 14ème séminaire : jeudi 24 mai, 15h45

Maurice Gabriel (AGO)

Mois précédent Mois suivant Juillet 2012
Séminaire précédant Séminaire suivant 15ème séminaire : lundi 02 juillet, 15h45
Supernova Remnants in Distant Galaxies
You-Hua Chu (University of Illinois at Urbana-Champaign, USA)

Séminaire précédant Séminaire suivant 16ème séminaire : mardi 03 juillet, 11h00
Resolved Massive Star Formation at Low-Metallicity Environment
Rosie Chen (Max Planck Institute for Radio Astronomy Astronomy, Bonn, Germany)

Massive stars drive the evolution of the interstellar medium and hence play an important role in the evolution of their host galaxies, yet their formation remains poorly understood. Recent Spitzer mid-IR surveys reveal a large number of individually resolved massive young stellar objects (YSOs) in the Magellanic system (LMC, SMC, and Magellanic Bridge). This system covers metallicities of 1/3-1/8 Zo and a range of galaxy-galaxy interactions, providing an excellent opportunity to examine environmental effects on massive star formation and to illuminate what occurred in the early universe. We have used Spitzer and complementary near-IR and optical data to study massive YSOs in HII complexes in the LMC and high N(HI) portion of the Magellanic Bridge. We have modeled spectral energy distributions of YSOs and found their masses ranging 4-45 Mo in the LMC, while 4-10 Mo in the Bridge. Furthermore, for the same mass range, YSOs in the Bridge appear less embedded as almost all of them are visible at optical, opposed to only half in the LMC. The smaller extinction is likely due to the Bridge's lower dust content in the molecular clouds or circumstellar envelopes, or both. To assess the environmental effects, we have estimated the instantaneous star formation efficiency (SFE) using complete lists of YSOs in the LMC and Bridge. We found that the LMC has ~3 times higher SFE than the Bridge, but the trend reverses at N(HI) < 1021 cm-2. This reverse is likely caused by different formation mechanisms of molecular clouds, such as colliding flows.
Séminaire précédant Séminaire suivant 17ème séminaire : mercredi 04 juillet, 15h30
Chemical composition of a tiny grain returned from Itokawa and its implications to planetary sciences
Mitsuru EBIHARA (Cosmochemistry Laboratory, Tokyo Metropolitan University, Tokyo, Japan)

Mois précédent Mois suivant Août 2012
Séminaire précédant Séminaire suivant 18ème séminaire : vendredi 17 août, 14h00
The mechanical energy budget of the World Ocean
Rob Scott (LPO-Université de Brest)

The problem of reaching a mechanical equilibrium for the World Ocean between forcing at large scales by surface wind stress and dissipation at centimetre scale by viscose dissipation is described. Satellite measurements showing an "inverse energy cascade" are briefly described, as well as attempts to quantify global turbulent bottom boundary layer dissipation from about 1000 in situ measurements. Finally we present a global calculation of the rate of internal gravity wave generation from abyssal flows over rough topography. This is argued to be a key process accounting for (at least) half the dissipation.
Mois précédent Mois suivant Septembre 2012
Séminaire précédant Séminaire suivant 19ème séminaire : mardi 04 septembre, 10h30
The Two Higgs Doublet Model Post the Higgs Discovery
Pedro Ferreira (Lisbon University)
Séminaire précédant Séminaire suivant 20ème séminaire : jeudi 20 septembre, 15h45

Maurice Gabriel (AGO)

Mois précédent Mois suivant Octobre 2012
Séminaire précédant Séminaire suivant 21ème séminaire : jeudi 11 octobre, 16h00
Joint Colloquium :

Georges Meynet (Observatoire de Genève)

Séminaire précédant Séminaire suivant 22ème séminaire : jeudi 25 octobre, 15h45

Maurice Gabriel (AGO)

Séminaire précédant Séminaire suivant 23ème séminaire : lundi 29 octobre, 15h45
Chiral corrections to nucleon GPDs
Alena Moiseeva (Theoretical Hadronic Physics Group, Ruhr University of Bochum, Germany)

In the framework of the heavy baryon chiral perturbation theory we obtain the leading chiral corrections to nucleon GPDs. We discuss difficulties of consideration of non-local light-cone operators within the heavy baryon approach and methods to address them. We also discuss effects appearing at the scales x~mπ/MN and x~mπ2/MN2. We argue that being relevant at the region x~1, the Mellin moments method fails to restore GPDs at the region of small x.
Séminaire précédant Séminaire suivant 24ème séminaire : mercredi 31 octobre, 11h00
How to define and access the different contributions to the proton spin
Cédric Lorcé (IPNO & LPT, Université Paris-Sud, Orsay, France)

We propose a short summary of the present situation concerning the proton spin decomposition. We discuss some of the main controversies about the issues of gauge invariance, Lorentz covariance, uniqueness, physical interpretation and measurability. As a conclusion, we argue that part of the controversies is actually undecidable.
Mois précédent Mois suivant Novembre 2012
Séminaire précédant Séminaire suivant 25ème séminaire : jeudi 08 novembre, 15h45
Ionospheric-magnetospheric current systems at Jupiter and Saturn
Licia Ray (UCL London)

Intense volcanic activity at Io, Jupiter's innermost Galilean moon, leads to a large plasma disc inside the jovian magnetosphere. Similarly, cryovolcanic activity at the Saturnian moon Enceladus results in a large plasma population in the saturnian magnetosphere. These plasma populations are coupled to the parent planets via the magnetic field, along which field-aligned currents flow transferring angular momentum and energy between the magnetosphere and planetary atmosphere. Bright auroral emissions result from this current system and offer, along with in situ data from spacecraft, constraints with which to test our theoretical understanding of the physical system. I will discuss limitations to transfer of information in the coupled system and current research using the UCL thermosphere-ionosphere-magnetosphere model.
Séminaire précédant Séminaire suivant 26ème séminaire : vendredi 09 novembre, 11h00
The Weak Wind Stars
Lida Oskinova (Brockhaus Institut für Physik und Astronomie, Potsdam)

The hottest and most massive stars on the main sequence have spectral types O and B. The standard theory of line driven winds predicts that these stars possess strong stellar winds with high mass-loss rates. These predictions have been verified for the hottest O-stars by means of spectral analyses in the optical, UV, and radio range - albeit there are still uncertainties due to the effects of unknown wind inhomogeneities. However, for cooler O stars, the same analysis techniques yield mass-loss rates that are at least one order of magnitude below the values expected from the wind theory. Thus, there is a severe discordance. which is often referred to as 'the weak wind problem' in the literature. Our new multi-wavelength observations and their analyses shed new light on this issue.
Séminaire précédant Séminaire suivant 27ème séminaire : jeudi 15 novembre, 11h00
Infrared Logs in Effective Field Theories
Prof. Maxim Polyakov (Institut fuer Theoretische Physik II, Ruhr-Universitaet Bochum)

We developed a new method for calculation of infrared logs in nonrenormalizable field theories. Using this method we computed 3D parton distributions in pion in a model independent way.
Séminaire précédant Séminaire suivant 28ème séminaire : jeudi 15 novembre, 15h45
Determining the contribution of BAL quasars to AGN feedback
Benoit Borguet (Virginia Tech, USA)

The potential impact of AGN outflows on their environment has recently become recognized including effects on the growth of supermassive black holes, chemical enrichment of the IGM, quenching of the star formation, evolution of the host galaxy etc. However, for the lack of a better alternative, the theoretical studies use the kinetic luminosity of the outflows as a free parameter with few observational constraints. In this talk I will describe the research program carried out at Virginia Tech by Pr Arav and its team in order to quantify the kinetic luminosity of these outflows and discuss some of the recent results published by our group.
Séminaire précédant Séminaire suivant 29ème séminaire : mardi 20 novembre, 15h45
The peculiar solar chemical composition: Does the Sun have a subsolar metallicity?
Martin Asplund (Australian National University, Mt. Stromlo Observatory, AUSTRALIA)

The photospheric solar abundances have undergone a drastic revision over the last decade, in particular for the most abundant metals carbon, nitrogen, oxygen and neon, which has far-reaching consequences not only for solar physics but for astronomy as a whole since the Sun functions as a fundamental yardstick. I will describe the main reasons for this new picture of the Sun. While solving many problems the new lower solar metallicity is in stark conflict with evidence from helioseismology as will be discussed. The second half of the talk will discuss whether the Sun is chemically normal. I will present a detailed comparison of the solar chemical composition with those of otherwise identical stars, which has yielded some surprising and exciting results, namely that the Sun differs in a significant and systematic way to the majority of stars. This peculiar abundance pattern can be traced to the process of planet formation, which opens the truly enthralling and completely new prospect of identifying stars likely to host planets, perhaps even terrestrial planets, through a detailed determination of their chemical compositions.
Séminaire précédant Séminaire suivant 30ème séminaire : jeudi 22 novembre, 15h45

Maurice Gabriel (AGO)

Séminaire précédant Séminaire suivant 31ème séminaire : jeudi 29 novembre, 14h00
LHC results
Thomas Hebbeker (University of Aachen)

I will briefly introduce the LHC and the detectors ATLAS, CMS and LHCb and present selected recent results. Examples will illustrate how well the Standard model of particle physics has been tested so far, and to what extent models of new physics have been ruled out. Of course, I will also show the latest update of the higgs search. Some comments on the mid term and long term future of the LHC will conclude the seminar.
Mois précédent Mois suivant Décembre 2012
Séminaire précédant Séminaire suivant 32ème séminaire : jeudi 06 décembre, 16h00
Joint colloquium :

(Quantum) complexity in biological tissue - why could coherence matter?
Andreas Buchleitner (Universität Freiburg)

New spectroscopic data from biochemistry suggest that evolution might employ quantum coherence effects to steer relevant performances in energy transduction. The issue is still widely open, but this makes it also very intriguing and interesting, in particular since the systems under scrutiny are "dirty" in the best sense, and have everything most quantum opticians are educated to DISlike: disorder, noise, interactions. I will try to describe the basic phenomenology, and adopt a statistical point of view, to address the possible role of quantum coherence effects for robust "bio-design".
Séminaire précédant 33ème séminaire : mardi 18 décembre, 14h00 
The search for particle dark matter
Pat Scott (McGill University)

Interest in particle dark matter has exploded in recent years. I will describe some complementary approaches to the problem of identifying dark matter: indirect searches for dark matter annihilation, direct searches in terrestrial detectors, and attempts to produce dark matter at the LHC. I will discuss how these different searches can be integrated into a global, multi-messenger, multiwavelength fit to all available astronomical and terrestrial data.
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.