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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 2018 Année suivante  
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Mois précédent Mois suivant Février 2018
Séminaire suivant  1er séminaire : mercredi 21 février, 11h00
Cosmology with quasar time delays: a short history of Refsdal’s idea and of its implementation
Frédéric Courbin (EPFL Lausanne)

Time delays in gravitationally lensed quasars in principle allow to measure H0 independently of other cosmological parameters. I will review the field of quasar time delays from the very first measurements to the most recent ones and will show what are the main advantages and drawbacks of the method over others. Future prospects are given, especially in the context of Euclid, LSST, and monitoring with dedicated telescopes.
Séminaire précédant Séminaire suivant 2ème séminaire : mardi 27 février, 14h00
On critical thinking and cognitive pitfalls
Johan Braeckman (UGent)

In this lecture we investigate why people are so vulnerable to mental infections with totally irrational believes. Insights developed in social psychology, informal logic or neuroscience, make clear how quick human reasoning can go wrong, how easy one makes wrong connections, wrong statistical estimations and all to quick generalizations. Scientists doing research are often better armed against the danger of infection by irrational and pseudoscientific views. However, they are very good in rationalizing wrong views, picked up along the way, which often makes them stick to bad ideas much longer. Nobody is immune! Pseudoscientific theories will be discussed together with historical and current examples of apparent scientific and objective views that turned out to be infected by fallacies or wrong assumptions. The differences between science and pseudoscience and between rational and irrational thinking will be clarified. A pure rational way of thinking is most probably never to be reached, and may even be something we should not wish for, but we can get a better insight in how our brain processes information and creates false realities.
Mois précédent Mois suivant Mars 2018
Séminaire précédant Séminaire suivant 3ème séminaire : mercredi 14 mars, 15h45
Extrasolar planets meet star spots
Jürgen Schmitt (Universität Hamburg)

Transits of extrasolar planets offer not only the possibility to study the physical properties of planets, they also provide a new possibility to diagnose the surfaces of active stars, which allows the study of surface inhomogeneities with unprecedented angular resolution. I will discuss the modeling of extrasolar planet transit light curves, and in particular, how the analysis is affected by star spots and how the derived extrasolar planet parameters depend on the activity state of the spots. I will specifically discuss how the transit light curves change due to the presence of star spots and how this information can be used to construct surface maps of active stars and deduce stellar properties. I will discuss the potential of transit studies at shorter wavelengths and show how high-energy observations constrain the physical properties of extrasolar planets.
Séminaire précédant Séminaire suivant 4ème séminaire : vendredi 16 mars, 10h00
Digital Holographic Microscopy
Kent Wallace (Jet Propulsion Laboratory)
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 29 mars, 15h45
DOTIFS - a multi-deployable fiber-fed IFU Spectrograph
Sabyasachi Chattopadhyay (STAR)

Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a new multi-object integral field spectrograph being built by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India for the 3.6m Devasthal Optical Telescope, (DOT). The Devasthal Observatory has been constructed by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. DOTIFS is mainly designed to study the physics and kinematics of ionized gas, star formation, and H II regions in the nearby galaxies. DOTIFS is a novel instrument in terms of multi-IFUs, built in deployment system, and high throughput. A magnifier at the Cassegrain side port of the telescope feeds sixteen integral field units (IFUs). The IFUs can be deployed over an 8’ diameter focal plane by orthogonal actuators. An intelligent deployment algorithm has been developed to allow optimized reconfiguration and to avoid any collision between IFUs. The whole deployment system has a complex 3-dimensional structure to allow maximum positioning freedom to the IFUs. The IFUs are developed using the novel technique of photolithography which makes the instrument precise but cost-effective. Digital correlated double sampling is implemented as the detector readout to minimize the readout noise with a thorough analytical understanding of the noise components. The speaker will provide details of the instruments and the challenges. The instrument is in the phase of fabrication and is scheduled to be commissioned in late 2018.
Mois précédent Mois suivant Mai 2018
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 03 mai, 15h45
On the determination of stellar ages, masses and radii from theoretical models
Andrea Bonfanti (STAR)

Determining the ages of stars is a very challenging task. Several indicators are available, but no single method works well for a broad range of spectral type or for each evolutionary phase of a star. My PhD project was related to the building of an algorithm for the determination of stellar ages, considering evolutionary tracks and isochrones. This model-dependent approach, which has been complemented by using gyrochronology, stellar magnetic activity and scaling relations coming from asteroseismology, also enables to retrieve other useful stellar parameters such as radius or mass. Here I will briefly discuss the problems of inferring ages from theoretical models and the characterization of solar-type stars of the solar neighbourhood, with a specific attention to the realistic uncertainties to be attributed to the main stellar parameters as a sum of internal and model-related ones. Moreover, considering that the determination of exoplanet properties requires the knowledge of stellar parameters, I will also show you the synergy between the characterization of stars and the exoplanetary science with particular references to the future Cheops mission and the analysis of stellar light curves.
Séminaire précédant Séminaire suivant 7ème séminaire : jeudi 24 mai, 16h00
L’océanographie opérationnelle au service de la conservation des tortues marines
Philippe GASPAR (CLS - Toulouse)

Toutes les espèces de tortues marines sont soumises à d’importantes pressions anthropiques qu’elles soient directes (braconnage des nids, pêche) ou indirectes (pollution marine, réchauffement climatique).

Après avoir rapidement passé en revue ces diverses pressions, nous nous focaliserons sur celles qui affectent les juvéniles en mer. Ce stade de vie, mal observé et donc mal connu, est pourtant crucial. En effet, l’évolution (expansion ou extinction) des populations de tortues marines dépend fortement de la mortalité juvénile. C’est pour étudier ce stade de vie critique que nous avons développé STAMM (Sea Turtle Active Movement Model), un modèle individu-centré qui permet de simuler la dispersion des tortues juvéniles en mer ainsi que les conditions de vie qu’elles y rencontrent. Dans ce modèle, les individus simulés se dispersent sous l’impact combiné de la dérive induite par les courants marins et des mouvements de nage motivés par la recherche d’habitats favorables. Ces habitats sont caractérisés par des eaux suffisamment chaudes et riches en nourriture.

Nous présenterons ici les premières simulations réalisées avec le modèle STAMM forcé par des champs de courant et de température issus d’une réanalyse longue de la circulation océanique fournie par MERCATOR, le centre européen d’océanographie opérationnelle. Ces simulations concernent les populations de tortues luth de l’Atlantique Nord-Ouest et du Pacifique Ouest.

L’analyse des résultats montrent que :

- les schémas de dispersion spatiale simulés par STAMM sont cohérents avec les rares observations disponibles ; - la variabilité de la circulation, de la température, et la productivité océanique modulent de façon très importante la mortalité naturelle ; - les mouvements de nage orientés vers les zones productives tendent à concentrer les individus dans des zones exploitées de façon intensive par les pêcheries thonières.

La comparaison des simulations Atlantique et Pacifique fournit également des éléments susceptibles d’expliquer, au moins partiellement, pourquoi la population de tortues luth de l’Atlantique Nord-Ouest se développe alors que celle du Pacifique Ouest diminue de façon alarmante.
Mois précédent Mois suivant Juin 2018
Séminaire précédant Séminaire suivant 8ème séminaire : vendredi 22 juin, 11h00
Artificial Neural Networks and Applications to Astronomy
Ranjan Gupta (IUCAA, Pune, Inde)

Artificial Neural Networks (ANN) have been known as a powerful tool for pattern recognition in various applications over past several years since the multi-layer-back-propagation algorithm (MBPN) was developed. In the recent years, ANN have been successfully used in classification type applications in Astronomy. The talk would highlight ANN as a tool for pattern recognition in general and Astronomical applications in particular. It would also review the stellar spectral classification trends and new applications carried out by our group recently viz. extracting stellar atmospheric parameters from observed stellar spectra, determination of color excess from IUE-UV spectra and use of PCA as a pre-processor for ANN applications. Its application to a fairly large sample of 2000 spectra of IRAS and subsequent classification results will be shown. Recent applications of ANNs by our group are on the large 1273 spectra of CFLIB INDO-US spectral library and estimation of interstellar extinction from UV simulated satellite data etc. and star-galaxy classification for upcoming satellite missions TAUVEX/ASTROSAT/GAIA etc. It has been most recently applied to a very large spectral data base of LAMOST.
Mois précédent Mois suivant Octobre 2018
Séminaire précédant Séminaire suivant 9ème séminaire : jeudi 04 octobre, 16h00
Atmosphere-ocean interactions in the Adriatic basin at different scales: cold air outbreaks, storm surges and meteotsunamis
Matjaz Licer (NIB, Slovenia)

Adriatic sea is a NW-SE oriented elongated semi-enclosed basin in the Northern Central Mediterranean, communicating with the Ionian Sea through the Otranto strait in the south. It is about 800 km long and 200 km wide and surrounded from all sides with mountain ridges, which exert significant influence on the basin dynamics through topographic control of the air-flow. Topographic control plays a role during the two dominant wind forcing regimes: cold northeasterly bora and warm southeasterly sirocco wind. We will take a bird's eye view at several examples of extreme air-sea interactions in the basin. Hurricane bora wind event from February 2012 will be presented, along with the related turbulent air-sea fluxes, circulation and consequent dense water formation on the shelf. We show the role of two-way atmosphere-ocean feedback during numerical modelling of these transient events. Sirocco wind, on the other hand, is the leading factor causing Adriatic storm surges, which cause coastal erosion and flooding of northern coastal towns like Venice and Piran. We will discuss why Adriatic storm surges are easy to understand but difficult to forecast, and how this problem can be tackled through numerical ensemble modelling. Finally, the physics of meteotsunamis, i.e. tsunamis of meteorological origin, will be discussed. These are strong harbor seiches in the tsunami frequency band, induced by high frequency air pressure modulations due to travelling atmospheric disturbances. They are quite frequent (several event per year) in the Mediterranean and Adriatic and can cause severe damage. We will revisit historic meteotsunami occurrences in the Adriatic and make a quick digression to show some propagation and amplification properties of these waves over the Balearic archipelago (Spain).
Séminaire précédant Séminaire suivant 10ème séminaire : jeudi 04 octobre, 16h00
Sorting out CP symmetries in a basis-invariant way
Igor Ivanov (CFTP, Instituto Superior Técnico, Lisbon)

The quest for the origin of CP violation leads many to build and explore multi-Higgs models, in which is arises naturally. But one first needs to understand what is actually broken in CP violation. Surprisingly, there can exist exotic forms of CP symmetry, which are physically distinct from the usual CP, and multi-Higgs models realizing them started to appear only very recently. I will explain how to recognize the hidden presence of such CP symmetries and their breaking in basis-invariant way.
Séminaire précédant Séminaire suivant 11ème séminaire : vendredi 05 octobre, 11h00
Probing high-mass star formation: An observational perspective
Anandmayee Tej (Indian Institute of Space Science and Technology, Trivandrum, INDIA)

Massive stars play a vital role across the universe given their radiative, mechanical and chemical feedback. They dictate the energy budget of the galaxies through enormous radiation, powerful winds and supernovae events. However, most aspects of the processes involved in their formation are far less understood in contrast to the low-mass regime. In this talk I will dwell upon observational manifestations of the interaction of the massive stars with the surrounding interstellar medium at various evolutionary stages and emphasize on the role of multiwavelength observations in understanding high-mass star, their formation and feedback on the surrounding medium.

I will spend a few minutes towards the end of the talk in discussing about my institute which is the academic cradle of the Indian Space research Organization.
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 18 octobre, 16h00
New physics in B-meson decays
Avelino Vicente (Instituto de Física Corpuscular, Valencia)

Current B-physics data contain two intriguing tensions. First, the LHCb collaboration has reported some anomalies in b-s transitions, with discrepancies with the Standard Model predictions in some angular observables and branching ratios and intriguing hints for lepton universality violation. Second, BaBar, Belle and LHCb have found compatible deviations in observables associated to b-c transitions, again hinting at the violation of lepton universality. We will review the proposed explanations for these tensions and focus on new physics models that can simultaneously address both anomalies. In particular, we will show that a simple gauge extension of the Standard Model can achieve such goal.
Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 25 octobre, 16h00
Could primordial black holes be the dark matter?
Sébastien Clesse (UClouvain et UNamur)

After a brief review on the interest of gravitational-wave astronomy for cosmology, I will focus on a scenario that has recently received a lot of attention: massive primordial black holes (PBH) as a dark matter candidate. I will present the current status of this scenario, including motivations coming from the gravitational waves detected by LIGO/VIRGO, the various astrophysical and cosmological constraints on their abundances, as well as a series of observations and theoretical arguments pointing towards PBH dark matter. Finding evidences of the existence of PBH would have groundbreaking consequences for our understanding of the early Universe and of High Energy physics.
Séminaire précédant Séminaire suivant 14ème séminaire : mardi 30 octobre, 16h00
Magnetic field and accretion in the young eruptive star EX Lupi
Agnès Kospal (Konkoly Observatory, Budapest, Hungary)

While the Sun is a quiet and well-balanced star nowadays, during its first few million years it possessed a strong magnetic field and accreted actively. Theoretical models predict that under certain circumstances the interaction of a strongly magnetic star and its circumstellar disk may lead to short busts of increased accretion onto the star. The observable examples of this phenomenon may be a group of young stars called EXors, named after the prototype EX Lupi, which show irregular brightenings due to elevated accretion. EX Lupi had its historically largest outburst in 2008. Our group observed the system during this event, and discovered the crystallisation of amorphous silicate grains in the inner disk by the heat of the outburst. Spectroscopic evidence from the quiescent and outburst periods suggests that the mass accretion proceeds through the same magnetospheric accretion channels in both periods but with different mass flux. However, no information on the magnetic field of EX Lup can be found in the literature. Here, we explore the magnetic field structure of EX Lup using spectropolarimetric monitoring with the CFHT/ESPaDOnS taken during the quiescent period. We detected strong and largely poloidal topology with a prominent cool polar cap and an accretion spot above it. If EX Lup is a good proxy for the proto-Sun, similar magnetic field-disk interactions and the resulting outbursts might have happened during the early evolution of the Solar System as well, significantly affecting the material available for planet formation.
Mois précédent Mois suivant Novembre 2018
Séminaire précédant Séminaire suivant 15ème séminaire : jeudi 22 novembre, 16h00
Multi-sensor satellite-based water quality monitoring in the North Sea
Dimitry van der Zande (RBINS)

Over the last decade, services for marine monitoring and management have emerged using data from medium resolution ocean colour remote sensors such as SeaWiFS, ENVISAT/MERIS and MODIS/AQUA. The success of these mainstream ocean colour sensors has stimulated the follow-up missions, Sentinel-3/OLCI and VIIRS, giving continuity to this family of medium resolution ocean colour sensors. Despite considerable advantages of the medium resolution sensors in coverage with respect to in situ monitoring techniques, they have critical limitations of spatial and temporal resolution (typically 300m, 1/day) with respect to user requirements. Today’s availability of Earth Observation (EO) data is unprecedented including traditional medium resolution ocean colour systems, high resolution land sensors (e.g. Landsat-8, Sentinel-2, 10-60m, 1/5 days) and geostationary satellites (e.g. Seviri, 4-6km, 1/15min). In this seminar we will present the necessary steps needed to build an operational water quality monitoring service based on these multi-scale satellite data including scientific algorithm development, water quality product validation, multi-scale synergy products and the development of data cubes to extract relevant information out of the terabytes of data. This concept will be demonstrated in a use case highly relevant to the user community: 'eutrophication assessment of the Belgian part of the North Sea for European Directives (MSFD, WFD)'
Mois précédent Mois suivant Décembre 2018
Séminaire précédant Séminaire suivant 16ème séminaire : jeudi 06 décembre, 16h00
Strong gravitational lensing as a probe of Gravity: multi-messenger approach
Tao Yang (Beijing Normal University)

Strong gravitational lensing by galaxies provide us a unique opportunity to understand the nature of gravity on the galactic and extra-galactic scales. In this talk, I will introduce our recent work in which we propose a multi-messenger approach by combining data from both gravitational wave and the corresponding electromagnetic counterpart to probe the deviations from GR. Our work shows that with one typical strongly lensed GW+EM event in the future, the multi-messenger approach is able to distinguish about 10% modified gravity effect on tens of kiloparsec scale.
Séminaire précédant Séminaire suivant 17ème séminaire : jeudi 13 décembre, 16h00
Climate prediction: where are we?
François Massonnet (UCL)

The evolution of the atmosphere beyond a few days is governed, on the one hand, by variations in the so-called "slow" components of the climate system (oceans, sea ice, ice sheets, land) and, on the other hand, by changes in the atmospheric composition -- from natural or anthropogenic origins. Climate prediction accounts for these two sources of predictability and attempts to produce skillful and useful climate information at time scales ranging from a few weeks to a few decades.

Numerical models of the general circulation of climate (GCMs) are primary tools in this emerging area of research. They allow (1) exploring the very notion of predictability (what are the physical mechanisms that underpin potential predictions) and (2) delivering the predictions themselves. The use of GCMs is, however, not a cakewalk. These models are expensive in terms of computational and storage requirements, they feature systematic biases and their (ensemble) predictions are not always straightfoward to verify.

During this seminar, I will review recent advances in the area of climate prediction and will introduce several concrete examples linked to my research. In particular, I will aim at answering four questions: (1) What is a climate prediction system? (2) What is a good climate prediction? (3) Are today's climate predictions good? (4) How can these predictions be improved?

All welcome!
Séminaire précédant 18ème séminaire : jeudi 20 décembre, 14h30 
Odderon - mystery and reality
O.V. Selyugin (BLTPh, JINR, Dubna, Russia)

The talk is related to one of mainstream particle physics - the search for the odd-signature partner of the Pomeron - the Odderon, as it was named by B. Nicolescu. Now there is a wide discussion about the Odderon contribution in elastic hadron scattering (see e.g. CERN Courier n.4 april 2018). I will make a short review of the possible effects of the Odderon in the different reactions and attempt to find the Odderon contributions.

The soft diffraction phenomena in elastic proton-proton scattering are reviewed from the viewpoint of experiments at the LHC (TOTEM and ATLAS collaboration). I will especially examine the recent experimental data obtained at the LHC up to a center-of-mass energy of 13 TeV taking into account the requirements on the main properties of the scattering amplitude (analyticity, unitarity) and discussing the possible energy dependence of the real and imaginary parts of the Odderon amplitude.

I will show that in the framework of the High Energy General Structure (HEGS) model, taking the same intercept for the Odderon (maximal Odderon) and the Pomeron leads to a good fit of the new LHC data at 13 TeV. and show that the main effect of the Odderon can be seen in the region of the diffraction minimum of the differential elastic cross section.
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.