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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)
Belgique

Tel.: 04.366.9774
Fax: 04.366.9729
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Mois précédent Mois suivant Janvier 2015
Séminaire suivant  1er séminaire : jeudi 08 janvier, 15h45
Spectroscopie d'étoiles sous-naines chaudes dans Omega Centauri
Marilyn Latour (Bamberg, Germany)

Les sous-naines chaudes sont une classe d'étoiles qui défient encore les théories de l'évolution stellaire. Expliquer leur existence est d'autant plus complexe que celles-ci se divisent en plusieurs sous-catégories qui nécessitent des mécanismes de formation différents. En plus du champ galactique, on retrouve aussi des sous-naines dans certains amas globulaires où leur distribution dans le diagramme couleur-magnitude est parfois difficile à expliquer; comme la présence d'un "blue hook" situé à l'extrémité bleue de la branche horizontale. Ce phénomène est observé dans quelques amas globulaires dont Omega Centauri. Notre analyse spectroscopique d'étoiles sous-naines chaudes dans Omega Cen a pour but de caractériser plus en détail cette population particulière. Je présenterai donc les résultats de notre analyse, soit les paramètres atmosphériques et la composition chimique (hélium et carbone) des étoiles de notre échantillon, ainsi que la comparison entre nos résultats et les prédictions théoriques.
Mois précédent Mois suivant Février 2015
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 12 février, 15h45
Exoplanetary Atmospheres through the eyes of the VLT
Monika Lendl (AGO)

Planetary transits play an important role in the study of extrasolar planets as multi-wavelength observations of transits provide measurements of the planetary transmission spectrum. This in turn encodes information on the planet's atmospheric composition, and the presence of high-altitude cloud structures. I will present our ongoing observing program targeting several hot giant planets with ground-based facilities, focusing on results obtained with the VLT/FORS2 instrument. We made use of FORS2's multi-object spectroscopy mode, and I will briefly discuss strategies to deal with the instrumental limitations affecting FORS2. Finally, I will discuss the transmission spectrum of the hot Saturn WASP-49b.
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 26 février, 16h00
Conférence organisée dans le cadre de la Société Royale des Sciences de Liège et du cours d'astrobiologie :

Habitabilité dans le système solaire
Véronique Dehant (Observatoire Royal de Belgique, Bruxelles)

Les scientifiques unissent leurs savoirs, dans un effort multidisciplinaire, pour comprendre dans quelles conditions et par quels processus la vie est apparue et a évolué sur la Terre, et pourquoi et comment notre planète est devenue une planète biologique, avec un élément essentiel à la vie : l’eau. Certaines planètes telluriques comme Mars ont connu une période dans leur existence pendant laquelle l’eau a été abondante à leur surface. La planète Mars n’ayant pas à l’heure actuelle de tectonique des plaques, les témoins du passé restent visibles en grande partie à sa surface. On voit des traces d’eau, des ravinages, des traces de boue séchée, des vallées, des traces de glacier, des dunes... On observe également d’énormes volcans comme Olympus Mons ( 27km de hauteur) et on a compris qu’il y a eu, dans le passé lointain de Mars, un champ magnétique intense. Mais on ne connaît pas encore grand-chose sur l’intérieur de Mars. On sait que cette planète ressemble à la nôtre et possède une croûte, une lithosphère, un manteau et un noyau. Pourquoi Mars, Vénus, Mercure, des planètes proches de la Terre, ont-elles évolué de manière différente ? Les missions spatiales vers ces planètes telluriques ont et auront pour objectifs de comprendre leurs similitudes et leurs différences avec la Terre. Nous nous intéresserons également à leur habitabilité et présenterons des résultats d’études théoriques et de missions spatiales dans ce cadre. Nous nous attarderons également sur les lunes habitables du système solaire, des mondes de glace fascinants, possédant, pour certaines, des océans internes.
Séminaire précédant Séminaire suivant 4ème séminaire : vendredi 27 février, 11h00
Ground based search for planets: from WASP to NGTS
Marion Neveu (Université de Genève)

The Wide Angle Search for Planets (WASP) has been one of the most productive ground based surveys. It has discovered more than 130 hot Jupiters transiting bright (Mv<13) solar type stars. Close-in giant exoplanets are particularly interesting since their migration is still poorly understood. The presence of a companion could be triggering the migration process. In the context of the WASP survey, a search for additional objects has been conducted using the spectrograph CORALIE. I will present some results of WASP planetary systems including extra bodies. Improving the concept of WASP for a better precision, the Next Generation Transit Survey (NGTS) just got its first light in Paranal. I will present the system, and describe the expected yield of NGTS comprising Neptunes and SuperEarths orbiting bright stars.
Mois précédent Mois suivant Mars 2015
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 19 mars, 15h45
Evolution of massive single and binary stars - their fate and remnants
Ilka Petermann (AGO)

The final fate of massive stars, the type of explosion and the remnant they leave behind, is mostly governed by the masses of their helium cores and hydrogen envelopes in the latest stages of evolution. While for single stars wind mass loss is the only channel to reduce their mass, stars that are a member of a binary system are also assumed to loose their hydrogen envelope due to Roche lobe overflow or a common envelope phase after core hydrogen burning. We aim at assigning the ZAMS masses of stars in the range 15-45 solar masses to their remnant masses and in quantifying their compactness predict their most likely remnants, neutron stars or black holes.
Séminaire précédant Séminaire suivant 6ème séminaire : lundi 23 mars, 11h00
A CubeSat for a photometric study of Beta Pictoris
Sylvestre Lacour (LESIA, Obs. Paris)

Getting novel concepts onboard space telescopes is difficult due to low turnover and the no-risk policy of space agencies. In times of low budgets, CubeSats might help to resume the technology race that has spawn during the cold war. In the context of astronomy, CubeSats have the disadvantage of a low collecting area. However, they give access to long coherence times, large spectral windows, and continuous observations. We propose to launch a CubeSat mission with the objective of studying the photometry of Beta Pictoris. The main objective is to catch the 2017 transit of beta Pictoris b to probe its surrounding (rings, moons, etc…). The second objective is to observe for the first time exocomets as they pass in front of their host star. The third objective is to study inhomogeneities in the debris disk. The technical challenge is to fit a photometer into a 10cm^3 box with a 100ppm accuracy. To get that, we present a concept made of single-mode fibers, piezos, and a single-photon avalanche diode, i.e. components that wouldn’t be accepted for an M4 ESA mission.
Mois précédent Mois suivant Avril 2015
Séminaire précédant Séminaire suivant 7ème séminaire : mercredi 01 avril, 11h00
What can we learn about comets by using narrowband filters?
Matthew Knight (Lowell Observatory)

Comets are the most accessible primitive bodies in the solar system, and their study gives insight into the origin and evolution of our planetary system. Detailed studies of comets through in situ measurements like those currently being conducted by ESA’s Rosetta mission at comet 67P/Churyumov-Gerasimenko are only possible for a handful of comets. Earth-based observations allow the study of a large number of comets, helping us to understand the variety of properties comets possess and, therefore, to better understand the conditions of the early solar system. One of the most efficient techniques for studying comets is by using narrowband filters to isolate gas emission or dust continuum. Photometry of comets with narrowband filters at different locations in their orbits and on multiple apparitions yields information about cometary composition, seasonal variations, and evolution. Narrowband imaging frequently reveals coma structures that cannot be seen with broadband imaging. Temporal variations in these structures can be used to infer properties of the nucleus such as the rotation period, rotation state (simple or non-principal axis), and the location(s) of active regions on the surface. Narrowband imaging can also yield valuable information about the gas and dust comae such as outflow velocities, parent/daughter gas species lifetimes, and possible compositional heterogeneities. I will discuss some recent and ongoing studies using narrowband filters at Lowell Observatory, including support of NASA’s EPOXI mission to comet 103P/Hartley 2, and bright comets C/2014 Q2 Lovejoy and C/2012 S1 ISON.
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 02 avril, 16h00
Joint colloquium
Le magnétisme stellaire: son rôle sur la vie des étoiles et la nôtre.

Coralie Neiner (LESIA, Observatoire de Meudon)

Grâce aux instruments puissants installés sur des grands télescopes à Hawaï, au Chili et en France, les astronomes peuvent aujourd'hui mesurer des champs magnétiques à la surface des étoiles. L'origine de ces champs magnétiques dépend du type d’étoiles : dans les étoiles chaudes ils sont présents depuis la naissance de l’étoile, alors que dans les étoiles froides ils sont fabriqués au sein même de l'étoile. L'amplitude des champs magnétiques stellaires varie également selon le type d’étoiles, de moins de 1 Gauss jusqu'à cent mille milliards de Gauss. Ces champs magnétiques ont une grande influence sur la structure des étoiles, la distribution de leurs éléments chimiques et leur évolution au cours de leur vie. Ils influencent aussi l'environnement de l’étoile et produisent des cycles de variations d’activité de l’étoile. Cette activité affecte directement les planètes autour de l’étoile. En particulier le champ magnétique du Soleil a un impact sur notre Terre et influence par exemple nos satellites, nos avions, notre système électrique et donc notre vie de tous les jours.
Séminaire précédant Séminaire suivant 9ème séminaire : jeudi 16 avril, 15h45
Dancing in the dark: galactic properties trace spin swings along the cosmic web
Yohan Dubois (Institut d'Astrophysique de Paris)

A large-scale hydrodynamical cosmological simulation, Horizon-AGN, is used to investigate the alignment between the spin of galaxies and the large-scale cosmic filaments. The analysis of more than 150 000 galaxies with morphological diversity shows that the spin of low-mass is preferentially aligned with their neighbouring filaments. High-mass galaxies tend to have a spin perpendicular to nearby filaments. We also make predictions on intrinsic alignements of galaxies, which is crucial for putting constraints on the cosmic shear signal. I will show how the subtle combination of mergers and AGN feedback lead to such results, while shaping the morphology of galaxies.
Séminaire précédant Séminaire suivant 10ème séminaire : lundi 20 avril, 15h45
Recent results and perspectives in microlensing exoplanets search
Arnaud Cassan (Institut d'Astrophysique de Paris)

In this seminar, I will review recent discoveries and developments in exoplanet search through gravitational microlensing. I will first recall the basics of the method, in particular what quantities can be measured and how (observational strategy, instruments, modeling). I will then discuss current microlensing detections and statistics, with a special focus on three topics: the Spitzer follow-up of microlensing events using space-based parallax, the recent detection of several new objects in the brown dwarf desert, and future observations of microlensing events through interferometry. I will conclude by raising scientific challenges facing exoplanetary sciences today, in which microlensing should significantly contribute thanks to recent improvements in telescopes and instruments.
Séminaire précédant Séminaire suivant 11ème séminaire : jeudi 23 avril, 16h00
Three dimensional structure of circulation of giant planet's magnetospheres
Pr David Southwood (Imperial College)

All too often magnetospheric circulation theory has started by analogy with Earth. The fast rotation of Jupiter and Saturn can lead to very different situations, particularly concerning the entry of plasma from the exterior, ie the solar wind. Entry is preferentially off the equator and the centripetal acceleration can be dramatic even for a solar wind particle. The system scales are so large that a second feature makes for strange effects; charged particles entering in one longitude (say by day) may not return to the equator until they are on the night side. In the situation, northern and southern hemispheres become in many respects independent despite apparently being linked by the field. We'll describe consequences of this as well as other pathological features of both Jupiter and Saturn systems. Many of the odder features may have counterparts in other astrophysical systems.
Séminaire précédant Séminaire suivant 12ème séminaire : mardi 28 avril, 11h00
Updates on axion-like particles in astrophysics: what we can learn from dying stars
Alexandre Payez (DESY)

In this seminar, I will first give an overview of light axion-like particles, explaining why they can be interesting in astrophysics. Then, I will present how we have derived the most stringent bound on their electromagnetic coupling from SN1987A, and will further discuss what we can learn from future supernova explosions. I will finally mention how polarimetric observations of magnetic white dwarfs might be a promising tool to search for such elusive hypothetical particles.
Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 30 avril, 15h45
Interferometric direct imaging techniques for exoplanets detection
Fabien Patru (Observatoire de la Côte d'Azur)

The detection of exoplanets remains a challenge in direct imaging in term of separation and contrast of intensity planet-star. An evolution of the imaging techniques is presented here by showing the parallel between a large telescope and a large array of telescopes (interferometer). The very high-contrast imaging is up to now achieved only on large telescopes by means of efficient adaptive optics (AO) and coronagraphic techniques, while the very high-angular resolution imaging remains only accessible to the long baseline interferometry. However, recently, these two fields converge and complement each other. The modern stellar interferometry uses adaptive optics, and new interferometric concepts appear on large telescopes, as for instance the pupil masking.

Another innovative approach is the "interferometric direct imaging". It has already been shown that a "hypertelescope" (formed of numerous telescopes) is able to produce an image directly in the focal plane of an interferometric beam combiner by means of "pupil densification". We propose here a new technique of "pupil discretization" (DAM) based on the spatial filtering and the interferometry. DAM improves the ultimate contrast of an AO-equipped telescope, simply by using an integrated optic low-pass filter removing out the high spatial frequencies.
Mois précédent Mois suivant Mai 2015
Séminaire précédant Séminaire suivant 14ème séminaire : lundi 04 mai, 15h45
High-tech optical telescopes: From liquid mirrors to ELTs
Paul Hickson (University of British Columbia)

Advanced technologies are revolutionizing astronomical observations, particularly for ground-based facilities. The next generation of extremely-large telescopes will increase the light-collecting area and resolution by more than an order of magnitude compared to the best current telescopes. For many observations, this will increase sensitivity several hundred times. These gains will be achieved largely by active and adaptive optics that rely on sophisticated hardware and software systems. Perhaps surprisingly, these high-tech telescopes are being supported, and will be complemented by, relatively-simple telescopes that employ rotating liquid mirrors. The Large Zenith Telescope, a 6-metre liquid-mirror telescope in Canada, has been providing input to the design of ELT adaptive optics systems, and the first such telescope dedicated to astronomical surveys, the International Liquid-Mirror Telescope, is being built by a collaboration lead by the University of Liege. From a mountain top in the Indian Himalayas, the ILMT will survey a wide area of sky each night to detect and study quasars, gravitational lenses, supernovae and other variable objects, providing new targets for ELTs.
Séminaire précédant Séminaire suivant 15ème séminaire : jeudi 21 mai, 15h45
Discriminating between stable vs. metastable vacua in the two-Higgs-doublet models
Igor Ivanov (CFTP-IST)

In models with complicated Higgs sectors, the scalar potential can have several minima at different depths. If the universe resides in a local minimum, it renders the vacuum metastable against decay, even at the tree level. If one prefers to avoid this issue, one must discriminate between the global and the local minima. I will discuss how this issue can be efficiently resolved in the two Higgs doublet model, both in the popular softly-broken Z_2 case, and in the most general case. It offers an example of how the knowledge of intricate algebraic properties of a model assists in its phenomenological investigation.
Mois précédent Mois suivant Juin 2015
Séminaire précédant Séminaire suivant 16ème séminaire : jeudi 25 juin, 15h45
Nucleon form factors and properties of the elastic scattering
amplitude at low and LHC energies

Oleg Selyugin (BLTPh, JINR, Dubna, Russia)

On the basis of the representation of the generalized structure of nucleons a new model of hadron interactions at high energies is presented. The new t dependence of the generalized parton distributions (GPDs) is obtained from the comparative analysis of different sets of parton distribution functions (PDFs), based on the description of all the sets of experimental data of electromagnetic form factors of the proton and neutron.Taking into account the different moments of GPDs of the hadron a quantitative description of all existing experimental data on proton-proton and proton-antiproton elastic scattering from sqrt(s)= 9.8 GeV to 8 TeV (including the Coulomb-hadron-interference region and recent LHC data of the TOTEM and ATLAS Collaborations) is obtained. That allow us to use a minimum of free parameters in the quantitative description of the full sets of experimental data and to examine the contributions of the crossing-even and crossing-odd parts of the two and three reggenized gluons in the t channel in the scattering amplitude. The specific features of the slope of the eikonalized scattering amplitude was found. The energy dependence of the overlapping function and possibility of the saturation regime at LHC energies are analyzed. Our result contradict some other obtained in recent time.
Mois précédent Mois suivant Juillet 2015
Séminaire précédant Séminaire suivant 17ème séminaire : mardi 14 juillet, 15h45
Quasi-degenerate Majorana Neutrinos and Large CP Violation
Daniel Wegman (CFTP-IST, Lisbon)

The limit of exact degeneracy of Majorana neutrinos is not trivial, as leptonic mixing and even CP violation may occur. Even more, the mixing matrix must have a vanishing element, which, could be an explanation to the smallness of |V13| compared to other elements. The lifting of the mass degeneracy can lead to the measured value of |V13| while at the same time accommodating the observed solar and atmospheric mixing angles. For Majorana neutrinos, a new parametrization for leptonic mixing of the form V=O23*O12*K*O, reveals interesting aspects that are less clear in the standard parametrization. The existence of only one CP violating phase, already present in the limit of exact degeneracy, generates, upon the lifting of the degeneracy, both Majorana and Dirac-type violation in the leptonic sector.
Mois précédent Mois suivant Septembre 2015
Séminaire précédant Séminaire suivant 18ème séminaire : vendredi 11 septembre, 15h45
CP violation in D Mesons: a window to New Physics
David Delepine (Universidad de Guanajato, Mexico)

In this talk, we shall review the CP violation (CPV) in D mesons. Particularly, we shall focus on why the D0 system could be a very good place to look for sources of CPV beyond Standard Model. We shall describe in details the contributions coming from Left-right models to CP asymmetries in Cabibbo favoured processes as D0 into K- pi+ or D+ into K- pi+ pi+.

(email: david_delepine@hotmail.com)
Mois précédent Mois suivant Octobre 2015
Séminaire précédant Séminaire suivant 19ème séminaire : jeudi 22 octobre, 15h45
Prospects for accreting black holes from X-ray polarimetry
René Goosmann (Observatoire de Strasbourg)

In the ongoing selection for the M4 ESA and NASA SMEX missions a total of three X-ray polarimetry satellites are currently under phase A study. This confirms a growing interest of the X-ray community and beyond in (re-)opening this new observational window. I am going to briefly explain how polarimetry in the X-ray spectral range can be realized applying so-called gas pixel detectors. Then I am going to point out the possibilities of X-ray polarimetry to put additional, independent constraints on the physics of accreting black holes in X-ray binaries and active galactic nuclei. These include the geometry of the ejected jets and winds on parsec scales and of the innermost parts of the accretion flow, as well as the structure of the space-time metric close to the event horizon of the black hole.
Mois précédent Mois suivant Novembre 2015
Séminaire précédant Séminaire suivant 20ème séminaire : mardi 03 novembre, 15h45
Neutrino Mixing, A4, and Dark Matter
Ernest Ma (Physics & Astronomy Department, University of California, Riverside, CA, USA)

The non-Abelian discrete symmetry A4 is well-known for obtaining tribimaximal neutrino mixing. It is shown that it is also applicable to cobimaximal mixing (theta13!=0, theta23=pi/4, and deltaCP=+/-pi/2). Three simple examples are discussed, one with a prediction of the ratio of Delta m221 to Delta m213. The origin of neutrino mass is also linked to the existence of dark matter in the context of A4 with cobimaximal mixing.
Mois précédent Mois suivant Décembre 2015
Séminaire précédant Séminaire suivant 21ème séminaire : jeudi 03 décembre, 15h30
Rosetta, Philae et la comète Tchouri
Emmanuel Jehin (AGO)

Rosetta est une des missions spatiales les plus incroyables, les plus ambitieuses et les plus risquées jamais envoyées dans l'espace ! Lancée il y a plus de 10 ans depuis la base de Kourou par l'Agence Spatiale Européenne (ESA) et après avoir parcouru environ 6 milliards de km dans le système solaire, elle a atteint son objectif : la comète 67P/Churyumov–Gerasimenko. Les comètes sont des astres énigmatiques encore mal compris des astronomes et qui, pour les plus brillantes d'entre-elles, effrayaient, dans le passé, les populations. Pourtant ces petits astéroïdes de glace de quelques kilomètres de diamètre renferment les clés des origines du système solaire, de la formation des planètes et peut être même de l'origine de l'eau et de la vie sur Terre. Dans cet exposé, Emmanuel Jehin reviendra rapidement sur le déroulement de la mission, et il présentera les résultats les plus importants obtenus jusqu'à présent. Il montrera et tentera d'expliquer ce que l'on peut apercevoir sur les images à haute résolution et tout à fait extraordinaires envoyées par la sonde. Pour la première fois, on peut observer en détail la surface d'une comète comme si on y était!
Séminaire précédant Séminaire suivant 22ème séminaire : vendredi 04 décembre, 11h00
Neutrino mass origin and Higgs decays at LHC
Miha Nemevsek (Stefan Institute, Ljubljana)

Neutrino oscillations provide an unambiguous experimental evidence for physics beyond the Standard Model. While the discovery of the Higgs boson allows us to test the origin of charged fermions, the theory of neutrino mass remains to be discovered. We will discuss the issue of neutrino mass, in particular the possible existence of Majorana neutrinos and the associated lepton number violation. Textbook search for rare nuclear processes will be revisited and contrasted with existing LHC searches. Finally, we will discuss in detail a recent proposal to search for the origin of neutrino mass at the LHC in rare Higgs decays to a pair of Majorana neutrinos.
Séminaire précédant Séminaire suivant 23ème séminaire : mercredi 09 décembre, 15h30
Dark Matter and Dark Energy and their astrophysical signatures
Peter Biermann (MPI for Radioastronomy, Bonn)

There has been lots of astronomical evidence for the presence of dark matter since 1933, when it was originally discovered in clusters of galaxies by Zwicky. Today, due to the magnificent data analysis using the Planck satellite (2015), we know with exquisite precision, how much baryonic matter, dark matter, and dark energy we have in the universe. But we do not know what all this is, and we are not even sure, where most of the baryonic matter is, although we can venture a probably a good guess, in the form of hot diffuse gas in groups and clusters of galaxies. There have been a number of claims that dark matter shows its true nature in energetic photons, or unusual positrons or anti-protons, with odd energies and spectra. So first we demonstrate that all the high energy phenomena have a rather natural explanation considering the physics of exploding stars with a bit more attention to detail; in fact, the data match quantitatively the extrapolation of an old model of 1993. Next we explore the early star formation in the universe, building on the arguments by Hogan & Dalcanton, that dark matter is in fact a keV particle, and show that star formation is possible very early. Then we discuss the early formation of super-massive black holes, and show how an observed giant arc of super-massive black holes, formed early in the universe, can be understood, using early disturbances and a process which I call the cosmic amplifier. Finally I note that there is an odd coincidence in that the energy turnover of the formation of the first generation of super-massive black holes corresponds to within a large uncertainty to dark energy. Using solutions to the Einstein equations I then speculate how this might be interpreted. If this specific speculation is borne out, then precision satellites such a Gaia and perhaps Euclid will detect dark energy. I conclude with the prediction, that the activity of the formation epoch of the first generation of super-massive black holes ought to be detected soon, in all channels, accessible to us, from photons, to neutrinos, to gravitational waves, to residual energetic particles. (Relevant publications 2006 PRL, 2010 AA, and 2014 MN.)
Séminaire précédant 24ème séminaire : lundi 14 décembre, 15h45 
Galaxies and the cosmic web: view from Tartu Observatory
Maret Einasto (Tartu Observatory)

I give a short review about the highlights of the studies of the large scale structure of the Universe in Tartu Observatory cosmology group: the studies of galaxy groups, clusters, filaments and superclusters at low and high redshifts.
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.