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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 2017    
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Mois précédent Mois suivant Janvier 2017
Séminaire suivant  1er séminaire : jeudi 26 janvier, 15h45
Exploring the Inert doublet model through the LHC and dark matter results
Igor Ivanov (CFTP, Departamento de Física, Instituto Superior Técnico)

The Inert doublet model (IDM) is a simple yet rich and well-motivated model containing scalar dark matter candidate. It has received much attention in the last few years both in the context of collider searches and cosmological/astroparticle observations. I will present our recent results (arXiv:1612.00511) of a thorough scan of the entire five-dimensional parameter space of IDM which takes into account constraints from theory, LEP, electroweak precision tests, the LHC Higgs data, as well as from DM relic density measurements, and DM direct detection limits. We identified new regions in the parameter space which were missed in previous scans. We also gave predictions for the mono-jet, mono-Z, and mono-Higgs processes at the LHC, and looked into how these processes and the future DM DD experiments can further constrain the model. In short, this seminar will serve as an illustration of how a typical DM model is probed through several complementary channels.
Mois précédent Mois suivant Février 2017
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 09 février, 14h00
A polarized view of planetary atmospheres
Frans Snik (Sterrewacht Leiden, Universiteit Leiden)

Starlight that is scattered within a planetary atmosphere becomes polarized. By accurately measuring this polarization as a function of wavelength and scattering angle, one can infer microphysical details of atmospheric properties and thus characterize planetary atmospheres. Now we know that virtually every star harbors at least one planet, we employ polarimetry to be able to directly study such exoplanets. First of all, we use the fact that planets appear polarized to distinguish their scattered light from the bright halo of unpolarized starlight. We introduce patterned liquid-crystal techniques and polarization tricks to manipulate the stellar PSF such that it contains a broadband dark hole in which much fainter planetary companions can be detected and characterized. With the 39-m European Extremely Large Telescope that is currently under construction, we aim to provide direct images of rocky exoplanets in the habitable zones of nearby stars, by optimally combining extreme AO with coronagraphy, focal-plane wavefront sensing, polarimetry, and spectroscopy. Once such a planet is detected, we can use spectropolarimetry to unambiguously prove the existence of liquid water, molecular oxygen, and photosynthesis. To provide benchmark observations for such a detection of extraterrestrial life, we are developing a spectropolarimetric Earth-observing instrument (LOUPE) to be mounted on a future lunar lander. In addition, we are performing circular polarization measurements of leaves and bacteria in the lab to establish the ultimate remotely accessible biomarker that is connected to homochirality. Our interest in atmospheres goes beyond astronomical applications, and we have initiated a range of spin-off activities to furnish remote sensing of aerosol particles in our own atmosphere, which is crucial to assess their impact on our health and climate. With a consortium of Dutch institutes we have developed the SPEX instrument concept to characterize atmospheric aerosols through accurate multi-angle spectropolarimetry, based on a novel spectral polarization modulation technique. We have demonstrated breakthrough polarimetric accuracy with this technique, despite the fact that it does not employ any moving parts or active elements. A prototype of a SPEX satellite instrument is now operational on a former spy-plane at 21-km altitude, and we are working towards a flight opportunity on a climate satellite mission. A first ground-based SPEX instrument has been successfully commissioned at an air quality measurement station. In addition, several thousand citizen scientists have used the iSPEX smartphone add-on to provide measurements of atmospheric particle properties that match professional data, and yield the spatial and temporal coverage that professional equipment cannot deliver.
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 16 février, 15h45
Basic Implications of Astrophysical Neutrino Backgrounds for Direct Detection Dark Matter Searches
Diego Aristizabal Sierra (Universidad Tecnica Federico Santa Maria - Departamento de Fisica)

Next-generation dark matter direct detection searches will be subject to unavoidable backgrounds from astrophysical neutrinos (solar, atmospheric and diffuse supernova neutrinos), the so-called neutrino floor. In this talk I will discuss very basic aspects of the physics challenges that the neutrino floor gives and of the opportunities that it provides. I will mention the importance that neutrino non-standard-interactions have on the determination of the background.
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 23 février, 15h45
Planetary Applications for Small Telescopes: Mercury, Io & Comets
Carl Schmidt (LATMOS)

For bright planetary objects, telescopes <1 m can generally offer two simple advantages: time is allocated freely and operational expenses are modest. This talk will give an overview of some current studies of the atmospheres of Mercury, Io and comets using small aperture telescopes. Particular attention is given to the bright sodium component of these atmospheres due to its unique resonant scattering property. Such observations have proved effective in characterizing and disentangling the different processes sustaining Mercury’s thin atmosphere, in which sodium is a primary component. Small near-IR telescopes are an ideal tool to monitor volcanism on Io, and sodium observations provide a valuable proxy for its atmospheric loss processes and interaction with the plasma torus. The relative sodium abundance in cometary comae varies by nearly two orders of magnitude, and is released through a combination of nuclear and dusty grain sources. While the Io observations evidence sodium-bearing molecular ions as a parent species (most likely NaCl+), cometary comae show marked differences between the ion and Na spatial distributions that cannot be attributed to solar radiation pressure or ion pick up.
Séminaire précédant Séminaire suivant 5ème séminaire : vendredi 24 février, 16h00
Are We Alone? Search for Life in the Universe
Pete Worden (Breakthrough Initiatives)

Pete Worden, Chairman of the Breakthrough Initiatives, will lead a talk on the work the Breakthrough Foundation is doing to help humanity investigate the possibility of life forms on other planets, and how scientists can get involved. He will present the Star Shot initiative—a plan to send a spacecraft to another star system in the next 25 years. Dr. Worden will also discuss the Foundation’s other major initiatives: Listen and Watch. Listen is the search for extraterrestrial intelligence using RF (1 GHz to 30Ghz) and visible light. Watch is the search for earth-sized planets in the habitable zone of nearby stars.
Mois précédent Mois suivant Mars 2017
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 02 mars, 15h45
Update on the nearby ultracool dwarf star TRAPPIST-1 and its unique planetary system
Michael Gillon (STAR Institute)

Last year, my team and I announced our detection of three temperate Earth-sized planets around TRAPPIST-1, a very-low-mass red dwarf twelve parsecs away. The discovery made the headlines, because of the potential habitability of the three planets, and their unique suitability for detailed atmospheric characterization, including biosignatures detection, with current technology. During the last eight months, we have intensively followed-up the system from the ground and from space. I will present the results of this follow-up, and how they improve our view of the TRAPPIST-1 system.
Séminaire précédant Séminaire suivant 7ème séminaire : jeudi 09 mars, 15h45
The VLT-FLAMES Tarantula Survey
Hugues Sana (KU Leuven)

The VLT-Flames Tarantula Survey (VFTS) has obtained optical spectroscopy of over 800 OB and Wolf-Rayet stars in the 30 Doradus region with the aim to investigate a number of questions regarding the formation, evolution and final fate of the most massive stars and the dynamics of the region. In this presentation, I will review some of the most important results obtained by the VFTS so far, including the integrated properties of the starburst, the spin distribution and multiplicity of massive stars and the upper initial mass function.
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 16 mars, 15h45
Calculation of Momentum Distribution Function of a Non-thermal
Fermionic Dark Matter

Aritra Gupta (Harish-Chandra Research Institute, Allahabad, India)

The most widely studied scenario in dark matter phenomenology is the thermal WIMP (Weakly Interacting Massive Particle) scenario. Inspite of numerous efforts to detect WIMP, till now we have no direct evidence for it. A possible explanation for this non- observation of dark matter could be because of its very feeble interaction strength and hence, failing to thermalise with the rest of the cosmic soup. In other words, the dark matter might be of non- thermal origin where the relic density is obtained by the so called freeze-in mechanism. Furthermore, if this non-thermal dark matter is itself produced substantially from the decay of another non-thermal mother particle, then their distribution function may differ in both size and shape from the usual equilibrium distribution. In this talk I will discuss about such a non-thermal (fermionic) dark matter scenario in the light of a new type of U(1)B-L model. The model is interesting, since, besides being anomaly free, it can give rise to neutrino mass by Type II see-saw mechanism. Moreover, we will see, that it can accommodate a non-thermal fermionic dark matter as well. Starting from the collision terms, I will briefly outline the calculation of momentum distribution function for the dark matter by solving a coupled system of Boltzmann equations and compare the result with that obtained by using the conventional procedure.
Séminaire précédant Séminaire suivant 9ème séminaire : vendredi 17 mars, 18h00
Ocean forecasting: from descriptive to quantitative science
Nadia Pinardi (Université de Bologne)

Numerical ocean forecasting, as well as weather forecasting, represent a continuous advancement in oceanographic knowledge and the source of inspiration for practical applications of societal relevance. The ocean dynamics is multi-scale and nonlinear, limiting the deterministic predictability to few weeks and requiring statistical and deterministic models of the ocean dynamics to be coupled in an attempt to extend such limits. Moreover ocean forecasting is a unique way to verify theories about the general circulation and its variability. Today, numerical ocean forecasting provides every day the means to verify our knowledge of the oceans and seas. (http://events.ulg.ac.be/oceanconference-dhc-nadia-pinardi/)
Séminaire précédant Séminaire suivant 10ème séminaire : jeudi 30 mars, 15h45
Multiwavelength study of the flaring activity of the supermassive black hole
Sgr A* at the center of the Milky Way

Enmanuelle Mossoux (STAR Institute)

Sgr A* is the closest supermassive black hole, located at the center of our Galaxy at only 8kpc from the Earth. is an extremely low luminosity black hole experiencing several increases of flux (named flares) in near-infrared (NIR), X-rays and radio. On 2011, the DSO/G2 object was detected on its way towards Sgr A*. The goal of my Ph.D. thesis was to study the impact of the pericenter passage of the DSO/G2 close to Sgr A* on the flaring activity.

I first analyzed the 2011 X-ray campaign for the study of Sgr A* to constrain the physical parameters of the flaring region. I then studied the large multiwavelength campaign of 2014 Feb.­-Apr. which includes observations in radio, NIR and X-rays. Thanks to the NIR observations of this campaign, we were able to conclude that the DSO/G2 is a pre­-main sequence star of 1-­2 solar masses emitting by magnetospheric accretion. We observed it after its pericenter passage which occurred on 2014 Apr. 20 which allowed us to conclude that it survived to the tidal forces and that the flaring activity of Sgr A* observed during this campaign is not different from those observed before the DSO/G2 pericenter passage.

I finally reprocessed the X-ray observations of Sgr A* from 1999 to 2015 obtained with XMM-Newton, Chandra and Swift to study the overall X-ray flaring activity. I detected 107 flares during these observations. I computed the detection efficiency of each instrument to compute the intrinsic flaring rate by correcting from the detection bias. I detected a smaller flaring activity for the less energetic flares which occurring between 2013 July 27 and Oct. 28 and a larger flaring activity for the more energetic flares occurring on 2014 Aug. 31. This change of flaring rate can be explained by the energy balance between the decay and the increase of the X-ray flaring rate. The DSO/G2 pericenter passage is thus not needed to explain the change of flaring rate from Sgr A*.
Mois précédent Mois suivant Avril 2017
Séminaire précédant Séminaire suivant 11ème séminaire : jeudi 20 avril, 15h45
Experimental constraints on the differentiation of Planet Mercury
Olivier Namur (ULg - Pétrologie, géochimie endogènes et pétrophysique)

Chemical composition from Mercury’s surface was obtained by the X-Ray spectrometer of the NASA’s MESSENGER spacecraft. Together with high quality photographs, they revealed that the surface of the planet is made up of a secondary volcanic crust. We reproduced some of these compositions in the laboratory and performed high-temperature, low- to high-pressure experiments in furnaces and pistons. We use our experimental data to describe the conditions of Mercury’s differentiation, e.g. formation of the metal core and silicate mantle, the conditions of mantle melting and production of the secondary crust as well as the minerals stable at the surface of Mercury.
Mois précédent Mois suivant Mai 2017
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 04 mai, 15h45
Polarization, X-ray and optical variability of peculiar AGN
Beatriz Agis-Gonzalez (STAR Institute)

Active Galactic Nuclei (AGN) are the focus of observational efforts in every frequency band, from radio to gamma-rays, since they can help us to answer open questions related with extreme gravity, black holes, their formation and fueling. On one hand, X-rays are generated in the innermost regions of the AGN providing us with information about the central black hole. On the other hand, optical polarimetry can provide information on the geometry structures that are below the resolution limit of the telescope. We take advantage of both powerful tools (X-rays and polarimetry) to carry out a deep multi-wavelength (X-ray/optical) study of an interesting and exceptional changing-look AGN: ESO 362-G18.
Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 11 mai, 15h45
Effects on oscillations of high energy neutrinos from Dark Matter
Roberto A. Lineros (Instituto de Física Corpuscular - U.Valencia/CSIC)

The observation of PeV neutrinos has opened a window to study astrophysics and New Physics processes. Among PeV neutrino observables, the neutrino flavor composition become very interesting because it can reveal underlying interactions during the neutrino propagation. We consider the effect of galactic dark matter interactions on the neutrino oscillations. We estimate the effective interaction strength required to produce sizable deviations with respect to expected flavor composition from oscillations in vacuum. In addition, the spatial distribution of dark matter can lead to even larger deviations and can also produce a flavor composition that depends on the neutrino's arrival direction. These features might be observed in neutrino telescopes, like IceCube and KM3NET, depending on the telescope's sky coverage. Also, a positive signal has interesting insights for particle physics models.
Séminaire précédant Séminaire suivant 14ème séminaire : mardi 23 mai, 10h00
Inventer une mission spatiale : L’Innovation fille de l’Audace
Roger-Maurice Bonnet (International Space Science Institute)

Plus de 60 années d’exploration spatiale nous ont montré que les centaines de machines que nous avons envoyées dans l’espace pour en explorer les structures et les limites, ont -pour la plupart- été caractérisées par leur unicité tant scientifique que technique, et aussi par leurs coûts élevés. On dit souvent qu’elles sont innovantes. Est-ce bien vrai puisque leur développement (du moins pour les plus grosses) peut embrasser plusieurs décennies au bout desquelles leurs technologies sont immanquablement obsolètes ? La tendance aujourd’hui, est de céder la place du risque à la prudence et à la précaution afin de ne programmer que les machines dont le niveau technologique est assuré. Est-ce donc la fin de l’innovation ? La gestion du développement de ces machines doit reposer sur une discipline féroce respectant à la fois les coûts et les calendriers afin de ne pas les abandonner en cours de route tout en leur permettant d’être toujours à la pointe dans leur domaine. Le séminaire s’appuiera sur l’exemple de la mission Herschel de l’ESA (d’ailleurs testée au CSL). Il se conclura par quelques réflexions adressées aux générations futures de scientifiques, d’expérimentateurs, de techniciens et de gestionnaires dans le but de leur permettre d’avancer sans avoir à « refaire le Monde » à chaque fois, tout en adoptant l’Innovation et l’Audace comme lignes de conduite en vue d’explorer toujours plus loin, toujours mieux.
Mois précédent Mois suivant Juin 2017
Séminaire précédant 15ème séminaire : jeudi 29 juin, 15h45 
Shaping the flavour sector with CP symmetry of order 4
Igor Ivanov (CFTP, Lisboa, Portugal)

Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.