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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.: 04.366.9779
Fax: 04.366.9729
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Previous month Next month January 2017
Next seminar  1st seminar: thursday 26 january, 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.
Previous month Next month February 2017
Previous seminar Next seminar 2nd seminar: thursday 09 february, 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.
Previous seminar Next seminar 3rd seminar: thursday 16 february, 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.
Previous seminar Next seminar 4th seminar: thursday 23 february, 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.
Previous seminar Next seminar 5th seminar: friday 24 february, 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.
Previous month Next month March 2017
Previous seminar Next seminar 6th seminar: thursday 02 march, 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.
Previous seminar Next seminar 7th seminar: thursday 09 march, 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.
Previous seminar Next seminar 8th seminar: thursday 16 march, 15h45

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.
Previous seminar Next seminar 9th seminar: friday 17 march, 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. (
Previous seminar Next seminar 10th seminar: thursday 30 march, 15h45

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*.
Previous month Next month April 2017
Previous seminar Next seminar 11th seminar: thursday 20 april, 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.
Previous month Next month May 2017
Previous seminar Next seminar 12th seminar: thursday 04 may, 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.
Previous seminar Next seminar 13th seminar: thursday 11 may, 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.
Previous seminar Next seminar 14th seminar: tuesday 23 may, 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.
Previous month Next month June 2017
Previous seminar Next seminar 15th seminar: thursday 15 june, 15h45
Three spiral arms and a protoplanet in the disk of MWC 758
Valentin Christiaens (Universidad de Chile & Université de Liège)

Although more than 3000 exoplanets have been discovered to date, only a handful are protoplanet candidates. The direct imaging of such planets caught at birth could constrain both the location and the timescale within which giant planets form, and hence validate planet formation theories. Using the instrument Keck/NIRC2 equipped with its new VORTEX coronagraph, we obtained new high contrast near-IR images on the Herbig Ae star MWC 758. This system was known to host both a large sub-mm cavity and two spiral arms in its protoplanetary disk, both hinting towards the presence of embedded planets in the disk. Our new images reveal both a bright point-like feature, at roughly 20 au separation, and a third spiral arm. In this talk, I will briefly discuss the nature of the point-like source and argue that it is consistent with being a nascent planet. Then, I will present the geometrical modeling of the spiral arms that allowed us to constrain their origin: one of the spiral arms is likely due to the protoplanet, and the other two could be launched by another companion, yet unseen.
Previous seminar Next seminar 16th seminar: thursday 29 june, 15h45
Shaping the flavour sector with CP symmetry of order 4
Igor Ivanov (CFTP, Lisboa, Portugal)

It is known since long ago that, in quantum field theory, the CP transformation may be of higher order. However no specific example based on such symmetry has been constructed so far. I will present the minimal multi-Higgs model which implements CP symmetry of order 4 (CP4) without leading to accidental symmetries. This single assumption is surprisingly strong: it leads to a unique three-Higgs-doublet model with a well shaped Yukawa sector. After spontaneous breaking of CP4, it can accommodate all fermion masses, mixing, and CP violation, and can also keep the flavor-changing neutral currents under control.
Previous month Next month September 2017
Previous seminar Next seminar 17th seminar: friday 08 september, 15h00
Les débris spatiaux
Christophe Bonnal (CNES)

La situation en orbite terrestre devient préoccupante en raison du nombre croissant de débris spatiaux. Le nombre de gros objets a doublé ces dix dernières années et une collision entre deux satellites a eu lieu début 2009, début d'une longue série. De plus une véritable réaction en chaîne s'est amorcée. Pourtant impossible de se passer des satellites pour les télécommunications, l'environnement et de nombreuses observations scientifiques : l'espace est indispensable, stratégique et globalement irremplaçable. Les réglementations au niveau international ne suffiront peut être pas. Diverses solutions sont envisagées, visant à préserver les opérations spatiales futures et conserver un situation pérenne à long terme en orbite
Previous month Next month October 2017
Previous seminar Next seminar 18th seminar: wednesday 11 october, 10h00
Jupiter's X-ray aurora observed with XMM-Newton and Chandra
William Dunn (University College London - MSSL, ESA and Harvard-Smithsonian CfA)

Jupiter’s X-ray aurora is concentrated into a bright and dynamic hot spot that is produced by precipitating high charge-state ions (e.g. O7+) [Gladstone et al. 2002; Elsner et al. 2005; Branduardi-Raymont et al. 2007]. These highly energetic emissions exhibit pulsations over timescales of 10s of minutes and change morphology, intensity and precipitating particle populations from observation to observation, pole to pole and with solar wind varying conditions. The acceleration process/es that allow Jupiter to produce these high-energy emissions are not well understood, but are concentrated in the most poleward regions of Jupiter's multi-waveband aurora, where magnetic field lines map [Vogt et al. 2015] to the noon-dusk outer magnetosphere [Kimura et al. 2016]. We present XMM-Newton and Chandra X-ray observations from Summer 2016 (during Juno approach) and Spring 2007 (during New Horizons approach), when the observing geometry provided good visibility of Jupiter’s South Pole. These observations reveal that Jupiter’s Southern X-ray aurora also appears to be concentrated into a hot spot. However, X-ray timing analysis suggests that, for these observations, Jupiter’s Northern and Southern polar X-ray aurora behave independently of one another. We finish the seminar by presenting some very initial comparisons between X-ray signatures from the last decade of observations and UV polar emissions at similar (but not simultaneous) times. This is work we hope to continue to build on with your group by testing whether there are connections between simultaneous UV and X-ray observations. This will allow us to further enrich multi-wavelength connections and deepen our understanding of how Jupiter is able to generate its highly energetic polar auroral precipitations.
Previous seminar Next seminar 19th seminar: thursday 12 october, 15h45
The bright future of X-ray polarimetry
Frédéric Marin (Observatoire de Strasbourg)

50 years after the pioneering experiments, X-ray spectroscopy and timing techniques can be considered as well established. Nonetheless, one prominent feature of X-ray light has not been explored as scrupulously as others: its polarization. Between 1980 and 2000, the instruments were not sensitive enough to go beyond the first X-ray polarimetric results acquired in the 70s but the development of new detection techniques in the early 2000s revived the field. The first X-ray spatial mission to fly a new generation polarimeter will be launched by NASA in 2021 and a couple of balloon-borne experiments are being considered. Following the increasing interest of the community to the unexplored phase space of X-ray polarization, I will present the discoveries X-ray polarimetry is about to make.
Previous seminar Next seminar 20th seminar: thursday 19 october, 15h45
Study of comets using TRAPPIST telescope network.
Franscisco Pozuelos Romero (STAR Institute)

Comets are remnants of the early stages of the Solar system and, likely, the most pristine solar system bodies. Understanding their nature and their evolution is a must to understand the history of our Solar System. Comets contain complex organic molecules, and may have played a key role in the transfer of water and organics from the interstellar medium to the early Earth, contributing to the origin of life. This interest is well illustrated by the fact that several space missions have targeted small bodies of the solar system, and particularly comets like the very successful ESA Rosetta/Philae mission currently returning impressive science data that are going to revolutionize our knowledge of comets. The nucleus of a comet, typically a few kilometers in diameter, is essentially composed of water ice mixed with carbon oxides, methane, ammonia, and dust particles. When the comet approaches the Sun, the ices sublimate, forming a gaseous and dusty coma. Solar radiation and wind blow this material to form spectacular cometary tails. Investigations of the chemical composition of comets are important for a variety of reasons. In addition to revealing the characteristics of comets themselves, the composition of comets holds unique clues to conditions in the early solar nebula and the Solar System’s formation processes, since comets remain the most pristine objects available for detailed studies. In particular, knowledge of the bulk chemical composition of comets and how the composition varies among individuals and/or with exposition to solar radiation can provide strong constraints on the composition and temperature of the proto-planetary nebula at the time solid bodies began to form some 4.6 billion years ago. Depending on the region of formation in the protosolar nebula, comets are currently stored in three main reservoirs: the Oort cloud, the Kuiper belt and the main asteroid belt. By studying comets from different reservoirs we can probe the different environments in which they formed, and also better understand their role in the Solar system as suppliers of water and organics.
Previous seminar Next seminar 21st seminar: thursday 26 october, 15h45
Open clusters: Their usage in star formation study
Beomdu Lim (STAR Institute)

Open clusters are one of stellar systems consisting of a few hundreds to thousands of stars. The cluster members are, in general, believed to be a coeval stellar population at the same distance, and therefore they have almost the same properties in chemical composition and kinematics. Owing to these advantages, the clusters are utilized in many astronomy studies, such as the calibrations of distance and stellar age scales, assessments of stellar evolution theories, and the chemical evolution of the Galactic disk. Recently, the advent of high-sensitive instrument allow us to identify cluster members in the wide mass range, and thereby we can provide better descriptions of star formation with large samples. In this talk, I will introduce the usage of these open clusters in star formation studies based on my ongoing work on the stellar initial mass function and an age spread problem.
Previous month Next month November 2017
Previous seminar Next seminar 22nd seminar: thursday 09 november, 15h45
Strongly interacting dark matter doesn't explain the DAMA signal
Maxim Laletin (STAR Institute)

The main strategy of dark matter (DM) direct searches is to look for nuclear recoils from DM particles scattering on the detector medium. Of all the existing DM direct detection experiments only the DAMA experiment claims to observe the characteristic annually oscillating DM signal with the right phase at the significance level of 9.3 σ. Since many other experiments using various methods and having, in principle, better sensitivity to nuclear recoils detect nothing and put severe constraints on the DM mass and cross section, the conventional interpretation of the DAMA results, i.e. weakly interacting DM scattering on nuclei, becomes questionable. One of the possible explanations is related to the model of DM which interacts strongly with the ordinary matter. Given some assumptions about the peculiar features of DM interaction one can expect the signal in DAMA and the absence of any signal in other existing detectors. In my talk I am going to discuss why such kind of models fails to reproduce the DAMA signal.
Previous seminar Next seminar 23rd seminar: thursday 23 november, 15h45
Gravitational waves: origins, detections, implications.
Gustavo E. Romero (IAR, CONICET / University of La Plata, Argentina)

The existence of gravitational waves was predicted by Albert Einstein 100 years ago. Their detection has being extremely elusive and difficult. It was finally achieved with the gigantic laser interferometer LIGO in 2015. Since then, several events produced by the coalescence of binary black hole systems have been detected and measured. In this talk I will review the nature of gravitational waves, discuss how they can be detected depending on their frequency, and elaborate about the implications of this momentous discovery.
Previous seminar Next seminar 24th seminar: thursday 30 november, 15h45
The intimate relationship between ocean and sea ice in the Southern Hemisphere
Olivier Lecomte (Université Catholique de Louvain)

Owing in particular to contrasting geographical situations (Arctic sea ice surrounded by continents, Antarctic sea ice surrounding Antarctica) and much larger ocean – sea ice heat fluxes in the Southern Ocean, the processes governing the seasonal, interannual and multidecadal variability of sea ice are very different from one hemisphere to the other. After a brief contextual setting of Antarctic sea ice with respect to what is known by most about the recent decay of Arctic sea ice, the presentation will give an overview of the processing driving the evolution of Antarctic sea ice. The talk will then cover the various existing hypotheses behind the changes in Antarctic sea ice cover over the last decades, with a focus on ice – ocean interactions, and in a twofold modelling and observational perspective.
Previous month Next month December 2017
Previous seminar Next seminar 25th seminar: thursday 14 december, 15h45
Winds of Magnetic Massive Stars
Asif ud-Doula (Penn State Worthington Scranton, USA)

Massive stars (at least eight times as massive as the Sun) possess strong stellar winds driven by radiation. With the advent of the collaborations such as MiMes and BoB, an increasing number of these massive stars have been confirmed to have global magnetic fields. Such magnetic fields can have significant influence on the dynamics of these stellar winds which are strongly ionized. Such interaction of the wind and magnetic field can generate copious amount of X-rays, they can spin the star down, they can also help form large scale disk-like structures. In this presentation I will discuss the nature of such radiatively-driven winds and how they interact with magnetic fields.
Previous seminar Next seminar 26th seminar: tuesday 19 december, 15h45
On the incidence of MgII absorbers along the blazar sightlines
Sapna Mishra (Aryabhatta Research Institute of Observational SciencES (ARIES))

It is widely believed that the cool gas clouds traced by MgII absorption, within a velocity offset of 5000 km/s relative to the background quasar are mostly associated with the quasar itself, whereas the absorbers seen at larger velocity offsets towards us are intervening absorber systems and hence their existence is completely independent of the background quasar. Recent evidence by Bergeron et al. (2011, hereinafter BBM) has seriously questioned this paradigm, by showing that the number density of intervening MgII absorbers towards the 45 blazars in their sample is nearly 2 times the expectation based on the MgII absorption systems seen towards normal QSOs. Given its serious implications, it becomes important to revisit this finding, by enlarging the blazar sample and subjecting it to an independent analysis. Here, I first report the outcome of our re-analysis of the available spectroscopic data for the BBM sample itself. Our analysis of the BBM sample reproduces their claimed factor of 2 excess of dN/dz along blazar sightlines, vis-a-vis normal QSOs. I have also assembled a ~3 times larger sample of blazars, albeit with moderately sensitive optical spectra. Using this sample together with the BBM sample, our analysis shows that the dN/dz of the MgII absorbers statistically matches that known for normal QSO sightlines. Further, the analysis indicates that associated absorbers might be contributing significantly to the estimated dN/dz upto offset speeds Delta_v = 0.2c relative to the blazar.
Previous seminar Next seminar 27th seminar: thursday 21 december, 15h45
AFTER@LHC : A fixed-target programme at the LHC for heavy-ion, hadron, spin and astroparticle physics
Jean-Philippe Lansberg (I.P.N., U. Paris Sud)

Using the LHC proton and lead beams in the fixed-target mode allows one to study proton-proton and proton-nucleus collisions at a center-of-mass energy per nucleon √sNN ~ 115 GeV as well as lead-proton and lead-nucleus collisions at √sNN ~ 72 GeV with extremely high precision in a completely original kinematical set-up. Such studies, ranging from precision spin physics measurements to innovative quark-gluon plasma studies, can greatly complement conventional collider experiments, in particular those of the EIC project or RHIC (with luminosities larger by 1 to 3 orders of magnitude). In addition, it allows one to explore the large-x QCD frontier for particle and astroparticle physics. After a brief survey of the possible implementations and of selected flagship measurements, I will focus on the case for astroparticle-physics-related studies.
Previous seminar 28th seminar: friday 22 december, 11h00 
Le traitement des binaires spectroscopiques dans le pipeline Gaia
Yassine Damerdji (Center for Research in Astronomy and Astrophysics Geophysics, Algiers)

La mission Gaia donnera accès, pour la première fois, à la la troisième dimension de notre galaxie. En effet, plusieurs millions d'étoiles seront observées en moyenne 50 fois par l'instrument RVS avec une résolution suffisante pour la détection d'étoiles binaires. Le traitement de ces séries temporelles permettra la découverte d'environ un million de binaires spectroscopiques.

Durant ce talk, je décrirai les méthodes utilisées pour la mesure de vitesses radiales des objets assumés étoiles simples mais aussi des objets assumés étoiles doubles. Je parlerai des tests statistiques utilisés pour le repérage d'étoiles binaires et les étoiles variables spectroscopiques et les limites de ces tests.

A la fin, je décrirai l'algorithme de résolution des orbites des étoiles SB1 et SB2 en insistant sur les méthodes de recherche de périodes utilisées. L'établissement de niveaux de signification fiables et le traitement des séries temporelles SB2 "désordonnées" étant nos priorités actuellement.
University of Liège > Faculty of Sciences > Department of Astrophysics, Geophysics and Oceanography : CoWebAGO, June 2009.