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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 2019    
Jan Fév Mar Avr Mai Jun Jul Aoû Sep Oct Nov Déc
Mois précédent Mois suivant Janvier 2019
Séminaire suivant  1er séminaire : mardi 29 janvier, 16h00
The second generation of VLTI: new opportunities
Antoine Mérand (ESO)

I will present the recent results obtained by ESO's Very Large Telescope Interferometer. The VLTI is at the end of a transformation period which started in 2015. With the advent of the two second generation beam combiners, GRAVITY and MATISSE, outstanding results are coming out of this unique facility.
Mois précédent Mois suivant Février 2019
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 14 février, 16h00
Neutrino low-energy interactions beyond the standard model and dark-matter direct searches
Diego Aristizabal Sierra (Santa Maria U., Valparaiso)

Next-generation and next-to-next generation dark matter (DM) detectors will be subject to irreducible solar and atmospheric neutrino backgrounds that will challenge the identification of an actual WIMP signal. In this talk I will discuss the implications that neutrino non standard interactions (NSI) have on this background. I will show that despite the constraints to which NSI are subject they can still leave sizable imprints. They can either enhance or deplete the neutrino background, thus if present they can be discovered in next-generation experiments. Finally, I will comment on the potential experimental differentiation between general vector (of which NSI are a subset) and scalar neutrino-nucleus interactions.
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 21 février, 16h00
Radiative Feedback in Massive Star Formation at Sub-au Length Scales
Nathaniel Dylan Kee (KULeuven)

The process of forming massive stars is a competition between rapid accretion and the growing feedback of the newly born central star, especially though the extreme stellar luminosity and mass loss. However, simulations of massive star formation generally track the infalling gas only to a distance of a few au from the star. To be accreted, material must contend with these feedback processes all the way down to the stellar surface. In this near-star region, the scattering of UV photons off the spectral lines of ionized metal species can generate accelerations tens of times stronger than local gravity, providing a difficult barrier for accretion to overcome. This talk reviews the state-of-the-art in massive star formation, presents simulations of radiative feedback on these final miles of accretion, and discusses the potential role of this feedback in setting the upper mass limit of stars.
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 28 février, 16h00
Gravitational-wave searches with Advanced LIGO and Virgo data: challenges and methods
Sarah Caudill (Nikhef-Virgo)

The recent detections of gravitational waves from binary black hole mergers and a neutron star merger have ushered in the era of multi-messenger astronomy with gravitational waves. Using sophisticated data analysis techniques, these chirp signals were extracted from LIGO and Virgo detector data and clearly distinguished from non-Gaussian noise transients. The methods used by LIGO and Virgo analysis pipelines to find these modeled signals will be discussed. Additionally, techniques used in searches for other sources of gravitational waves including generic transient bursts and continuous signals will be highlighted.
Mois précédent Mois suivant Mars 2019
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 28 mars, 16h00
DustKING: revealing the dust attenuation in nearby galaxies
Marjorie Decleir (U Gent)

Dust attenuation is a crucial but highly uncertain parameter that hampers the determination of intrinsic galaxy properties, such as stellar masses, star formation rates and star formation histories. The shape of the dust attenuation law is proven to vary between galaxies, and within a galaxy. Our DustKING project sets to study these variations in nearby galaxies of the KINGFISH sample. To this aim, we use the CIGALE SED fitting code to fit models with varying dust extinction properties to a multi-wavelength dataset from the UV to the IR. Particularly important for our goal are UV data from the SWIFT space telescope, whose filters uniquely cover the curious bump feature in the attenuation curve at 2175 Å. This enables us to characterize the strength of this bump and the UV slope of the attenuation curve.

In this talk, I will first present the method and results of our spatially resolved study of the spiral galaxy NGC628 (Decleir et al. 2019), which clearly illustrates the potential of the SWIFT data in obtaining the characteristics of the dust attenuation curve. We observe variations in the shape of the attenuation law within the galaxy, but the average curve is fairly steep and has a Milky Way-like bump. Secondly, I will discuss the current status and future goals of our ongoing global dust attenuation curve study of the KINGFISH galaxy sample.
Mois précédent Mois suivant Avril 2019
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 04 avril, 16h00
Exoplanet imaging with NASA/WFIRST: yield predictions and spectrograph development
Christian Delacroix (STAR)

One of the most exciting challenges in exoplanet science is to take pictures of planets in the habitable zones of nearby low mass stars and look for signs of life in their atmospheric composition. This can be achieved by blocking the starlight with a coronagraph instrument (CGI) like the one onboard the Wide Field Infrared Survey Telescope (WFIRST) now in phase B and scheduled for 2025. WFIRST-CGI will demonstrate key technologies for broadband starlight suppression, wavefront control, and ultra-low noise detectors (among others) that will help future flagship missions (e.g. HabEx, LUVOIR) to finally image Earth twins. In this talk, we report on WFIRST science yield simulations with the EXOSIMS software developed at Cornell University, using realistic mission observing constraints, and optimal (dynamically responsive) target scheduling. We also report on our recent development of an Integral Field Spectrograph (IFS) for WFIRST at Princeton University, downstream of a Shaped Pupil coronagraph. Our final lenslet-based design calls for the light in an 18% band around 660 nm to be dispersed with a spectral resolution of 50. We discuss the IFS first light results, reaching a contrast of 10^-5 using in-house focal-plane wavefront control and estimation algorithms with two deformable mirrors.
Séminaire précédant Séminaire suivant 7ème séminaire : jeudi 11 avril, 16h00
Probing dark matter in galactic scales with gravitational lensing
Georgios Vernardos (University of Groningen)

The tension between dark matter theory and observations that exists in sub-galactic scales has given rise to challenging problems, among which the infamous `missing satellites’ and `cusp-core’ problems. Gravitational lensing is a unique tool to address these problems due to its ability to detect dark matter properties and its connection to baryons at cosmological distances. I will present recent advances in the gravitational imaging technique – a method used to reconstruct the lensing potential and the source brightness profile from strong lensing features in observed lenses, like arcs and rings. In particular, a new, general, and powerful statistical treatment will be introduced, which enables the coherent study of small scale dark matter perturbations, or higher order moments in the global lens potential, allowing for a simultaneous derivation of their degeneracies for the first time. An initial application to a few simulated lens systems will be presented as well.
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 25 avril, 14h00
Simulating the late glacial and the deglaciation with a comprehensive climate model
Uwe Mikolajewicz (Max-Planck-Institut f. Meteorologie, Hamburg)

Paleo proxy data indicate strong and rapid climate changes (e.g. Heinrich events or the Younger Dryas cold spell) during the last deglaciation. Here modelling could be very helpful for the interpretation of the proxy data, but the models are not really suited for the simulation of these long time periods, as the boundary conditions (e.g. topography and land sea masks) should not be treated as constant anymore.

A new developed model system consisting of the atmosphere model ECHAM, the ocean model MPIOM, the ice sheet model PISM and the solid earth model VILMA (important for glacial isostatic adjustment) with automatic adaptation of land-sea mask, ocean bathymetry, land orography and river routing designed for long-term simulations is currently in the test phase.

Here results are presented from simulations with different subsystems focussing on the deglaciation. It is shown, that changes in river routing due to retreating ice sheets can explain the occurrence of an abrupt cold event due to a strong reduction of the Atlantic heat transport. Changes in the land-sea mask turned out to be important as well, especially for the late phase of the last deglaciation.

Another focus of the presentation are mechanisms of millennial scale climate variability during the Glacial. In a coupled atmosphere-ocean-northern hemisphere ice sheet model Heinrich events occurred as internal variability. In certain parameter ranges, an atmosphere-ocean model showed long-term fluctuations of the Atlantic overturning which signatures remind of Dansgaard-Oeschger events. The model simulations allow to investigate the underlying mechanisms.
Mois précédent Mois suivant Mai 2019
Séminaire précédant Séminaire suivant 9ème séminaire : jeudi 02 mai, 16h00
Orbital characterization of giant exoplanets and brown dwarfs with VLT/SPHERE
Anne-Lise Maire (STAR)

The monitoring of the orbital motion of young imaged low-mass companions around their star is a powerful tool to measure their orbital parameters, analyze potential dynamical interactions with other bodies in the systems and/or the circumstellar disks, and, for close companions, assess their dynamical mass when combining imaging with radial velocity (RV) and/or astrometry. The advent of the dedicated exoplanet imaging facility SPHERE allowed to measure the position of brown dwarfs and giant planets close to stars down to accuracies of about 1-2 mas. This is possible thanks to the very high contrasts at close-in separations that the instrument delivers and dedicated procedures to monitor the location of the star behind the coronagraph and the scale, orientation, and distortion of the images. As a member of the SPHERE GTO consortium, I developed the tools used to astrometrically calibrate the survey data and carried out orbital studies of low-mass companions observed during the campaign. After briefly presenting the SPHERE GTO survey, I will discuss the orbital properties of the brown dwarf HR 2562B and of the giant exoplanet 51 Eridani b.
Séminaire précédant Séminaire suivant 10ème séminaire : jeudi 16 mai, 16h00
Primordial black holes and merger rate
Hardi Veermae (CERN)

The abundance of primordial black holes (PBH) in the mass range 1−100 solar masses can potentially be tested by gravitational wave observations. In the talk I will focus on our recent results on formation and evolution of PBH binaries in the early universe and discuss the implications for the BH-BH merger rate and the stochastic gravitational wave background.
Séminaire précédant Séminaire suivant 11ème séminaire : jeudi 23 mai, 16h00
Ultracool dwarf stars and temperate planets - the SPECULOOS Survey
Daniel Sebastian (STAR)

The discovery of TRAPPIST-1 planets has revealed that the lowest-mass stars can harbor compact systems of temperate Earth-sized worlds. The SPECULOOS transit survey aims to explore further this planetary population by targeting the ~1000 brightest (K<=12.5) ultra-cool dwarfs (spectral type M7 or later). As TRAPPIST-1, most planets to be found by SPECULOOS should be well-suited for a detailed atmospheric characterization with upcoming JWST and ELTs. In this talk, I will present our newly installed network of robotic observatories, its current status, as well as our first results.
Mois précédent Mois suivant Juin 2019
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 27 juin, 16h00
Unmodelled Searches for Minute-Long Gravitational Waves
Maxime Fays (University of Sheffield)

A third-generation gravitational wave detector might be built right in our back garden, which would bring unprecedented opportunities for ULiège researchers to take part in developing the field of gravitational physics. In this context, searches for unmodelled gravitational waves are accessible and bring the potential to discover new, unexpected physics.

After introducing key concepts in gravitational wave theory and current generation detectors, I will present state-of-the-art techniques used to probe minute-long gravitational waves with minimal assumptions about the signal properties. I will then highlight areas of possible future developments that could benefit from the expertise present in the department. Finally, I will show the application of techniques used for gravitational wave analysis to the medical field.
Mois précédent Mois suivant Août 2019
Séminaire précédant Séminaire suivant 13ème séminaire : mardi 27 août, 16h00
Clusters of primordial black holes
Konstantin Belotsky (NRNU MEPhI)

Primordial black holes (PBHs) are a well-established probe of new physics in the very early Universe. I am going to discuss the possibility of PBH agglomeration into clusters that may have several interesting observable features. The clusters can form due to the production of closed domain walls in the natural and hybrid inflation models whose subsequent evolution leads to PBH formation. Such model inherits all the advantages of uniformly distributed PBHs -- it can possibly explain the early formation of quasars and the rate of binary black hole mergers registered by LIGO/Virgo, these clusters can contribute to the reionization of the Universe. The model also potentially alleviates the existing constraints on the abundance of uniformly distributed PBH, thus allowing clusters of PBH to be a viable dark matter candidate. I am going to show that most of the existing constraints on uniform PBH density should be reconsidered in the case of PBH clustering.
Séminaire précédant Séminaire suivant 14ème séminaire : mercredi 28 août, 16h00
The local positron flux: what do pulsars have to say about it?
Ruben Lopez-Coto (INFN Padova)

Pulsars and their associated nebulae are the most commonly invoked astrophysical sources to explain the highest energy local cosmic ray positrons. However, a recent measurement of particle propagation around nearby pulsars by HAWC combined with the latest measurement of the local cosmic all-electron spectrum up to 20 TeV by HESS seemed to exclude this possibility. I will show in this presentation the latest experimental results on the Very-High-Energy gamma-ray emission surrounding Geminga and PSR B0656+14 by HAWC and discuss their implications. I will also show that the new observational facts can be reconciled with a pulsar origin, even in the case of a low diffusion close to the Earth, if an undiscovered nearby pulsar is the sole contributor to the local electron spectrum at the highest energies. Furthermore, I will give the predicted characteristics of this pulsar and show that the existence of such a pulsar with the required properties is not unlikely taking into account the properties of the pulsar population.
Mois précédent Mois suivant Septembre 2019
Séminaire précédant Séminaire suivant 15ème séminaire : jeudi 12 septembre, 16h00
Configuration mixing of excited baryons in the large Nc limit of QCD
Cintia T. Willemyns (Nuclear and Subnuclear Physics Department, University of Mons)

The asymptotic freedom in QCD allows for accurate calculations at high energy using perturbation theory. At low energies, typical of hadronic systems, a perturbative approach using the coupling constant as the expansion parameter is not appropriate. Baryon spectroscopy has been essential for our understanding of QCD in the low-energy, strong-coupling regime. In this context, the quark model which is based on the spin-flavor group O(3)×SU(2Nf) has since a long time been a useful tool to analyze the spectrum and properties of excited baryons. This symmetry is not something that follows from the fundamental QCD theory. An analytic scheme to study the phenomenology of baryons and their excited states, whose connection with QCD is clearly stated, can be obtained by generalizing QCD from three colors and an SU(3) gauge group to Nc colors and an SU(Nc) gauge group. In this talk, I will present a complete analysis of the masses of the positive parity excited baryons in the quark model O(3)×SU(6) multiplets contained in the N=2 band in the large Nc limit. We find that the mixing of the spin-flavor states is much simpler than what is naively expected in the quark model. The obtained mass degeneracies and mixing pattern constitute a signature of the contracted spin-flavor symmetry for baryons in this limit.
Mois précédent Mois suivant Octobre 2019
Séminaire précédant Séminaire suivant 16ème séminaire : jeudi 03 octobre, 16h00
Gautier Mathys (ESO)
Séminaire précédant 17ème séminaire : vendredi 11 octobre, 11h00 
Steve Ertel (Université d’Arizona.)
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.