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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
Fast rewind Previous year Seminars: Archives 2023    
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Previous month Next month January 2023
Next seminar  1st seminar: thursday 12 january, 16h00
Atmospheric Reconnaissance of Trappist-1b and Trappist-1g with JWST
René Doyon (Université de Montréal)

Prof. Doyon will present us exciting (and unpublished yet) first results gathered by Program 2589 for two of the seven Earth-sized planets of the system, including one orbiting within the habitable zone of the star.
Previous month Next month February 2023
Previous seminar Next seminar 2nd seminar: thursday 16 february, 16h00
Parameter estimation in Cosmology with Cobaya and Machine-Learning
Jesus Torrado (Padova University)

I will briefly present Cobaya, an inference framework aimed at model pipelines with complex interdependencies between parameters and intermediate quantities, and use it to illustrate some aspects of classic Bayesian inference in Cosmology. Next, I will discuss the effort by me and my collaborators towards a no-pre-training, drop-in replacement for classical parameter inference on very slow posteriors, using a Gaussian Process surrogate model that actively learns the posterior distribution and converges in O(100) fewer evaluations.
Previous month Next month March 2023
Previous seminar Next seminar 3rd seminar: thursday 23 march, 16h00
Probing gravity and its fundamental properties with radio pulsars
Paulo Freire (Max-Planck-Institut für Radioastronomie, Bonn, Germany)

Over the last few years, a set of new results from pulsar timing has not only introduced some of the most precise tests of general relativity (GR) done to date, but have also introduced much tighter constraints on violations of a fundamental principle, the strong equivalence principle (SEP), which is embodied by GR. This was done via a direct verification of the universality of free fall for a pulsar in a triple star system and with tests of the nature of gravitational waves, in particular a search for dipolar gravitational wave emission in a variety of binary pulsars with different masses. No deviations from the SEP have been detected in our experiments. These results introduce some of the most stringent tests of GR, which introduce the tightest constraints on several classes of alternative theories of gravity and complement recent results from the ground-based gravitational wave detectors.
Previous seminar Next seminar 4th seminar: thursday 30 march, 16h00
2.5D FRADO: Simulation of the dynamics and geometry of broad line region in quasars
Mohamad Naddaf (Center for Theoretical Astrophysics, Warsaw, Poland)

Broad emission lines are the most characteristic feature in the quasar’s spectra, known since 60 years. There have been many attempts to explain the formation and geometry of broad line region in active galaxies via different scenarios. The most successful non-ad-hoc physically-motivated model during the last decade which consistently explains the formation of low-ionized broad emission lines in the spectra of quasars and provides the information on the location of broad line region is the failed radiatively accelerated dusty outflow (FRADO) model. The model currently available in the 2.5D advanced version, which I developed, has taken very progressive concrete steps toward establishing the FRADO model as a new standard. The model is so far successfully tested with observational and dynamical features including radius-luminosity relation and shape of emission line profiles etc. I will review all the progress with the model and new tests and prospects.
Previous month Next month April 2023
Previous seminar Next seminar 5th seminar: thursday 20 april, 16h00
I. Search for amino acids in star-forming regions (S. Iglesias-Groth). II. Plans for high-contrast imaging at IAC (R. Rebolo).
Rafael Rebolo & Susana Iglesias-Groth (Instituto de Astrofísica de Canarias)

I. Amino acids are the building blocks of proteins. I will present current efforts to detect mid-IR bands of amino acids in star-forming regions. Using Spitzer IRS spectra of the gas in various star-forming regions, we find evidence for the strongest mid-IR bands of common molecules as H2, OH, H2O, CO2 and NH3 and of several carbonaceous molecules which may play an important role in the production of more complex hydrocarbons: HCN, C2H2, C4H2, HC3N, HC5N, C2H6, C6H2, C6H6, PAHs and fullerenes. In addition, evidence for the most prominent mid-IR bands of several amino acids will be reported with a preliminary estimate of their abundances in the diffuse gas of these regions.

II. Results on our RV searches for terrestrial exoplanets using HARPS (North and South) and ESPRESSO will be reported. In addition, I will present a description and status of the project for an AO-based nulling interferometer in the near-IR, small-ELF, with a diameter of 3.5m to be installed at Teide Observatory. This is a technology demonstrator for new light-mirror technologies, mechanical concepts and AI control of adaptive optics and a pathfinder for the construction of much larger diameter systems able to perform imaging of terrestrial planets from the ground.
Previous month Next month June 2023
Previous seminar Next seminar 6th seminar: thursday 01 june, 16h00
Small bodies and Large Surveys
Benoît Carry (Observatoire de la Côte d'Azur, France)

The small bodies (asteroids, comets, and Kuiper-belt objects) are the remnants of the blocks that accreted to form the planets 4.6 Gyrs ago. Their importance as witnesses of the Solar System history emerged in past decades, but the current description of their dynamical, surface, and physical properties is insufficient to guide theoretical works.

I will describe how astronomical sky surveys can be mined for Solar system objects. Over the last few years, this approach has provided samples much larger than decades of targeted observations, by extracting observations from, e.g., VISTA, SDSS, and Gaia surveys. I will highlight the strength of this approach with examples that changed our understanding of the asteroid population.

Finally, I will present a prospective of the contribution of the ESA Euclid mission to Solar system science. Scheduled for launch next July, Euclid will conduct a six-years visible and near-infrared imaging and spectroscopic survey over 15,000 sq. deg down to 24.5 mag. Although the survey will avoid ecliptic latitudes below 15$^circ$, the survey pattern in repeated sequences of four broad-band filters is well-adapted to Solar System objects detection and characterization. I will present how Euclid will constrain the orbits of Soalr system objects, their morphology (activity and multiplicity), physical properties (rotation period, spin orientation, and 3-D shape), and surface composition.
Previous seminar Next seminar 7th seminar: monday 12 june, 16h00
Strong lensing of gravitational waves, results and challenges
Justin Janquart (Universiteit Utrecht)

Like electromagnetic signals, gravitational waves can undergo gravitational lensing when a massive object (e.g. galaxy or galaxy cluster) is present on the path from source to observer. For gravitational waves, lensing manifests itself as repeated events with the same frequency evolution but magnified, phase-shifted, and arriving at different times. Depending on the lens, the time delay can go from seconds to months. According to current forecasts, there are real chances of observing lensing in the Advanced LIGO and Advanced Virgo in the coming years. Computationally, finding lensed events is a real challenge as one needs to analyze all the event pairs present in the data, and more when accounting for sub-threshold events. Additionally, there is a serious risk of false claims as events can resemble each other by chance. Here, we start by presenting some search techniques and avenues to address challenges related to the detection of strong lensing. Then, we present the most recent results from the LIGO-Vigo-KAGRA collaboration. We conclude by outlining the perspective for gravitational wave lensing with possible applications.
Previous seminar Next seminar 8th seminar: thursday 15 june, 16h00
A Collage of Exoplanets on the Mass-Radius Diagram
Ji Wang (Ohio State University)

I will talk about different populations of exoplanets and their interconnection. Specifically, I will present chemical composition measurements for hot Jupiters and directly-imaged young jovian planets, in an attempt to answer questions such as how stellar chemical composition controls the planet formation; how the difference of planetary and stellar chemical abundance reveals the history of orbital migration. In addition, I will highlight the recent progress in comparative planetology by contrasting (1) small planets with different densities and structures; and (2) Earth-size rocky planets vs. gas dwarf planets in the habitable zone. These comparative studies shed light on the origin of the diverse outcome of planet formation and the search for biosignatures with current and future facilities.
Previous month Next month September 2023
Previous seminar Next seminar 9th seminar: friday 22 september, 11h00
A Mechanism for creating the hard X-rays of gamma Cas (B0.5e): Clues from Multi-wavelength Observations
Myron Smith (NOIRlab, Tucson, Arizona, USA)

In this talk the X-rays of gamma Cas will be examined. gamma Cas is the prototype of a subgroup of Be stars, the spectra of which exhibit hydrogen line emission, a signature of episodically ejected, flattened disks. Members of the gamma Cas subgroup also emit X-rays ~30 times more intense than the X-rays produced by winds of normal B and Be stars, and host an equally greater high plasma temperature. The mechanism responsible for this emission has been long debated. I will confine attention to one that is most consistent with observations, one positing magnetic interactions between gamma Cas and its disk. In this scenario, small-scale magnetic fields extending from the Be star entangle with a toroidal disk field. The stresses so produced release high energy particle beams that impact the star's surface explosively, resulting in observed X-rays 'flares.' This explanation is implied by correlations of X-ray, UV, and optical light curves. The narrative is also supported by features in X-ray spectra. Altogether, observations suggest an environment near gamma Cas stars unlike from those near other hot massive stars, though there are some similarities to magnetospheres of cool stars, including the Sun.
Previous seminar Next seminar 10th seminar: thursday 28 september, 10h00
Enhancing stellar characterization through seismic inversions: selected insights and future prospects
Jérôme Bétrisey (Université de Genève)

With the rapid development of asteroseismology in the last two decades thanks to space-based photometry missions such as CoRoT, Kepler, and TESS, stellar characterisation has reached unprecedented levels. The field will further develop with the future PLATO mission, to be launched in 2026. The data quality of these missions enables the use of cutting-edge techniques, the so-called seismic inversions, until then restricted to helioseismology, where they were applied with tremendous success. One of the key challenges of PLATO is the precision requirements on the stellar mass, radius, and age, for which these inversion techniques will play a key role. It is therefore crucial to compare how current modelling strategies perform, and discuss the limitations and remaining challenges for PLATO, such as the so-called surface effects, the choice of the physical ingredients, and stellar activity. In this context, I will present the developments and improvements I carried out during my PhD to achieve an even more precise and accurate stellar characterization, following two guiding principles, refining the modelling strategies, and better constraining the physics in stellar models.
Previous seminar Next seminar 11th seminar: friday 29 september, 16h00
My scientific legacy: are the universe and cosmology inside a black hole?
Pierre Magain (AGO)
Previous month Next month October 2023
Previous seminar 12th seminar: thursday 05 october, 16h00 
Semi-annihilating Z3 scalar dark matter model and gravitational waves
Maxim Laletin (National Centre for Nuclear Research (NCBJ), Warsaw, Poland)

We study dark matter phenomenology with early kinetic decoupling, cosmic phase transitions and their gravitational wave signal in the semi-annihilating Z3 dark matter model, whose dark sector comprises of an inert doublet and a complex singlet. We take into account constraints from perturbativity, unitarity, vacuum stability, electroweak precision tests, direct detection and LHC measurements of the Higgs boson. We discuss the prospects for direct detection searches and gravitational wave searches.
University of Liège > Faculty of Sciences > Department of Astrophysics, Geophysics and Oceanography : CoWebAGO, June 2009.