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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
Recul rapide Année précédente Séminaires : Archives 2023    
Jan Fév Mar Avr Mai Jun Jul Aoû Sep Oct Nov Déc
Mois précédent Mois suivant Janvier 2023
Séminaire suivant  1er séminaire : jeudi 12 janvier, 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 Doyon will present us exciting (and unpublished yet) first results gathered by Program 2589 for two of the seven Earth-sized planets of the system, including one orbiting within the habitable zone of the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.
Mois précédent Mois suivant Février 2023
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 16 février, 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.
Mois précédent Mois suivant Mars 2023
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 23 mars, 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.
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 30 mars, 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.
Mois précédent Mois suivant Avril 2023
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 20 avril, 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.
Mois précédent Mois suivant Juin 2023
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 01 juin, 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.
Séminaire précédant Séminaire suivant 7ème séminaire : lundi 12 juin, 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.
Séminaire précédant 8ème séminaire : jeudi 15 juin, 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.
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.