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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 Année suivante  
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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 Doyon will present us exciting (and unpublished yet) first results gathered by Program 2589 for two of the seven Earth-sized planets of the system, including one orbiting within the habitable zone of the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 Séminaire suivant 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.
Mois précédent Mois suivant Septembre 2023
Séminaire précédant Séminaire suivant 9ème séminaire : vendredi 22 septembre, 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.
Séminaire précédant Séminaire suivant 10ème séminaire : jeudi 28 septembre, 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.
Séminaire précédant Séminaire suivant 11ème séminaire : vendredi 29 septembre, 16h00
Mois précédent Mois suivant Octobre 2023
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 05 octobre, 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.
Mois précédent Mois suivant Novembre 2023
Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 09 novembre, 16h00
Bolometric Corrections from a Large Multi-Wavelength Study of Nearby Unobscured AGN
Kriti Gupta (AGO)

Accreting supermassive black holes or Active Galactic Nuclei (AGN) are powered by mass accretion and emit electromagnetic radiation mainly at optical, ultraviolet, and X-ray wavelengths. Hence, a detailed analysis of the multi-wavelength spectral energy distributions (SEDs) of AGN can provide fundamental insights into their accretion properties. A complete and consistent study of broadband AGN SEDs can be used to estimate what fraction of the total accretion luminosity of AGN is emitted at different wavelengths (bolometric corrections), additionally shedding light on how the X-ray coronal emission and the optical/UV disk emission are linked.

In my work, I used an almost unbiased sample of hard-X-ray-selected AGN in the local universe. All these sources have multi-wavelength coverage thanks to the BAT AGN Spectroscopic Survey (BASS). I compiled and processed high-quality, simultaneous, optical, UV, and X-ray data for my sample of 240 unobscured AGN to construct and fit their optical to X-ray SEDs. In this talk, I will present the main results from my Ph.D. research, including optical to X-ray spectral indices and optical, UV, and X-ray bolometric corrections over a wide range of black hole masses, luminosities, and Eddington ratios. I will discuss the key parameters regulating these bolometric corrections and also mention the implications of my results on our current understanding of accretion flow and emission arising in the innermost regions of AGN.
Séminaire précédant Séminaire suivant 14ème séminaire : jeudi 23 novembre, 16h00
Strong lensing: Illuminating galaxy clusters and the structures behind them
Guillaume Mahler (AGO)

The strong gravitational lensing effect is a powerful technic to study both the deflector of light and the magnified sources behind it. In this talk, I will first review mass modeling approaches of galaxy clusters and present a state-of-the-art lensing model combining at the same time HST or JWST imaging with large spectroscopic coverage. Such a combination allows us to have a detailed mass distribution of both dark matter and baryonic masses of a cluster of galaxies. Furthermore, previous analysis of a large sample of strong lensing clusters reveals that the lensing strength has a stronger correlation with the slope of the density profile rather than the total mass itself, indicating that the details of the mass distribution are more important than the total mass for future surveys. Additionally, I will present recent analyses revealing how cluster lens models could be a new probe for cosmology with giant arcs being sensitive to wandering supermassive black holes (SMBH). The second part of the talk will focus on the lensed universe. Strong lensing offers unique opportunities that have no match in blank fields, from the highly magnified galaxies at z~2, resolved by lensing down to tens of pc scales, to the high-redshift lensed luminosity function that reaches fainter and smaller sources, Finally, I will discuss how the JWST and future facilities such as Rubin or Euclid combined with strong lensing will revolutionize our view of the universe in the near future.
Séminaire précédant Séminaire suivant 15ème séminaire : jeudi 30 novembre, 16h00
The needs and means of Galactic magnetic field tomography
Vincent Pelgrims (ULB)

Magnetic fields are ubiquitous in our Galaxy and influence the detailed study of extragalactic and cosmological signals. The Galactic magnetic field makes it difficult to understand the sources of ultra-high-energy cosmic rays and to study extragalactic magnetic fields. Moreover, coupled to the Galactic magnetic field, matter in the interstellar medium produces polarized emission that prevents us from detecting primordial B modes in the polarization of the cosmic microwave background, and thus from validating the cosmological scenario of primordial inflation. In this talk, I will review some of the observations demonstrating the need to take into account the three-dimensional geometry of the Galactic magnetic field in these research areas. I will then discuss how the polarization of starlight helps in this topic, and present recent developments towards the first tomographic map of the magnetized interstellar medium. I will discuss these results in the context of ongoing efforts and the promise of future surveys such as Pasiphae.
Mois précédent Mois suivant Décembre 2023
Séminaire précédant Séminaire suivant 16ème séminaire : jeudi 07 décembre, 16h00
Electro-dynamic moon-magnetosphere interactions in our Solar System
Bertrand BONFOND (University of Liège)

The electro-dynamic interactions between moons and the magnetosphere of their host planets have been investigated since the mid-20th century and the implication of the Alfvén waves was recognized right away. However, in the first models, Alfvén waves were only considered as current carriers. It is only after the Voyager missions that the possibility of complex reflection patterns was considered and their ability to accelerate particles became fully appreciated only recently. For this seminar, I will review the history of our understanding of the various cases of moon-magnetosphere interactions in our Solar System. The presence of the largest of these moons in the stream of the magnetospheric plasma generates powerful large-scale Alfvén waves, which can break up into smaller scales, reflect off density gradients and accelerate particles, ultimately impacting the atmosphere of the planet to generate auroras and trigger radio emissions. The best-known case is the Io-Jupiter interaction, since its observational signatures are the richest and most obvious. As our means of investigation improved, signatures of similar interactions have also been discovered for the other Galilean moons, as well as for moons orbiting Saturn. Interestingly, similar interactions can occur on rare occasions between the planets themselves and the solar wind and most likely take place in exo-planetary systems as well.
Séminaire précédant 17ème séminaire : jeudi 14 décembre, 16h00 
Star-Planet Interactions: How the structural and rotational properties of the host star shape the evolution of exoplanetary systems
Camilla Pezzotti (AGO)

The great variety of exoplanets discovered in the last few decades has revealed an incredible richness in their architectures, planetary compositions, and host star properties. In this context, many questions have been raised about the mechanisms driving the formation and evolution of these systems as a whole. Thanks to the increasing amount of data provided by ground and space-based missions, key features on exoplanetary systems and populations have been revealed. Nevertheless, a comprehensive and detailed understanding of the mechanisms governing their evolution is still missing.

Since the earliest formation stages, stars interact with their orbiting planets (through tides, radiation, magnetic fields, stellar winds …), determining their properties, shaping the architecture of their systems and governing their final fate. All these interactions intimately depend on the structural and rotational properties of the host star, and for certain system’s evolutionary phases, some interactions may dominate over others. Accounting for a detailed description of the host star’s evolution is thus crucial in the attempt to unveil the processes that concurred in forming and characterizing different exoplanetary systems.

In this seminar, I will talk about the impact of tidal and radiative interactions on the evolution of star-planet systems. I will show the results obtained by simulating the evolution of systems under the simultaneous impact of these two interactions, for which the structural/rotational evolution of the host star is coupled to the one of the planet. The properties of real exoplanetary systems (Kepler-444, TOI-849, …) will be investigated, showing that star-planet interactions may establish key constraints (predictions) on their past (future) evolution.
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.