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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 2022 Année suivante  
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Mois précédent Mois suivant Mars 2022
Séminaire suivant  1er séminaire : jeudi 03 mars, 16h00
Gravitational Wave Astronomy and Physics with Strong Lensing of Binary Mergers
Srashti Goyal (LIGO and International Centre for Theoretical Sciences, Bengaluru)

Gravitational lensing has been one of the main tests of Einstein's theory of relativity. Like light, gravitational waves can also get lensed and we might be able to detect this with the current ground based gravitational waves observatories. I will talk about the various prospects for the search of gravitational waves lensing signatures. Further, I will mention two of my research works, 1. polarisation tests of general relativity using strongly lensed signals and 2. identifying strongly lensed signals using machine learning.
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 10 mars, 16h00
Multidisciplinary monitoring of the active submarine volcanism of the Canary Islands and its physical-chemical and biological perturbation on the marine ecosystem: El Hierro (2011) and La Palma (2021)
Eugenio Fraile Nuez (Spanish Institute of Oceanography (IEO-CSIC))

Submarine volcanoes and active hydrothermal vents affect marine ecosystems in very different ways. The VULCANA project of the Spanish Institute of Oceanography (IEO-CSIC) in Spain has two fundamental objectives: (i) carry out exhaustive monitoring of the physical-chemical, biological and geological properties of active submarine eruptive processes. (ii) provide a response through science to the requirements of the public institutions of the Spanish State for decision-making in emergency situations and the safety of the population. In this talk, we will describe not only the facts that occurred during these two seismic-volcanic crises, the eruption of the underwater Tagoro volcano on the island of El Hierro (2011) and the eruption of the volcano at Cumbre Vieja, La Palma (2021) with the generation of lava deltas and marine damage, but also some of the scientific milestones that our research team has been able to demonstrate with the data collected.
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 17 mars, 16h00
VLT/FORS2 optical imaging polarimetry: the active galactic nucleus in Circinus
Djordje Savic (STAR)

Recent high angular resolution observations resolved for the first time the mid-infrared (MIR) structure of nearby active galactic nuclei (AGN). Surprisingly, a major fraction of their MIR emission comes from the polar regions. This is at odds with the expectation based on AGN unification, which postulates a dusty torus in the equatorial region. An archetype, the Circinus galaxy offers one of the best opportunities for studying the AGN central engine in greater details. The observations were carried out with VLT/FORS2 instrument in optical imaging polarimetry mode operating in U, B, V and R filters. Since polarimetry is highly sensitive to geometric and orientation effects, we built a model for simulating dust scattering. We used the 3D Monte Carlo radiative transfer code SKIRT for obtaining optical polarization maps. The host galaxy foreground extinction as well as the starlight emission was taken into account. Finally, we compare the results of simulations with observations.
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 24 mars, 16h00
Colliding Black Holes, Exploding Stars and the Dark Universe: Status and Prospects for Gravitational-Wave Astrophysics
Tjonnie Li (KU Leuven)

In 2015, scientists discovered ripples in the fabric of spacetime from the violent collision of two black holes, now known as gravitational waves. These gravitational waves are now detected at a rate of once per week by kilometre-scale detectors, giving scientists a rare insight into black holes and the Universe. Next-generation detectors, including one proposed in the Dutch-Belgian border area, may observe up to a million gravitational-wave signals per year from various known and unknown types of sources.I will review some of the existing results and discuss several exciting opportunities for gravitational-wave astrophysics.
Mois précédent Mois suivant Avril 2022
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 28 avril, 16h00
Comprehensive investigation of fast-rotating Galactic O stars and B supergiants. From where do they come from?
Nikolay Britavskiy (STAR)

Rotation is one of the important parameters affecting the evolution and final fate of massive stars but the origin of fast rotators remains unclear (imprint of the star formation process, result of binary interactions). In this work, we aim at investigating the binary status, photometric variability, and runaway status of a statistically meaningful sample of Galactic fast-rotating O stars and B supergiants. We perform a comprehensive multi-epoch analysis of new high-quality spectroscopic observation gathered within the different surveys. We notably found that fractions of one- and two-component binary systems in the slow- and fast-rotating O-type domain are similar to each other and equal to ~22%. However, the fraction of runaway stars in the fast-rotating domain (~35-50%) is significantly higher than in the slow-rotating domain (~20-30%) for the massive O-type stars. By combining all these observational results we will evaluate each scenario about the origin of fast-rotators.
Mois précédent Mois suivant Mai 2022
Séminaire précédant Séminaire suivant 6ème séminaire : mardi 17 mai, 16h00
Surprises from MAVEN at Mars: Aurora, meteor showers, and a new paradigm for Mars’ missing water
Nick Schneider (University of Colorado, College of Arts and Sciences, Astrophysical & Planetary Sciences , LASP)

The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft carries the Imaging Ultraviolet Spectrograph (IUVS) to study the Mars atmosphere and atmospheric escape. After nearly three Mars years in orbit, IUVS has gained new insights on key phenomena at Mars including dayglow, nightglow, aurora, meteor showers, clouds, solar-planetary interactions and atmospheric evolution. In this presentation, I will highlight three key results obtained by IUVS:

(1) Mars exhibits a surprisingly high level of auroral activity of three distinct types;

(2) Comet Siding Spring caused the solar system’s largest meteor shower in modern times;

(3) Mars dust storms dramatically enhance water loss from the planet.

I’ll conclude with a discussion of the implications of these findings for understanding Mars atmospheric dynamics and evolution.
Mois précédent Mois suivant Juin 2022
Séminaire précédant Séminaire suivant 7ème séminaire : jeudi 16 juin, 16h00
Direct Imaging of Newborn Planets and the Curious Case of CQ Tau
Iain Hammond (Monash University (Australia))

One of the great unsolved problems in astrophysics is the formation and early evolution of systems with embedded planets. Since the first exoplanet detection in 1995, thousands of confirmed planets and companions have been observed through a variety of observational techniques - primarily indirect methods such as transit and radial velocity. This has resulted in a detection bias towards planets with short orbital periods in main sequence systems. Direct imaging of planets has grown rapidly and become feasible in the last decade thanks to adaptive optics systems, dedicated telescopes, coronagraphs and evolving image processing techniques. With new directly imaged planets we are able to begin populating our parameter space to better understand the occurrence rate of large planets on wide orbits - however this is not without its challenges. I will present an overview of the field of direct imaging, the indicators of planet presence in protoplanetary discs, and our analysis of disc structures in CQ Tau.
Mois précédent Mois suivant Septembre 2022
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 08 septembre, 16h00
JWST in 2022: unfolding, aligning and revolutionary capabilities
Laurent Pueyo (STSci)

In this seminar I will discuss how, over the course of half a year, JWST transitioned from stowed and folded inside the Ariane rocket to a transformational machine for astronomical observations. The focus of this presentation will be two-fold. First, I will discuss the challenges the team encountered and overcame when phasing the telescope, starting with millimeter deployment residuals all the way to stability tests showing drifts of tens of nanometers over periods of a few days. I will then discuss the scientific capabilities of the observatory, measured during science commissioning, that directly flow from these optical performances. I will discuss all four key science themes, The End of the Dark Ages, Assembly of Galaxies, Birth of Stars and Planetary Systems +the Origins of Life, and emphasize observations pertaining as they are the most impacted by optics alignment quality. I will conclude by presenting a few representative Early Release Science results and discuss what JWST capabilities mean for the future of exoplanetary science.
Séminaire précédant Séminaire suivant 9ème séminaire : jeudi 15 septembre, 16h00
Radar and polarimetry as a tool to study potentially hazardous asteroids
Maxime Devogèle (Arecibo Observatory)

Every year more and more near-Earth objects (NEOs) are discovered with 3000 NEOs discovered in the last 12 months. Moreover, their rate of discovery is expected to increase by at least one order of magnitude with the upcoming Vera Rubin Telescope and NEO surveyor mission. An NEOs is defined as any object in the Solar System whose orbit display a perihelion distance smaller than 1.3 astronomical unit. As their name suggest and as a consequence of their definition based on their orbit, these are the objects that can perform close approaches to the Earth.

After the discovery of Apophis in 2004 and its high probability of impact 2029 and 2036 the American congress mandated NASA to discover 90% of the NEOs larger than 140m by 2020. Moreover, after the impact of an unknown ~20m object in Chelyabinsk (Russia) in 2013 the Planetary Defense Coordination office (PDCO) was created to oversee planetary defense objectives. Since then, the planetary defense community is working to discover, assess the threat, and characterize potentially hazardous objects. Last year, the first planetary defense mission (Double Asteroid Redirection Test; DART) was launched to impact the moon of the asteroid Dydimos on September 26 of this year to study asteroid deflection techniques

In this talk I will discuss the importance of planetary radar for planetary defense. The planetary radar system that was present at the Arecibo Observatory before the Dec 1st 2020 collapse will be discussed. I will then talk about how to use radar data and combine them with optical observations, such as polarimetry, to determine the size and albedo of potentially hazardous NEOs.
Séminaire précédant Séminaire suivant 10ème séminaire : jeudi 22 septembre, 16h00
Searching for long-duration transient gravitational waves from glitching pulsars using Convolutional Neural Networks
Luana Modafferi (Universitat de les Illes Balears and LIGO)

Pulsars are spinning neutron stars which emit an electromagnetic beam. We expect pulsars to slowly decrease their rotational frequency due to the radiation emission. However, sudden increases of the rotational frequency have been observed from different pulsars. These events are called "glitches", and are followed by a relaxation phase with timescales from days to months. Gravitational-wave (GW) emission may follow these peculiar events, including long-duration transient continuous waves (tCWs) lasting hours to months. These are modelled similarly to continuous waves but are limited in time. Previous studies have searched for tCWs from glitching pulsars with matched filtering techniques and by computing a detection statistic, the F-statistic. This method is very sensitive, but the computational costs can easily increase when widening the frequency and spindown search bands and the duration of the potential signals.

In order to reduce computational and human effort, we present a procedure for detecting potential tCWs using Convolutional Neural Networks (CNNs). For our initial configuration, we train the CNN on F-statistic "atoms", i.e. quantities computed during the matched filtering step from signal/noise data. This still constrains the frequency evolution of the signal to be continuous-wave-like, but already allows for flexible amplitude evolution and significant speed-up compared to the traditional method.
Mois précédent Mois suivant Octobre 2022
Séminaire précédant Séminaire suivant 11ème séminaire : jeudi 06 octobre, 16h00
The Perkins INfrared Exosatellite Survey (PINES): Survey Overview and Transit Candidates
Patrick Tamburo (Boston University)

The Perkins INfrared Exosatellite Survey (PINES) is a search for transiting planets and moons around a sample of almost 400 L and T dwarfs, objects that occupy a largely unexplored region of exoplanet parameter space. The survey is performed at near-infrared wavelengths (J- and H-bands) with Boston University's 1.8-m Perkins Telescope Observatory in Flagstaff, Arizona, and the photometric performance permits the detection of 2.5-Earth-radius planets and larger around our median brightness targets. In this talk, I will provide an overview of the PINES survey, describing our facility, target sample, observing strategy, and photometric performance. I will also describe a detection algorithm that we developed to search for single transit candidates in sparse PINES data. Finally, I will discuss the two candidates that this algorithm has identified in our data so far, one of which is feasibly due to a transiting companion. I will detail our follow-up efforts on this candidate and potential implications for L and T dwarf planet occurrence rates if the candidate can be confirmed.
Séminaire précédant Séminaire suivant 12ème séminaire : jeudi 13 octobre, 16h00
Seasonal evolution of mesoscale eddies on the vertical : observation from surface temperature and mixed layer in the Mediterranean sea.
Alexandre Barboni (Laboratoire de Météorologie Dynamique, Ecole Polytechnique, 91128 Palaiseau, France)

Mesoscale eddies have a signature on many ocean physical properties, such as sea surface temperature (SST), vertical density distribution, and the mixed layer driven by atmospheric fluxes. However these eddy signatures were studied in without temporal variations, and using composite smoothing individuals structures. In particular anticyclones were thought to always show warm SST anomalies and slightly deepens the mixed layer depth (MLD), whereas cyclones show cold SST signature and have shallower MLDs. Recent observations in the Mediterranean sea with high resolution images show a significant seasonal cycle of the eddy-induced SST signature, shifting from surface warm anticyclones in winter to cold core signature in summer, coinciding with spring restratification, and the opposite for cyclones. In the vertical, several Argo floats being trapped for months in long-lived Mediterranean anticyclones, allow one to follow the seasonal inside-eddy evolution. The winter MLD deepening is stronger in anticyclones, MLD continuing to cool and deepen at the anticyclone core one month longer on average. Mixed layer connexion with a preexisting subsurface anticyclonic core are recorded and can lead to extreme MLD anomalies deeper than 300 m. On the opposite a winter mixed layer remaining separate from deeper core leads to a double-core anticyclone. Seasonal evolution observed with high resolution measurements highlight the complexity of mesoscale eddy signature and interaction between surface, mixed layer and subsurface density anomaly. These interactions could be key for the eddy impact on its lifetime, physical and biological impact.
Séminaire précédant Séminaire suivant 13ème séminaire : jeudi 27 octobre, 16h00
Is your multi-planet system stable? Reflexions on chaos and its utility
Manu Stalport (Université de Genève)

The formation and evolution of planetary systems has been, and remains, one of the big questions of Astronomy. With more than 800 multi-planet systems discovered so far, as many outcomes of these formation and evolution processes are in reach of characterization. These represent precious pieces of the big puzzle. In order to extract the most constraints from these observations, a precise knowledge of each system architecture is crucial: it is key to identify the leading processes in shaping those systems, would they emanate from a combination of formation processes and/or subsequent evolution.

In this presentation, I will introduce a technique aiming at refining the planetary orbital parameters and masses. This technique uses orbital stability arguments on top of a bayesian approach for the parameters' estimation. This stability-driven refinement technique can be applied to any type of multi-planet systems, and notably in the context of planets in multiple-star systems. Besides the advantage of reducing the uncertainties on the dynamical parameters (orbital elements and planetary masses), such an approach can also provide additional insights into the dynamical states of the studied systems. I will present the revision of a few multi-planet systems in light of this approach, and particularly, I will describe a comprehensive dynamical analysis of the Kepler-444 planetary system.
Mois précédent Mois suivant Novembre 2022
Séminaire précédant Séminaire suivant 14ème séminaire : jeudi 03 novembre, 16h00
Higher-spin gravity and the quest for quantum gravity
Evgeny Skvortsov (UMONS)

I will describe the well-known problems to combine the postulates of quantum field theory with General Relativity, which is a so-called quantum gravity problem.

Next, I will present several ideas to attack this problem where a great attention will be paid to the fact that physical theories of fundamental interactions depend a lot on the spin of the particles involved. Then, I will present one of the ideas - Higher spin gravity and discuss what is known about these theories as theories of quantum gravity and their relations to physics.

I will conclude by reviewing the very recent results on application of higher spin particles to the problem of gravitational waves.
Séminaire précédant Séminaire suivant 15ème séminaire : jeudi 10 novembre, 16h00
COVID-19 lockdown measures reveal human impact on water transparency in the Venice Lagoon
Vittorio Brando (CNR, Italy)

The lagoon of Venice has always been affected by the regional geomorphological evolution, anthropogenic stressors and global changes. Different morphological settings and variable biogeophysical conditions characterize this continuously evolving system that rapidly responds to the anthropic impacts. When the lockdown measures were enforced in Italy to control the spread of the SARS-CoV-2 infection on March 10th 2020, the ordinary urban water traffic around Venice, one of the major pressures in the lagoon, came to a halt. This provided a unique opportunity to analyse the environmental effects of restrictions to mobility on water transparency. Pseudo true-colour composites Sentinel-2 satellite imagery proved useful for qualitative visual interpretation, showing the reduction of the vessel traffic and their wakes from the periods before and during the SARS-CoV-2 outbreak. A quantitative analysis of suspended matter patterns, based on satellite-derived turbidity, in the absence of traffic perturbations, allowed us to focus on natural processes and the residual stress from human activities that continued throughout the lockdown. We conclude that the high water transparency can be considered as a transient condition determined by a combination of natural seasonal factors and the effects of COVID-19 restrictions.

Séminaire précédant Séminaire suivant 16ème séminaire : jeudi 17 novembre, 16h00
Multi-step phase transitions and gravitational waves in the inert doublet model
Nico Benincasa (National Institute of Chemical Physics and Biophysics, Tallinn, Estonia)

The inert doublet model is a well-motivated extension of the Standard Model that contains a dark matter candidate and modifies the dynamics of the electroweak symmetry breaking. In order to detail its phenomenology, we perform a comprehensive study of cosmic phase transitions and gravitational wave signals implied by the framework, accounting for the latest results of collider experiments. We require the neutral inert scalar to constitute, at least, a subdominant part of the observed dark matter abundance. While most of the phase transitions proceed through a single step, we identify regions of the parameter space where the electroweak vacuum is reached after multiple phase transitions. The resulting gravitational wave spectrum is generally dominated by single-step transitions and, in part of the parameter space, falls within the reach of near-future gravitational wave detectors such as LISA or BBO. We find that direct detection experiments efficiently probe the part of parameter space associated with multi-step phase transitions, which remain unconstrained only in the Higgs resonance region testable with future monojet searches.
Séminaire précédant Séminaire suivant 17ème séminaire : jeudi 24 novembre, 16h00
Mesoscale and submesoscale dynamics in the Western Mediterranean Sea
Nikolaos Zarokanellos (Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB))

Mesoscale features and their associated submesoscale structures can induce a significant vertical flow of carbon and biogeochemical tracers from the surface to the interior. The Alboran and the Balearic Seas are noticeable for their strong mesoscale and submesoscale activity linked to instabilities. During the CALYPSO pilot project in 2018, repeated glider transects across the Almeria – Oran front monitored mesoscale instability at the frontal boundary between inflowing Atlantic waters and recirculating Mediterranean waters for a period of about six weeks. Vertical perturbations in the frontal boundary are observed as a repeated ‘pumping’ like steepening and relaxation of the isopycnal surfaces across the front. We will present clear signals of highly oxygenated water descending underneath ascending, more weakly oxygenated water as the process of baroclinic instability at the front brings light Atlantic inflow waters of the eastern Alboran Gyre up and over denser recirculating Mediterranean waters. Conversely, the ascending filaments provide a mechanism for the "express" ventilation of weakly oxygenated deeper waters; also the potential for the supply of nutrients to the surface waters that could contribute to the enhancement of the phytoplankton biomass. During the CALYPSO experiment in 2022 at the Balearic Sea, we examined the uplift of the isopycnal surface 28.9 as the eddy formed showed consistency between the movement of the tracers. The glider observations reveal the evolution of a cyclonic eddy in the study area, where the vertical velocities tended to be downward at the periphery of the eddy. The eddy extended during its growing phase, showing a westward shift of the eddy axis. The size of the cyclonic eddy varies between 20 - 30km. The uplift of the isopycnal within the pycnocline can supply nutrients to the euphotic layer. While the original cyclonic feature has decayed, another strong shoaling of 28.9 isopycnal appeared in the east at the end of April 2022. This shoaling of the isopycnal is associated with forming a new cyclonic feature that has been propagating in the region and gets stronger for a few days before splitting into two smaller cyclonic eddies (> 15km) at the beginning of May. The two smaller cyclonic eddies propagated northward and westward until they disappeared from our study area. However, within their separation, we have the formation of an anticyclonic feature with a size of 20 km. In the manner of baroclinic instability, the vertical velocity tended to be downward on the dense side of the front and upward on the light side, flattening the eddy characteristic. The glider observations reveal horizontal density gradients up to 0.5 kg/m³ over ~10 km. The obtained maximum velocities were up to 30 cm/s in the region. The vertical distribution of chlorophyll fluorescence, oxygen, and acoustic backscatter indicated a potential occurrence of both upwelling and downwelling at the frontal interface. The glider observations were combined with remote sensing and modeling simulations to evaluate the mesoscale and submesoscale variability in both study areas and their impact on biological carbon storage.
Mois précédent Mois suivant Décembre 2022
Séminaire précédant Séminaire suivant 18ème séminaire : jeudi 01 décembre, 16h00
The impact of non-equilibrium effects on the relic density of dark matter
Maxim Laletin (University of Warsaw)

The standard method of dark-matter (DM) relic-density calculation (which is widely used for the freeze-out mechanism of DM production, but is not limited to it) is based on solving the Boltzmann equation for the number density and relies on the assumption that DM particles are in thermal equilibrium with the SM plasma or a secluded thermal equilibrium in the dark sector is maintained. The interplay of different interactions in some DM models can lead to a deviation of the DM energy distribution from the equilibrium shape before the relic abundance is established and this deviation can have a considerable impact on the predicted amount of DM in the Universe.

In my talk I am going to outline more elaborate approaches to calculating the distribution function of DM particles (and the corresponding DM number density) and consider the application of these methods to two DM scenarios: 1) freeze-in production of DM from semi-annihilation processes; 2) DM models with a strong velocity-dependence of the annihilation rate and the absence of self-interactions.

Finally, I am going to discuss possible connections between non-equilibrium effects and DM phenomenology after the relic density of DM is settled.
Séminaire précédant Séminaire suivant 19ème séminaire : jeudi 08 décembre, 16h00
Enhancing Bayesian analysis and post-processing with machine-learning
Virginia D'Emilio (Cardiff University)

Gravitational-wave (GW) astrophysics is largely based on Bayesian inference results of individual observations. These are what we call parameter estimation products. During the last GW observing run, the LIGO-Virgo-KAGRA collaboration detected around 90 signals from compact binaries coalescences. We expect the number of such detections to increase to O(1000) over the next two observing runs, which is challenging for our current analysis and post-processing pipelines. Several efforts in our community have been devoted to boost parameter estimation, especially with the use of machine-learning. In many cases, neural networks seem to offer a powerful alternative to tackle expensive computation, an example being simulation-based inference. But in other cases, as shown by Williams and Rasmussen (1996), real world data modelling problems are well solved by sensible smoothing methods, such as Gaussian Processes. In this talk, I will outline how both these techniques address important interdisciplinary problems and as such are both being investigated in GW and cosmology. Finally, as a concrete example of how they could improve the accuracy and speed of Bayesian data analysis, I will consider the case of dark sirens cosmology with GW.
Séminaire précédant 20ème séminaire : jeudi 15 décembre, 16h00 
Environmental impacts of deep-sea mining (TB edited)
Pierre-Antoine Dessandier (IFREMER)
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.