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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 2024    
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Mois précédent Mois suivant Janvier 2024
Séminaire suivant  1er séminaire : jeudi 25 janvier, 16h00
SN 1987A in its third decade imaged by the Hubble Space Telescope: Evolution of the ejecta and equatorial ring
Sophie Rosu (KTH Royal Institute of Technology, Stockholm, Sweden)

The spatially resolved view of the transition into a young supernova (SN) remnant offered by SN 1987A makes it the most thoroughly studied SN so far, from ground to space, at all wavelengths. Its evolution has notably been followed by the Hubble Space Telescope (HST) since its launch in 1990 with an excellent spatial resolution.

We present the recently (2022) acquired HST imaging observations of SN 1987A. For the first time since 2009, the observations cover the entire optical domain between 200 and 1100 nm. We make use of these and earlier observations to study the recent evolution of the spectral energy distribution (SED) and morphology of all parts of the system. We also use the annual imaging in the blue and red filters to provide lightcurves for the different parts of the system.

The recent imaging provides us with a spatially resolved view of both the freely expanding ejecta and the interaction of this latter with the circumstellar medium, revealing the asymmetric ejecta structure in increasingly greater detail.

We observe a decay in the lightcurve of the equatorial ring (ER), explained by the continuous fading of the hotspots that started ∼8000 days after the explosion. A noticeable increase in the ejecta flux is observed until day ∼ 11000, after which the flux seems to flatten around a constant value, owing to the X-ray input coming from the ER.

We do not observe any clear evidence for a point source at the center of the ejecta that would be associated with the direct detection of a compact object. We discuss the implication of our findings in terms of both the energy sources contributing to the ejecta emission and limits on the compact object.
Mois précédent Mois suivant Février 2024
Séminaire précédant Séminaire suivant 2ème séminaire : jeudi 08 février, 16h00
Physics opportunities of CEvNS experiments
Diego Aristizabal Sierra (Santa Maria U., Valparaiso)

Experimental facilities that study coherent elastic neutrino-nucleus scattering, or CEvNS (pronounced sevens), provide a rich environment for precise measurements of Standard Model parameters and searches of new physics. In this talk, I will discuss a few aspects of this program involving solar neutrinos and third-generation dark-matter detectors as well as directional detectors in the Fermilab neutrino beamlines.
Séminaire précédant Séminaire suivant 3ème séminaire : jeudi 22 février, 16h00
Future "firsts" in gravitational-wave observations
David Keitel (IEB, Mallorque)

Beyond the highly successful detection efforts for compact binary coalescences (CBCs), gravitational-wave astronomy also comprises other long-standing search efforts, such as those for continuous waves (CWs) from individual spinning neutron stars. Furthermore, the field is diversifying with new searches for additional astrophysical effects and source types.

I will summarise some recent progress towards three such potential "next first detections":
  • . The search for signatures of gravitational lensing on CBC signals, where heavy masses along the signals' long voyage to Earth can magnify, multiply or deform them. Here I will focus in particular on recent work regarding the effects of waveform systematics and Bayesian sampler choices, which are crucial to understand for making robust detections.
  • . A wide range of searches pursued within the LVK collaboration for known or unknown neutron stars as CW emitters, or even for more exotic sources involving dark matter.
  • . Searches for long-duration transient CW-like signals from newborn or perturbed neutron stars, such as binary neutron star remnants or glitching pulsars.
Mois précédent Mois suivant Mars 2024
Séminaire précédant Séminaire suivant 4ème séminaire : jeudi 28 mars, 16h00
Searching for Evidence of Life Beyond the Solar System with the Giant Magellan Telescope (GMT) and the GMT-Consortium Large Earth Finder (G-CLEF)
Andrew Szentgyorgyi (Harvard-Smithsonian Center for Astrophysics)

Two of the highest priority programs in astrophysics are the discovery and characterization of Earth 2.0 – rocky, Earth-mass exoplanets orbiting Solar-type stars in their habitable zone and the search for biomarkers in the atmospheres of exoplanets in general, The first program is enabled by precision radial velocity (PRV) measurements of the line-of-sight reflex motion of host stars in response to the gravitational influence of low-mass exoplanets that orbit those stars. The search for biomarkers and the characterization of the molecular composition of exoplanets requires extremely high spectral resolution spectrographs on large aperture telescopes. The G-CLEF spectrograph has been designed to provide these capabilities. Before deployment at the GMT, G-CLEF will be delivered to the Magellan telescopes in 2027, to do several pathfinder observational programs that will allow observers to optimize G-CLEF for its delivery to the GMT in 2032. A key project for G@M+MagAO-X will be to resolve and search for O2 in the atmosphere of a habitable zone planet orbiting the star nearest to the Sun – Proxima Cen b. The talk will discuss several aspects of habitability, habitability searches and several technical innovations we will deploy to optimize the Proxima Cen b habitability search.
Mois précédent Mois suivant Avril 2024
Séminaire précédant Séminaire suivant 5ème séminaire : jeudi 11 avril, 16h00
From heartbeat to heartbreak: the story about eccentric binary systems, tidally excited oscillations and collapsing tidal waves
Piotr Kolaczek-Szymanski (STAR - ULiège)

Currently, no one is surprised by the information that most stars in the Universe reside in binary or even multiple systems. Furthermore, in the case of massive stars (with initial masses >8Msun), we can be almost certain that they have at least one companion, which is most likely also a high- or intermediate-mass star. This means that the evolution of massive stars cannot be studied without taking into account their common binarity. Due to the relatively young age of these systems, many of them still have eccentric orbits. However, significant non-zero orbital eccentricity is not restricted only to young massive stars, but it is also observed in evolved systems, containing red giant(s). The tidal forces acting within them determine the further fate of the system, which under favorable conditions can lead to the stellar merger at very different stages of evolution. Periodically varying tidal potential leads to a series of interesting and significant phenomena from an evolutionary point of view. Among them, so-called heartbeat stars are the prominent ones, due to their characteristic light curves resembling an electrocardiogram. In eccentric binary systems, we can also observe tidally induced oscillations, which directly participate in the evolution of the system's orbit, leading to its accelerated tightening. In some systems, the components pass so close to each other at periastron that the resulting huge tidal deformation cannot return to equilibrium and spectacularly collapses onto the star's surface. During my seminar, I will discuss all these processes, primarily considering the effects of my recently defended PhD thesis and outlining certain research plans for the future.
Séminaire précédant Séminaire suivant 6ème séminaire : jeudi 18 avril, 16h00
Linking stellar compositions and planet formation: implications for solar models and stellar surface abundances
Masanobu Kunitomo (Kurume University)

Stars grow by accretion from the protoplanetary disk where planets are formed. Planet formation theory predicts that the composition of the disk gas, and thus of the gas accreted by protostars, must have been variable: the growth and inward drift of dust in the disk leads to the generation of a temporal "pebble wave" of increased metallicity, followed by a phase in which the exhaustion of the pebbles and the formation of planets leads to the accretion of metal-poor gas. How does accretion affect stellar composition? First I will show our solar models with the accretion in the early Solar System which can have a larger central metallicity by up to 5% and thus higher neutrino fluxes, demonstrating that the formation history of the Solar System constitutes a key element in resolving the "solar modeling problem". I will also discuss the implications for chemical peculiarities in other stars: the surface compositions of refractory-poor solar twins, binary systems, and lambda Boo stars.
Mois précédent Mois suivant Mai 2024
Séminaire précédant Séminaire suivant 7ème séminaire : jeudi 16 mai, 16h00
Matteo Pracchia (Université de Liège)
Séminaire précédant Séminaire suivant 8ème séminaire : jeudi 23 mai, 16h00
Dixeena Lopez (Université de Liège)
Mois précédent Mois suivant Juin 2024
Séminaire précédant 9ème séminaire : mercredi 26 juin, 16h00 
Victoria Bonidie (Pittsburgh University)
Université de Liège > Faculté des Sciences > Département d'Astrophysique, Géophysique et Océanographie : CoWebAGO, Juin 2009.