Séminaires

Comet C/2020 F3 (NEOWISE): From naked eye spectacle to scientific insights
Aravind Krishnakumar (STAR Institute Université de Liège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Comets are among the most primitive bodies in the Solar System, preserving a record of the physical and chemical conditions prevalent during their formation. The study of cometary comae through photometry and spectroscopy provides critical insights into volatile composition and outgassing processes. In particular, production rates of commonly observed species such as OH, NH, CN, C₂, and C₃ serve as key diagnostics of the nucleus composition and its evolutionary state. The abundance of molecular nitrogen relative to CO and H₂O, however, remains poorly constrained. In the optical regime, these parent volatiles can be probed only indirectly through their ionic emissions, making their detection both essential and challenging due to their extremely low densities. The Great Comet of 2020, C/2020 F3 (NEOWISE), has been extensively studied using very high-resolution spectroscopy; however, ionic emissions have not been previously reported. In contrast, long-slit low-resolution spectroscopy of such a bright comet enables detailed investigation of spatial emission profiles, offering a complementary and powerful diagnostic. In this seminar, I will take you through the realm of cometary science and present the detection of ionic emissions, including N₂⁺, CO⁺, and H₂O⁺ in C/2020 F3 (NEOWISE), along with other unusual spectral features. I will discuss the derived relative abundances and their implications for cometary formation conditions and volatile chemistry, alongside an overview of production rates of key neutral species. Additionally, I will highlight the detection of a particularly intriguing optical emission and explore its potential significance.

Characterizing the physical properties of strong lenses and local galaxies with Euclid
Angelos Nersesian (STAR Institute Université de Liège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

In this talk, I will present my work on the local Universe in the context of the Euclid mission, with a focus on its applications to the nearby strong-lens system NGC 6505. I will then introduce preliminary results from a sample of strong gravitational lenses, including measurements of redshifts, stellar masses, Einstein radii, and galaxy sizes. Finally, I will discuss what this statistically significant sample can reveal about the properties of strong-lens populations and their role in galaxy evolution.

Mars aurora: discovery, imaging and relation to solar wind
Jean-Claude Gérard (LPAP, STAR, ULiège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Auroral emissions on the Mars nightside were initially observed as individual events of MUV emission by the SPICAM spectrometer on board Mars Express in 2005. These observations have shown the auroral ultraviolet emissions are highly correlated with crustal magnetic fields structures. MAVEN's Imaging Ultraviolet Spectrograph (IUVS) has measured hundreds of individual discrete MUV electron auroral events since 2014 and showed that they can also occur globally, in regions of weak or absent crustal fields. Another type of event is the ‘’diffuse’’ aurora which occurs following Solar Energetic Particle (SEP) events and covers a large fraction of the planet. It is caused by the interaction of very energetic electrons and protons with the atmosphere. Since April 2021, the EMUS EUV/FUV spectrograph on board the Emirates Mars Mission (EMM) has shown that the FUV electron auroral emission is not necessarily "discrete" but is observed in a variety of morphologies. Crustal field aurora and enigmatic "sinuous" aurora have well-defined edges, while most emission away from strong crustal fields is fainter and "patchy". Finally, on the dayside, enhancements of Lyman-a have also been observed, resulting from the interaction of solar wind protons with the hydrogen corona surrounding the planet. We will show that visible counterparts to the UV emissions would probably be detectable and visible to future Mars astronauts. This seminar will also describe the current state of Mars aurora modelling and future investigations.

TBD
Martin Farnir (STAR Institute Université de Liège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

TBD

Orion’s Massive Stars: Delta and Epsilon Ori
Alžběta Oplištilová (STAR Institute Université de Liège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Massive stars are cosmic engines. By exploding as supernovae, they power galaxies, shape the interstellar medium, and enrich it with heavy elements. Yet, their inner workings remain among the most challenging frontiers in stellar astrophysics. The evolution of massive stars is critically influenced by multiplicity; most have one or more companions, while a few remain single. This raises the question: could these single stars be the end products of multiple systems? Interferometry is one of the best methods for detecting and characterising stellar multiplicity. The Orion complex is the nearest massive-star-forming region with multiple OB stars, and thus the most suitable for detailed studies. It hosts a number of massive stars, particularly in the Orion Belt. I constructed two complex models: the triple star Delta Ori and the single star Epsilon Ori using interferometric data in synergy with astrometry, photometry, high-resolution spectroscopy, and spectral energy distribution. Delta Ori is currently in the pre-mass-transfer evolutionary stage, while Epsilon Ori is a significantly oblate supergiant due to its rapid rotation. As the only massive single star in the Orion Belt, Epsilon Ori likely follows a non-standard evolutionary path.

Genesis: the ESA mission to measure Earth down to the millimeter
Gilles Wautelet (LPAP, STAR Institute, ULiège)