Retrieval and seasonal variations of aerosols in the Martian atmosphere from the NOMAD instrument on board the Trace Gas orbiter
Zachary Flimon (LPAP/STAR/ULiège)

Mars is a terrestrial planet with a mass and a much thinner atmosphere compared to Earth. Although its rotation period is similar to Earth’s day, its revolution around the Sun takes nearly twice as long. The planet’s elliptical orbit results in strong seasonal variations in its atmosphere. Martian aerosols composed of dust, H2O ice, and CO2 ice clouds are strongly influenced by these seasonal cycles. This work focuses on retrieving the optical properties of aerosols, specifically extinction and particle size, using solar occultation measurements from the Nadir and Occultation for Mars Discovery (NOMAD) instrument aboard the ExoMars Trace Gas Orbiter (2016–present). NOMAD consists of three channels: UVIS (Ultraviolet–Visible, 200–650 nm), SO (Solar Occultation, 2.3-4.3 μm), and LNO (Limb Nadir and Occultation, 2.2-3.8μm). In solar occultation, we can probe the vertical structure of the atmosphere and derive vertical opacity profiles. In the first part of this work, we use the UVIS channel alone to study aerosol optical properties. Although UVIS cannot determine aerosol composition, its large number of spectral points and low noise level make it well suited for retrieving sub-micron particles. We then studied aerosols using the SO channel, which allows us to retrieve aerosol composition as well as larger particle sizes at lower altitudes. Finally, to take advantage of the simultaneous measurements from both channels, we merged the spectra from UVIS and SO and retrieve aerosol properties jointly. This combined approach improves vertical coverage and provides both size and composition information in a single, consistent retrieval. Using the combined UVIS and SO dataset, we produced a global climatology spanning mid–Martian Year (MY) 34 to MY 37. This climatology captures the seasonal evolution of aerosols, including dust storm activity and H2O ice distributions during all Martian seasons. Our results are consistent with previous datasets and reveal that dust and H2O ice can coexist at specific altitudes, providing new insights into their coupled behavior in the Martian atmosphere.

From Small Worlds to Giant Planets: Uncovering New Exoplanets with Ground-Based Observations
Mathilde Timmermans (University of Birmingham)

Discerning patterns and trends in the physical properties of exoplanets is now possible thanks to the growing number of planet discoveries. In particular, TESS has been instrumental in adding to the sample with the detection of over 7800 potential planets, of which more than 750 have been confirmed in the last 8 years. The distinct subpopulations that have emerged from grouping planets in different parameter spaces are now being tested against formation and evolution theories. Linking the two is still proving challenging in some cases, highlighting the need either to revise the current theories or increase the size of the statistical sample for the rarer planets.

In this talk, I will discuss the efforts to validate planet candidates with the SPECULOOS and ASTEP ground-based facilities, focusing on small and giant planets orbiting M dwarfs. I will highlight the key advantages of these facilities and present ongoing projects. Particularly, I will discuss the latest discoveries of the MANGOS programme which I am currently leading.

The Solar Modelling Problem
Gaël Buldgen (STAR Institute Université de Liège)

The revision of the solar abundances in the early 2000’s has proven to be a thorny issue that is still causing trouble to solar modelers 20 years later. Subsequent re-analyses in 2009, 2011, 2021 and 2022 (Asplund et al. 2009, Caffau et al. 2011, Asplund et al. 2021 and Magg et al. 2022) have provided contradicting result, leading to a lasting debate between “high-metallicity” and “low-metallicity” solar models. In this talk, I will discuss the more general aspects of the so-called “solar modelling problem” and how it cannot be reduced to a simple problem of chemical abundances but rather a more fundamental issue linked with our current modelling capabilities of the solar interior.

Absence of Spin‑Up Companions in Half of Wide Hot Subdwarf Binaries
Xiaoyu Ma (STAR Institute Université de Liège)

Binary stars play critical roles across a wide range of astrophysical contexts, including the formation of exotic stellar objects and planetary systems, the progenitors of supernovae, and the sources of gravitational waves. They are widely believed—both from theoretical models and, more recently, from observational evidence—to be a primary channel for the formation of hot subdwarfs (sdO/B stars). Here we report an unexpected result that only about half of companions in a golden sample of wide hot subdwarf binaries exhibit measurable rotational signals attributable to magnetic modulation, based on a comprehensive survey of nearly 5000 TESS and Kepler sdO/B targets. Their rotation periods are predominantly shorter than 5 days, a distribution strikingly different from that of single field MS stars, whose rotation periods peak around 20 days. This markedly faster rotation suggests that the old MS companions in wide sdO/B binaries must have undergone a spin-up process through past mass accretion, as their rotation rates are comparable to those of much younger MS stars in open clusters. However, the absence of any detectable rotational signal in the remaining near half of companions, even among relatively bright targets, poses a challenge to the commonly held view that sdO/B formation universally requires binary interaction.

The AI Revolution in Academia: A Practical & Honest Guide for Researchers and Teachers
Maxime Fays (ULiege - STAR - Ograv)

Ready or not, Generative AI is reshaping how research is done and how students learn. This talk cuts through the noise with practical techniques and honest assessments of both the potential and the pitfalls: what these tools actually are, where they reliably fail, and how to direct them effectively whether for writing grants, designing exams, or reclaiming time spent on tasks AI handles in seconds.

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

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)

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)

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.

Seismology of solar-like stars along their evolution
Martin Farnir (STAR Institute Université de Liège)

The advent of space-borne missions lead to the acquisition of extremely precise data. This allowed us to unveil the secrets harboured by stars with unmatched accuracy. This was thanks to asteroseismology, the science of stellar oscillations and their relation with the stellar structure. In this talk, I will present tools I develop to take full advantage of the information held by stellar oscillations of solar-like stars - i.e. stars with masses similar to our Sun - along their evolution, from the main sequence all the way to the red-giant phase. These are WhoSGlAd, for the study of acoustic glitches - sharp feature in the stellar structure leaving a signature in the oscillation spectrum - EGGMiMoSA, suited to the study of the complex mixed-modes - modes displaying both a pressure and gravity nature - pattern displayed by subgiant and red-giant stars, and PORTE-CLES, a minimisation tool for the search of optimal stellar models, representative of a set of observables.

Galaxy Evolution in the Fornax Cluster
Marc Sarzi (Armagh Observatory and Planetarium)

Galactic environment is thought to be one of the key factors in driving the cosmic quenching of star formation in galaxies. The Fornax cluster is a nearby intermediate-mass cluster that is more representative of the clusters found in the Universe compared to other nearby clusters such as Virgo and Coma. Fornax thus represents an ideal environment to understand the relative role of hydrodynamic and gravitational processes affecting galaxies in crowded environment.

In this context, I will discuss the results of the Fornax3D magnitude-limited survey of galaxies in the Fornax cluster with MUSE integral-field spectral. Additionally, I will present the results of ancillary studies based on deep optical and radio observations (with VST and MeerKAT) revealing objects currently on-going star-formation quenching. To further gain insight on the physical mechanisms behind such phenomena, we derive the star-formation history of Fornax galaxies with a spectrophotometric approach to both MUSE integral-field spectroscopic and S-PLUS imagining data. At the same time we also explore Fornax-like clusters in the TNG-50 simulations to derive the neutral-gas predicted distribution both across the whole cluster and around individual galaxies, following this also in time. This gives us a view of both on-going gravitational and hydrodynamical interactions in the Fornax cluster galaxies as well as a gauge on the past impact that these had in driving their star-formation histories, which we can compare to model predictions.

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

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)

TBD