An Overview of the 4m International Liquid Mirror Telescope
Kuntal Misra (ARIES India)

The 4m International Liquid Mirror Telescope (ILMT) is the first optical survey telescope in Devasthal, India. The telescope achieved its first light on 29 April 2022. The primary mirror is made of liquid mercury, continuously spinning to achieve a paraboloid shape. It constantly scans a 22 arcmin wide strip of the zenithal sky and records the images in three broadband filters (g', r' and i') using a 4k X 4k CCD camera in Time Delay Integration (TDI) mode. In about 10-12 hours of observations during a single night, approximately 15 GB of data volume is generated. To process this data, different automated pipelines are developed to perform the astrometric and photometric calibration, image subtraction to detect new transients and machine learning based tools to classify these transients. In this talk, I will give a brief overview of the ILMT and its science drivers, the initial results and the availability of data to the users.

The wonders of X-ray polarimetry
Frédéric Marin (CNRS, Observatoire de Strasbourg)

The Imaging X-ray Polarimetry Explorer (IXPE) is the first satellite dedicated to observing the polarization of X-rays from almost any cosmic source. Since its launch in December 2021, IXPE has revolutionized our understanding of high-energy physics, from the structure and composition of relativistic jets to surface models of magnetars, from the topology of magnetic fields in supernova remnants to the geometry of X-ray coronas around black holes, and even probing the accretion cycle of our own galaxy’s supermassive black hole. In this talk, I will review these results and highlight the major discoveries made by this modest satellite that are paving the way for many more to come.

The TROY project: Do trojan exoplanets really exist?
Olga Balsalobre (Center for Astrobiology, Madrid)

The existence of co-orbital (or trojan) planets has been theorized for over two decades. These are pairs of planets sharing the orbital path around their star. Hydrodynamical simulations suggest that co-orbitals could be a natural by-product of planet formation. Recently, this hypothesis has gained observational support with the discovery of co-orbital gas and dust in a handful of young systems. Yet, the absence of confirmed trojan planets in mature systems remains an open question. A dedicated search for these configurations is crucial to dermine whether current detection techniques are systematically overlooking them, or if trojans are disrupted as the planetary systems evolve. In this talk, I will present the multi-technique approach we follow in the TROY project. We search for co-orbital candidates across different evolutionary stages of planetary systems combining Radial Velocities, Transits, and Direct Imaging.

Exploring the X-ray activity of M Dwarfs: a focus on the benchmark planet host Proxima Centauri
Enza Magaudda (University of Tübingen)

The magnetic activity of the Sun and solar-like stars is driven by an αΩ-dynamo, where differential rotation and convection regenerate the magnetic field, producing strong optical, UV, and X-ray emissions. M dwarfs are also magnetically active, though the underlying mechanism remains unclear, and their X-ray emission significantly impacts the evolution of orbiting planets.

This talk explores the X-ray activity of M dwarfs, examining its dependence on mass and rotation using the largest and most uniform dataset of new X-ray observations and rotation periods, supplemented by literature data. Additionally, I present a detailed study of Proxima Centauri, a benchmark planet host and known flare star. Using XMM-Newton and eROSITA data, I derived for the first time the relation between coronal temperature and X-ray luminosity based on the variability of a single star. Compared to solar-type stars, Proxima Centauri exhibits higher coronal temperatures, and a temperature spread at a given X-ray luminosity, likely due to variations in electric currents shaping its magnetic loops. These findings enhance our understanding of stellar magnetic activity and its role in shaping planetary atmospheres and habitability.

Treatment of magnetic activity effects in an era of high-precision asteroseismology
Jérôme Bétrisey ('Université d'Uppsala.)

Following the success of missions like CoRoT, Kepler, and TESS, asteroseismic modelling is poised to play a pivotal role in upcoming space-based missions such as PLATO, CubeSpec, and Roman. Despite remarkable achievements, asteroseismology has also revealed significant discrepancies between observed data and theoretical stellar models, leading to non-negligible biases in stellar characterisation in our era of high-precision asteroseismology. In the past decades, magnetic activity effects were typically neglected in asteroseismic modelling of solar-type stars, assuming that these effects could be accounted for in the parametrisation of the so-called ‘surface effects’. This picture has, however, been challenged in recent years, as it was demonstrated that magnetic activity can have a significant impact on the asteroseismic characterisation using both forward and inverse methods. In this presentation, I will present these results and show that magnetic activity effects cannot be suppressed with standard methods employed to mitigate surface effects. Subsequently, I will also discuss how magnetic activity effects are averaged with longer observations and what conclusions can be drawn for future photometry missions.

Influence of a subsurface ocean on the rotation variations of large icy satellites
Alexis Coyette (UNamur)

We use an angular momentum approach to study the Cassini states (CS) of large natural satellites such as the Galilean satellites and Titan. Unlike classical approaches where obliquity is the solution of a trigonometric equation, our approach allows us to identify not only the mean obliquity of satellites, but also their nutation in space as well as their polar motion (PM) with respect to the solid surface. Triaxiality of the satellite has a significant effect on the mean obliquities of CSI, CSII and CSIV. We assess the stability of the Cassini states over a wide range of free and forced precession frequency ratios and find that CSI and CSIII are always stable. Even if the different Galilean Moons are thought to occupy CSI, we therefore also analytically study CSIII. We here solve the dynamic equations governing CSI and CSIII up to order two in small quantities and without averaging the external torque over the mean anomaly to obtain the time-variable obliquity and polar motion (at long-period and short-period). By extending the system of equations governing CSI, including gravitational and pressure couplings between misaligned layers, we predict the orientation of the spin axes of the outer shell, internal ocean and solid interior for an ocean-bearing body.

The dust and molecular gas in the torus of NGC 1068
Violeta Gamez-Rosas (STAR)

In the context of the AGN unification paradigm, the concept of the ‘dusty torus’ plays a crucial role in explaining the difference between Type-1 and Type-2 AGNs. NGC 1068, a well-studied AGN across the electromagnetic spectrum, is a nearby barred galaxy (d=14.4 Mpc) considered the prototypical Seyfert 2. Using the mid-infrared spectro-interferometer MATISSE at the VLTI, we have obtained direct evidence of the dusty torus enshrouding the AGN in NGC 1068. The multi-band capabilities of the instrument and the high spatial resolution achievable through interferometry (down to 3 mas) have enabled us to study in detail the characteristics of the obscuring dust and its spatial distribution. My presentation will delve into these findings and discuss our latest research on the molecular counterpart of the dusty torus. Using ALMA observations of the HCO+ (J = 4 -> 3) and CO (J = 3 -> 2) molecular lines, we are able to resolve structures with a comparable angular resolution. Based on these ALMA data, I will present our results, including the significant asymmetry of the nuclear disk in terms of morphology, velocity, and line intensity, on the possible origin of the broad lines seen in the inner 2 pc, of the sub-Keplerian rotation velocities outside this radius, and of the extremely low CO/HCO+ line ratio at the nucleus. I will also show evidence which we find of an infalling high-velocity cloud. These results show the fundamental importance of high spatial resolution studies to understand the physical processes at play near supermassive black holes to unravel the AGN feeding and feedback mechanisms taking place there.

Linking the chemical composition of stars and exoplanets: impact of transport processes and planet angulfment
Morgan Deal (Université de Montpellier)

Stars and exoplanets are formed from the same accretion disk and are expected to have the same initial chemical composition. However, once the host-star is not fully convective anymore, its surface abundance changes with time because of several processes. Firstly, internal transport processes of chemical elements such as atomic diffusion, rotation-induced mixing, or penetrative convection affect the surface abundances with different efficiencies. The abundance changes depend on the age of the host star but also on its spectral type. Secondly, the host star may also undergo accretion of rocky bodies in the system at different periods of its evolution. It can go from the accretion of small asteroids to the engulfment of planetoids, and all these events may leave a chemical signature at the surface of the star. In this presentation, we will show how we can derive the initial chemical composition of the planetary systems by modelling the host star with a realistic transport of chemical elements. Moreover, we will show that the accreted matter from planet engulfments does not remain at the surface of stars because of the same transport processes. Such accretion events also trigger additional efficient transport processes, such as the thermohaline convection, which strongly reduce the remaining signature at the surface of stars. We also show that the timing of such an event during the evolution of the host star strongly affects the amplitude of the chemical signature. The accurate modelling of transport processes in stars is crucial for the interpretation of chemical signature in this context.

Black holes and revelations: unseen companions in stellar binaries
Kareem El Badry (California Institute of Technology)

The Milky Way contains of order 10^8 stellar-mass black holes (BHs). Yet, fewer than 100 BH candidates are known, and only about 20 are dynamically confirmed. Our view of the BH population has been shaped almost entirely by observations of X-ray binaries and gravitational wave sources, both of which represent an extremely rare outcome of binary evolution. I will discuss recent efforts to uncover the (probably) much larger population of Galactic black holes in non-interacting binaries, focusing both on interpretation of confirmed dormant BHs and on what can be learned about binary evolution from the menagerie of interacting binaries and stripped stars that have masqueraded as dormant BH binaries. Finally, I will discuss our emerging view of the BH mass distribution from observations of X-ray binaries, dormant BH binaries, BHs detected via photometric and astrometric microlensing, and BHs in gravitational wave events.

High-contrast imaging of massive stars: characterizing companions down to the brown dwarf mass regime
Tinne Pauwels (KU Leuven)

A comprehensive study of the multiplicity properties of massive stars down to very low mass ratios is essential for constraining massive star and binary formation theories. However, past spectroscopic and interferometric multiplicity studies have not reached the contrasts needed to probe the low-mass end of the companion mass function around such massive objects. The Carina High-contrast Imaging Project of massive Stars (CHIPS) recently demonstrated that high-contrast imaging (VLT/SPHERE) enables us to explore the brown dwarf mass regime around massive stars at separations between 0”.15 and 6” (~400-15000 AU). These observations provide key insights into whether low-mass, possibly substellar, companions can form and survive in the harsh UV radiation fields of massive stars. In this seminar, I will present the results of recent high-contrast imaging surveys of massive stars in different environments (Carina region, Sco OB1, M17), including the follow-up of multiple low-mass stellar and substellar companions in Sco OB1 and M17. Finally, I will discuss how bias correction can be applied to determine the intrinsic multiplicity fractions, ultimately providing crucial constraints on massive star and binary formation models.

Semi-analytical study of stellar high-order gravity modes
Yoshiki Hatta (Graduate School of Advanced Studies, SOKENDAI, Tokyo)

Modern space-borne missions such as CoRoT, Kepler, and TESS have enabled us to find a few hundreds of intermediate-mass (1.4-8.0 solar mass) main-sequence stars that are pulsating with gravity (g) modes whose restoring force is the buoyancy. The measured g-mode periods are quite informative on internal properties of the stars, but they are difficult to interpret because of a rather complex relation between the g-mode period and internal dynamics and structure of the stars. In this talk, I present semi-analytical studies of high-order g modes, where relations between the g-mode period and internal properties, namely, the Brunt-Väisälä (BV) frequency profile and internal rotation rate, have been established. Such semi-analytical studies of high-order g modes will possibly allow us to put further constraints on, e.g., mixing processes inside intermediate-mass main-sequence g-mode pulsators such as beta Cep, SPB, and gamma Dor stars that have been principal targets in asteroseismology and will be observed by the PLATO telescope. 

Hidden magnetic fields in stellar interiors probed by asteroseismology.
Antoine Fort (Paris-Meudon observatory)

Understanding the role of internal magnetic fields in stars remains a major stumbling block for the description of angular momentum transport and stellar evolution. In this work, we present a new implementation of the 2D oscillation code ACOR, which incorporates the effects of both stellar rotation and magnetic fields. The code has been rendered modular, allowing to specify the set of equations to solve and the hypotheses through a symbolic calculus approach. The full set of adiabatic, non-radial pulsation equations is solved using a spectral approach in the angular direction and high-order finite differences in the radial direction. As a first step, we focus on a simplified case in which the magnetic field is purely toroidal, axisymmetric, and aligned with the star’s rotation axis. The numerical results are validated against first-order perturbative predictions in the weak-field regime. We show that internal magnetic fields leave signatures in the period spacing of g-modes. These features could provide a promising seismic diagnostic to probe deep stellar magnetism. Future work will aim to extend this framework to more realistic magnetic field topologies and a broader range of pulsating stars, including red giants.

Plasma conditions at the orbits of Io, Europa, and Ganymede derived from the lead angle of the satellite auroral footprints observed by Juno-UVS
Shinnosuke Satoh (Tohoku University)

Io, Europa, and Ganymede act as an obstacle to the corotating plasma in the Jovian magnetosphere. Through the electrodynamic interaction at the moons (e.g., Kivelson et al., 2004), Alfvén waves are launched and propagate along the magnetic field. Auroral electrons are accelerated toward/away from Jupiter's atmosphere by the Alfvén waves and ultimately induce multiple satellite auroral footprints and a diffuse auroral tail in Jupiter's atmosphere (e.g., Clarke et al., 2002; Bonfond et al., 2008).

The Alfvén velocity depends on the local magnetic field magnitude and the local plasma mass density. The position of satellite auroral footprints is detemined by the Alfvén wave propagation time. The angular separation between the satellite body and the auroral footprint is called the lead angle. The footprint lead angle has been proven to be useful to investigate temporal variations of plasma parameters in the Io plasma torus (Moirano et al., 2023) and the plasma disc at Europa's orbit (Satoh et al., 2024). Both studies traced the Alfvén waves from the moon to the MAW spot in the plasma sheet with various plasma parameters and estimated the lead angle to find the best fit parameters. Estimation of the plasma parameters at the orbits of the icy moons is important because the magnetospheric plasma controls source and loss of neutral atmospheres in the icy moons.

Now, using the same fitting procedure as Satoh et al. (2024), we’re trying to derive the three ion parameters (atomic mass, number density, and temperature) at the orbits of Io, Europa, and Ganymede, from the footprint lead angle measured by Juno-UVS. In addition to the MAWs, we also use the lead angle of the Transhemispheric Electron Beam (TEB) spot (Bonfond et al., 2008). The TEB spot is generated by the electrons accelerated away from Jupiter in the other hemisphere. Hence, the TEB spot in one hemisphere is strongly associated with the other hemisphere's MAW spot. Using the TEB spot, we can trace the Alfvén waves that have different propagation paths than the ones corresponding to the MAW spot observed in the same hemisphere at the same time, which is expected to add another constraint for the estimation of ion parameters.

Unveilling stellar interiors: coupling fully compressibles simulations and asteroseismology 
Arthur Le Saux (CEA Paris-Saclay)

Thanks to the study of global stellar oscillations modes, asteroseismology have revolutionised our understanding of stars, providing unique access to their internal structure and dynamics. Complementing this, stellar hydrodynamical simulations provide a powerful tool to study physical processes occurring in stellar interiors, offering new insights for interpreting observational data and guiding future missions. However, the synergy between asteroseismology and stellar hydrodynamics have been difficult to develop as most of the observed oscillations are acoustic modes, which cannot be modelled in most stellar hydrodynamics codes. The reason for that is that these codes use the Boussinesq or anelastic approximations, and thus filter out sound waves.

In this presentation, I explore the properties of compressible – acoustic and fundamental – and gravity modes in stars using two-dimensional simulations of low-mass stellar models conducted with the fully compressible MUSIC code. In a solar model calibrated to match observational data, our analysis reveals an unexpected global mode at lower frequency: a mixed f /g mode with a period of about one hour. Crucially, we show that this mixed-mode is sensitive to the Sun’s core rotation rate, a fundamental characteristic that remains undetermined so far and constitutes one of the main challenges in our understanding of the Sun. Finally, I will present recent results on the characterisation of acoustic modes in a solar-like model, opening new pathways to a synergy with asteroseismology.

PyLMT: A transient detection pipeline for the 4-m International Liquid Mirror Telescope
Kumar Pranshu (STAR)

The 4m International Liquid Mirror Telescope (ILMT) is India’s first optical survey telescope, which uses a spinning mercury mirror as its primary reflector. It is the only operational liquid mirror telescope globally, with a 22.3' FoV and limiting magnitude of g-mag ~22. The ILMT captures ~15 GB of imaging data per night, producing nearly 30 science frames. A key goal is discovering optical transients and variables, which is facilitated by an automated detection pipeline called the PyLMT. The pipeline employs image subtraction to generate difference frames, followed by a CNN-based classifier to distinguish real sources from artefacts in the resulting images. A second CNN classifies real sources based on host morphology, and known asteroids and solar system objects are identified for rejection. In a recent modification to the pipeline, new CNN models for transient detection and classification were trained using the transfer learning technique, employed between images from the Zwicky Transient Facility and the ILMT. Operational since November 2023, the pipeline has identified various transients and variables, including AGNs, asteroids, T Tauri outbursts, RR Lyrae, Eclipsing Binaries, and 21 supernova-like transient candidates. Five of the detected supernova candidates, viz. AT 2023yjc, 2024fxn, 2024zsm, 2024agkc, and 2024aifv were reported to the transient name server (TNS) as new discoveries.

The impact of rotational mixing in intermediate-age star clusters with extended main-sequence turn-offs and extended red clumps
Lorenzo Martinelli (University of Newcastle (Australia))

The extended main-sequence turn-offs (eMSTOs) and extended red clumps (eRCs) observed in intermediate-age star clusters challenge the traditional understanding of star clusters as simple stellar populations. In recent years, eMSTOs have been interpreted as signatures of fast stellar rotation, but the role of rotational mixing in shaping the colour–magnitude diagram (CMD) of these clusters remain uncertain. I will present a comparison between observed and synthetic CMDs for two intermediate-age clusters, NGC 419 and NGC 1817. Both clusters show a clear eMSTO and eRC, with turn-off stars showing large v sin i values. We used two grids of rotating stellar models, identical in input physics except for the efficiency of rotational mixing, to build synthetic clusters. Our results show that models with weak rotational mixing best reproduce both the eMSTO and eRC features and match the red clump luminosities and asteroseismic masses in NGC 1817. Strong mixing leads to post main-sequence CMD features that are too bright and inconsistent with observations. Overall, our findings suggest that rotational mixing might play a role in shaping eRCs, but its influence on intermediate-mass stellar evolution is definitely weaker than most stellar models predict.

Non-LTE modelling and stellar abundances of heavy Elements
Sema Caliskan (University of Uppsala)

The cosmic origin of elements heavier than iron remains one of the open questions in astrophysics. These elements are produced through neutron-capture processes in diverse astrophysical sites, but to disentangle their contributions and galactic evolution, we rely on accurate stellar abundances. Deriving these abundances requires reliable non-LTE models of stellar spectra. However, for many heavy elements, non-LTE modelling is still missing due to the scarcity of accurate atomic data. This challenge highlights the interconnected nature of atomic physics and astrophysical interpretation: without reliable atomic data, we cannot fully exploit the wealth of stellar observations.

During my PhD, I have worked at this intersection, aiming to improve atomic data and construct more accurate non-LTE models for heavy elements. I will present results from different stages of this work: from theoretical calculations of atomic structure and transition probabilities, to non-LTE modelling of copper and silver. I will show how improved atomic data, such as hydrogen collision rates and photoionisation cross-sections, impact non-LTE abundance determinations of these elements, and how refined abundance trends in turn sharpen our understanding of nucleosynthetic origins and galactic chemical evolution.