The colour–magnitude diagrams (CMDs) of star clusters underpin stellar astrophysics. They calibrate stellar evolution models, enable age-dating of stellar populations, and provide templates for interpreting unresolved galaxies. Yet the CMDs of young massive clusters show surprising features, such as split main sequences and extended turn-offs. This raises the question of whether we truly understand the mechanisms governing stellar distributions across the CMD.
In this talk, I will show how binary interactions and stellar rotation reshape CMD morphologies. Using observations of young massive clusters in the Magellanic Clouds obtained with HST and MUSE, we measure the spin velocities of large stellar samples and characterise the clusters’ binary populations. Our results reveal distinct populations of slow and fast rotators occupying different loci in the CMD. The detection of post-interaction binaries, such as blue stragglers and stripped stars, further enables us to constrain population synthesis models and to assess the contribution of massive star clusters to the cosmic rate of compact binary mergers observed via gravitational waves.

The cosmic web, consisting of large empty voids, cosmic walls, filaments and clusters, is characterised by multi-stream regions. A finite set of caustics can classify the geometry and formation histories of these regions. In particular, the cosmic walls correspond to the cusp caustic while the filaments correspond to either the swallowtail or the elliptic/hyperbolic umbilic caustics. In this talk, I will discuss how these structures are realised in our Universe with constrained N-body simulations.

Furthermore, I will discuss the first application of caustic skeleton theory to a cosmological redshift survey using the Manticore-Local simulations. With these Bayesian-constrained reconstructions of the Local Universe from the 2M++ galaxy catalogue, we extract the three-dimensional multi-scale caustic skeleton of two canonical web-like structures in our Local Universe, namely the Coma Cluster and the Pisces-Perseus ridge, as they represent the most prominent cluster node and filamentary artery in the nearby Universe. The Caustic Skeleton network of caustic singularities accurately reproduces the observed large-scale organisation of galaxies in redshift space for one of the Manticore realisations. Remarkably, while the Coma cluster seems to be governed by swallotail filaments, Pisces-Perseus is dominated by umbilic filaments.

The intracluster light (ICL) is a uniquely luminous probe of galaxy cluster halo shape and orientation, but it's extremely low surface brightness has historically made robust morphological measurements challenging. In this talk, I present ICL shape measurements from Euclid's Quick Release (Q1) for nearly 200 clusters at 0.1 ≤ z ≤ 0.8, selected from the eROSITA All-Sky Survey and the Dark Energy Survey. The ICL ellipticity distribution peaks at e ≃ 0.5, in close agreement with halo ellipticities from strong and weak lensing — supporting the view that the ICL traces the cluster's large-scale structure. Radially, BCG-dominated cores are relatively round, while the diffuse component becomes progressively more elongated before plateauing at large radii. By stacking clusters in redshift bins, we extend these measurements to larger cluster-centric radii and find no detectable evolution with redshift — a result that challenges theoretical expectations. Comparing to the Hydrangea simulations, we show that the ICL's measured shape depends sensitively on how it is defined and extracted: only fully forward-modelled mock observations reproduce the observed distribution, underscoring that realistic mock observations are essential for direct comparison with theory. This methodology provides a benchmark for testing hydrodynamical simulations, and forthcoming Euclid data releases will enable substantially tighter constraints.

The stellar metallicity influences the occurrence of giant and small hot exoplanets. However, the role of elements other than iron on planetary formation is still unclear. In this talk, I will discuss the relations between the abundances of 13 chemical elements (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Cu) for a sample of 561 Kepler exoplanet-hosting stars and the radii and orbital periods of their planets. These possible connections are investigated through comparisons between stars that host different planetary systems. I will also discuss the role of alpha elements in the formation of giant planets and examine the depletion of refractory elements in the Sun. The analysis of 25 solar twins in our sample suggests that this chemical peculiarity might be caused by processes other than planetary formation.

Bulges and discs in nearby galaxies have complex structures, resulting from a large diversity of possible assembly histories. In this seminar, I will show how we use deep MUSE observations of nearby edge-on disc galaxies to study the connection between galaxy morphology and assembly history, and to probe the growth of discs with time and constrain disc settling and vertical heating. I will show that discs can settle very early, and can form bars quickly, and I will discuss the complex impact of mergers on disc thickening and bulge growth. I will also show that lenticular galaxies in the Fornax cluster form an interesting comparison point, with weak secular evolution and stunted radial growth because of the lack of fresh gas. Finally, I will give an overview of GECKOS, an ongoing MUSE survey of 36 nearby edge-on Milky Way-mass galaxies.

RR Lyrae stars have long been considered unequivocal tracers of old (>10 Gyr) metal-poor (<-0.5) stellar populations. First, because these populations are where they are most easily found; but also because, according to canonical stellar evolution models for isolated stars, these are the only populations where RR Lyrae should exist. Recent independent results, however, are challenging this view and pointing at the existence of intermediate-age RR Lyrae, only a few (2-5) Gyrs old.

In this seminar I will present the first detection of an RR Lyrae star reliably associated to an intermediate-age cluster: the nearby 2 Gyr-old Trumpler 5. I will frame this result in the context of recent works and of our findings for the expected and observed rates of these stars per unit mass, both from observations of intermediate-age clusters in the Magellanic Clouds, as well as from previous results on possible binary evolution origins for these stars. The association of an RRL star to a decidedly intermediate-age simple stellar population is, so far, the most direct evidence of the existence of these ‘young’ RRLs and adds firm support to the evidence that has been systematically accumulating toward the existence of these highly controverted stars.