Seminars and Colloquia at ESO Garching and on the campus

Stellar population synthesis models implicitly rely on the assumption of a fully sampled initial mass function (IMF). However, with current technological developments pushing towards high angular resolution and ultra deep observations, this assumption does not necessarily hold true. The possibility of an incomplete sampling of the IMF poses therefore a fundamental challenge to all state-of-the art stellar population models currently available. In this talk, I will describe how the same principles and ingredients of the standard evolutionary stellar population synthesis can be naturally combined with a partially sampled IMF. This so-called semi-resolved regime requires profound methodological changes but also offers unique and promising observational opportunities.

Probing the composition of exoplanet atmospheres reveals the physical processes at play and provides insights into their interior and formation history. Atmospheric temperatures are key in shaping these atmospheres and setting molecular abundances. However, warm exoplanets (Teq < 1000 K) are not well understood. JWST opened a new window into these atmospheres thanks to its broad coverage from red to mid-infrared wavelengths and unprecedented sensitivity. Carbon- and sulphur-bearing species are now detected with high significance and their abundances can be measured. In this talk, I will give new insights on the atmospheres of transiting gas giant exoplanets focusing on the warm Neptune WASP-107b, the warm sub-Saturn HAT-P-12b, and the hot Jupiter WASP-43b that has a warm nightside. These studies highlight the importance of processes that alter thermochemical equilibrium and the role of the atmospheric temperature, provide clues on the presence and composition of clouds, but also leaves unanswered questions. I will also present other projects that I conduct with JWST, from the calibration of the MIRI instrument to the search for unknown asteroids.

PDS 70 is the first confirmed multi‑planet system imaged within a protoplanetary disk, but the evolutionary state of its companions depends strongly on the poorly constrained age of the system and its Upper Centaurus–Lupus (UCL) environment. I will present a kinematic approach to this problem using Chronostar, a Bayesian forward‑modelling framework that decomposes stellar populations in six‑dimensional phase space into expanding Gaussian components. Applied to a candidate population associated with the T component of Sco–Cen, our reconstruction identifies PDS 70 as part of an extended, elongated young stellar structure with a membership‑weighted age of approximately 12–15 Myr. I will discuss how this kinematic age compares to other UCL age estimates, and what it implies for the luminosities, masses, and formation scenarios of PDS 70 b and c when combined with planetary cooling tracks and dynamical mass constraints.

How environment shapes dwarf galaxies and their star clusters is still an open question. Satellite counts around nearby hosts both exceed and fall short of ΛCDM predictions depending on the system, so the Milky Way and M31 alone are not a reliable reference. Meanwhile, deep surveys of Virgo and Fornax have revealed strong environmental trends in nucleation fractions and globular cluster (GC) populations, yet equivalent characterization in low-density groups remains scarce. The Neighborhood Watch (NW) survey targets nearby groups (D < 18 Mpc) with deep DECam u'g'r'i' + Hα imaging. It reaches μ_i ≈ 28 mag arcsec⁻² out to at least the virial radius, a depth that rivals the Next Generation Virgo and Fornax surveys. NW also reaches LSST 10-year depth in u-band a full decade before that survey finishes. I will present first results from the NGC 6744 group, a Local Group analogue at 9.2 Mpc: a catalogue of nucleated and non-nucleated dwarf candidates and an initial GC selection. Finally, I will show my ESO internship work with VLT/MUSE spectroscopy of 12 of these dwarfs, where we measure stellar velocities and dispersions to confirm group membership and characterize their star-forming regions and globular cluster systems, to test how the group environment shapes dwarf galaxies.