This week's PhD colloquia are highlighted.
| Date | Time | Title/Abstract | Speaker | Affil. |
|---|---|---|---|---|
| 04/09 Thursday DM 1.09 | The Sky is Made of Lava - How lava worlds reveal their interiors through their atmospheres Hot rocky exoplanets are a class of planets that have seen a surge of interest in the last decade. Due to their proximity to their host stars, they have surface temperatures exceeding 1500 K—enough to melt their crusts and create vast lava oceans that can cover a significant portion, if not all, of their surface. Such lava oceans provide an interface between a planet's interior and atmosphere, allowing the atmospheric chemical composition to be directly influenced by the interior - providing a unique view into rocky planet interiors. This thesis focuses on developing lava vaporisation models and implementing them within larger code frameworks used to produce atmospheric spectra of these planets. | Christiaan van Buchem | ||
| 08/09 Monday BW0.32 | 15:00 | Patterned detectors: From design to science Patterned detectors are an existing technology that can be found in almost all color cameras. These patterned detectors consist of adding optical filters in a pattern on a pixel level on top of a detector. In common cameras the filters are broadband red, green and blue color filters. However, in this talk (and thesis) I focus on more varied spectral filters and polarimetric filters. I will first show a design framework for a patterned detector for hyperspectral imaging. This framework makes use of automatic differentiation to train on existing hyperspectral datasets to determine the best spectral filters and the best layout of those spectral filters on the detector. I extend this framework by adding polarimetric filters as well, enabling the design of a spectro-polarimeter. Halfway the colloquium, I shift focus from the theoretical design to an already existing commercial patterned detector for color and gray-scale polarimetric imaging. I will describe a calibration campaign that we conducted for these patterned detector cameras and the accuracies that we can expect from them. Finally, we used one of the now calibrated patterned detectors and integrated it into a new instrument that measures the linear polarization properties of the northern lights. | Thijs Stockmans | |
| 20/10 Monday DM1.15 | Destroy, Create, Transform and Sublimate. Laboratory Dissociation Studies on Polycyclic Aromatic Hydrocarbons and Analogues Polycyclic aromatic hydrocarbons (PAHs) and their nitrogen analogues (PANHs) are widely considered as carriers of the aromatic infrared bands (AIBs), which are observed throughout the interstellar medium (ISM). Yet, there are still many uncertainties regarding the dissociation behavior and astrochemical role of PA(N)Hs in the ISM. In this colloquium, I will present the work done during my PhD to elucidate these topics. Using dissociative photoionization I was able to determine seven fragmentation pathways of benzonitrile, and formation routes potentially relevant for space. Mid-infrared (mid-IR) spectra of 1,5,9-triazacoronene (TAC), a triply nitrogenated coronene molecule, and its protonated counterpart show close correspondence with observed AIB features. Photodissociation experiments on TAC show the potential formation of nitrogen-bearing fragments linked to interstellar cyanopolyynes. Additional experiments on the dissociation fragments of PA(N)Hs show that they readily react with water, revealing a new potential bottom-up formation pathway towards complex organic molecules (COMs) in the ISM. Finally, the IR spectrum of doubly dehydrogenated (i.e. molecular hydrogen loss) naphthalene is investigated and showed significant isomerization, leading to the formation of five-membered carbon rings. These results highlight how (polycyclic) aromatic species can act as key drivers of molecular complexity in the ISM and further broaden our understanding of their chemical role. | Jerry Kamer | ||
| 28/10 BE0.18 | From a Biased Perspective: Quasars, Mergers, and Planet-Forming Discs My PhD has been a (biased) journey across diverse topics: from quasars and emerging AGN populations to gravitational-wave signals and protoplanetary discs. In this colloquium, I will focus on the core theme of my thesis: the growth of supermassive black holes as traced by quasar activity across cosmic time. I will show how the spatial clustering and luminosity function of quasars, taken together, constrain the dark-matter halos that host quasars and the duty cycle of accretion. These diagnostics are especially powerful at high redshift, where the appearance of billion-solar-mass black holes within a few hundred million years of the Big Bang remains a central puzzle. I will also highlight the impact of JWST in mapping early quasar environments and revealing new AGN candidates—most notably the "little red dots"—that challenge our understanding of black hole evolution. I'll conclude with the key open questions arising from this work and a roadmap for addressing them. | Elia Pizzati | ||
| 11/11 BW.0.39 | 15:15 | Chronicles of Cosmic Dawn - High redshift quasars as probes of supermassive black holes and the intergalactic medium In my PhD, I have explored the first billion years of cosmic history, investigating how quasars illuminate the intergalactic medium (IGM) during the Epoch of Reionization (EoR). By combining new spectroscopic observations, proximity zone size measurements, and forward-modeling techniques, this work aims to understand how the first supermassive black holes grew and how their radiation shaped the surrounding Universe. I will first present a dataset of 45 quasars at 6.50 < z < 7.65, uniformly reduced and used to construct high-quality composite spectra. These reveal that the broad UV emission properties of quasars have remained remarkably stable across cosmic time, hinting at universal accretion physics even in the early Universe. I will then show new measurements of proximity zone sizes for 59 quasars at 5.76 < z < 7.55, which confirm the expected luminosity dependence but reveal a steeper redshift evolution than previously found. The large observed scatter points to a combination of short quasar lifetimes, environmental effects, and variations in the IGM neutral fraction. Finally, I will introduce a forward-modeling framework that directly compares observed Lyα transmission statistics with realistic mock spectra for 21 E-XQR-30 quasars at 5.76 < z < 6.59. The results show good agreement within proximity zones but growing tension in the Lyα forest, suggesting that our models still miss key physical ingredients such as patchy reionization or ultraviolet background fluctuations. Together, these studies provide a coherent picture of how quasars probe and transform the IGM near the end of reionization, offering new clues to the complex interplay between black holes and the early Universe. | Silvia Onorato | Leiden Observatory |
| 12/11 Wednesday DM1.15 | 13:00 | Lighting Up Dark Exomoons: Observational signatures of tidally induced volcanism in other worlds Solar system moons show great diversity in their physical and orbital characteristics, and some of them are notable for their geological activity. Io, Jupiter's innermost satellite, is the most volcanically active body in the solar system. Enceladus, an icy moon of Saturn, possesses surface fractures, active plumes of water vapor and a global subsurface ocean. A common driver behind these phenomena seen in the solar system moons is tidal heating: as a moon revolves on an eccentric orbit around a planet, changing gravitational pulls flex the body and generate internal heat. Because every gas giant in the solar system hosts natural satellites, it is reasonable to expect that many of the gas giant exoplanets we have found are also orbited by moons (exomoons). Yet,no exomoon detection has been unambiguously confirmed until today. Observing the light from the planet and detecting faint companions like moons is difficult because the overwhelming brightness of their host stars must be suppressed, and even then the planet itself can outshine its moons. Yet, in infrared wavelengths, where heat emission becomes important, a special class of objects, tidally heated exomoons (THEMs), may stand out. These are analogous to Jupiter's volcanically active moon Io, and provide a unique opportunity: powered by tidal forces, these moons can reach high surface temperatures and, in some infrared wavelength bands, be as bright or brighter than their host planets. Unlike transit observations, direct thermal detection does not depend on a specific orbital phase or repeated events. This opens a search window for identifying moons around giant planets orbiting at large distances from their stars. This thesis focuses on the detectability of THEMs through a variety of methods, while also examining the interior and orbital properties that make them observable. It takes steps toward finding such moons, and explores when tides can heat them enough to glow in the infrared, and whether their brightness or its variability can be measured with current and upcoming telescopes. By combining putative observations with models of tidal heating, the thesis further explores the constraints that can be placed on planetary and satellite interiors. Tidal heating models are finally used to study the interiors of icy exoplanets, that are thought to resemble the icy moons of our solar systems. Here, the focus is on Trappist-1 f, g, and h, examining whether internal heat could sustain subsurface oceans, and whether signs of volcanic activity might be detectable. Together, these studies highlight the role of tidal heating as both a detection pathway and a window into interior processes of extrasolar worlds. | Elina Kleisioti | Leiden Observatory / TU Delft |
| 05/02 Thursday | TBA TBA | Osmar Guerra-Alvarado |
For questions and/or suggestions concerning the colloquium series. Please contact Andrew Sellek (e-mail ).