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• 05.12.2025 - Simon Schleich (Uni. Vienna) & Anuja Raorane (Uni. Vienna)

  Simon Schleich (Uni. Vienna)

  How much do you trust this atmosphere? Sensitivity of atmospheric retrievals to perturbations in data

  The James Webb Space Telescope (JWST) is providing us with exoplanet atmospheric spectra of unprecedented quality. This improved data presents new challenges in retrieving exo-atmospheric properties. One of these is determining the reliability of atmospheric signals from observations. Reliable signal extraction is crucial for robust atmospheric characterisation. I will present an investigation into the impact of small-scale variations in spectroscopic data on the retrieval of exoplanetary atmospheric properties, using the hot Jupiter WASP-39 b as a case study. We compared results from homogenised atmospheric retrievals performed on three transmission spectra, all produced with the same data reduction pipeline. The resulting parameter estimates can be classified into several groups, based on their stability under perturbations of the data. These findings underscore the importance of assessing the stability and sensitivity of atmospheric parameter inferences. Stable, robust frameworks are essential for reliable population-level characterisation of exoplanetary systems.

  Anuja Raorane (Uni. Vienna)

  Non-thermal Escape of Atmospheres

  The three rocky planets of our Solar System, Earth, Venus, and Mars, each once had the potential to sustain habitable conditions, yet today only Earth remains habitable. Planetary habitability is closely linked to the composition and surface pressure of an atmosphere, both of which are significantly influenced by atmospheric escape processes. Among these, non-thermal escape plays a key role and is primarily driven by interactions between a planet’s upper atmosphere (magnetosphere) and the solar (stellar) wind.

  Today, atmospheric loss from all three terrestrial planets is dominated by non-thermal escape processes. These mechanisms differ significantly from one planet to another, as they depend sensitively on the planet’s magnetic state and the level of solar activity. This makes studying them challenging. In this seminar, I will focus on key non-thermal escape processes, namely, solar wind charge exchange and polar outflow on Earth, and ion pickup on Venus. While present-day escape rates on Earth, Venus, and Mars are too low to substantially cause thinning of atmosphere, these processes were likely far more efficient earlier in Solar System history. Their cumulative effects may have played an important role in shaping the evolution, composition, and climate of the rocky planets.
• 28.11.2025 - Sylvia Ploeckinger (Uni.Vienna) & Janus Brink (Uni. Vienna)

  Sylvia Ploeckinger (Uni.Vienna)

  The first results from the COLIBRE project

  The COLIBRE project (http://colibre-simulations.org) is a brand-new (Schaye et al. 2025, arXiv:2508.21126) large cosmological simulation project. The flagship simulations include cosmological cubic volumes with side lengths of 400 Mpc and 200 Mpc resolved with a particle mass (dark matter and baryons) of 10^7 and 10^6 solar masses, respectively, as well as smaller volumes (25, 50, and in a second stage 100 Mpc) with a particle mass of 10^5 solar masses. I will present the first results from the COLIBRE project, which includes the evolution of the galaxy stellar mass function between redshifts 0 and 17, and compare the agreement to observations to previous simulation projects, such as EAGLE, IllustrisTNG, and Firebox. 

  Janus Brink (Uni. Vienna)

  A SALT road travelled - my journey in astronomical instrumentation development

  As I "recently" joined the Institute I would like to use this talk to introduce myself, but more importantly introduce my previous place of work and illustrate how it may be of scientific relevance to you! Without giving too much away here, my talk will include a bit of background on SALT, discuss my involvement in a number of projects there over the last two decades and highlight the instrument and science capabilities of the facility.  If your research involves solar system, exoplanetary, galactic, extra-galactic or time-domain observational astronomy there may well be collaboration opportunities to explore!
• 21.11.2025 - Michael Cecil (MPIA) & Werner Weiss (Uni. Vienna)

  Michael Cecil (MPIA)

  Structure, Evolution and (In)stability of the inner regions of protoplanetary disks

  The inner protoplanetary disk is the cradle of the terrestrial planets in our Solar System, as well as a large number of exoplanets that have been detected to date. The small spatial scales and the conglomeration of numerous physical processes pose extraordinary challenges to studying these inner regions and the origin of planets close to their host star from both observational and modelling perspectives. We intend to put several puzzle-pieces into place by employing radiation-hydrodynamic simulations of these elusive regions to investigate their evolution and long-term stability. Our models show the emergence of large-scale instability mechanisms, that periodically reshape the structure of the inner disk and lead to observable variability of accretion onto the central star on various scales. I will discuss the physical foundations of the inner disk structure and explore the origins of these instabilities together with the potential consequences for the formation of planets or planetesimals in the inner disk. In addition to producing a variety of accretion burst signatures, such numerical simulations represent another step forward in sorting out the complexities of the evolution of planetary birthplaces.

  Werner Weiss (Uni. Vienna)

  The BRITE-Constellation

  UniBRITE and BRITE-Austria are the first satellites listed for Austria in the UN space register. UniBRITE was funded by the Science-Ministry in 2005 as part of a program dedicated to develop Austrian Universities. A  year later, a joint proposal of the Technical University of Graz and the University of Vienna was accepted by the FFG, which triggered BRITE-Austria. These two BRIght Target Explorer cubesats (BRITE) triggered a cooperation with Canda and Poland, which resulted in an ensemble of six similar cubesats devoted to astrophysics, in particular to asteroseismology. This ensemble is known as BRITE-Constellation.

  Cubesats were originally intended as testing tools for technical components in space and as a learning tool for students. But BRITE cubesats are the first, which explicitly were devoted to astrophysical research. Specified for a lifetime of 2 years, data are still produced after 10 years of operation and resulted meanwhile in more then 200 papers. Spectacular research highlights are, e.g., observations of a nova with high time resolution, starting before it became visible from ground, or discovering the onset of pulsation during periastron passages of very eccentric binaries. Another first and highlight is a new method for determining the stellar mass' of RG stars from the granulation signal which is buried in their Fourier spectrum.
• 14.11.2025 - Ivan Stanković (Uni. Vienna) & Sudeshna Boro Saikia (Uni. Vienna)

  Ivan Stanković (Uni. Vienna)

  How does chemistry control exoplanet atmospheric stability?

  Exoplanet atmospheres are very chemically diverse. Parameters like metallicity and the C/O ratio are often used to describe them, but while these work relatively well for hydrogen-rich gas giants, they are not suited for describing rocky planets. To identify better metrics and explore which compositions are actually stable and which are more susceptible to loss, I investigate how different elemental mixtures behave over long timescales against thermal escape using our atmospheric model, Kompot.

  I construct a grid of upper atmospheric compositions for an Earth-like planet by varying the amounts of H, C, N, O, and S. This extends previous applications of our model, which focused on CO2-N2 atmospheres, to a broader chemical space.

  I will show that atmospheric lifetime depends strongly on the bulk elemental composition: it increases with oxygen and carbon content, but decreases with the amount of nitrogen. In terms of elemental ratios, the mass loss is correlated with H/O, H/S, C/O, and N/O, in that order. Sulfur shows little effect on its own, while the role of hydrogen requires further exploration, as the current model set only covers low-H cases.

  Sudeshna Boro Saikia (Uni. Vienna)

  Titan as a laboratory for exoplanet chemistry

  Saturn’s moon Titan is the only other body in the solar system with surface liquids and a thick atmosphere rich in organic compounds. In addition to its huge astrobiological potential, it also possesses the only nitrogen-rich atmosphere besides Earth. Understanding its complex atmospheric composition is essential for identifying similar chemical signatures in distant exoplanets. In this talk, I will discuss simulations of the thermal and chemical structure of Titan's upper atmosphere using the Kompot code, and provide observational context from Cassini and ground-based data. I will also highlight how self-consistent modeling helps resolve current degeneracies between observations and theory, offering a more robust framework for interpreting atmospheric chemistry in the Solar System and beyond.
• 07.11.2025 - Christoph Saulder (MPE) & Chiara Buttitta (INAF Naples)

  Christoph Saulder (MPE)

  Cosmology with the DESI peculiar velocity survey

  While the main science goal of DESI is to measure the expansion rate of the universe using Baryon Acoustic Oscillations, the incredible amount of spectra collected by the instrument allows for additional cosmological measurements using other probes. The DESI peculiar velocity survey derives peculiar velocities using the fundamental plane and Tully-Fisher relation and it will provide the largest peculiar velocity sample every observed. This unique and vast dataset will allow us to measure the strength of gravity via the growth rate of structure at unprecedented precision. I will present the results from the early DESI data, as well as provide an outlook on the upcoming DESI DR1 analysis of peculiar velocity and the scope of DESI DR2 peculiar velocity key project.

  Chiara Buttitta (INAF - Osservatorio Astronomico di Capodimonte, Naples)

  Probing the limits of spectroscopy in the low-surface brightness Universe with LEWIS

  In the standard cosmological framework of ΛCDM, low-surface brightness (LSB) galaxies are the building blocks of the Universe. Ultra-diffuse galaxies (UDGs) play a crucial role. This class of extreme galaxies have a central surface brightness fainter than μ₀ ≥ 24 arcsec² and an effective radius larger than Re ≥ 1.5 kpc, thus can be considered as the extreme LSB tail of the size-luminosity distribution of the dwarf galaxies population. Due to their extremely faint and diffuse nature, collecting deep spectroscopic data is challenging and time-consuming, and only a few dozen UDGs have been studied with spectroscopy. In this context, the LEWIS project (Looking into the faintEst WIth MUSE, P.I. Enrica Iodice) promises to revolutionise the scientific panorama of the UDGs doubling the number of spectroscopically studied UDGs to date. It aims to study for the first time the structural properties of a nearly complete sample of UDGs in the Hydra I cluster of galaxies. In this contribution, I would like to present the recent groundbreaking results we achieved with LEWIS, highlighting the challenges we faced in the extraction of structural properties of these extremely faint objects.

   

   
• 31.10.2025 - Turan Ali

  Turan Ali

  Storytelling for Scientists

  Storytelling is the only way we can profoundly communicate as humans. Often, when scientists try to communicate, they prioritise information-transfer over storytelling, treating their “audience” as information processors, not storytelling creatures. If information is embedded in great stories, integral to the plot, the story is understood and the information remembered. Information delivered without story is quickly lost.

  In this taster session, Turan Ali, producer/writer/director of BBC drama, on-stage storyteller and stand-up comedian, who is a former biologist, introduces the major elements of story theory and explores at which points in a story learning, persuasion and memorising happen. He touches on how to harness the intrinsic power of stories for any subject and also explores the role of emotion and symbols in storytelling, and how not to leave a story’s impact to chance.

  Lastly, the myriad ways that stories can be delivered will be summarised, pinpointing general principles of which formats of storytelling are suitable for what sort of stories and goals. Choosing the right or wrong way to tell your story will make or break its impact. The amount of information in your story will dictate which formats (or combinations) could be used to tell the story effectively, and which formats (or combinations) would kill the story. Powerful communication is achieved by consciously combining story structure, information-quantity and appropriate format(s). Yes, storytelling is rapidly becoming a precise science with provable, measurable, cause and effect.

  We will touch on all these elements, in this lively, participatory taster session.
• 17.10.2025 - Yannic Pietschke (Uni. Heidelberg) & Laurane Fréour (Uni. Vienna)

  Yannic Pietschke

  Reconstructing Reionization with 21cm Summaries and Galaxy Synergies

  The Square Kilometre Array (SKA) enables precise measurements of 21cm fluctuations that trace ionization, temperature, and density fluctuations of the intergalactic medium. However, directly reconstructing the timeline of reionization in terms of the evolving neutral hydrogen fraction remains challenging due to the highly non-Gaussian nature and thus intractable likelihood of the 21cm signal. In this talk, I will introduce EoRFlow, a simulation-based inference (SBI) framework that yields fast, unbiased posterior estimation of the $x_\mathrm{HI}$ evolution in narrow redshift slices, allowing for piecewise reconstruction of the global reionization history. To demonstrate the applicability of our method, we validate it on realistic mock datasets generated using the SKA-Low AA* telescope configuration, and demonstrate how the choice of summary statistics, from power spectra to network-learned features, impacts the accuracy and robustness of SBI. Finally, I will highlight the potential of combining SKA and galaxy survey data to unlock new insights into the epoch of reionization.

  Laurane Fréour

  Astronomers for Planet Earth, a grassroots movement of more than 2300 Volunteers

  Since its founding in 2019, Astronomers for Planet Earth (A4E) has been working to share the powerful view astronomers have of Earth. We, as astronomers, know how rare life on a planet is. We, as astronomers, know that there is no planet B. This perspective not only helps communicate the urgency of the climate crisis, but also reminds us of what is at stake. 

  We focus on outreach and education, creating and sharing tools to help communicate and teach on climate change. We also foster a strong sense of community among members, united by shared values around justice, sustainability, and the preservation of life on Earth, and driven by our passion for astronomy.

  In this talk, I will explain how A4E is structured. I will highlight recent projects and milestones, and explore how collaborative efforts can amplify impact. Finally, I will suggest concrete ways that individuals, whether students, astronomers, or institutions, can get involved. 
• 10.10.2025 - Alvaro Hacar (Uni. Vienna) & Emily Hunt (Uni. Vienna)

  Alvaro Hacar

  On the origin of clusters within the filamentary ISM

  Recent ALMA observations indicate that young proto-clusters originate at the intersection point of large-scale filaments in the so-called hub-filaments systems (HFS). While formed as part of the filamentary structure of the ISM, the properties of these HFS largely depart from their parental filaments in terms of mass, size, column density, stability, and accretion rates. During my talk I will show how the formation and properties of these HFS, and thus of stellar clusters, can be explained by a geometric phase-transition between filamentary and spheroidal gas configurations during the assembly of these HFS.

  Emily Hunt

  Twitter is dead. How can we do better for networking and outreach?

  Twitter spent ten years as the de facto online platform for astronomy networking and outreach. However, semi-recent events have seen it devolve into a politicized and ineffective platform for science communication and networking. The loss of Twitter has shown how fleeting online spaces can be. It begs the question: can we do better, or are astronomers doomed to always have their online homes tied to the whims of a billionaire?

  In this talk, I will present The Astrosky Ecosystem: an open source project to build independent social media infrastructure with the AT Protocol, the social media protocol that powers Bluesky (a prominent Twitter challenger). After discussing the basics of the AT Protocol, I will discuss what our project does, and how we are building ways for the astronomy community to have full, independent online sovereignty of its data. I will also discuss how you can use Bluesky and our tools to build an online network.