Upcoming seminars
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Held seminars in 2025
November 3, 2025 at 13:00 AM
Planetary Systems around White Dwarfs + Physical properties of the nebulae of two Herbig Ae/Be stars
Leila Saker
(Universidad Nacional de Córdoba, Argentina)
This seminar will be divided into two parts. In the first part, I will present my main research work, which focuses on the characterization of debris discs and the search for planets around white dwarfs. In recent years, the number of white dwarfs accreting debris discs, formed by the tidal disruption of rocky bodies from their original planetary systems, has grown significantly. By determining their accretion rates through numerical simulations with the LPCODE stellar evolution code, we can infer properties of the original planetary systems, such as the lower mass limit estimated for these systems. Furthermore, I will discuss a photometric study using data from the TESS space mission aimed at detecting possible transit signals in white dwarfs with debris discs, produced by rocky bodies that have survived the evolution of their host stars. In the second part of the seminar, I will present the project I have been carrying out at ASU under the OCEANS program, focused on determining the physical properties of the nebulae surrounding two Herbig Ae/Be stars.
September 17, 2025 at 13:00 AM
Heartbeat Star Signatures in TIC 349480752 and Eccentric Disk Effects in QT Peg from TESS Observations
Andrii Maliuk
(Astronomical institute of SAV, Slovakia)
TIC 349480752 exhibits unusual pre- and post-transit brightening features in its light curve. We hypothesize that this system is a heartbeat star and are modeling its light curve using the ELLC code to better understand its geometry and the origin of the observed variability. We are also modeling the light curve of QT Peg based on TESS observations. QT Peg is an eclipsing binary system in which the primary eclipse consists of a narrow component (caused by the Roche-lobe-filling secondary star) and a broad component, which we interpret as originating from an eccentric accretion disk whose apocenter is oriented toward the secondary. This system is being modeled using the SHELLSPEC code.
August 21, 2025 at 11:00
Looking at vampire stars with fringes
Henri Boffin
(ESO)
Symbiotic stars serve as exceptional laboratories for investigating mass transfer processes in binary systems. While radii inferred from rotational velocities or spectral types suggest small Roche-lobe filling factors, the presence of ellipsoidal variability in their light curves, presumably caused by tidally deformed giants in many symbiotic systems, indicates the opposite. Interferometric observations of symbiotic giants – in this case, with the PIONIER instrument on the VLTI – combined with distance measurements provided by the Gaia satellite, offer a promising avenue to resolve this discrepancy. I will present the analysis of 13 symbiotic stars and another symbiotic-like system, showing what we can learn on their Roche lobe filling factor and their evolutionary state. I will also show what is the perhaps the most convincing case of tidal deformation of a red giant being observed directly, thanks to the interferometric technique. I will finish by highlighting the implications of these results.
August 21, 2025 at 10:00
Avenues for radial velocity extraction – s-BART & PoET
André M. Silva
(Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal)
One of the boldest challenges of present-day astrophysics is to find and characterize other Earths: rocky planets that are capable of sustaining liquid water on their surface over long periods of time. One of the most prolific extra-solar planet discovery methods is radial velocities (RV). However, the identification of Earth-like planets faces significant challenges due to the small amplitudes of such signals and the difficulties introduced by two factors: i) Earth’s atmosphere; and ii) the stellar surface presenting temporal and spatial variability. The level of precision needed to detect Earth-like planets orbiting other suns thus motivated new developments in both instrumentation (e.g. ESPRESSO) and data analysis. In this seminar, I will start by discussing the methodology behind the s-BART (Silva+2022) algorithm. present an overview of its most recent results, and discuss systematic contaminations on RV time-series. At its core, s-BART is a Bayesian implementation of the widely used template-matching algorithm, extracting RVs through a comparison of stellar spectra with a stellar model. Afterwards, I will briefly present the PoET solar telescope with first light predicted for Q3 2025. PoET will connect to the “planet hunter” ESPRESSO spectrograph (ESO-VLT), allowing us to acquire both disk resolved and disk integrated (“sun-as-a-star”) observations of the Sun. This unique dataset will cover the full optical domain (380-780 nm) in one single shot and open the door to better understand the impact of stellar activity on stellar spectra.
August 5, 2025 at 13:00 AM
Rise of Habitability on Young Rocky Exoplanets: Systems Science Approach
Vladimir Airapetian
(American University, Washington, DC, USA)
Discovery of over 5700 exoplanets with Kepler mission, TESS, the Hubble Space Telescope, and JWST suggests that rocky exoplanets in the habitable zones around G, K, and M dwarfs are common in our Galaxy. These detections open a new era in the characterization of the planetary atmospheric environments, the critical step in the search for conditions suitable for life and signatures of their biospheres. Are biospheres of terrestrial-type exoplanets a common phenomenon? How can we detect a (pre)biosphere from a rocky exoplanet? Can we search for Earth twins? Critical examination of the heliophysical and physico-chemical conditions that supported the emergence of life on the early Earth and other inner planets in our Solar System is a promising way to address these fundamental questions. Understanding the conditions for habitability requires the characterization and assessment of several factors: retention of a relatively thick atmosphere, presence of basic molecular compounds, and availability of persistent external energy fluxes. The consistent characterization of space environments and their impact on exoplanetary upper atmosphere and climate requires a new system science approach to characterize habitability as the evolving physico-chemical phase of an exoplanetary system. In this talk, I suggest that while we have no consistent ideas about forms of exoplanetary life other than our own, prebiotic conditions that required the formation of prebiotic chemistry can be well specified under laboratory conditions. These factors could have promoted the emergence and complexification of biological systems on early Earth and possibly Mars. First, I will describe our recent observational campaigns of young solar-like analogs, and data-constrained state-of-the-art MHD and kinetic models of stellar coronae, transient events (CMEs and SEPs) and discuss the impact of solar/stellar eruptive events on atmospheric escape. Second, I will discuss how the extreme space weather in the form of flares, coronal mass ejections, and energetic particle events (like 775AD event) from the recent past of our Sun provides critical insights into the atmospheric chemistry of young terrestrial-type exoplanets, assessment of their role in the formation of biologically relevant molecules and pre-biosignatures to be detected with Habitable World Observatory. Third, I will present the recent results of recent laboratory experiments that reproduce the energy fluxes of particles from the young Sun and study the expected formation of amino acids, carboxylic acids, the chemical precursors of life and nitrous oxide. I will also introduce the design of our recently approved Exoplanetary Particle Irradiation Chemistry laboratory (EPIC Lab) at NASA GSFC.
June 24, 2025 at 13:00 AM
Spectroscopic and photometric studies of hot, massive stars in open star clusters using Artificial intelligence (AI) approaches
Ahmed Shokry & Mohamed Darwish
(National Research Institute for Astronomy and Geophysics, Helwan (Egypt))
Abstract: Clusters of stars are essential for studying the dynamic and chemical evolution of the galaxy and its neighbors. They are among the most important laboratories for testing the theory of stellar evolution. Studying hot massive stars (e.g. B and O-type stars) in open clusters is particularly useful because it allows a constant stellar age to be correlated with the cluster’s age. It is also very informative in astronomical research since it provides important information about stellar evolution, cluster dynamics, and population interactions. Hot, massive stars are important in the evolution of the chemical composition and structure of the Galaxy. Moreover, knowledge of the characteristics and age of the main sequence of hot, massive stars is crucial to a better understanding the next stages of evolution. Also, the derived stellar parameters within the cluster can significantly impact the generally hot, massive star population, as they can be used to infer the general properties of the stars in the clusters. Additionally, we aim to utilize the trained machine learning models to estimate key parameters of hot massive stars, including elemental compositions, kinematics, and stellar parameters. Quantify uncertainties associated with these estimations to assess the reliability of the results.
April 23, 2025 at 10:30 AM
Data driven exoplanet detection methods
Nikol Škvařilová
(Brno University of Technology, Faculty of Information Technologies)
The aim of this work is to design and implement an approach for analysing data from the transit method for exoplanet detection. The data comes from the Kepler and TESS space telescopes in the form of light curves, which record the observed brightness of a star over time. In this work, I focused on data-driven modelling and detection of exoplanets using Gaussian process regression. Both non-periodic and periodic kernel models were used to identify light curves suitable for detrending and to remove unwanted trends. Following this, models with periodic kernels were used to investigate the periodicity of the data. Finally, models with non-periodic kernels, trained on folded transits, were applied to detect transits in other light curves by correlation. The approaches described in this thesis provide an automated way to pre-process the data and identify possible transits.
April 1, 2025 at 13:00 PM
Observational evidence of a potential link between the short-term magnetic activity cycle and planet engulfment
Ján Šubjak
(ASU AV ČR)
The recent discovery of an increasing number of F-type stars displaying short-term magnetic cycles has sparked interest in understanding the cause behind this phenomenon. One hypothesis suggests that planet engulfment could be a potential explanation. A newly found mini-Neptune from the TESS space mission, TOI-2458 b, has been observed in a polar orbit around one of these stars. This finding not only supports the idea of planet engulfment but also indicates that the polar orientation of the planet could provide evidence that a hot Jupiter may have formed in situ. Additionally, our analysis suggests that the population of F-type stars with short magnetic cycles shows deviations within the framework of gyrochronology, further strengthening the case for the planet engulfment hypothesis.
February 4, 2025 at 10:30 AM
Probing the magnetospheres of chemically peculiar stars through the dips in their light curves
Zdeněk Mikulášek
(ÚTFA PřF MU Brno)
The advent of extensive photometric surveys such as Kepler or TESS missions has enabled the recent unexpected unveiling of short-term dips in the phase light curves of the majority of magnetic chemically peculiar stars of the upper main sequence. We explain this characteristic type of stellar variability caused by repeating transits of semi-transparent structures of stellar plasma trapped in the corotating magnetospheres of stars with a global magnetic field. In the light curves of such stars, we detect dips with a typical depth from fractions of mmag to several mmag, the configuration of which is persistent in the scale of decades. The occurrence of photometric dips, frequency, and prominence in the light curves of rotationally modulated objects allows us to judge magnetospheres’ dimension and strength, making this analysis a universally available instrument for diagnosing stellar magnetic fields. We will demonstrate dip analysis on notorious mCP stars such as V901 Ori, CU Vir, V545 Lyr, 56 Ari, or EE Dra.