Seminars
Presenter: Dr Chandra Shekhar Saraf
Affiliations: Korea Astronomy and Space Science Institute (KASI), South Korea
Abstract
Our understanding of the Universe has undergone a revolution over the past century, revealing a cosmos governed by dark energy, shaped by dark matter, and expanding ever faster. We are now at a stage where cosmology has transformed into a precision science. In this talk, I will introduce the key concepts and challenges of our standard model of cosmology. I will highlight recent insights from major experiments, including the Atacama Cosmology Telescope (ACT), which has refined our view of the cosmic microwave background, and the Dark Energy Spectroscopic Instrument (DESI), which
is mapping the large-scale structure of the universe with unprecedented precision. Finally, we will reflect on the capabilities of experiments such as the Vera C. Rubin Observatory, Euclid, SPHEREx, Simons Observatory to further enhance our understanding of the Universe.
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Presenter: Christian Ikechukwu Eze
Affiliations: University of Nigeria, Nsukka, Nigeria and Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland
Abstract
Massive stars occur mostly in binaries or multiples, with some hosting pulsating components. Just as the sound of a guitar is produced when its strings excite resonances in the guitar body at natural frequencies, the energy trapped within a star causes it to oscillate at its natural eigenfrequencies. These pulsations cause the outer layers of the star to vary in brightness as it expands and contracts. These rare systems, where massive stars both pulsate and orbit in eclipsing binaries, offer an unparalleled laboratory for probing the internal physics of high-mass stars. The combination of
precise photometric and spectroscopic data from eclipses with asteroseismic signals gives new insights into stellar interiors, including core structure, rotational profiles, and mixing processes. Leveraging data from space-based missions such as Kepler and TESS, alongside ground-based campaigns, this seminar explores how the interplay between stellar pulsations and binary interactions enables precise constraints on fundamental stellar parameters and evolutionary pathways of massive stars. Join us as we decode the rhythmic pulses of the cosmos and uncover the hidden symphony within these extraordinary stellar duets.
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Presenter: Dr. Piotr Kołaczek-Szymański
Affiliation: University of Liège, Belgium
Abstract
Currently, we know that stellar binarity is a common phenomenon, particularly important for massive stars whose evolutionary tracks are predominantly affected by the presence of a (nearby) companion. Moreover, a significant fraction of binary systems at various stages of their evolution is characterized by eccentric orbits, either due to their relatively young age or eccentricity-pumping mechanisms. Hence, the close investigation of eccentric binary systems is crucial for the verification of various tidal interaction theories that greatly influence our predictions of the evolution of these objects. During the seminar, I will focus on eccentric ellipsoidal variables (EEVs), occasionally dubbed as "heartbeat stars", tidally excited oscillations, and their impact on the evolution of EEVs.
Additionally, I will discuss other effects associated with the periastron passages that can mimic EEVs, such as massive systems with stellar wind collisions.
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Presenter: Prof. Lorenz Roth
Affiliation: School of Electrical Engineering and Computer Science KTH Royal Institute of Technology Stockholm,
Sweden
Abstact
Since the Voyager mission flybys in 1979, we have known Jupiter moon Io to be extremely volcanically active as well as to be the main source of plasma in the vast magnetosphere of Jupiter. While the volcanic activity is generally dynamic and variable, the Jupiter magnetospheric plasma environment is stable on timescales from days to months. However, various observations suggest that occasionally (roughly 1-2 times per decade) the plasma environment undergoes major transient changes over several
weeks, apparently overcoming any stabilizing mechanisms.
I review the current knowledge on Io’s volcanic activity, atmosphere, and the magnetospheric neutral and plasma environment in view of their roles in the mass transfer from Io to the plasma torus and magnetosphere. At the end, I will briefly discuss what current and future space missions (Juno, JUICE, Europa Clipper) might contribute to address this topic.
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Presenter: Dr. Alicreance Hiyadutuje
Affiliation: Space Science, South African National Space Agency (SANSA)
Abstract
The law of conservation of energy states that energy is neither created nor destroyed; it can only transform into different forms or transfer from one place to another. This principle is crucial in understanding many natural phenomena, including those occurring within Earth's magnetosphere. A significant portion of the magnetospheric energy input originates from the Sun, primarily through solar wind, Coronal Mass Ejections (CMEs), and solar flares. These energetic solar events influence the magnetosphere, leading to various phenomena, including the generation of waves.
Waves are one of the key effects driven by space weather and terrestrial conditions. Different types of waves are involved, including atmospheric waves such as planetary waves, tides, and Atmospheric Gravity Waves (AGWs). AGWs are particularly important in influencing ionospheric behavior and can lead to disturbances known as Travelling Ionospheric Disturbances (TIDs). These disturbances are often the result of processes such as Perkins Instability and other mechanisms that generate AGWs. The interaction between AGWs and the ionosphere plays a key role in the formation and propagation of TIDs.
Groups of AGWs and TIDs are discussed in detail, highlighting their interactions and how they contribute to the overall dynamics of the ionosphere. Additionally, the presentation explores other mechanisms that can give rise to TIDs, such as the impact of geomagnetic storms, lightning, and other space weather phenomena.
At the conclusion of the presentation, we explore the significant impacts of TIDs on High Frequency (HF) communications. These disturbances can affect radio signal propagation, leading to communication outages, signal degradation, and interference. Understanding the behavior of TIDs is essential for predicting and mitigating their effects on HF communication systems, which are critical for global communication networks, particularly in remote and military applications.
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Presenter: Prof. F.C. Odo
Affiliation: University of Nigeria, Nsukka.
Abstract
The distributions of observed γ-ray properties, as well as orientation parameters of a sample of Fermi-LAT AGNs were used to investigate the hypothesis that γ-NLS1 objects are beamed sources with γ-ray emitting axes inclined at close angles to the line of sight. Based on these parameters we investigate the relationship between γ-NLS1s and other subclasses of γ-ray emitting jetted AGNs. Results show that γ-NLS1s are more highly beamed than both FSRQs and BL Lacs with mean value of core-dominance parameter Rγ ~ 9507. γ-NLS1s and jetted Seyfert galaxies are continuous in distribution of the orientation parameter with average cone angles ϕm ~ 8o and 44o respectively. Furthermore, the spectral energy distribution of γ-NLS1 is comparable to those of FSRQs and BL Lacs suggestive that γ-NLS1s and blazars form a continuous spectral sequence. There is a significant anti-correlation (r ~ -0.9) between the γ-ray dominance (Dγ) and γ-ray luminosity. There is a strong dependence of Dγ on redshift (r ~ -0.7) suggestive that Dγ is more sensitive to environmental factors than intrinsic γ-ray luminosity. The results suggest that γ-NLS1s are highly beamed γ-ray sources whose de-beamed counterparts can be found among Seyfert galaxy populations.
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