General Seminar (2026)
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General Seminar takes place every Monday at 11.15 in Piwnice, radioastronomy seminar room.
Remote participation via the BigBlueButton (BBB).
13 April 2026
“Challenges for CMB B modes: Lensing Reconstruction, Subtraction, and Diffuse Foregrounds”
mgr Kishan Deka
The National Centre for Nuclear Research
Abstract:
In the era of high precision Cosmic Microwave Background (CMB) anisotropy measurements, detection of the primordial gravitational waves (PGW) will be one of the main goals of the upcoming CMB experiments. To make it possible, precise cleaning of the CMB polarisation maps from diffused contamination coming from polarised galactic emission and CMB gravitational lensing effect is needed. We investigate the impact of residual galactic foregrounds in lensing reconstruction and delensing of B modes for stage-4 CMB experiments. In this work, we pay special attention to forecast constraints for the amplitude of the primordial gravitational waves and their sensitivity to different foreground models with varying complexity. We are currently exploring a tomographic delensing method on simulations of LSST and Simons Observatory. We aim to achieve optimal delensing efficiency by using a multi-tracer approach, where we split the LSST observations into tomographic redshift bins. We aim to understand the impact of photometric redshift bin mismatch error on the estimation of primordial gravity wave amplitude.
20 April 2026
“Tracing radiation pressure instability signatures in the X-ray light curves and spectra of GRS 1915+105”
dr Kiki Vierdayanti
Bandung Institute of Technology, Indonesia
Abstract:
GRS 1915+105 is widely known as one of the most peculiar Galactic black hole X-ray binaries. It has been observed exhibiting quasi-periodic outbursts with both long and short-term variability in its light curves and spectra for more than twenty years before entering a fainter state in mid-2018. We combined analyses of the short-term light curves with the spectra of GRS 1915+105 using the NuSTAR data (2012–2024) and the long-term MAXI light curves in the 3–20 keV to trace the signature of radiation pressure instability in GRS 1915+105. We discovered a new group of variability classes, which consists of several variability classes, that can be associated with an increased advection rate, which occurs as the mass accretion rate increases even further and the disk becomes geometrically thicker than that of a standard disk but remains optically thick (known as slim disk). Our study showed that highly variable classes that have been studied extensively, such as \rho and \kappa, marked the transition from standard to slim disc, indicating the beginning of the radiation pressure instability. This transition occurs at around 50 per cent of its Eddington luminosity. Meanwhile, the most stable, less variable classes, \chi and \phi2, can be associated with the thermo-viscous instability that occurs in a standard disc, commonly found during the outbursts of the other, less peculiar, black hole X-ray binaries.
27 April 2026
“Modelling tidal decay of hot Jupiters through wave breaking”
mgr Jan Golonka
Institute of Astronomy, Nicolaus Copernicus University
Abstract:
Tidal interactions shape the evolution of close-in giant planets and internal gravity-wave breaking offers an efficient pathway for dynamical-tide dissipation, although its population-wide impact remains poorly constrained. In this talk I will focus on detailed predictions of wave-breaking for a large sample of hot Jupiter systems, discussing both population level trends and results for individual systems. These include predictions for currently operating tidal interactions, and simulations of the orbital evolution of known hot Jupiters until their engulfment or disruption by their host star. Additionally I will present the results of my follow-up observations dedicated to testing the predicted shifts in central times of transits from tidal theory.
4 May 2026
“Cosmic Dipole Anomaly”
prof. Roya Mohayaee
Institut d’Astrophysique de Paris, Sorbonne University, France
Abstract:
I will review the cosmic dipole anomaly, which refers to the discrepancy between the predictions of the FLRW model and observational data. I will explain how this anomaly emerges in analyses of quasars and radio datasets, where it currently exceeds the 5\sigma significance level. I will also review that this result has withstood rigorous systematic tests and persists across multiple datasets, methodologies and analyses.
11 May 2026
“Probing the baryon cycle of primordial galaxies in the ALMA and JWST era”
dr Prasad Sawant
Institute of Astronomy, Nicolaus Copernicus University
Abstract:
The ALMA Large Program ALPINE provides a unique multiwavelength perspective on star-forming galaxies at redshift z ~ 5, offering fundamental insights into their gas and dust content, morphological and kinematic properties, and the physical mechanisms governing their baryonic cycle. In this work, we employ chemical evolution models to investigate the co-evolution of gas and dust within this population of primordial galaxies.
We systematically explore the parameter space of dust production and destruction mechanisms, including Type II supernovae (SNII), asymptotic giant branch (AGB) stars, and grain growth within the interstellar medium (ISM) to reproduce the observed gas and dust properties across the ALPINE sample. Our models successfully account for the gas and dust content of the majority of these galaxies, pointing to SNII as the dominant dust production channel, with galactic outflows and moderate infall of gas playing a key role in regulating the overall dust budget.
A subset of galaxies, however, exhibit an anomalously rapid dust build-up on timescales of order ~ 20 – 100 Myr, which cannot be readily explained within a standard framework. We demonstrate that invoking a top-heavy initial mass function (IMF) which preferentially enhances the formation of massive stars and accelerates dust enrichment partially reconciles this tension, suggesting that variations in the stellar IMF may be a non-negligible factor in the early dust assembly of high-redshift galaxies.
Finally, I will discuss future directions enabled by the latest James Webb Space Telescope (JWST) observations and their synergies with radio continuum surveys through stacking analyses, for constructing a comprehensive picture of baryonic cycle across cosmic time.