Upcoming seminars
April 28, 2026 at 13:00 CEST
Spotting Gravitational Wave progenitors in Hubble’s FUV spectra
Dorottya Szécsi
(Institute of Astronomy, Nicolaus Copernicus University, Toruń, Poland)
Amongst the stellar evolutionary pathways leading to GW emission, the so-called “chemically homogeneous evolution” channel predicts hot, early O type stars on the main sequence and Wolf–Rayet stars of class WO on the post-main sequence. But how can we find these objects observationally? Our best chance is to look into Hubble’s FUV spectroscopy of metal-poor local starbursts such as I Zwicky 18. However, doing that one faces the challenge of cross-matching STIS vs COS measurements for a dwarf galaxy that is spatially extended—a task that is far from trivial. In this talk, I present my decade-long hunt for proving the existence of chem.-hom.-evolving GW progenitors, which recently led me to conclude that Hubble did in fact probably see these stars (Szécsi+25, A&A): after a careful re-examination of the archives, observations seem fully consistent with what the theory predicts. This includes the presence/absence of famous emission bumps like C-IV (1550 Å) and He-II (1640 Å), the amount of He-II photoionization and spectral hardness, and more. Additionally, I discuss what this means for a potential future JWST detection.
Held seminars in 2026
February 17, 2026 at 13:00 CET
Planetary Tidal Disruption Events as a Driver of Extreme Stellar Variability
Matías Montesinos Armijo
(Académico Departamento de Física, Universidad Técnica Federico Santa María, Chile)
Large-amplitude, long-duration stellar variability is often attributed to intrinsic instabilities in young stars or erratic accretion from protoplanetary disks. However, recent time-domain surveys have uncovered a population of “What Is This” (WIT) objects—transients whose light curves and thermal evolution defy standard classification as classical outbursts or stellar winds. In this talk, I propose that many of these extreme variability events can be explained by the Tidal Disruption Event (TDE) of a giant planet. Using 2D hydrodynamic simulations, I model the catastrophic disruption of Jupiter- and Neptune-mass planets and the subsequent formation of a luminous transient disk. I will show that the accretion of this planetary material produces multi-year transients with peak luminosities L ~ 10^38 erg s^-1 that can overwhelm the host star. A key focus is placed on how orbital eccentricity drives the variability: while circular inspirals produce smooth plateaus, plunging eccentric orbits create highly volatile, multi-peaked light curves. These signatures, combined with a characteristic “bluer-when-brighter” color evolution, provide a new framework for identifying planetary consumption in our galaxy and distinguishing it from classical stellar outbursts.
February 13, 2026 at 13:00 CET
Stellar Content and Star Formation in IRAS 18456-0223
Nilesh Pandey
(Astronomical Institute of CAS, CZ)
Star formation plays a critical role in galaxy evolution, yet the detailed relationship between local environmental conditions and the early stages of stellar and cluster formation remains constrained. In my master’s thesis at Indian Institute of Astrophysics (IIA), India, we address this research gap by performing a comprehensive multiwavelength investigation of star formation in IRAS 18456-0223. We identified young stellar objects (YSOs) using infrared color–color criteria, with proper motion and distance to the cloud refined by Gaia astrometry. The spatial distribution of YSOs was quantified via statistical techniques, revealing a hierarchical clustering that traces the filamentary structure of their natal molecular clouds. Individual physical parameters of the YSOs were constrained by fitting their spectral energy distributions (SEDs), yielding mass, temperature, and evolutionary stage estimates. Optical spectroscopy data reduction and analysis for selected sources were carried out utilizing the Himalayan Chandra Telescope’s HFOSC. Herschel far-infrared observations were analyzed produce high-mid resolution maps of dust temperature and column density. Our integrated approach demonstrates that regions with enhanced dust temperature and column density coincide with peaks in YSO clustering, thereby constraining the physical conditions that regulate star formation and the early evolution of embedded clusters.