Wednesday Colloquium


"On halo and galaxy connection with the cosmic web"

Wojciech Hellwing (Center for Theoretical Physics, PAN, Warsaw)

The Cosmic Web -- an intricate network of clusters, filaments, walls, and voids -- can be identified in a myriad of possible ways leading to a vast ocean of its aspects and properties. We are still quite far-away from possessing widely accepted standards. Because of this the Cosmic-Web impact on the formation and evolution of haloes and galaxies is a subject to ongoing debate. In this talk, I will demonstrate, using the NEXUS+ definition for the Cosmic Web identification, how indeed the disparate environments affect the local formation histories and hence properties of dark matter clumps and galaxies living within. I will focus on internal kinematics and morphological features and distribution of satellite systems. Our findings indicate a fundamental role that the local cosmic environment plays in shaping galaxy and halo formation histories, which in turn have profound implications for their intrinsic properties.

The seminar in a hybrid form. In person in the Lecture Hall at the Copernicus Astronomical Center, and online on Zoom platform and YouTube.


"Heartbeat stars and their tidally excited oscillations among massive stars and red giants"

Piotr Kołaczek (Wrocław University)

The majority of massive main-sequence stars reside in binary or even multiple systems. Moreover, many of them can be found in close and eccentric configurations, i.e. such that they will interact with the companion before the supernova explosion. These facts directly imply that binarity is inherent in the evolution of massive stars and cannot be ignored when studying these objects as well as their final outcomes. For this reason, eccentric ellipsoidal variables (EEVs, aka heartbeat stars) are excellent observational `laboratories' of the ongoing tidal evolution of the aforementioned systems. The orbital phase-dependent tidal potential, acting on both components, can also induce tidally excited oscillations (TEOs) which have quite different properties compared to e.g. self-excited oscillations. Surprisingly, EEVs (and TEOs) can be found even among red giants. These eccentric and evolved systems point to the efficient eccentricity pumping mechanism(s), needing further investigation. During my talk I would like to focus on the latest observational studies concerning EEVs and their TEOs among two distinct groups of stars – massive/intermediate-mass main-sequence stars and red giants. I will mention the `extreme' case of massive EEV, namely MACHO 80.7443.1718, the importance and content of the OGLE collection of heartbeat stars, and the effects of theoretical modeling of TEOs in massive EEVs.


"High-frequency quasi-periodic oscillations and oscillations of accretion disks"

Jiří Horák (Astronomical Institute of the Czech Academy of Sciences)

Accreting black holes and neutron stars show remarkable variability in their X-ray light curves. In this talk, we will concentrate on the high-frequency variability and its possible theoretical explanations. Most of the attention will be devoted to models based on orbital motion and oscillations of accretion disks. In particular, we will discuss basic properties of linear modes of thin disks and their nonlinear excitation.


"Revisiting Asteroseismology with state-of-the-art pre-main sequence models"

Thomas Steindl (University of Innsbruck | Institute for Astro- and Particle Physics)

The pre-main sequence phase of stellar evolution often gets branded as very simple. While the simple classical model of pre-main sequence evolution is incredibly successful, for example, in describing the basic features of young open clusters, the early stellar evolution is much more complicated. The details of the accretion process lead to a chaotic evolution, both in the Hertzsprung Russel diagram and stellar interiors. The advent of space telescopes, in combination with the study of stellar pulsations, provides the opportunity to test stellar structure in an unprecedented way. For asteroseismic studies of young stars, we need to embrace this chaotic phase of stellar evolution in order to harvest its full potential. In this presentation, I will talk about our recent results in the effort to combine asteroseismology and state-of-the-art pre-main sequence models and give an outlook for future research.