|657. ROK AKADEMICKI 2020/2021
Czas i miejsce
Seminaria OAUJ odbywają się w piątki po angielsku. Początek o godzinie 12:00, czas trwania: 45 minut + dyskusja. Ze względu na epidemię COVID-19 wszystkie seminaria odbywają się (do odwołania) jedynie jako zdalne sieciowe sesje przy użyciu ZOOM Video. Specyficzne adresy (linki) sesji będą rozsyłane w ogłoszeniach mailowych i udostępniane na życzenie. Zainteresowani, jak również osoby chętne do zaprezentowania referatów, powinny zgłaszać się w tej sprawie bezpośrednio do Łukasza Stawarza.
|2020-10-02||dr ADAM ZADROŻNY||National Centre for Nuclear Research, Warsaw|
|ZN OA 1537||
LSC-Virgo O3 Science Run, Multi-messenger astronomy and future possibilities
The aim of a talk is to give an overview current state gravitational wave observations. During three science runs (2015-2016, 2016-2017, 2019-2020) of Advanced LIGO-Virgo detectors observe multiple binary merger events. Most of the events are binary black hole mergers, but nine detected events had neutron star component. Those observations, especially GW170817, brought additional way to study neutron stars. In the last part of the talk I would focus on multi-messenger astronomy that could be done and possible future challenges and opportunities in gravitational wave astronomy.
|2020-10-09||mgr DOMINIKA KRÓL||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1538||
Accretion Induced Black Hole Spin-up in Numerical GR MHD Simulations
I will present an investigation of the accretion-induced spin-up of a black hole via numerical simulations. The method is based on general-relativistic hydrodynamics of the slowly-rotating flows in the Kerr metric, with change of mass and spin of the black hole during accretion taken into account. Simulations were performed using modified versions of HARM code. The aim of this study was to verify whether the high mass stellar black holes may be produced with large spins, even though at birth the collapsars might have contained non-spinning, or moderately-spinning cores.
|2020-10-16||prof. dr hab. EWA L. ŁOKAS||Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Warsaw|
|ZN OA 1539||
Tidal evolution of galaxies in clusters
Galaxies are subject to strong tidal evolution in the environment of clusters. I will discuss this process using the example of the most massive cluster of the IllustrisTNG-100 simulation that traces the formation and evolution of galaxies in the cosmological context. For the purpose of this work, I selected 112 galaxies in the cluster, with the largest stellar masses at present, and followed their properties over time. Using their orbital history, the sample is divided into unevolved (infalling), weakly evolved (with one pericenter passage), and strongly evolved (with multiple pericenters). The samples are clearly separated by the value of the integrated tidal force from the cluster the galaxies experienced during their entire evolution and their properties depend strongly on this quantity. As a result of tidal stripping, the galaxies lose mass and become significantly less dark matter dominated. The cluster environment is also very efficient in stripping the galaxies of their gas and quenching the star formation. The strongly evolved galaxies lose their gas earlier and faster, and they become redder and more metal rich, so that at redshift z=0.5 the population of galaxies in the cluster becomes predominantly red. As a result of tidal stirring, the morphology of the galaxies evolves from oblate to prolate and their rotation is diminished, thus the morphology-density relation is reproduced in the simulated cluster. The strongly evolved sample contains at least six convincing examples of tidally induced bars and six more galaxies that had their bars enhanced by their interaction with the cluster.
|2020-10-23||dr MARIUSZ TARNOPOLSKI||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1540||
Time Series and Power Spectral Density Analysis of Astronomical Light Curves: Blazars and Gamma-Ray Bursts
Light curves of astronomical objects, like active galactic nuclei or gamma-ray bursts (GRBs), often exhibit complex variability. Current instruments provide numerous high quality data, which allow to analyse them with novel methods both in the temporal and spectral domains. I will discuss some of these methods, and show the most recent results: investigation of power spectral densities using global periodograms and wavelet based approaches, as well as classification schemes of blazar and GRB light curves in the A-T plane.
|2020-10-30||dr PRZEMYSŁAW MRÓZ||Division of Physics, Mathematics, and Astronomy,|
California Institute of Technology, Pasadena CA, USA
|ZN OA 1541||
Exploring the free-floating planet population with gravitational microlensing
Thousands of extrasolar planets have been discovered up to date. Although many of the known exoplanets do not resemble those in our solar system, they have one thing in common - they all orbit a star. However, theories of planet formation and evolution predict the existence of free-floating planets, gravitationally unattached to any star. Gravitational microlensing is uniquely suited for finding free-floating planets. I will present the current constraints on the frequency and properties of rogue planets in the Milky Way based on long-term observations of microlensing events in the Galactic bulge by the OGLE sky survey. I will also present several of the most promising candidate free-floating planets discovered to date. Finally, I will briefly discuss the future prospects for determining the frequency and mass function of rogue planets by the planned microlensing experiments.
|2020-11-06||mgr ANITHA RAVISHANKAR||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1542||
Kinematics of Coronal Mass Ejections and their association with Solar Energetic Particles
Solar transients such as solar flares, coronal mass ejections (CMEs) and solar wind are topics that require utmost importance of research as they generate geomagnetic storms causing catastrophic damages to power grids on Earth and are serious radiation threat to satellites on low-Earth orbit and their crew during spacewalks. As a consequence of these powerful outbursts on the Sun, energetic protons and ions, known as solar energetic particles (SEPs), are accelerated at high speeds. The acceleration is mainly due to shocks induced by CMEs or at the magnetic reconnection regions of solar flares. As a practical consequence, Earth-directed (halo) large SEPs are of immediate concern as they can penetrate the magnetosphere causing widespread electrical disruptions in the regions close to the poles and to the passengers of high-altitude aircraft flying in polar routes. This is an introduction to an interesting topic called Space Weather where I would stress the importance of this field of research highlighting it's beauty and the danger. In addition we present results of our recent statistical analysis on 38 non-interacting CMEs and their associated SEPs during the quadrature configuration of Solar TErrestrial RElations Observatory (STEREO) with respect to the Earth.
|2020-11-13||dr hab. MICHAŁ MICHAŁOWSKI||Astronomical Observatory Institute, Adam Mickiewicz University, Poznań|
|ZN OA 1543||
The fate of the interstellar medium in early-type galaxies
The way galaxies stop forming new stars (quenching) is a key aspect of galaxy evolution. This is connected with removal of gas, the fuel of star formation. I will review what we know about the mechanism of the removal of interstellar medium (ISM) from galaxies and how fast this process is. I will then present an alternative way to study the ISM removal by selecting dusty early-type galaxies, for which the decrease of gas and dust can be tracked as a function of age. This led to the first direct measurement of the ISM removal timescale and to the conclusion that the cold ISM is likely removed by feedback from old stellar populations.
|2020-11-20||dr hab. JERZY KRZESIŃSKI||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1544||
Search for planetary-mass companions to evolved stars and binaries from Kepler Field
According to recent studies, the vast majority of the stars in our Galaxy are orbited by exoplanets. Most of them have been detected around main sequence stars. However, the number of detected exoplanets around subdwarfs or white dwarfs remains very low. This is in spite of the fact that these evolved and compact stars should be the most suitable objects for exoplanetary study. In this talk you will hear about the current status of our investigation on the substellar bodies presence in the proximity of the pulsating blue subdwarfs (sdB), white dwarfs (WD) and short period binary systems containing sdB or WD stars. Our methods of analysis rely on the detection of exoplanetary signals hidden in photometric time series data from the Kepler space telescope, and they are based on natural clocks within the data itself, such as stellar pulsations and eclipse times.
|2020-11-27||dr MICHAL PAWLAK||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1545||
Connection between the Long Secondary Period phenomenon and the red giant evolution
The mechanism behind the Long Secondary Period (LSP) observed in pulsating red giants still remains unknown. I investigate the connection between the Red Giant Branch and Asymptotic Giant Branch evolution and the appearance of the LSP. I use the OGLE-III sample of the Long Period Variables in the Large Magellanic Cloud. I construct the density maps in the period-luminosity as well as color-magnitude planes for the stars showing LSP and compare them to the remaining giants. I also fit the spectral energy distribution to test whether additional source of reddening is present in the LSP stars. I show that the LSP phenomenon is clearly related to a transition between different pulsation period-luminosity sequences. I also show that the overabundance of the stars showing Long Period Variables can be observed around the Tip of the Red Giant Branch, and much more prominently, at the upper end of the Asymptotic Giant Branch. The main over-density region appears to be slightly fainter and redder than the bulk of the Asymptotic Giant Branch. It also seems to correspond to the area of the Hertzsprung-Russell diagram, where stable winds and high mass loss are present. The LSP is likely to be a recurring phenomenon appearing and disappearing in various points of the red giant evolution. The LSP stars appear to be more reddened than other giants, which suggests the intrinsic nature of the reddening, likely related to large dust emission. The analysis seams to confirms the hypothesis about relation between the mass loss due to the presence of strong stellar wind and the appearance of LPS.
|2020-12-04||prof. dr hab. JERZY W. MIETELSKI||Institute of Nuclear Physics, Polish Academy of Sciences, Kraków|
|ZN OA 1546||
Baryonic dark matter impacts and their possible isotopic record on Earth
The existence of not discovered yet ultra-dense baryonic dark matter came
from astrophysicist Edward Witten (Witten, 1984). In his concept the
pieces of early Universe containing quarks s did not underwent inflation
and could exists currently as one of a kind of dark matter. It was
suggested, that due to ultrahigh density such matter can penetrate the
Earth (Herrin & Toeplitz, 1996, Rafelski et al., 2012). It was also
proposed, that such penetration can left traces in Earth in form of
kimberlite pipes (Paszkowski & Mietelski, 2013). The kimberlite pipes are
perhaps the most unique geological structures present on Earth. There are
narrow tubes having even few meters in diameter but at least several tens
of kilometers length. They are filled with ultramafic mantle breccia
mixed with crustal xenoliths, connecting the deep mantle with the
planet's surface. Almost 6000 such objects were found so far on Earth
(Tappe et al., 2018). They are famous due to their diamond content, which
is evidence for the direct mantle origin of kimberlite rock. The present
state of knowledge cannot propose a widely convincing mechanism to explain
how these structures were formed. The most popular ("classical") model
try to explain their formation by gas eruption from mantle gas deposits,
originating from decomposition of subducted sediments. In our dark matter
impact model, the high-energy massive projectile forms a narrow tunnel
which is immediately enlarged by explosive degassing of deeper rocks. The
empty tunnel is then raidly filled up with pyroclastic material from
mantle mixed with some crust rocks fallen from tunnel walls.
|2020-12-11||prof. dr hab. GERALD HANDLER||Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, Warsaw|
|ZN OA 1547||
Tidally tilted pulsators
The tidally tilted pulsators are a new type of oscillating stars in close binary systems. They appear to pulsate principally in one hemisphere because their pulsation axes have been tilted into the orbital plane by the tidal forces exerted by a close companion star. We have so far discovered three of those systems in TESS space photometry data as well as noticed some related cases in the literature. Aside from all pulsators being Delta Scuti stars, and the orbital periods being shorter than two days, all those systems are different in terms of their pulsational behaviour, secondary star and Roche Lobe filling factor. We will present an overview of those stars, as well as our initial results and work in progress.
|2020-12-18||dr Marek Weżgowiec||Obserwatorium Astronomiczne UJ|
|ZN OA 1548||
Can we observe reconnection heating in the magnetic arms of spiral galaxies?
In some spiral galaxies the so-called 'magnetic arms' have been reported, being interarm areas with significant polarized radio emission that suggests high ordering of the magnetic field. The most prominent example of such a galaxy is NGC6946. The nature of these magnetic features is still under debate. One of the possible explanations is the action of reconnection heating that could convert the energy of the turbulent magnetic field into thermal energy of the surrounding gas, which would result in a higher ordering of the magnetic field and increase in the temperature of the gas. We summarize the analysis of the radio and X-ray emission (measured with XMM-Newton) from NGC6946 and M83 and conclude that we might see hints for such reconnection heating. A similar analysis is on-going for further galaxies that show prominent magnetic arms in their polarized radio intensity maps.
|przerwa świąteczna / Holiday break|
|przerwa świąteczna / Holiday break|
|2021-01-08||dr hab. SEBASTIAN SZYBKA||Obserwatorium Astronomiczne UJ, Kraków|
|ZN OA 1549||
Exact spacetimes: waves beyond linear approximation
Gravitational waves detected by LIGO and VIRGO are extremely weak and as such they are well described far from sources by linearized general relativity. However, Einstein field equations are highly nonlinear. The exact solutions which correspond to gravitational waves imply effects not predicted by the linear theory. In this talk, I will present the motivation behind our recent research on exact gravitational wave spacetimes. The details of our results will be discussed next week in the second part of the presentation.
|2021-01-15||mgr SYED NAQVI||Obserwatorium Astronomiczne UJ|
|ZN OA 1550||
Freely-falling bodies in a standing-wave spacetime
The phenomena of standing waves are mostly studied in the context of mechanical or electromagnetic waves. In the context of General Relativity, the issue of how to define standing gravitational waves was addressed by Bondi and later by Stefani. We investigate an expanding universe filled with standing gravitational waves. We study how freely falling particles in this spacetime behave, namely, we investigate the geodesic equation and the geodesic deviation equation. We show that antinodes attract freely falling particles and we trace the velocity memory effect.
|2021-01-22||mgr SZYMON NAKONECZNY||National Centre for Nuclear Research, Warsaw|
|ZN OA 1551||
Photometric selection and redshifts for quasars in the Kilo-Degree Survey Data Release 4
During the talk, I will present a catalog of quasars with their corresponding redshifts derived from the photometric Kilo-Degree Survey (KiDS) Data Release 4. We achieved it by training machine learning (ML) models using optical ugri and near-infrared ZYJHKs bands. We define inference subsets from the 45 million objects of the KiDS photometric data limited to 9-band detections, based on a feature space built from magnitudes and their combinations. The model selection and fine-tuning employs two subsets of objects: those randomly selected and the faintest ones, which allows us to properly fit the bias vs. variance trade-off. We test three ML models: Random Forest (RF), XGBoost (XGB) and Artificial Neural Network (ANN). We find that XGB is the most robust and straightforward model for classification, while ANN is the best for combined classification and redshift. The ANN inference results are tested using number counts, Gaia parallaxes and other quasar catalogs external to the training set. Based on these tests, we derive the minimum classification probability for quasar candidates which provides the best purity vs. completeness trade-off. We find 158,000 quasar candidates in the safe inference subset (r < 22), and further 185,000 in the reliable extrapolation regime (22 < r < 23.5). Test-data purity equals 97%, completeness is 94%, the latter dropping by 3% in the extrapolation to data fainter by one magnitude than the training set. The photometric redshifts are derived with ANN and modelled with Gaussian uncertainties. Test-data redshift error (mean and scatter) equals 0.009 +/- 0.12 in the safe subset, and -0.0004 +/- 0.19 in the extrapolation, averaged over redshift range 0.14 < z < 3.63. Our success of the extrapolation challenges the way that models are optimised and applied at the faint data end. The resulting catalog is ready for cosmological and Active Galactic Nucleus (AGN) analysis. We publicly release the catalog at kids.strw.leidenuniv.nl/DR4/quasarcatalog.php.
|przerwa egzaminacyjna / Exam break|
|przerwa egzaminacyjna / Exam break|
|ferie zimowe / Holiday break|
|przerwa egzaminacyjna / Exam break|
|Wielki Piątek / Holiday break|
|2021-05-14||mgr RAMESHAN THIMMAPPA||OA UJ|
A Comprehensive and Novel Analysis of the Chandra X-ray Observatory Data for the Pictor A Radio Galaxy
Pictor A, recognized as the archetypal powerful radio galaxy of the FR II type, is not only one of the brightest radio sources in the sky, but is also particularly prominent in the X-ray domain. In this talk, I will summarize our analysis of all the Chandra X-ray Observatory data available for the Pictor A radio galaxy, consisting of multiple pointings spanning over 15 years and the total exposure time of 464 ks. In particular, the following three main research results discussed during my talk will be: (i) investigating the X-ray structure of the termination shocks of relativistic jets in Pictor A, the so-called "hotspots", by means of detailed image deconvolution and timing analyses; (ii) investigating correlations between the X-ray and radio emission features within the extended lobes of the source; and (iii) an approach to the X-ray spectroscopy of the active nucleus in Pictor A radio galaxy, carried out in a regime of a severe instrumental pile-up.
|piątek po Święcie Bożego Ciała / Holiday break|