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Seminaria Piątkowe

Seminaria odbywają się (zasadniczo) w piątki w OA UJ (Fort Skała). Zwykle w języku angielsku. Początek o godzinie 12:00. Czas trwania: 45 minut + dyskusja. Wstęp wolny. Chętni do zaprezentowania referatów powinni zgłaszać się do Marka Weżgowca.

Lista Seminariów w roku 2023/2024 (strona zewnętrzna)



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Październik/October 2019

Radio sources in the SDSS spectroscopic catalogues

Based on the catalogue of Radio sources associated with Optical Galaxies and having Unresolved or Extended morphologies I (ROGUE I), I will discuss the problem of identification and classification of radio sources in the large radio surveys. The catalogue was created by cross-matching galaxies from the SDSS with the FIRST and NVSS catalogues. It contains more than 32,000 galaxies with a FIRST core within 3arcsec of the optical position, and is the largest, handmade catalogue of this kind.
However, as most catalogues with a low flux density limit, it contains the mixture of radio sources, and the separation of radio AGNs from the radio emission arising in the star-forming regions is a challenging task. In recent papers (Best & Heckman 2012, Sabater et al. 2019) separation of these two populations was made based on several different diagrams. But this procedure is complicated and requires the knowledge of many different parameters, like optical emission line ratios or galaxy mass. Therefore, during my talk I will also discuss a single diagram that can be used to distinguish radio emission produced by jets from the one emitted in star-forming regions.

Uroczyste podziękowanie Pani Profesor Katarzynie Otmianowskiej-Mazur za długoletnią współpracę naukową oraz zaangażowanie w budowę stacji LOFAR-a w Polsce. Po uroczystości dr Błażej Nikiel-Wroczyński wygłosi wykład "LoTSS - najnowszy przegląd nieba realizowany przez LOFAR-a".

A special gathering in honor of Prof. Katarzyna Otmianowska-Mazur, to express our gratitude for a long-term scientific collaboration, as well as for her involvement in setting up the LOFAR station in Poland. After the gathering, dr Błażej Nikiel-Wroczyński will give a talk "LoTSS - LOFAR newest sky survey".

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Listopad/November 2019

Kinds of things and our choices. Ontology and presuppositons

Contemporary ontology tells us what exists, specifying the categories of objects that we should assume. I address some complications that arise when we try to build a philosophical reconstruction of the link between individuals and categories, with some examples mutuated from bio-medical research. These complications arise from the fact that given a domain of individuals, any classificatory principle determines a set of things. Therefore, there are many alternative ways of classifying things in classes according to their shared properties, producing different patterns of classification in categories guided by different theoretical assumptions. In fact, if we are not able to specify the strategy of the intended relevant properties and our preferences in advance, the empirical data themselves do not help us spot the perspicuous kinds. These theoretical assumptions can be considered the metaphysical background of any theory that assumes the notion of intrinsic property and pertinent and meaningful category.

P. Valore (2018). “Resemblance, Exemplification, and Ontology”. In: American Philosophical Quarterly, 55 (2): 131-140
P. Valore (2018). “The Quest for Higher Order Criteria for Meta-Ontology: Metaphysics Vindicated”. In: Philosophy. Journal of the Higher School of Economics, I, 4: 13–26
P. Valore (2017). “Natural Kinds, Similarity, and Individual Cases. Ontological Presupposition and Ethical Implications”. In: Psychological, Emotional, Social and Cognitive Aspects of Implantable Cardiac Devices. Ed. G.M. Manzoni, R. Proietti, G. Pietrabissa, G. Castelnuovo. Dordrecht, New York, London: Springer Nature
P. Valore (2016). Fundamentals of Ontological Commitment. Berlin-Boston: De Gruyter

Primordial Dark Matter Halos from fifth forces

Dark matter is an essential ingredient of modern cosmology, its fundamental nature being one of the biggest open enigmas in physics. I discuss the possibility to provide the entire dark matter content in form of screened dark compact objects which could be potentially generated during the radiation dominated era. In the standard cosmological scenario, this would be suppressed due to the fast expansion rate of the Universe lead by radiative pressure. Nevertheless, the introduction of an additional long-range attractive interaction stronger than gravity enhances the growth of fluctuations in the density field of a non-interacting matter fluid, which eventually collapse in Primordial Dark Matter Halos. Finally, I analyse in which conditions these structures might evade microlensing constraints and cosmic microwave background energy injection bounds.

Construction of Kinematical Transformations in Special Relativity

In the didactics of Special Relativity, kinematical transformations are usually introduced by imposing on general linear transformations the condition that the principle of constancy of light velocity. However, this way does not enable catching an intuitive meaning of the transformations analogous to the one enabled for Galilean transformations by their construction, supported by the standard figure. Two versions of such construction for proper Lorentz transformations will be presented, first based on familiar experimental results and the standard signal synchronizing procedure, and second on some more general assumptions, the synchronizing procedure by infinitely slow clock transport, and the condition that the transformations form a group. Both are supported by the same standard figure as for Galilean transformations.

Optical variability modelling of newly identified blazar candidates behind Magellanic Clouds

We present an optical variability study of 44 newly identified blazar candidates behind the Magellanic Clouds, including 27 flat spectrum radio quasars (FSRQs) and 17 BL Lacertae objects (BL Lacs). The objects in the sample possess optical OGLE light curves (LCs) spanning several (up to 17) years. The LCs were analysed with the Lomb-Scargle periodogram, and it was found that the power spectral densities (PSDs) exhibit breaks for several objects, which allowed to constrain the black hole masses of 18 FSRQs. Many sources have very steep PSDs, with high frequency spectral index in the range 3-7. An alternative attempt to classify the LCs was made using the Hurst exponents and the A-T plane.

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Grudzień/December 2019

Gamma-Ray Emission from Radio Galaxies

Centaurus A (Cen A), the nearest radio galaxy, was detected as a faint emitter of very high energy (VHE) gamma rays by the H.E.S.S. telescopes in Namibia. The flux derived from the H.E.S.S. data is notably higher than that expected from a single zone synchrotron self-Compton model, which adequately describes the emission from Cen A at lower energies. New observations with H.E.S.S. were performed to clarify the spectral characteristics of the VHE emission from Cen A. I will report on the results of the analysis of the complete H.E.S.S. data set with twice the exposure time of the previously published data set and also the update of the Cen A spectrum obtained with Fermi-LAT at GeV energies. I will also discuss prospects for H.E.S.S. observations of the radio galaxy, Fornax A.

Stellar Structure in f(R)-Gravity

The modified Lane-Emden Equation for stellar structure in f(R)-Gravity is derived and solved numerically. This equation is derived in the Newtonian limit by assuming a polytropic relation between the pressure and the density. This is an integro-differential equation whose integral part can have an oscillating behaviour with the proper choice of the Green Function taken to derive it that can be used to describe the behaviour of variable stars or a Yukawa-like behaviour. We solve this equation both in the non-oscillating and oscillating case for different values of the polytropic index and confront the different solutions with the General Relativity case. This approach allows us to include in this theoretical scheme exotic very massive objects and variables objects.

How electron-positron pair plasma fills pulsar magnetosphere, heats NS surface, and generates radio emission

I give an overview of recent pulsar magnetosphere models emphasizing the importance of pair plasma generation. I discuss how much pair plasma can be produced in pair cascades and what it means for the physics of Pulsar Wind Nebulae. Relativistic particles accelerated in pair formation zones heat the neutron star surface, I demonstrate that the temperatures of pulsar polar caps predicted in the frame of modern pair cascade models agree with observations quite well. I also present a novel robust mechanism for direct generation of coherent radio emission in pair discharges and discuss its implications.

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Styczeń/January 2020

Hot subdwarfs as common-envelope evolution outcomes

Hot subwarfs allow us to explore possible outcomes of common-envelope (CE) ejection in a close binary. Depending on the observational results (i.e. orbital period, mass ratio, chemical abundances, etc.) a conclusion for these exotic systems can be reached regarding an idea of the formation and evolution of He-rich subdwarf binaries. Besides a general perspective on their formation, they also help us to go further on stellar evolution and confirm our current knowledge about the outcomes of CE evolution. Some case studies will be shown as examples.

Powerful AGN jets and unbalanced cooling in the hot atmosphere of IC 4296

Giant elliptical galaxies are the largest galactic structures in the Universe. They were formed within the first few Gyr after the Big Bang and overcome only brief and explosive star formation and afterward grew only by dry mergers and are embedded in hot X-ray emitting atmospheres. AGN radio-mechanical feedback is considered to be balancing the heating and cooling in these structures. A detailed study was done for giant elliptical galaxy IC 4296 located in the group Abell 3565. The new Karl G. Jansky Very Large Array (VLA, 1--2 GHz) radio data, supported by archival radio, X-ray (Chandra, XMM-Newton) and optical (SOAR, HST) observations revealed uniqueness of this source. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intra-cluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff-Riley Class I (FR I) system, the D configuration image reveals two large (160 kpc), well-defined lobes (one of which is associated with an X-ray cavity) at a projected distance 230 kpc. The total enthalpy of the radio lobes is 7 × 1059 erg and the mechanical power output of the jets is 1044 erg/s. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm Hα+[NII] nebula and a cold molecular CO disk.

Light propagation in space-time

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Luty/February 2020

Searching for Young Stellar Objects in the Outer Galactic Plane

I will present the results of the study aimed to uncover the population of Young Stellar Objects (YSOs) in the relatively poorly studied star-forming regions in the Outer Galaxy. We use the data from the "Spitzer Mapping of the Outer Galaxy" survey (SMOG) that covered 24 deg2 region in the Outer Galaxy (dubbed L105), l ∼ (102 -109) and b ∼ (-0.2 3.2 ), in the IRAC 3.68.0m and MIPS 24 m bands. The SMOG data have been combined with the data from the 2MASS (JHKs) and WISE (3.5-22 m) all-sky surveys. We have selected YSO candidates based on the color-color selection criteria (more than 1000), and then applied a series of filters to remove contaminating sources (e.g., background galaxies). We have also performed an additional search for YSO candidates among the Spitzer/SMOG sources with the WISE counterparts by using an automated source identification scheme based on the Machine Learning algorithms (Solarz et al. 2017). This method identified additional YSO candidates, which were missed by classical color-color based selection criteria.

Detection of chaotic behaviour in time series generated by charged particle motion around magnetized Schwarzschild black hole

Time series, generated by nonlinear particle motion around magnetized/regular black hole has been studied using standard and machine learning methods for chaos detection. Test particles constituting neutral Kepplerian accretion disc around magnetized black hole can get easily ionized and will start to feel external uniform magnetic field. New type of motion for now charged particle will be possible, ionized particles can leave the circular orbits located in accretion disc infinitesimally thin plane and this ionization process could lead to the disk thickening or even complete disk destruction. Detection of charged particle trajectory chaoticity can be used in determination of accretion disk future.

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Marzec/March 2020

Hierarchical correlation reconstuction - between statistics and machine learning

While machine learning techniques are very powerful, they have some weaknesses, like iterative optimization with many local minima, large freedom of parameters, lack of their interpretability and accuracy control. From the other side we have classical statistics based on moments: not having these issues, but providing only a rough description. I will talk about kind of intermediate approach combining their advantages: with MSE-optimal moment-like coefficients, designed such that we can directly combine them into probability density. I will show some applications examples, like modelling conditional distributions, or time series analysis - including multivariate and nonstationary.

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Kwiecień/April 2020

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Maj/May 2020

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Czerwiec/June 2020