|653rd ACADEMIC YEAR 2016/2017
|2016-10-07||mgr MARIUSZ TARNOPOLSKI||OA UJ|
|ZN OA 1432||
Analysis of gamma-ray burst duration distribution using mixtures of skewed distributions
Two classes of gamma-ray bursts (GRBs) have been confidently identified thus far. A third, intermediate in duration class, was suggested to be present in previous catalogues, such as BATSE and Swift, based on statistical tests regarding a mixture of two or three lognormal distributions of T90. However, this might possibly not be an adequate model. Mixtures of standard normal, skew-normal, sinh-arcsinh and alpha-skew-normal distributions are fitted using a maximum likelihood method. The preferred model is chosen based on the Akaike information criterion. It is found that mixtures of two skew-normal or two sinh-arcsinh distributions are more likely to describe the observed duration (T90) distribution of Fermi than a mixture of three standard Gaussians, and that mixtures of two sinh-arcsinh or two skew-normal distributions are models competing with the conventional three-Gaussian in the case of BATSE and Swift. Based on statistical reasoning, it is shown that other phenomenological models may describe the observed Fermi, BATSE, and Swift duration distributions at least as well as a mixture of standard normal distributions, and hence the existence of a third (intermediate in duration) class of GRBs in Fermi data is rejected.
|2016-10-14||dr ARTI GOYAL||OA UJ|
|ZN OA 1433||
Multi-frequency variability study of blazars from decades to minutes
The power spectral densities (PSDs) of blazar light curves, P(f) = A f-β, where A is the normalization and β is the slope, indicate that the variability is generated by the underlying stochastic processes which is of colored noise type (i.e., β ≃ 1-3). Study of power-law slopes, normalization or characteristic timescales (if any), in the PSD is important for constraining the physics of emission and energy dissipation processes in the blazar jets. We present the results of PSD analysis of 4 blazars at GeV (Fermi-LAT), X-ray (Swift-XRT and RXTE), optical (R-band) and radio (GHz band from UMRAO and OVRO programmes) frequencies covering few decades to minutes timescales. The novelty of this study is that at optical frequency, by combining long-term (historical optical light curves) and densely sampled intra-night lightcurves, the PSD characterisitics are investigated for temporal frequencies ranging over 7 orders of magnitude. Our main results are : (1) nature of processes generating flux variability at optical/radio frequencies is different from those at GeV freqeuncies (β ∼ 2 and 1, respectively); this could imply, that γ-ray variability, unlike the Synchrotron (radio-to-optical) one, is generated by superposition of two stochastic processes with different relaxation timescales, (2) the main driver behind the optical variability is same on years, months, days, and hours timescales (β ∼ 2), which argues against the scenario where different drivers behind the long-term flux changes and intra-night flux changes are considered, such as internal shocks due to the jet bulk velocity fluctuation (long-term flux changes) versus small-scale magnetic reconnection events taking place at the jet base (intra-night flux changes). Implications of these results are discussed in the context of blazar emission models.
|2016-10-21||prof. DAVID VALLS-GABAUD||Observatoire de Paris-Meudon, France |
Churchill College, Cambridge, UK
|ZN OA 1434||
The MESSIER orbiter: lifting the veil on the ultra-low surface brightness universe
The S-class MESSIER satellite has been designed to explore the extremely low surface brightness universe at UV and optical wavelengths. The two driving science cases target the mildly- and highly non-linear regimes of structure formation to test two key predictions of the LCDM scenario: (1) the detection of the putative large number of galaxy satellites, and (2) the identification of the filaments of the cosmic web. The satellite will drift scan the entire sky in 6 bands covering the 200-1000 nm wavelength range to reach the unprecedented surface brightness levels of 34 mag/arcsec2 in the optical and 37 mag/arcsec2 in the UV. Many important secondary science cases will result as free by-products and will be discussed in some detail, such as the luminosity function of galaxies, the contribution and role of intracluster light, the cosmological background radiation at UV and optical wavelengths, the molecular hydrogen content of galaxies at z=0.25, time domain studies of supernovae, GRBs and tidal disruption events, the chemical enrichment of the interstellar medium through mass loss of red giant stars and the accurate measure of the BAO scale at z=0.7 with over 30 million galaxies detected in Lyman-alpha at this redshift. It will provide the astronomical community the first space-based reference UV-optical photometric catalogue of the entire sky, and synergies with GAIA, EUCLID and WFIRST will also be discussed. Technical issues will likewise be addressed for possible improvements on the current design.
|2016-10-28||prof. JACQUES DELABROUILLE||Laboratoire Astroparticule & Cosmologie,|
Université Paris Diderot, France
|ZN OA 1435||
The future of the CMB: from temperature to polarization
The ESA Planck space mission has fully exploited the cosmological information available in Cosmic Microwave Background temperature anisotropies. A standard cosmological model has emerged. Our Universe, however, remains a mystery. What are the invisible matter and energy that seem to constitute 96% of our universe? Did the Universe truly begin with an superluminal expansion that stretched quantum fluctuations to cosmological scales to generate the initial perturbations that eventually gave raise to galaxies, stars, and ultimately ourselves? In this talk, I will review the theoretical motivations for digging even further in the CMB, and in particular to accurately measure the properties of CMB polarization with a future Cosmic Origins Explorer space mission, to probe physics ranging from the absolute mass of all neutrino species to grand unification physics at an energy scale thousand billion times bigger than that of the LHC.
|2016-11-04||dr OLEH KOBZAR||Institute of Nuclear Physics PAN, Poland|
|ZN OA 1436||
Search of the Ultra High Energy Cosmic Rays from Virgo A
Virgo A (M87) is the second closest to the Milky Way active galaxy. According to existing estimations it can be a prominent source of ultra high energy cosmic rays (UHECR). However not many events have been registered in the sky region near Virgo A, possibly due to the magnetic field influence. In the present work we carried out the simulation of UHECR motion from Virgo A taking into account their deflections in galactic (GMF) as well as extragalactic (EGMF) magnetic fields according to the latest models. The maps of expected UHECR arrival directions have been obtained as a result. We also check the UHECR events from recent sets of data (AUGER, Telescope Array etc.) for possibility of their origination in this AGN.
|seminarium nadzwyczajne: wtorek, godzina 15:00 / Tuesday at 3:00 p.m.|
|2016-11-08||Prof. INEKE DE MOORTEL||University of St Andrews, Scotland UK|
Transverse Velocity Perturbations in Solar Coronal Loops
In this talk, I will give an overview of transverse, propagating velocity perturbations observed in solar coronal loops. These ubiquitous perturbations are observed to contain substantial amounts of energy and undergo strong damping as they propagate. Using both numerical and analytical modelling, we demonstrate that these can be understood in terms of coupling of different wave modes in the inhomogeneous boundaries of the loops: we perform 3D numerical simulations of footpoint-driven transverse waves propagating in a coronal plasma with a cylindrical density structure. Mode coupling in the inhomogeneous boundary layers of the loops leads to the coupling of the transversal (kink) mode to the azimuthal (Alfven) mode, observed as the decay of the transverse kink oscillations. In addition, recent analysis of CoMP (Coronal Multi-channel Polarimeter) Doppler shift observations of a large, off-limb, trans-equatorial loops system show that Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. We suggest that this excess high-frequency FFT power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvenic) turbulence, potentially contributing to heating of the loops.
|2016-11-18||mgr JUSTYNA ŚREDZIŃSKA||CAMK Warszawa, Poland|
|ZN OA 1437||
Mg II line in intermediate redshift quasars, and its connections with dark energy
The Universe day after day give us more discoveries and even more surprises. Current astronomical observations indicate that the Universe consists in only 5% of the well-known matter, but in 95% of invisible and not understood substances: dark matter and dark energy. This last component is most difficult to understand. Dark energy acts in the opposite way to gravitational attraction: it causes the acceleration of the universal expansion. This conclusion is extremely peculiar. Precise and independent measurement methods of this effect are necessary to understand the nature of dark energy. Quasars are very luminous centres of active galaxies, which are observed from very large distances (wide range of redshift) and it turned out they are ideal candidates for this purpose. They are not standard candles, but their use is based on the determination of the absolute luminosity for each of them. This can be achieved by measuring the time delay between the variable nuclear continuum and the emission lines, as confirmed by the delay measurement of the Hβ line done for nearby AGNs. The time delays in quasars are of the order of a few years, so the project requires sparse monitoring over an extended period of time. We monitor quasars at redshift z=1, which requires using the MgII line, and such monitoring has never been done before. The observations performed so far with SALT showed that we achieve the requested accuracy (below 2%) of the MgII measurement to determine its variability, and the simulations indicate that the program can provide accuracy of 0.06-0.32 mag in the distance modulus for each single quasar.
|2016-11-25||dr GOPAL BHATTA||OA UJ|
|ZN OA 1438||
Constraining Jet Structures in the blazars S5 0716+714 and OJ 287 using exceptionally dense optical observations
Blazars exhibit variability in diverse timescales ranging from a few minutes up to a few decades. Variability studies, therefore, offer important insight into the various physical mechanisms occurring in both the jets and the disks. Here we present the summary of our studies involving exceptionally dense optical observations of blazar S5 0716+714 and OJ 287. 0716+714 was monitored in multi-frequency photo-polarimetric bands during Whole Earth Blazar Telescope (WEBT) observation campaigns. The results of the analyses show that the source often displays fast variability with an amplitude as large as 0.3 mag within a few hours, as well as color variability on similar time scales often characterized by ``bluer-when-brighter'' trend. Similarly, the correlation between variability in flux and polarization appears to depend upon the configuration of the optical polarization angle relative to the positional angle of the innermost radio core of the jet. Other fascinating observations include a sudden and temporary disappearance in the observed variability lasting for ∼ 6 h. In addition, the modeling of individual microflares strongly suggests that the phenomenon of microvariability can be best explained by convolved emission from compact emission sites distributed stochastically in the turbulent jet. Besides, analysis of some of the well resolved micro-flares exhibiting high degrees of polarization points towards a complex magnetic geometry pervading the jet with the possible presence of small-scale regions of highly ordered and enhanced magnetic field. In another study, we detected a year like QPO in the long term optical light curve of the blazar OJ 287. The result is discussed in the contexts of various processes occurring in the disk and the jets.
|2016-12-02||prof. JERZY MACHALSKI||OA UJ|
|ZN OA 1439||
Dynamical Analysis of FRII-Type Radio Sources: Statistical Correlations between the model parameters in the large sample of sources
The FRII-type radio sources are characterised by the evident superluminal shocks at the extremities of their extended linear structure. These shocks originate from an interference of powerful jets (emanating from an AGN) with the external gaseous environment surrounding a galaxy comprising that AGN. A number of physical parameters characterising such radio structure, e.g. its age, the jet power, the ambient density, can be determined by the fit of the analytical model of the structure to its observational data (the size, volume, luminosities and spectrum) using the DYNAGE algorithm of Machalski et al. (2007). The statistical correlations between selected model parameters in the more or less homogeneous sample of 260 radio sources will be presented. Due to the fact that a direct correlation between any two parameters may arise or be contaminated by their correlations with the third (or the third and fourth) ones - the Spearman "partial rank correlation coefficient" test is used to determine which correlation is the strongest. A particular attention will be directed onto the correlation of the initial energy distribution of relativistic particles at the shock front with the jet power, external density, and redshift.
|2016-12-09||prof. MAREK SIKORA||N. Copernicus Astronomical Center PAN Warszawa, Poland|
|ZN OA 1440||
Broad-emission-line radio galaxies provide challenges to jet production
Accretion onto supermassive black holes located in broad-emission-line radio galaxies (BLRGs) is predicted by theory to proceed via geometrically very thin accretion disks, which makes them most challenging objects regarding their ability to produce powerful jets. As recent numerical simulations indicate, even the magnetically-arrested-disk (MAD) scenario is not able to reproduce the jet power observed in these objects - those are measured to approach and sometimes even exceed the accretion luminosities. Possible origins of this discrepancy are discussed.
|2016-12-16||dr hab. JACEK NIEMIEC||Institute of Nuclear Physics PAN, Poland|
|ZN OA 1441||
The IBEX ribbon and the pickup ion scattering in the outer heliosheath
The nearly circular band of an increased energetic neutral atom emission discovered the IBEX satellite can be naturally explained by the effect of charge exchange of secondary pickup ions gyrating around magnetic field lines in the outer heliosheath and the interstellar space beyond. This scenario requires that the distribution of the pickup ions remained stable against scattering on the waves they have generated on time scales much longer than required for the charge exchange. In my talk I will present the results of our recent studies of the stability of the pickup ion ring-like distributions and also a more realistic distributions obtained from modeling of atomic hydrogen in the heliosphere. The studies have been performed using theoretical analysis and numerical tools - hybrid kinetic and fully kinetic Particle-In-Cell simulations. The results will be discussed in the context of IBEX observations of the ribbon and the recent Voyager 1 in-situ measurements of the magnetic field fluctuations in the outer heliosheath.
|przerwa świąteczna / Holiday break|
|przerwa świąteczna / Holiday break|
|Święto Trzech Króli / Holiday break|
|2017-01-13||dr DOROTA KOZIEŁ-WIERZBOWSKA||OA UJ|
|ZN OA 1442||
Host galaxies of radio-loud and radio-quiet AGNs
Active galactic nuclei (AGNs) are known to cover an extremely broad range of radio luminosities and the spread of their radio-loudness is very large at any value of the Eddington ratio. This implies very diverse jet production efficiencies which can result from the spread of the black hole spins and magnetic fluxes. Magnetic fluxes can be developed stochastically in the innermost zones of accretion discs, or can be advected to the central regions prior to the AGN phase. In the latter case one might expect systematic differences between the properties of galaxies hosting radio-loud (RL) and radio-quiet (RQ) AGNs. In the former case the differences should be negligible for objects having the same Eddington ratio. To study the problem we decided to conduct a comparison study of host galaxy properties of RL and RQ AGNs. In this study we selected AGNs from SDSS spectroscopic catalogues. These AGNs were divided into RL and RQ based on the Best & Heckman (2012) catalogue. To compare RL and RQ galaxies that have the same AGN parameters we used pair-matching technique, and matched galaxies in black hole mass, Eddington ratio and redshift. We compared several properties of the host galaxies in these two groups of objects like galaxy mass, colour, concentration index, star-formation rate, line widths, morphological type and interaction signatures. Here, I will present the results of this comparison.
|2017-01-20||dr JULIAN SITAREK||Wydział Fizyki i Informatyki Stosowanej,|
Uniwersytet Łódzki, Łódź
|ZN OA 1443||
Observations of blazar variability with the MAGIC telescopes
I will present the selected, recent results of observations of flares from blazars performed with the MAGIC telescopes. In particular I will discuss the strong flare from a distant flat spectrum radio quasar PKS1441+25. I will show the first detection of a VHE gamma ray emission from a gravitationally lensed blazar B0218+357. I will also discuss the multiwavelength observations of flat spectrum radio quasar PKS1510-089 during the first detection of VHE gamma ray variability from this object.
|2017-01-27||mgr ARTEM BOHDAN||Instytut Fizyki Jądrowej PAN, Kraków|
|ZN OA 1444||
Turbulent magnetic reconnection and particle acceleration at
nonrelativistic shocks of young supernova remnants
Particle heating and acceleration, and the effects of spontaneous turbulent magnetic reconnection at high Mach number perpendicular nonrelativistic collisionless shocks for parameters that are applicable to conditions at young supernova remnants are studied with two-dimensional fully kinetic Particle-In-Cell (PIC) simulations. These unprecedented high-resolution large-scale simulations sample a representative portion of the shock surface to fully account for time-dependent effects of the cyclic shock reformation. The physics of strong shocks is governed by ion reflection that leads to the formation of magnetic filaments in the shock ramp, resulting from Weibel-type instabilities, and to electrostatic Buneman modes in the shock foot. Merging magnetic filaments can also trigger spontaneous turbulent magnetic reconnection in the shock transition. We discuss the nonlinear shock structure and particle energization processes with the emphasis on the dynamics of electron heating and pre-acceleration needed for their injection into diffusive shock acceleration. On this line we study physical and numerical parameter space to find conditions providing the most efficient acceleration. The importance of turbulent magnetic reconnection processes is scrutinized. Relevance of our results to the physics of fully three-dimensional systems is discussed.
|Przerwa egzaminacyjna / Egzam break|
|2017-02-10||dr GRAŻYNA STASIŃSKA
dr NATALIA VALE ASARI
|Observatoire de Paris - Univ. Paris Diderot, France|
Universidade Federal de Santa Catarina, Brasil
|ZN OA 1445||
BOND: Bayesian Oxygen and Nitrogen abundance Determinations
The abundances of chemical elements other than hydrogen and helium in a galaxy are the fossil record of its star formation history. Empirical relations such as mass-metallicity relation are thus seen as guides for studies on the history and chemical evolution of galaxies. Those relations usually rely on nebular metallicities measured with strong-line methods, which assume that HII regions are a one- (or at most two-) parameter family where the oxygen abundance is the driving quantity. Nature is however much more complex than that, and metallicities from strong lines may be strongly biased. We have developed the method BOND (Bayesian Oxygen and Nitrogen abundance Determinations) to simultaneously derive oxygen and nitrogen abundances in giant HII regions by comparing strong and semi-strong observed emission lines to a carefully-defined, finely-meshed grid of photoionization models. Our code and results are public and available at http://bond.ufsc.br
|Przerwa semestralna / Semester break|
|2017-02-24||mgr MAŁGORZATA SIUDEK||Centrum Fizyki Teoretycznej PAN, Warszawa|
|ZN OA 1446||
Formation and evolution of stellar population based on the red passive galaxies observed up to z ∼ 1
We would like to present the studies over the evolution and the star formation history of passive galaxies observed by the VIMOS Public Extragalactic Redshift Survey (VIPERS). We compare the 4000A break (D4000n) and the Hδ Lick index (HδA) measured on VIPERS stacked spectra with a grid of synthetic spectra to constrain the star formation epochs of these galaxies. Assuming a single burst formation, we find that high-mass passive galaxies formed their stars at zform ∼ 2, while low-mass galaxies formed their main stellar population more recently, at zform ∼ 1. The consistency of these results, obtained using two independent estimator of the formation redshift (D4000 and HδA), further strengthens a scenario in which star formation proceeds from higher- to lower-mass systems as time passes, i. e. what has become known as the 'downsizing' picture.
|2017-03-03||dr hab. ŁUKASZ STAWARZ||OA UJ|
|ZN OA 1447||
On the electron acceleration at Saturns bow shock observed with Cassini
A leading explanation for the origin of Galactic cosmic rays is acceleration at strong shock waves in the collisionless plasma surrounding young supernova remnants. Evidence for this is provided by multiwavelength non-thermal emission thought to be associated with ultrarelativistic electrons at these shocks. However, the dependence of the electron acceleration process on the orientation of the upstream magnetic field with respect to the local normal to the shock front (quasi-parallel/quasi-perpendicular), as well as on the shock Mach number, is still being debated. Data taken by the Cassini spacecraft at Saturns bow shock has revealed many examples of electron acceleration under quasi-perpendicular conditions, but also the first example of electron acceleration at a quasi-parallel shock up to at least MeV energies. Here we present those data surveyed in a systematic way, and make in particular the first detailed comparison between the electron energy spectra resulting in differing upstream magnetic field regimes. We discuss whether the acceleration is consistent with diffusive shock acceleration theory in each case, and comment on a role of energy-dependent interaction between the electrons and short, large-amplitude magnetic structures present in the upstream of high-Mach number quasi-parallel shocks.
|2017-03-10||dr PATRYK MACH||Instytut Fizyki UJ|
|ZN OA 1448||
Massive disks around black holes
I will give a brief introduction to the basic theory of selfgravitating rotating fluids both in Newtonian gravity and in General Relativity (GR). I will recall some basic results concerning the solutions representing selfgravitating disks (toroids) around point masses (in Newtonian theory) and black holes (in GR). I will then review recent results concerning general-relativistic Keplerian disks and the estimates of their masses and the angular momentum.
|seminarium nadzwyczajne: środa, godzina 14:00 / Wednesday, at 2:00 p.m.|
|2017-03-15||prof. RALF-JUERGEN DETTMAR||Ruhr-Univeristaet Bochum, Germany|
|A fresh look on cosmic rays and magnetic fields in disk galaxies|
|2017-03-17||dr hab. GRAŻYNA SIEMIENIEC-OZIĘBŁO||OA UJ|
|ZN OA 1449||
Gamma-ray emission from galaxy cluster outskirts versus radio relics
Galaxy cluster peripheries provide important information on the nature of ICM/IGM linkage. After commenting why cluster outskirts are particularly interesting and why they are extensively studied, we consider potential future observations in the gamma-ray domain at cluster edges involving the radio relic phenomenon. We postulate here that a merger shock together with a longliving accretion shock form the so-called double shock structure, which provides for larger efficiencies both in injection and CR acceleration. Therefore the multifrequency nonthermal emission i.e. gamma, and hard X should also be expected in the location of radio relic. We focus on the spectral signature of gamma radiation that should be evident in the energy range of Fermi--LAT, i.e. ≥ 10-2 GeV and the CTA energy range ∼ 102 GeV. As an example, we carried out analyses of two types of non-thermal diffuse radio emission: the radio relic of A 2256 and the radio halo of Coma cluster. We suggest that in both cases the expected spatially correlated gamma-ray spectrum should have a characteristic structure that depends on the strength of the local magnetic field. The revealed spectral dependence on the magnetic field would allow us to relate the future spectral observations, in particular the position of the gamma-ray signature, to the value of the magnetic field in the border area between galaxy clusters and their connecting filaments.
|Odwołane / Cancelled|
|2017-03-24||prof. dr hab. TOMASZ BULIK||Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Warszawa|
On the origin of merging binary black holes
The detection of merging binary black holes by LIGO leads to the question of where do they originate from. Several scenarios have been proposed: evolution of binaries in the filed, stellar evolution in globular clusters, and population III binaries. I will review the models and their consequence. I will discuss possible ways to distinguish between them with the use of various observations.
|2017-03-24||mgr ALEKSANDER KUREK||OA UJ|
|ZN OA 1450||
Usability of parametric light amplification (OPA) for high angular resolution astronomical imaging
High angular resolution imaging is crucial for many applications in modern
astronomy and astrophysics. The fundamental diffraction limit constrains
the resolving power of both ground- based and spaceborne telescopes. The
recent idea of a Quantum Telescope based on the Optical Parametric
Amplification (OPA) is aimed at bypassing this limit for imaging of
extended sources by an order of magnitude or more.
|2017-03-31||dr hab. MAGDALENA KUNERT-BAJRASZEWSKA||Uniwersytet Mikołaja Kopernika w Toruniu, Toruń|
|ZN OA 1451||
What have we learned so far about young radio sources?
Despite the intensive studies of the evolution of radio-loud AGNs we still don't know many details of this process. We already know that not all radio-loud AGNs follow the same evolutionary path. There are more of them and not all tracks finally lead to the development of large-scale radio structure. Possibly part of the young and small radio objects will never be able to grow up and become a large-scale radio sources. Thus we predict that they will appear as transients, the short-lived objects. The Caltech- NRAO Stripe 82 Survey (CNSS), a multi-epoch radio transient survey carried out recently with the Jansky VLA, has facilitated an unbiased study of such objects for the first time. The total number of 12 new radio transients have been discovered and they are the subject of our presentation. These objects did not occur previously in any catalog of radio sources until a sudden outburst of their AGN activity recorded by CNSS monitoring. This discovery gives us not only a possibility of investigation of the population of short-lived objects but also an unique opportunity to study fast-evolving young jets. Moreover, according to the preliminary calculations, the new sources have been radio-quiet so far. Thus, the recorded radio transient phenomenon is not only the moment of the birth of the radio source, but also the moment of transition from radio-quiet to the radio-loud state. I will present the new interesting conclusions on the evolution of radio-loud AGNs found by our group based on the previous studies and new discoveries.
|2017-04-07||dr AGATA KARSKA||Centrum Astronomii UMK, Toruń|
|ZN OA 1452||
Sunbathing around protostars - new insights from Herschel
Stars form in dense molecular clouds, where gas and dust are well-shielded from the interstellar UV radiation. Nonetheless, UV photons can be produced in situ in the surroundings of young protostars: either by the accretion of material onto the disk or its partial ejection in the powerful jets. Recent observations with the Herschel Space Telescope reveal that even relatively small UV fields dramatically alter the chemical composition of the gaseous envelopes. In my talk, I will show the main results from Space Telescope Herschel related to feedback from low-mass protostars. In particular, I will demonstrate that standard models of shocks do not agree with observations unless their irradiation by UV photons is included.
|Wielki Piątek / Holiday break|
|2017-04-21||dr KOSMAS GAZEAS||National and Kapodistrian University of Athens, Greece|
|ZN OA 1453||
Contact Binaries Towards Merging - (CoBiToM Project)
Contact binaries are the most frequently observed type of variable eclipsing star systems. They are small, cool, lightweight, and belong to the old stellar population group. They follow certain empirical relationships, which closely correlate physical parameters with each other, following Roche geometry. As a result, contact binaries provide an excellent test for stellar evolution, and specifically stellar merging scenarios. A consortium of observing campaigns have cataloged thousands of contact binaries, leading to statistical studies of many of their properties. As a corollary of such campaigns, many contact binaries have been found exhibiting extraordinary behavior, requiring follow up observations to study their peculiarities in detail. For example, a doubly eclipsing quadruple system consisting of a contact binary and a detached binary, offering a highly constrained gravitationally bound system. This is an excellent candidate to test orbital and evolutionary theories of star systems. CoBiToM is a new observing project, which was initiated at the University of Athens in 2012, in order to investigate the possible lower limit for the orbital period of binary star systems before coalescence, as a prediction from stellar evolution prior to merging.
|2017-04-28||prof. MASAHIRO HOSHINO||Department of Earth and Planetary Science, The University of Tokyo, Japan|
|ZN OA 1454||
Particle acceleration and reconnection in collisionless accretion disks
Nonthermal particles are ubiquitous in astrophysical plasmas, and explosive phenomena such as pulsar wind nebula, gamma ray bursts, and solar flares have demonstrated evidence for the production of high-energy particles. Yet the rapid magnetic energy dissipation and particle acceleration remains to be unresolved. While a great variety of acceleration processes are occurring in those astrophysical settings, magnetic reconnection is known to be one of major mechanisms of generating nonthermal high energy particles and of dissipating magnetic field energy. In my talk, I quickly review the basic physics of particle acceleration in magnetic reconnection, and then I argue about particle acceleration and angular momentum transport in collisionless accretion disks around massive black holes, by paying special attention to the role of reconnection. I discuss that the efficient particle acceleration and enhanced angular momentum transport can be realized by some kinetic effects of reconnection.
|2017-05-05||dr SZYMON SIKORA||OA UJ|
|ZN OA 1455||
An example of an inhomogeneous cosmological model; the problem of the averaging in cosmology
In this talk I present the topic of the inhomogeneities averaging in cosmology. I explain why this task is so complicated and describe the two important approaches: the Green-Wald scheme and the Buchert framework. In recent years there was an interesting dispute between these two viewpoints, concerning the role of the inhomogeneities in the estimation of the amount of the "dark energy". I show the simple cosmological model which approximates the periodically distributed dust overdensities on the Einstein-de Sitter background. The model construction enables application of the Green-Wald averaging scheme and the Buchert averaging technique simultaneously. On basis of this model I comment on the impact of the inhomogeneities on the luminocity distance observable.
|2017-05-12||dr MICHAŁ DRAHUS||OA UJ|
|ZN OA 1456||
Asteroid disruptions today
Disruptions of asteroids are often viewed as ancient events leading to the formation of asteroid families and pairs, binary and multiple systems, and discrete dust bands within the Zodiacal cloud. But thanks to the remarkable progress in solar system science over the last decade, we can now directly observe asteroidal disruptions occurring before our eyes. Various lines of evidence suggest that the disruption can be a consequence of a rapid rotation resulting from a long-term spin-up, or a result of a hypervelocity collision with another minor object. Up until recently the two mechanisms were difficult to distinguish because of the unknown rotation rates of the disrupting small asteroids, but this has changed after our team investigated the recently disrupted asteroid P/2012 F5. Using the Keck II telescope atop Mauna Kea we discovered several fragments of the object and obtained the highly anticipated measurement of the rotation rate, which turns out to be the fastest known among active asteroids and is fast enough to support the rotational disruption scenario. Further observations with the Hubble Space Telescope have revealed that the system is in fact the first ultra-young asteroid family identified to date, and given its likely formation via rotational disruption, it can also be the first known asteroid family of non-collisional origin.
|Odwołane / Cancelled|
|2017-05-19||dr SABRINA CASANOVA||Instytut Fizyki Jądrowej PAN|
|2017-05-26||prof. DAVID L. BLOCK||University of the Witwatersrand, Johannesburg, South Africa|
Priorities in Scientific Discovery - Stigler's Law of Eponymy
Stigler's Law of Eponymy states that no scientific discovery is named after the actual discoverer. This seminar highlights several examples within the realms of galaxy morphology and cosmology. The seminar will commence by focusing on a paper entitled "Un univers homogène de masse constante et de rayon croissant, rendant compte de la vitesse radiale des nebuleuses extra-galactiques" ("A homogeneous universe of constant mass and increasing radius accounting for the radial velocity of extra-galactic nebulae"). It is perhaps not widely known in undergraduate astronomy texts that Lemaître, although a master in relativity, had also spent the years 1924-25 at the Harvard College Observatory, and had a profound insight into aspects of observational astronomy, such as the effective temperatures of stars, trigonometric parallaxes, moving-cluster parallaxes, absolute bolometric magnitudes, dwarf branch stars and giant branch stars. Two years prior to the appearance of Hubble (1929), Lemaître (1927) derived a linear relationship between the radial velocities of galaxies and their distances. He then proceeded to use the radial velocities of 42 extragalactic nebulae tabulated by Strömberg (1925), to derive a value for the rate of expansion of the Universe of 625 km s-1 Mpcs-1. In view of the title of the paper by Lemaître, should Lemaître perhaps not be credited with the discovery (in 1927) of an expanding Universe? We then delve into other fascinating examples -- in galaxy morphology -- where the original discoverer has, for a variety of possible reasons, been eclipsed, in accordance with Stigler's Law of Eponymy.
|2017-06-02||mgr MARIUSZ TARNOPOLSKI||OA UJ|
|2017-06-09||dr KAROL SEWERYN||Centrum Badan Kosmicznych Polskiej Akademii Nauk, Warszawa|
|piątek po Święcie Bożego Ciała / Holiday break|
|2017-06-23||dr HELEN JERMAK||Liverpool John Moores University, Liverpool, UK|
|Przerwa wakacyjna / Summer Holiday Break|