Browsing Astronomy and Geoscience by Title
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Pavlović, Rade (Faculty of Mathematics, University of Belgrade , 2008)[more][less]
Abstract: We investigate the ful¯llment of conditions for application of Nekhoroshev theorem to real dynamical system, such as the motion of asteroids under the perturbation by major planets. We have in particular analyzed the regions of the phase space where asteroid families of Koronis and Veritas are located. The results obtained for a number of selected family members indicate that in these regions even stricter conditions (convexity, quasi-convexity and 3- jet), than the condition of steepness required by the theorem, are fullled. Consequently, the theorem of Nekhoroshev can be applied to members of Koronis family and to the members of Veritas family with regular motion. URI: http://hdl.handle.net/123456789/717 Files in this item: 1
phdRadePavlovic.pdf ( 3.135Mb ) -
Milisavljević, R. Slaviša (Belgrade , 2013)[more][less]
Abstract: The problem of the minimal mutual distances for two confocal elliptical orbits (local minima), in the literature known as the proximity calculation for minor planets and recognised recently as Minimal Orbit Intersection Distance – MOID, occupies a very important place in astronomical studies, not only because of the prediction of possible collisions of asteroids and other celestial bodies, but also because of the fact that by analysing the behaviour of asteroids during their encounters it is possible to determine their masses, changes of orbital elements and other important characteristics. Dealing with this problem in this thesis the author has analysed the distance function for two elliptical confocal orbits of minor planets combining analytical and numerical methods for proximity calculation. A survey of all relevant results in this field from the middle of the XIX century till our days indicates that the problem has been transformed from looking for a solution of two transcendental equations by applying various methods and approximations of long duration towards efficient and rapid solutions of vector equations of the system which describes the problem. In the thesis a simple and efficient analytic-numerical method has been developed, presented and applied. It finds out all the minima and maxima in the distance function and, indirectly, makes it possible to determine also the inflection points. The method is essentially based on Simovljevic’s (1974) graphical interpretation and on transcendental equations developed by Lazovic (1993). The present method has been examined on almost three million pairs of real elliptical asteroid orbits and its possibilities and the computation results have been compared to the algebraic solutions given by Gronchi (2005). The case of a pair of confocal orbits with four proximities found by Gronchi (2002), who applied the method of random samples and carried out numerous simulations with different values of orbital elements, gave the motivation to try here to find out such a pair among the real pairs of asteroid orbits. Thanks to the efficacy of the method developed in the thesis two such pairs have been found and their parameters are presented. In addition to the one meantioned above a further analysis of distance function through simulations including more than 20 million different pairs of asteroid orbits has resulted in several additional interesting solutions of the distance function. The results are given in the form of tables and plots showing the diversity of solutions for the distance function. URI: http://hdl.handle.net/123456789/2490 Files in this item: 1
phdSlavisaMilisavljevic.pdf ( 3.815Mb ) -
Simovljević, Jovan (None)[more][less]
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Pejović, Nadežda (Belgrade)[more][less]
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Kostić, Petar (b , 2023)[more][less]
Abstract: The models of radio synchrotron emission of supernova remnants (SNRs) imply uniform density ahead of shock wave, so the evolution of luminosity is usu- ally studied in such an environment, most often through the surface-brightness-to- diameter dependence, the Σ–D relation. This field aims to better understand the SNR evolution, the emission models, but also the methods for determining their distance. It is not an easy task because of a very large scatter in the Σ–D Milky Way sample. The dissertation puts a different perspective at the Σ–D relation (usually treated as power-law function), assuming that non-uniform environment around the stars considerably affects its shape and slope, that may vary during the SNR expansion. It makes the ambient density structure an important factor whose impact must be investigated. The numerical code for hydrodynamic (HD) simulations and the emission model were developed. The 3D HD simulations were performed in different non-uniform environments, including low-density bubbles and a variety of clumpy models. Based on the simulation results, a semi-analytical 3D spherically-symmetric model of HD and Σ–D evolution of SNRs in clumpy medium was developed, which is used to generate large Σ–D samples. The results show that after entering the clumpy medium the SNR brightness enhances, but afterward the Σ–D slope steepens, shortening the brightness evolu- tion lifetime. Despite the evident increase in slope in clumpy medium, the Galactic sample average slope flattens at ≈ 13–50 pc. After analyzing the generated SNR samples in clumpy medium it is concluded that the significant flattening and scatter in Galactic sample originates in sporadic emission jumps of individual SNRs in a limited diameter interval. The additional analyses of selection effects are needed to investigate these issues. URI: http://hdl.handle.net/123456789/5606 Files in this item: 1
Kostic_Petar_disertacija.pdf ( 1.947Mb ) -
Damljanović, Goran (Faculty of Mathematics, University of Belgrade , 2007)[more][less]
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Stojanović, Milan (Beograd , 2017)[more][less]
Abstract: The goal of this dissertation is to determine values of local dynamical constants. This goal is achieved through examination of multiple samples of selected stars near the Sun. The selection is done by using planar and vertical eccentricities as sampling criteria. The solution for calculating eccentricities is given. In the next step a large sample of stars is selected by defining upper limits for eccentricities and vertical amplitude. Then nested subsamples are formed in two ways: in the first one upper eccentricity limit is subjected to decreasing, in the other one this is the case with upper amplitude of oscillations perpendicular to the plane. The values of the local dynamical constants are deduced by analysing this material. URI: http://hdl.handle.net/123456789/4498 Files in this item: 1
Stojanovic_Milan_teza.pdf ( 8.577Mb ) -
Sadžakov, Sofija (Belgrade)[more][less]
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Stalevski, T. Marko (Belgrade, Gent , 2012)[more][less]
URI: http://hdl.handle.net/123456789/2487 Files in this item: 1
Marko_Stalevski_doktorska_disertacija.pdf ( 6.024Mb ) -
Popović, Georgije (Belgrade)[more][less]
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Kubičela, Aleksandar (Belgrade , 1973)[more][less]
URI: http://hdl.handle.net/123456789/120 Files in this item: 1
phdAleksandarKubicela.pdf ( 30.99Mb ) -
Komarčić, Lazar (Belgrade , 1902)[more][less]
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Valjarević, Aleksandar (Niš , 2012)[more][less]
Abstract: The territory of Kosovo and Metohia has alwaus represented the hidrology interesting area of study, in which they compared the parameters of water drainage and their physical properties. Generalization is one of the methods for these porposes and may be used and the results can be applied to various forms of digital maps. URI: http://hdl.handle.net/123456789/3118 Files in this item: 1
ValjarevicAleksandarDD.pdf ( 39.32Mb ) -
Mitić, Ljubiša (Belgrade)[more][less]
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Mišković, Vojislav (Belgrade , 1939)[more][less]
URI: http://hdl.handle.net/123456789/465 Files in this item: 1
VojislavMiskovi ... eLUniversiteDeBelgrade.pdf ( 2.547Mb ) -
MEASURING BLACK HOLE MASSES IN ACTIVE GALACTIC NUCLEI USING THE POLARIZATION OF BROAD EMISSION LINESSavić, Đorđe (Beograd , 2019)[more][less]
Abstract: Supermassive black holes (SMBHs) reside in the heart of nearly every massive galaxy in the Universe. Most of them lie dormant, but when the nearby gas is abundant, it will enter an active phase and form an active galactic nucleus (AGN). In their active phase, SMBHs have a profound effect on the host galaxy evolution and its environment. Reliable SMBH mass measuring is therefore an important task in modern astronomy. For that purpose, a method has been recently proposed by Afanasiev & Popović (2015) that uses the rotation of the polarization plane position angle across the broad emission line profile in order to trace the Keplerian motion and determine the SMBH mass. This method assumes that broad lines are emitted from a flattened disk-like region undergoing Keplerian motion, while the polarization is mainly due to the light scattering of the inner side of the coplanar dusty torus – the equatorial scattering. The goal of the thesis is to theoretically explore the possibilities of this method. We performed numerous Monte Carlo simulations for modeling equatorial scattering in AGNs using the radiative transfer code stokes (Goosmann & Gaskell 2007). We included complex motion of the emitting region in the form of radial inflows, vertical outflows, or due to the presence of the supermassive binary black holes (SMBBHs). We also selected fourwell known AGNs for observations: NGC4051, NGC4151, 3C273 and PG0844+349. Spectropolarimetry was done with the 6m telescope BTA of the Special Astrophysical Observatory of the Russian Academy of Science (SAO RAS) with the focal reducer SCORPIO. We modeled each of these AGNs using observational data available from the literature, and we compared the results of our models with observational data. We find that this method can be used as a new independent way to measure the SMBH masses in AGNs. The influence of the inflows and the outflows can be ignored if they are much lower than the Keplerian velocity. Additionally, when the scattering region is close to the broad line region, this method becomes independent of the viewing inclination. For SMBBHs, this method cannot be used, however, we obtained unique polarization profiles which are not common for a single SMBH, which could be used for identifying possible SMBBH candidates. SMBH mass estimates for the four observed AGNs are in good agreement with the masses obtained using other methods, such as the method of reverberation mapping. Method for independent SMBH mass measurements has been theoretically and experimentally verified in this work, which is very important for the future research that is dealing with the SMBH influence on its immediate environment. URI: http://hdl.handle.net/123456789/4821 Files in this item: 1
teza_Djordje_Savic.pdf ( 13.41Mb ) -
Arbutina, Bojan (Faculty of Mathematics, University of Belgrade , 2009)[more][less]
Abstract: The main research topic of this dissertation are extreme mass ratio contact close binary systems, q 0.1, of W Ursae Majoris (W UMa) type. These close binaries (CBs) represent an interesting class of objects in which ”normal”, approximately one solar mass main-sequence star is in contact with a significantly less massive companion, M2 ∼ 0.1 M . Earlier theoretical investigations of these systems found that there is a minimum mass ratio qmin = M2/M1 ≈ 0.085 − 0.095 (obtained for n = 3 polytrope - fully radiative primary) above which these CBs are stable and could be observed. If the mass ratio is lower than qmin, or, equivalently, if orbital angular momentum is only about three times larger than the spin angular momentum of a massive primary, a tidal instability develops (Darwin’s instability) forcing eventually the stars to merge into a single, rapidly rotating object (such as FK Com-type stars or blue stragglers). However, there appear to be some W UMa-type CBs with empirically obtained values for the mass ratio below the theoretical limit for stability. The aim of this dissertation is to try to resolve the discrepancy between theory and observations by considering rotating polytropes. By including in theory the effects of higher central condensation due to rotation we were able to reduce qmin to the new theoretical value qmin = 0.070 − 0.074, for the overcontact degree f = 0 − 1, which is more consistent with the observed population. Other candidate systems for stellar mergers such as AM CVn-type stars have also been discussed in the dissertation. URI: http://hdl.handle.net/123456789/716 Files in this item: 1
phdBojanArbutina.pdf ( 6.326Mb ) -
Rakić, Nemanja (Beograd , 2022)[more][less]
Abstract: Active Galactic Nuclei (AGN) are galaxy cores in which a supermassive black hole is being surrounded with an accretion disk, which emits powerful continuum emission. This continuum ionizes the surrounding gas which than emits the broad lines, detected in the optical band. The aim of this thesis is to model complex optical spectra of large numbers of type 1 AGNs (AGNs with broad emission lines) and study physical properties of the emitting gas, so-called broad line region. Understanding the physics of the broad line region, as well as the physics of AGN as a whole is important for understanding the galaxy formation and evolution. This thesis investigate a large sample of type 1 AGNs taken from the SDSS spectral database. In total, over 1500 spectra were analyzed, for which a completely new software for modeling of optical AGN spectra (named FANTASY) was developed. Automated simultaneous modeling of all emission components in the optical spectrum enables reliable measurement of spectral parameters, which can have significant application in future investigation of large AGN samples, collected within the upcoming large spectroscopic sky surveys. The physical properties in the broad line region were studied through the analysis of a still unexplained (anti)correlation between the equivalent width of the emission lines and the conti- nuum flux (the so-called Baldwin effect). It has been confirmed that the intrinsic Baldwin effect exists in the Balmer hydrogen lines in type 1 AGNs, and that a potential physical explanati- on for this effect might be presence of an additional non-ionizing optical continuum emission, which originates from the broad line region. Finally, the significant outcome of this thesis is is the new publicly available software package FANTASY, which can be widely used in the future spectral analysis of AGN. URI: http://hdl.handle.net/123456789/5451 Files in this item: 1
Doktorska_disertacija_nrakic.pdf ( 5.806Mb ) -
Pavlović, Marko (, 2017)[more][less]
Abstract: Supernova (SN) explosions disperse the different heavy elements across the Uni- verse. These elements are the building blocks which make up the world around and inside us. Supernova remnants (SNRs) are extraordinary astronomical objects that are also of high scientific interest, because they provide insights into aforementioned supernova explosion mechanisms, and because they are important sources of Galac- tic cosmic rays (CRs). Radio observations are among the oldest means to study these objects. The radio luminosity and spectra of SNRs, especially young ones, requires active acceleration of electrons by the SNR shocks. In this doctoral dissertation, radio evolution of SNRs is investigated by using three-dimensional hydrodynamic modelling and non-linear diffusive shock acceleration of CRs in SNRs. Hydrodynamic simulations, developed and adopted in this dissertation, allow us to explicitly account for the shock modification by CRs. We also include consistent numerical treatment of magnetic field amplification (MFA) due to CR resonant and non-resonant streaming instabilities. We modelled the peculiar nature of radio evo- lution of the youngest known Galactic SNR G1.9+0.3 and concluded that increasing radio emission is a common occurrence among very young SNRs. Our model ena- bled us to make important conclusions about the present and predictions about the future properties of radio emission from this SNR. We also developed more general model of the radio evolution of SNRs, by performing simulations for wide range of the relevant physical parameters, such as the ambient density, the supernova ex- plosion energy, the acceleration efficiency and the MFA efficiency. We confirm the reliability of our radio evolutionary tracks on a observation sample consisting of Galactic and extragalactic SNRs. This dissertation also deals with one of the most important questions surroun- ding our current understanding of the magnetic fields in SNRs. We conclude that equipartition is a justified assumption especially between the CR electrons and the magnetic fields in evolved SNRs, in the Sedov-Taylor phase of evolution. Our work also offers a possible explanation how can equipartition between CRs and magnetic field in the interstellar medium be achieved. Type of modeling, presented in this thesis, is expected to be a useful tool for fu- ture observers working on powerful radio telescopes such as ALMA, MWA, ASKAP, SKA and FAST. Simulations should provide important information about the evolu- tionary stage of the observed SNRs, as well as to characterize the physical conditions in the shocks where the relativistic particles are accelerated. Simulations could help us to predict the science output of future large scale surveys, as well as to explain new, often unexpected results obtained by observations. URI: http://hdl.handle.net/123456789/4759 Files in this item: 1
MPavlovic.pdf ( 14.32Mb ) -
Pavlović, Marko (Beograd , 2018)[more][less]
Abstract: Supernova (SN) explosions disperse the different heavy elements across the Uni verse. These elements are the building blocks which make up the world around and inside us. Supernova remnants (SNRs) are extraordinary astronomical objects that are also of high scientific interest, because they provide insights into aforementioned supernova explosion mechanisms, and because they are important sources of Galac tic cosmic rays (CRs). Radio observations are among the oldest means to study these objects. The radio luminosity and spectra of SNRs, especially young ones, requires active acceleration of electrons by the SNR shocks. In this doctoral dissertation, radio evolution of SNRs is investigated by using three-dimensional hydrodynamic modelling and non-linear diffusive shock acceleration of CRs in SNRs. Hydrodynamic simulations, developed and adopted in this dissertation, allow us to explicitly account for the shock modification by CRs. We also include consistent numerical treatment of magnetic field amplification (MFA) due to CR resonant and non-resonant streaming instabilities. We modelled the peculiar nature of radio evo lution of the youngest known Galactic SNR G1.9+0.3 and concluded that increasing radio emission is a common occurrence among very young SNRs. Our model ena bled us to make important conclusions about the present and predictions about the future properties of radio emission from this SNR. We also developed more general model of the radio evolution of SNRs, by performing simulations for wide range of the relevant physical parameters, such as the ambient density, the supernova ex plosion energy, the acceleration efficiency and the MFA efficiency. We confirm the reliability of our radio evolutionary tracks on a observation sample consisting of Galactic and extragalactic SNRs. This dissertation also deals with one of the most important questions surroun ding our current understanding of the magnetic fields in SNRs. We conclude that equipartition is a justified assumption especially between the CR electrons and the magnetic fields in evolved SNRs, in the Sedov-Taylor phase of evolution. Our work also offers a possible explanation how can equipartition between CRs and magnetic field in the interstellar medium be achieved. Type of modeling, presented in this thesis, is expected to be a useful tool for fu ture observers working on powerful radio telescopes such as ALMA, MWA, ASKAP, SKA and FAST. Simulations should provide important information about the evolu tionary stage of the observed SNRs, as well as to characterize the physical conditions in the shocks where the relativistic particles are accelerated. Simulations could help us to predict the science output of future large scale surveys, as well as to explain new, often unexpected results obtained by observations. URI: http://hdl.handle.net/123456789/4736 Files in this item: 1
MPavlovic.pdf ( 14.32Mb )