Browsing Astronomy and Geoscience by Title
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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 ) -
Nikolić, Silvana (Belgrade)[more][less]
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Racković Babić, Kristina (Beograd , 2022)[more][less]
Abstract: Interplanetary dust grains contain important information about the Solar System. Analyzing these particles is an important aspect of the heliosphere study. Dust impacts have been observed using radio and wave instruments onboard the spacecraft since the 1980s. The interac- tion between the impact-generated plasma cloud and antenna – space- craft system elements generates the characteristic signal waveform. The present work focuses on the detection and interpretation of the dust generated signals from radio instruments onboard various space- craft orbiting at 1 AU. In the first part of the thesis, we aim to develop a model which links the observed electric signals to the dust impact properties. We propose a new model which takes into account the effect of impact - ionization - charge collection and electrostatic-influence. Our model provides an analytical expression for the pulse. It allows us to measure the amount of total ion charge, the fraction of escaping charge, the rise timescale, and the relaxation timescale. The proposed model is simple and conve- nient for large data fitting. To validate the model, we use the Time Do- main Sampler (TDS) subsystem of the STEREO/WAVES instrument, which generates high-cadence time series of voltage pulses for each monopole. Since the beginning of the STEREO mission in 2007, we have collected all the dust events detected by S/WAVES/TDS simul- taneously on all three monopoles at 1 AU. Our study confirms that the rise time vastly exceeds the spacecraft’s short timescale of elec- tron collection by the spacecraft. Aside from electron dynamics, we also obtained interesting results regarding the cloud’s electron tem- perature. The presented model provides an effective tool for analyzing vii dust waveforms, and is applicable for different space missions which investigate the distribution of dust particles, e.g., Solar Orbiter and Parker Solar Probe. In the second part of the thesis, we focus on the interstellar dust (ISD). Interplanetary and interstellar dust are the two main dust pop- ulations at 1 AU. Our objective is to search for interstellar dust by analyzing the data sets collected by STEREO and Wind, starting from the beginning of the missions. Between 2007 and 2012, while being at the solar minimum with a solar dipole pointing southward, all three spacecraft recorded ISD flux at 1 AU. However, before and after that period, the disappearance of the interstellar component was noticeable. The observed change of the impact rate suggests that the flux of inter- stellar dust at 1 AU varies with the solar cycle. Each time the magnetic dipole field changes its polarity during the solar cycle, small interstel- lar grains experience focusing or defocusing. Consequently, the dust grains are systematically deflected either towards, or away from the solar magnetic equator plane by the solar wind magnetic field which thus affects the dust dynamics and the total interstellar dust flux in the inner heliosphere. Our study provides the first quantitative de- scription of the time variation of ISD flux at 1 AU. URI: http://hdl.handle.net/123456789/5547 Files in this item: 1
Teza_KRB.pdf ( 10.95Mb ) -
Milić Žitnik, Ivana (Beograd , 2017)[more][less]
Abstract: The subje t of this dissertation is intera tion between the mean motion resonan- es and the Yarkovsky e e t. This intera tion o urs when an asteroid due to the hanges of its orbital semi-major axis ( aused by the Yarkovsky e e t) rea h the re- sonan e. The resonan e indu es a periodi os illations in the asteroid's semi-major axis around its enter. The Yarkovsky e e t exa tly auses the permanent (se ular) evolution of the orbital semi-major axis. As a result of their intera tion the mean semi-major axis drift speed is modi ed with respe t to the one aused solely by Yarkovsky. One of the main goals of this investigation was to study this intera tion, and to establish and de ne how the time that an asteroid spend in the resonan e depends on some hara teristi s of this resonan e, as well as of the asteroid itself. So far, the impa t of the resonan e on the semi-major axis drift speed has not been studied to that extent neither from that point of view. In order to study the afo- rementioned intera tion the orbital motion of test parti les a ross the resonan es is numeri ally simulated using ORBIT9 integrator. The most important result of this dissertation ertainly is determination of fun tional relation between on one side the time-period that obje ts spend inside a resonan e, and, on the other side, the semi- majors axis drift speed, the orbital e entri ity and the resonan e strength. In this work not only that existen e of the above-mentioned relationship is on rmed, but for the rst time it was expli itly de ned. Two the most interesting results are that the time spent in the resonan e is inversely proportional to the semi-major axis drift speed aused by the Yarkovsky e e t, and that this time is dire tly proportional to the resonan e strength. URI: http://hdl.handle.net/123456789/4651 Files in this item: 1
Milic-Zitnik_Ivana.pdf ( 40.69Mb ) -
Milošević, Stanislav (Beograd , 2023)[more][less]
Abstract: In this dissertation, we presented galaxy mergers and the forming of stellar morphological substructures. We assume a large spiral galaxy and dwarf galaxy which is a satellite of the first one. We used N-body simulations to present different scenarios for the merger of two galaxies, and after that, we analyzed the properties of formed structures. The investigation of the formation of these structures and their properties is important for understanding the dynamics and evolution of galaxies. First, we did simulations where we investigated the influence of the properties of dwarf galaxies on the forming structures. We tested: 1. morphology of the dwarf galaxy where we used two models – dwarf with a disk and spheroidal dwarf galaxy; 2. inclination of the orbit in the case of a very radial merger, because in that case, we have the formation of the stellar shells and streams; 3. direction of rotation of the dwarf in the case of a dwarf with a disk. In each case, after the merger, we have stellar shells and streams formed. Morphology, inclination of the orbit, and direction of rotation have their influence on the properties of formed substructures, and on the timescale of disruption of the remnant of the dwarf. In the case of the merger of Andromeda galaxy (M31) and dwarf galaxy, the satellite of M31, we investigate the properties of the Giant Stellar Stream (GSS), as well as the Northeast shell (NE) and West shell (W). The orientation of the GSS, distances, and velocities of the GSS, NE, and W shells from our simulation are in agreement with the observed one. For the first time, we explained the observed metallicity distribution in these substructures. With a linearly decreasing gradient of the initial metallicity in the dwarf galaxy before the merger, using Monte Carlo (MC) simulations, we successfully explained the observed metallicity distribution in these substructures. These results are a contribution to the investigation of metallicity gradients in dwarf galaxies which is important for galaxy evolution in general. URI: http://hdl.handle.net/123456789/5583 Files in this item: 1
SM_Doktorat_18_07_2023.pdf ( 18.08Mb ) -
Jovanović, Milena (Beograd , 2021)[more][less]
Abstract: The subject of this thesis is a precise determination of the Baryonic Mass Func- tion (BMF) for a representative sample of nearby galaxies, where BMF stands for the distribution of the galaxies’ baryonic masses. Detailed dynamical models were derived for a sample of galaxies based on the publicly available THINGS (The HI Nearby Galaxy Survey) survey, based on the the 21 cm emission line of atomic hydrogen hi. THINGS rotation curves, that reflect dynamical mass, were fitted by the sum of the contributions from the stellar component, neutral atomic gas, and dark matter for 20 THINGS galaxies. The mass of stellar components is measured from the Spitzer photometry in the 3.6 μm band, while the amount of atomic gas is derived directly from the radio observations in THINGS. For the assumed dark matter dis- tribution we used the observationally motivated pseudo-isothermal profile (ISO) and the Navarro-Frenk-White (NFW) profile based on the ΛCDM cosmological model. Dynamical modeling of the total mass was performed with free scaling of the stellar component contribution (mass-to-light ratio, M/L), and also with the same parameter fixed on a value consistent with stellar evolution population models. Con- vergence of the fitting procedure was reached for all the dynamical models with the free mass-to-light ratio, while the modeling with the fixed ratio was successful for 16 objects. The mass of the stellar component, gas, dark matter, baryonic, and total mass, were derived for the sample of galaxies and the aforementioned four sets of dynamical models (two dark matter models with both free and fixed M/L values). The total BMF is constructed by summing the masses of the baryonic compo- nents (stars and gas) for galaxies in the given range of galactic masses. Furthermore, we discuss how typical our Galactic neighborhood and our Galaxy, the Milky Way, as a giant spiral, are in terms of component masses and their place on the global (and local) BMF. URI: http://hdl.handle.net/123456789/5244 Files in this item: 1
Doktorska_disertacija_Jovanovic_Milena.pdf ( 14.28Mb )