Browsing Astronomy and Geoscience by Title
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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 ) -
Jurković, Monika (, 2019)[more][less]
Abstract: The subject of this PhD thesis are Type II Cepheids. Type II Cepheids are pulsating Population II stars with masses of around 0.5 0.6 M⊙. Their mass determines where they are positioned on the Hertzsprung-Russell diagram (HRD), that is, their luminosity and eective temperature. These stars can be found in the Milky Way, the Magellanic Clouds, and in other distant galaxies. They occupy a narrow strip on the HRD which is called the instability strip. Here the radii and luminosity change periodically, and this change can be seen in the light curves. Because of their age, and their position on the HRD, these variables form a separate period-luminosity relation (PL relation). Using the spectral energy distribution models we determined in this thesis the eective temperatures and luminosities, and from evolutionary models the masses and radii, for Type II Cepheids and anomalous Cepheids in the Large and Small Magellanic Clouds. In the thesis, the rst period- luminosity relation was constructed using bolometric magnitude (Mbol). The thesis also presents the reclassication of Type II Cepheids from the Milky Way using the Fourier decomposition of the light curves measured in V lter. The Fourier decomposition was used to calculate the Fourier parameters, which were then used to compare the stars from the Milky Way with the sample of known Type II Cepheids and anomalous Cepheids from the OGLE-III catalogue for the Large Magellanic Cloud. From the 59 stars (taken from the General Catalogue of Variable Stars), 18 turned out to be anomalous Cepheids, 1 anomalous Cepheid pulsating in the rst overtone, 11 classical Cepheids, 2 peculiar W Virginis stars or classical Cepheids, and 7 were found not to be pulsating stars at all. URI: http://hdl.handle.net/123456789/4760 Files in this item: 1
Jurkovic_Monika.dok.dis.pdf ( 15.79Mb ) -
Jovanović, Bora (Beograd , 2014)[more][less]
Abstract: Одређивање разлике динамичког и светског времена и предвиђање промена у брзини Земљине ротације Апстракт Проблем прецизног предвиђања Земљине просторне оријентације је у директној вези са познавањем будућих вредности параметара Земљине ротациеј, помоћу којих се врше трансформације између небеског и терестричког система. Ти параметри су зависни од мноштва астрономских и геофизичких узрока, за чије збирно дејство још увек не постоје одговарајући теоријски модели, који би могли довољно прецизно да описују промене Земљине оријентације. Зато се предикције параметара Земљине ротације мање ослањају на геофизичке теорије, а више на математичка моделирања, која су заснована на разним нумеричким методама. Овај рад је имао за циљ да докаже да је искључиво математичким приступом(без коришћења геофизичких модела и корекција) могуће постићи унапређења у предвиђањима неравномерности скале светског времена UT1. Познато је да тај параметар има најбржу и највећу промену, јер у потпуности пресликава Земљину ротацију са свим њеним неравномерностима. Због чега његове предикције имају најмању тачност. У раду је коришћена оригинална нумеричка метода за извођење апроксимативних функција у облику суме хармоника и експоненцијала(HE). На основу реалних података рађене су предикције за 10 дана, 30 дана и 500 дана у непрекидном периоду од годину и по дана. Додатно, приказани су и, до сада остварени, резултати једне дуговремене предикције која је истим начином урађена раније. Сопствени резултати су упоређивани са одговарајућим резултатима других аутора, који су користили разне друге методе предикције, током реализације међународног пројекта “Earth Orientation Parameters Prediction Comparison Campaign”(EOPPCC). Показало се да HE метод даје сличне резултате као и друге методе када се ради о 10- дневним и 30-дневним предикцијама, али у случају 500 дневних предикција дао је убедљиво најбољи резултат. Да је овај метод заиста погодан за предикције на дужим временским интервалима, приказују и до сада (8 година) остварени резултати једне 10- годишње предикције. Може се закључити да је предикцију величине ΔТ, која се публикује у астрономским годишњацима, могуће знатно унапредити, коришћењем HE метода. Кључне речи: Време, светско време, терестричко време, референтни системи Научна област: Астрономија Ужа научна област: Земљина ротација УДК: 521.933:519:65(043.3) URI: http://hdl.handle.net/123456789/3508 Files in this item: 1
jovanovic_bora.pdf ( 11.69Mb ) -
Jurković, Monika (Beograd , 2018)[more][less]
Abstract: The sub ject of this PhD thesis are Typ e I I Cepheids. Typ e I I Cepheids are pulsating Population I I stars with masses of around 0.5 0.6 M ⊙ . Their mass determines where they are p ositioned on the Hertzsprung-Russell diagram (HRD), that is, their luminosity and e ective temp erature. These stars can b e found in the Milky Way, the Magellanic Clouds, and in other distant galaxies. They o ccupy a narrow strip on the HRD which is called the instability strip. Here the radii and luminosity change p erio dically, and this change can b e seen in the light curves. Because of their age, and their p osition on the HRD, these variables form a separate p erio d-luminosity relation ( P L relation). Using the sp ectral energy distribution mo dels we determined in this thesis the e ective temp eratures and luminosities, and from evolutionary mo dels the masses and radii, for Typ e I I Cepheids and anomalous Cepheids in the Large and Small Magellanic Clouds. In the thesis, the rst p erio d- luminosity relation was constructed using b olometric magnitude ( M b ol ). The thesis also presents the reclassi cation of Typ e I I Cepheids from the Milky Way using the Fourier decomp osition of the light curves measured in V lter. The Fourier decomp osition was used to calculate the Fourier parameters, which were then used to compare the stars from the Milky Way with the sample of known Typ e I I Cepheids and anomalous Cepheids from the OGLE-I I I catalogue for the Large Magellanic Cloud. From the 59 stars (taken from the General Catalogue of Variable Stars), 18 turned out to b e anomalous Cepheids, 1 anomalous Cepheid pulsating in the rst overtone, 11 classical Cepheids, 2 p eculiar W Virginis stars or classical Cepheids, and 7 were found not to b e pulsating stars at all. URI: http://hdl.handle.net/123456789/4751 Files in this item: 1
Jurkovic_Monika.dok.dis.pdf ( 15.79Mb ) -
Vučetić, Milica (Beograd , 2017)[more][less]
Abstract: In this dissertation we discuss in uence of H emission from supernova remnants (SNRs) on H derived star formation rates (SFRs). We present the detection of 16 optical SNR candidates in a part of nearby spiral galaxy IC342, and two more poten- tial SNRs in NGC 185 galaxy. The candidates were detected by applying [S ii]/H ratio criterion on observations made with the 2 m telescope at Rozhen National Astronomical Observatory in Bulgaria. Also, in this dissertation we present the most up-to-date list of nearby galaxies with optically detected SNRs. When deri- ving H star formation rates, assumption is that the radiation is coming from the ionized gas surrounding hot and young stars { Hii regions. In this case, emission from SNRs contaminates H ux used to derive SFR. We found that the contribu- tion of SNRs' ux to the total H ux, for 18 galaxies in our sample of galaxies with optical SNRs, is 5 5%. Due to the observational selection effects, the SNR contamination of SFRs derived herein represents only a lower limit. M83 is the galaxy with the most detected optical SNRs and in this galaxy SNRs account for 9 per cent of the total H emission. We expect that fraction similar to this would be close to the real contribution of SNR emission to the total H emission in spiral galaxies. Using two dwarf galaxies as an example, Holmberg IX and NGC 185, we show that the contamination of H ux by SNRs, or other sources, can be much larger, up to ten times higher than total H ux coming from Hii regions of the observed galaxy. URI: http://hdl.handle.net/123456789/4501 Files in this item: 1
Milica_disertacija_21.03.2017.pdf ( 26.28Mb ) -
Vučetić, Milica (Beograd , 2017)[more][less]
Abstract: In this dissertation we discuss in uence of H emission from supernova remnants (SNRs) on H derived star formation rates (SFRs). We present the detection of 16 optical SNR candidates in a part of nearby spiral galaxy IC342, and two more poten- tial SNRs in NGC 185 galaxy. The candidates were detected by applying [S ii]/H ratio criterion on observations made with the 2 m telescope at Rozhen National Astronomical Observatory in Bulgaria. Also, in this dissertation we present the most up-to-date list of nearby galaxies with optically detected SNRs. When deri- ving H star formation rates, assumption is that the radiation is coming from the ionized gas surrounding hot and young stars { Hii regions. In this case, emission from SNRs contaminates H ux used to derive SFR. We found that the contribu- tion of SNRs' ux to the total H ux, for 18 galaxies in our sample of galaxies with optical SNRs, is 5 5%. Due to the observational selection effects, the SNR contamination of SFRs derived herein represents only a lower limit. M83 is the galaxy with the most detected optical SNRs and in this galaxy SNRs account for 9 per cent of the total H emission. We expect that fraction similar to this would be close to the real contribution of SNR emission to the total H emission in spiral galaxies. Using two dwarf galaxies as an example, Holmberg IX and NGC 185, we show that the contamination of H ux by SNRs, or other sources, can be much larger, up to ten times higher than total H ux coming from Hii regions of the observed galaxy. URI: http://hdl.handle.net/123456789/4507 Files in this item: 1
Milica_disertacija_21.03.2017.pdf ( 26.28Mb ) -
Milogradov-Turin, Jelena (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/126 Files in this item: 1
phdJelenaMilogradovTurin.pdf ( 115.3Mb ) -
Ševarlić, Branislav (Belgrade)[more][less]
URI: http://hdl.handle.net/123456789/141 Files in this item: 1
phdBranislavMSevarlic.pdf ( 5.662Mb ) -
Teleki, Đorđe (Belgrade , 1964)[more][less]
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Šegan, Stevo (Belgrade , 1987)[more][less]
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Đurović, Dragutin (Belgrade)[more][less]
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Ninković, Slobodan (Belgrade)[more][less]
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Kuzmanoski, Mike (Belgrade)[more][less]
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Đurašević, Gojko (Belgrade)[more][less]