Browsing Astronomy and Geoscience by Title
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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]
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Atanacković-Vukmanović, Olga (Belgrade)[more][less]
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Angelov, Trajče (Belgrade , 1980)[more][less]
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Oskanjan, Vasilije (Belgrade)[more][less]
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Radović, Viktor (Beograd , 2017)[more][less]
Abstract: The main goal of this dissertation is improvement of an approach for identi- cation of the members of asteroid families, based on the hierarchical clustering method. An additional step is introduced in order to reduce a so-called chaining e ect. The introduced algorithm consists of four main steps. In the rst step, the hierarchical clustering method is applied to the initial catalogue of proper elements in order to obtain a preliminary list of family members. In the second step, using available physical properties, and based upon the de ned criteria, the interlopers are identi ed. In the third step, objects identi ed as interlopers in the second step, are excluded from the initial catalogue of proper orbital elements, producing a modi ed catalogue. Finally, in the fourth step, the HCM analysis is performed again, but this time using the modi ed catalogue of proper elements. It is shown that in this way a number of potential interlopers among family members is signi cantly reduced. Moreover, an on-line based portal (Asteroids Families Portal; AFP) to apply this procedure is developed, and is freely available to all interested researchers. The second goal of the dissertation is to determine the limitations of the backward integration method, used for estimation of ages of young asteroid families. This aim is achieved through numerical simulations of the evolution of a ctitious family. By determining instants of secular angles i $ clustering, a linear relationship is found between the depth of a clustering and the age of a family. According to the obtained results, the backward integration method could be successfully applied to families not older than 18 Myrs. URI: http://hdl.handle.net/123456789/4504 Files in this item: 1
Radovic_teza.pdf ( 22.32Mb ) -
Tsirvoulis, Georgios (Beograd , 2019)[more][less]
Abstract: Asteroid families are populations of asteroids in the Main Belt that share a common origin, that is they are the fragments of energetic collisions between two asteroids. Their study over the years has produced a number of important results concerning the collisional and dynamical evolution of the Main Belt, the physical properties of the primordial bodies of the Solar System and the physics of energetic collisions, to name a few. The contribution of the present thesis can be summarized into two main topics: The first is the discovery of a new mechanism that leads to significant perturbations on the orbits of asteroids, and consequently on the evolution of asteroid families affected by it, and the second is the discovery of a couple of new families, each with its own peculiarities. The first part of this thesis was initially motivated by the irregular shape of the (1726) Hoffmeister asteroid family. In an effort to explain this peculiarity we carried out a thorough dynamical analysis of its past evolution and found out that none of the mechanisms known to affect the orbits of asteroids could explain it. Investigating further we discovered that the linear nodal secular resonance with the most massive asteroid (1) Ceres, is the mechanism responsible for the anisotropic inclination distribution of Hoffmeister family members. Having established the importance of the nodal secular resonance with Ceres, we sought to expand on the subject with the study of all linear secular resonances, nodal and periapsidal, involving not only (1) Ceres, but (4) Vesta, the second most massive asteroid, as well. To do so we utilized numerical integrations of test particles across the whole Main Belt, and evaluated the impact of these resonances on their orbits. Furthermore we identified all asteroid families crossed by one or more of these resonances. Two of these cases, the families of (1251) Seinajoki and (1128) Astrid were then studied in more detail, confirming the importance of the previously ignored secular resonances with massive asteroids. The second part details the discovery of two new asteroid families. The first one, that of (326) Tamara family, was motivated by the unexpectedly high number of dark asteroids in the Phocaea region, a part of the inner Main Belt which is expected to consist mostly of bright ones. Using all available physical data we were able to show that most of the dark asteroids therein belong to a single dynamical family, which we then further analyzed finding that it is 264 ± 43 Myrs old and that it could have a significant contribution to the influx of small dark asteroids toward the Near Earth region. The second discovered family, that of (633) Zelima, is a small cluster, sub-family of the large (221) Eos family. After identifying its members, we derived the age of the Zelima family, which turned out to be only about 3.66 Myrs. URI: http://hdl.handle.net/123456789/4752 Files in this item: 1
Tsirvoulis_Georgios.pdf ( 76.51Mb ) -
Urošević, Dejan (Belgrade)[more][less]
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Ćatović, Zlatko (Belgrade)[more][less]
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Mitrašinović, Ana (Beograd , 2022)[more][less]
Abstract: The subject of this dissertation is to study the effects of galaxy flybys on the structural evolution of galaxies. Galaxy flybys are very close interactions that do not result in a merger. With the high frequency in the late Universe, their role in the evolution of galaxies is significant. Earlier studies focused on equal-mass flybys, which are extremely rare. We focus on typical flybys with a lower mass ratio. We aim to explore the structure and evolution of galaxies in greater detail and demonstrate that these flybys are just as important as equal-mass ones. We performed a series of N body simulations of typical flybys with varying impact para- meters. We demonstrated the applicability and importance of isolated N body simulations and developed an efficient method for reliable bar detection in galaxy discs. For the first time, we examined the evolution of the secondary galaxy, focusing on its dark matter mass loss. The results show that the leftover mass follows logarithmic growth law with impact parameter and suggest that flybys contribute to the formation of dark matter-deficient galaxies. The primary galaxy is affected in a similar way as in equal-mass flybys. Bars form in closer flybys, two-armed spirals form during all flybys, and the dark matter halo spins up. Most of the parameters of these structures are correlated or anti-correlated with the impact parameter. We also noticed that a double bar could form as evolving spirals wrap around the early-formed bar. We successfully demonstrated that frequent, typical flybys with lower mass ratios signifi- cantly affect the evolution of galaxies, producing various observed effects. Our results should serve as a warning not to disregard these interactions in future studies. URI: http://hdl.handle.net/123456789/5441 Files in this item: 1
mitrasinovic_ana.pdf ( 5.370Mb )