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Extensions of the main belt collisional model
Vávra, Michael ; Brož, Miroslav (advisor) ; Scheirich, Petr (referee)
The Main Belt, the region between the orbits of Mars and Jupiter, is the home to more than 1 million asteroids. These asteroids form orbital groups, i.e., asteroid families formed by collisions; and also spectral groups (taxonomies) with different chemical composition, in particular, carbonaceous (C-types) and silicate (S-types). In this thesis, we extend the existing collisional model by finding appropriate dependence of the strength vs. size (also known as the scaling law) for these two groups. We used color indices and geometric albedos of 56 and 72 spectroscopically confirmed C- and S-types (control samples) and statistical methods on 1 065 054 asteroids, to assign C-, S- or other-types (neither C- nor S-type). This allowed us to construct the observed size-frequency distributions (SFDs) for several sub-populations constrained either in the semi-major axis (inner, middle, outer) or taxonomy (C, S, other). Then we used the Monte-Carlo code Boulder (Morbidelli et al. 2009). to compute the long-term collisional evolution (4.5 billion years) and derive synthetic SFDs. We find that the scaling laws for C- and S-types disagree with the ones proposed by Holsapple & Housen (2019). Our best-fit scaling laws indicate that S-types must be weakened below approximately 1 km compared to C-types, to explain a...
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Orbital and internal dynamics of terrestrial planets
Walterová, Michaela ; Běhounková, Marie (advisor) ; Efroimsky, Michael (referee) ; Brož, Miroslav (referee)
Title: Orbital and internal dynamics of terrestrial planets Author: Michaela Walterová Department: Department of Geophysics Supervisor: RNDr. Marie Běhounková, Ph.D., Department of Geophysics Abstract: Close-in exoplanets are subjected to intense tidal interaction with the host star and their secular evolution is strongly affected by the resulting tidal dissipation. The tidal dissipation not only provides an additional heat source for the planet's internal dynamics but it also contributes to the evolution of the planet's spin rate and orbital elements. At the same time, the tidal dissipation itself is also determined by the planet's thermal state and by the spin-orbital parameters. The evolutions of the orbit and of the interior are, therefore, intrinsically linked. In this work, we combine analytical and numerical techniques to gain insight into the interconnection between the internal properties and the orbital evolution, with special focus on the role of tides. After a general study of parametric dependencies of the tidal heating and tidal locking, we present a semi-analytical model assessing the coupled tidally-induced thermal-orbital evolution in systems consisting of a host star and one or two planets. Specifically, we study the thermal-orbital evolution in three systems inspired by existing low-mass...
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The origin of Jupiter Trojans
Odehnal, Martin ; Brož, Miroslav (advisor) ; Ďurech, Josef (referee)
The Jupiter Trojans are a group of at least 12, 000 asteroids located in the vicinity of the Lagrange points L4 and L5. There are several theories for the origin of Trojans, such as the chaotic capture during the 1:2 resonance of Jupiter and Saturn, the Jumping Jupiter scenario, or the capture in a gaseous disk. New models, however, show important hydrodynamic phenomena in a gaseous disk during planetary migration, which could also affect Trojan capture, such as the growth of eccentricity or inclination of protoplanets (Chrenko et al. 2017, Eklund & Masset 2017). We performed two-fluid hydrodynamic simulations of a protoplanetary disk consisting of gas and pebbles, with one 20 ME Jupiter-like protoplanet rapidly growing via gas accretion, and computed trajectories and the capture efficiency of small asteroids, from 10 m up to 10 km in diameter. In our simulations, we found that 29 out of 100 hundred-meter planetesimals placed on circular orbits near the growing circular proto-Jupiter were captured in L4/L5. In the case of proto-Jupiter having non-zero initial eccentricity and inclination, the captured orbits of 100 m and 10 km planetesimals were unstable and eventually left the Trojan region. On the contrary, 10 m planetesimals stayed on stable orbits due to aerodynamic drag. The inclinations of captured...
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Hydrodynamical simulations of circumstellar discs
Vitovský, Kristián ; Brož, Miroslav (advisor) ; Švanda, Michal (referee)
In this work, we study the dynamics of circumstellar discs, with a focus on the β Lyræ A binary system. This system has been extensively observed by photometry, spectroscopy and interferometry. All these observations were recently interpreted by a radiation-transfer kinematic model [Brož et al. 2021]. In order to apply dynamical models, we first review the theory of steady-state viscous accretion discs, including the α-parametrisation of the viscosity. We modified the analytical models [Shakura and Sunyaev 1973] for a general opacity prescription, κ = κ0ρA TB , and derived radial profiles of various quantities (Σ, T, H). The profiles were computed for the accretion rate ̇M = 2·10−5 M⊙ yr−1 , inferred from the observed rate of change of the binary period. To achieve this rate, the surface densities Σ must be much higher (of the order of 10000 kg m−2 for α = 0.1) than in the kinematic model. Viscous dissipation and radiative cooling in the optically thick regime lead to high mid-plane temperatures. The disk is still gas pressure dominated. More general models were computed numerically. We used 1-dimensional radiative hydrodynamic models [Chrenko et al. 2017], accounting for viscous, radiative as well as irradiation terms. The initial conditions were taken from the analytical models. The simulations achieved a...
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Radiation transfer in protoplanetary disks vs ALMA interferometric observations
Janoška, Ondřej ; Brož, Miroslav (advisor) ; Grossová, Romana (referee)
We study observability of protoplanetary disc structures by the ALMA interferometer. Structures, which planets create in discs have a form of spiral arms, rings or gaps. Our goal is to calculate synthetic images of such discs. For this purpose, we created Faradit, a program for extending a two-dimensional hydrodynamical simulation of a protoplanetary disc to the third, vertical dimension. We studied 5 different cases: a vertically isothermal disc, an optically thick disk, an optically thin disc, a disc with a distribution of grain sizes and a disc with viscous heating and dust grain evaporation. In all of them, we calculated radiation transfer using RADMC-3D program and created ideal images for six different wavelengths. Eventually, we assessed whether these structures are observable, using a simulator of interferometric observations (ALMA OST). Despite the structures induced by protoplanets with masses 3 M⊕ were present, we concluded they are not observable with a realistic signal and noise of ALMA in continuum. The respective disc would have to be more evolved, with an opened gap. 1
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Study of inclination change for the eclipsing binaries
Juryšek, Jakub ; Zasche, Petr (advisor) ; Brož, Miroslav (referee)
This thesis deals with the study of the eclipsing binaries with inclination changes, caused by orbital precession due to third body in the system. Methods of semiauthomatic detection of the inclination changing eclipsing binaries among huge lightcurves databases have been developed. These methods have been applied to the ASAS-3 and OGLE III LMC databases. As a result, 39 new systems suspected of orbital precession have been found and 33 of them are situated in the Large Magellanic Cloud, with only one previously studied system. Increasing the number of known multiple systems especially those located outside Milky Way allows to study inter-galactic differences in star formation. In this work, we bring detailed study of ten new systems and restrictions on the third body parameters are presented. Powered by TCPDF (www.tcpdf.org)
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Simulation of the astrolabe of the Prague astronomical clock for PC
Makara, Tomáš ; Šolc, Martin (advisor) ; Brož, Miroslav (referee)
In this work we create a computer simulation of the astrolabe of the Prague astronomical clock. The result of this work will by a didactic instrument which will help users discover and understand the astronomical clock. The task is to create a realistic three-dimensional computer model of the astronomical clock and also to implement all movement of the clock. The application will offer three-dimensional realistic visualization of the astronomical clock, description of the clock's parts, and projection of the celestial sphere on the astronomical dial and information which can be read from the dial. The application will provide a possibility to see animation of the astronomical clock and also to set the clock to an arbitrary time during the year.
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Propagating star formation
Dinnbier, František ; Wünsch, Richard (advisor) ; Brož, Miroslav (referee) ; Naab, Thorsten (referee)
Massive stars are powerful energetic sources shaping their surrounding interstellar medium, which is often swept up into a cold dense shell. If the shell fragments and forms a new generation of massive stars, the stars may form new shells, and this sequence repeats recursively leading to propagating star formation. Using three dimensional hydrodynamic simulations, we investigate fragmentation of the shell in order to estimate masses of stars formed in the shell. We develop a new numerical method to calculate the gravitational potential, which enables us to approximate a part of the shell with a plane-parallel layer. Our main results are as follows. Firstly, we compare our numerical calculations to several analytical theories for shell fragmentation, constrain the parameter space of their validity, and discuss the origin of their limitations. Secondly, we report a new qualita- tively different mode of fragmentation - the coalescence driven collapse. While layers with low pressure confinement form monolithically collapsing fragments, layers with high pressure confinement firstly break into stable fragments, which subsequently coalesce. And thirdly, we study whether layers tend to self-organise and form regular patterns as was suggested in literature, and we find no evidence for this conjecture. Based on our...
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