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Simulation of rings surrounding the progenitor of SN1987A
Jireš, Michal ; Pejcha, Ondřej (advisor) ; Calderón Espinoza, Diego Nicolas (referee)
SN1987A, the first supernova visible by the naked eye since 1600s, is anomalous by existence of preexisting triple ring nebula around it. One candidate explanation of the nebula is a binary merger of SN1987A's progenitors. This was already modelled in previous work with smoothed-particle hydrodynamics code GADGET. This thesis aims to replicate this model using mesh-based hydrodynamics code Athena++ and compare it. We focus on ejected mass per latitude distribution and total ejected mass. 1
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Structure and evolution of stars deformed by a nearby companion
Vokrouhlický, David ; Pejcha, Ondřej (advisor) ; Krtička, Jiří (referee)
The tidal field from a nearby binary companion affects the structure and evolution of stars. We successfully applied the Kippenhahn averaging formalism to the Roche potential and used the method to formulate approximate models of tidally deformed primaries in close binary systems. We considered both the detached and the contact configurations and neglected chemical composition evolution. These tidally deformed models are thermally stable. We explored the parametric dependence of the results on three quantities: mass ratio q in the binary, surface equipotential C of the primary or the fill-out factor F(C), and mass M1 of the primary. We found that the depth of the surface convective layer of low mass primaries in- creased due to tidal deformation. All models decreased their effective temperature when compared to their spherical counterparts. Our results also predict a positive correlation between the effective temperature and the fill-out factor for contact systems. Further- more, the temperature negatively correlates with the mass ratio of the deformed system. Finally, when isolating the tidal deformation effects, a jump in temperatures was found around 1.2 M⊙ for most fill-out factors. These findings could help to explain the observa- tionally reported dichotomy of contact binary systems at the temperature...
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Resolving stellar surfaces with binary gravitational microlensing
Pejcha, Ondřej ; Heyrovský, David (advisor) ; Dovčiak, Michal (referee)
Binary gravitational microlensing has demonstrated excellent prospects for studying the surface brightness distribution of stars. In this work we study the extended-source eects that aect the amplication of the source ux. We identify regions in the geometry that are sensitive to the extended source and nd previously unknown areas between facing cusps of multi-part caustics. We nd out that the probability of detecting the extended-source eect can be as much as two times higher than the probability of observing pure caustic crossing. We explore the chromaticity of binary microlensing and compare two classes of models of limb darkening. We describe spectral changes during binary microlensing and compare their amplitude to the point-lens case. Finally, we investigate the linear fold approximation and nd signicant residuals even in cases favorable for the method.
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Dynamical perturbations of triple stellar and planetary systems seen in gravitational waves with LISA
Mezera, Matěj ; Pejcha, Ondřej (advisor) ; Švarc, Robert (referee)
We study gravitational waves from a binary system that is perturbed by the presence of a distant third body. We present three representative models of the hierarchical triple system and we numerically model the gravitational waveform. The motion of the bodies is simulated in the Newtonian approximation on a long timescale so that Lidov-Kozai oscillation can occur. This oscillation causes periodic exchange between relative incli- nation and eccentricity of the inner binary. We analyze the frequency spectrum of the waveform and identify the effect of perturbations on a timescale similar to the binary orbital period Tin, perturbations related to the orbital period of the third body Tout, and Lidov-Kozai cycles with an approximate period T2 out/Tin. It is expected that the upcoming space detector LISA (Laser Interferometer Space Antenna) will be able to detect these gravitational signals and it will be possible to derive information about the triple system from the waveform. 1
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Stability of stars undergoing rapid mass loss
Cehula, Jakub ; Pejcha, Ondřej (advisor) ; Krtička, Jiří (referee)
Binary mass transfer is a common phenomenon is stellar astrophysics. If the mass transfer proceeds on dynamical timescale, the binary can undergo a catastrophic interaction accompanied by tremendous loss of mass, angular momentum, and energy. This so-called common envelope evolution phase is a crucial step in the formation of close binaries composed of compact objects (white dwarfs, neutron stars, black holes), which includes progenitors of gravitational wave sources de- tected by LIGO. By improving existing models of binary mass transfer we can correct the predictions of common envelope evolution and constraint the rates of close binaries composed of compact objects. In this work, we introduce new model of binary mass transfer. We will treat the mass transfer as a special case of stellar wind. We will rely on the assumption that the Roche potential sets up a de Laval nozzle around the first Lagrange point. The mass is then transferred through the nozzle. Our binary mass transfer model predicts mass transfer rates in the same order of magnitude as the standard models which use the Bernoulli's law. But the advantage of our model is that it is extendable to account for radiation.
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Angular momentum loss from binary systems due to stellar winds
Hubová, Dominika ; Pejcha, Ondřej (advisor) ; Kurfürst, Petr (referee)
Massive binary evolution is crucial for our understanding of many pheno- mena in the Universe, such as high-mass X-ray binaries or the formation of compact systems emitting gravitational waves. In this work, we study the loss of angular momentum from binary systems caused by radiation driven stellar winds, which are characteristic for hot, massive stars. Calculating numerically ballistic trajectories of particles ejected from the binary surface, we establish the average specific angular momentum loss as a function of the system's mass ratio for binaries in semidetached and contact stages. We initiate the outflow on the Roche lobes or even on further equipotentials of the Roche potential in case of over-contact systems. Moreover, we implement two models of the radiation driven wind. Firstly, we eject particles from the surface of the binary with a non-zero initial velocity, but we then let them evolve only under the influence of the system's gravity. In the second model, we develop a simple method for computing the radiative acceleration due to the radiation pressure from the bi- nary surface. Our results can be used in further calculations of the evolution of massive binary systems.
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Dynamical perturbations of triple stellar and planetary systems seen in gravitational waves with LISA
Mezera, Matěj ; Pejcha, Ondřej (advisor) ; Švarc, Robert (referee)
We study gravitational waves from a binary system that is perturbed by the presence of a distant third body. We present three representative models of the hierarchical triple system and we numerically model the gravitational waveform. The motion of the bodies is simulated in the Newtonian approximation on a long timescale so that Lidov-Kozai oscillation can occur. This oscillation causes periodic exchange between relative incli- nation and eccentricity of the inner binary. We analyze the frequency spectrum of the waveform and identify the effect of perturbations on a timescale similar to the binary orbital period Tin, perturbations related to the orbital period of the third body Tout, and Lidov-Kozai cycles with an approximate period T2 out/Tin. It is expected that the upcoming space detector LISA (Laser Interferometer Space Antenna) will be able to detect these gravitational signals and it will be possible to derive information about the triple system from the waveform. 1
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Mass loss from binary stars
Hubová, Dominika ; Pejcha, Ondřej (advisor) ; Kopáček, Ondřej (referee)
In this thesis we investigate the loss of mass from binary systems from the vicinity of the second Lagrange point L2. This phenomenon arises mainly in the common envelope evolutionary phase of close binary systems when the cores of the components orbit inside a shared gaseous envelope. It is a crucial but poorly understood stage in the system's development with two substantially different possible outcomes - stellar merger or formation of a close binary system with compact components. Modifying mass, energy and angular momentum of the binary, mass loss through the L2 point might significantly impact the system's evolution throughout the common envelope phase. Using numerical integration of equations of motion, we evaluate final states of test particles ejected from the proximity of the L2 point with arbitrary initial velocity with respect to the corotating reference frame. Furthermore, we compute the amount of energy and angular momentum these particles carry away from the system. Previously, only the particles ejected from the L2 point from initial corotation were studied; this work is therefore the first to address this problem with general initial conditions. Firstly, we initiate the particles at the L2 point with velocity pointing in the direction of x-axis and y-axis. Secondly, we eject the particles from...
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Resolving stellar surfaces with binary gravitational microlensing
Pejcha, Ondřej ; Heyrovský, David (advisor) ; Dovčiak, Michal (referee)
Binary gravitational microlensing has demonstrated excellent prospects for studying the surface brightness distribution of stars. In this work we study the extended-source eects that aect the amplication of the source ux. We identify regions in the geometry that are sensitive to the extended source and nd previously unknown areas between facing cusps of multi-part caustics. We nd out that the probability of detecting the extended-source eect can be as much as two times higher than the probability of observing pure caustic crossing. We explore the chromaticity of binary microlensing and compare two classes of models of limb darkening. We describe spectral changes during binary microlensing and compare their amplitude to the point-lens case. Finally, we investigate the linear fold approximation and nd signicant residuals even in cases favorable for the method.
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