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Determination of the mass distribution in the Galactic centre from the stellar motions
Schovancová, Jaroslava ; Šubr, Ladislav (advisor) ; Mayer, Pavel (referee)
We present an implementation of the statistical approach to the stars-gas mass exchange cycle into an N-body code. First, we summarize available data on stellar mass-loss and derive the time-dependency of the mass-loss rate of a single stellar population. Since the adopted probabilistic scheme that served as a basis for our implementation was limited to the linear star formation law while observations seem to suggest a non-linearity, we derive the non-linear star formation scheme. Both sides of the mass exchange cycle are then implemented into the code with stellar and gaseous particles and compared with an analytic recipe to test their reliability. In the next step, the comparison of such an extended statistical approach with deterministic scheme is performed for a fully dynamical model. The aim of the comparison is to explore divergence between both models of different natures. As an illustration of the code application and sensitivity of the resulting galaxy disk dynamics, several comparisons with varying the key parameters are performed.
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Dynamics of young stars in the Galactic nucleus
Haas, Jaroslav ; Šubr, Ladislav (advisor) ; Mayer, Pavel (referee)
As observations show, there are two coherently rotating structures of a few tens of young stars in the centre of our Galaxy close to a supermassive black hole. One of them contains a very dense star cluster, so-called complex IRS 13E. There are some speculations there might be an intermediate mass black hole with mass of the order of 103 -104 M in its centre. Using numerical simulations of the stellar dynamics in the dominant potential of Sgr A* disturbed by IRS 13E and a spherically symmetric cluster of old stars, which is believed to be there too, I have set upper limits on the masses of both disturbers, which guarantee, that the disturbers' presence cannot be of a destructive inuence on observed conguration of the system. It comes out that the incidence of the spherically symmetric star cluster is very stabilizing. My results show that the upper mass limit of the IRS 13E can be an order of magnitude higher, when the spherical cluster is considered (6 × 104 M) in comparison to the case, when it is omitted (4,5 × 103 M).
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Studium atmosfér Be hvězd
Sokolovičová, Júlia ; Kubát, Jiří (advisor) ; Mayer, Pavel (referee)
Be stars are a group of hot, massive, emission-line stars characterized by intense radiatively-driven stellar wind and extremely rapid rotation. The typical emission in the Balmer series arises in a thin equatorial disc around the star. The detailed structure and most of all origin of the disc are still unknown. The aim of this thesis is to give a thorough review of the main directions of research into the eld. We describe observational features that set Be stars apart from the rest of the B spectral class: Balmer emission, linear polarization, infrared excess and superionized resonance lines in the far UV range; also main physical characteristics of the underlying star, and variability. We discuss the so-called Be phenomenon - the unknown mechanism creating the emission-producing circumstellar disc in Be stars, and providine an overview of the most successful models attempting to explain the Be phenomenon. Finally we discuss the rotation law of the disc and its importance in placing a physical constraint on possible models for Be stars, and apply one of the examined rotation parameter nding methods.
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