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Photometric study of dwarf nova EX Dra
Pilarčík, Lukáš ; Wolf, Marek (advisor) ; Mayer, Pavel (referee)
Photometry of eclipsing dwarf-nova EX Draconis was performed at the observatory of Astronomical Institute of the Academy of Sciences of the Czech Republic in Ondřejov and at the Astronomical Observatory on Kolonické sedlo during 63 nights. I calculated times of minimum light by two methods - the mirror method and the derivative method. The mirror method is more precise for these measurements with longer exposure time and smaller coverage of the light curve of eclipse. 53 new times of minima calculated by the mirror method and times of minima obtained from the older articles about EX Dra were included in the O-C diagram and fitted by the sine function and theoretical curve of LITE caused by an unseen third body. Period of cyclic changes for the sine function is 25 years, instead of 4 or 5 years period given in older papers.Period of the third body orbit is aproximately 17 years and its minimum mass is 53.5 Jupiter's mass. The sum of squared deviations is 5 times smaller for the LITE, which means that the LITE ilustrates the O-C diagram better. I determined the average outburst period for three observational seasons and I drew the phase curve of outburst. Finally, I calculated the short period of the light changes outside eclipse.
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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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Spectral analysis of the B[e] star FS CMa
Kříček, Radek ; Korčáková, Daniela (advisor) ; Mayer, Pavel (referee)
The thesis is dealing with spectral analysis of the B[e] star FS CMa, a prototype of FS CMa stars group. These objects are characterized by huge amount of matter in sourrounding shell which origin is not explained for many years. However, solving this issue could enrich stellar astrophysics by enhanced stellar evolution models. The goal of this thesis is to improve our understanding of FS CMa. We described spectral variability on various time scales and simulated spectra for different forms of the system in HDUST code. On the basis of new obtained spectra we confirmed long-term changes in variability of some spectral features and rapid variability of some spectral lines. We gained an estimate of the gas density. The simulations showed that spectral type of FS CMa is not certain and that the star could be surrounded by extended disk, many stellar radii wide. 1
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Atmospheric characteristics of white dwarfs
Krejčová, Kateřina ; Kawka, Adéla (advisor) ; Mayer, Pavel (referee)
We have analyzed the ultraviolet spectra of 40 hydrogen-rich (DA) white dwarfs. These spectra have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and are publicly available via the MAST FUSE database. We derived the effective temperature and surface gravity by fitting the hydrogen Lyman spectral lines with model spectra. By applying white dwarf evolutionary models, we were able to determine the white dwarf mass, cooling age and absolute magnitude. These then allowed us to determine the distance to each star and its predicted gravitational redshift. We have identified several chemical elements in the white dwarf spectra. We determined the abundances of C, Si, P and S by measuring the equivalent widths of selected lines of these elements. Finally, we studied the spectra of J0623-376 and LM Com in more detail.
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Spectral analysis of the B[e] star FS CMa
Kříček, Radek ; Korčáková, Daniela (advisor) ; Mayer, Pavel (referee)
The thesis is dealing with spectral analysis of the B[e] star FS CMa, a prototype of FS CMa stars group. These objects are characterized by huge amount of matter in sourrounding shell which origin is not explained for many years. However, solving this issue could enrich stellar astrophysics by enhanced stellar evolution models. The goal of this thesis is to improve our understanding of FS CMa. We described spectral variability on various time scales and simulated spectra for different forms of the system in HDUST code. On the basis of new obtained spectra we confirmed long-term changes in variability of some spectral features and rapid variability of some spectral lines. We gained an estimate of the gas density. The simulations showed that spectral type of FS CMa is not certain and that the star could be surrounded by extended disk, many stellar radii wide. 1
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