National Repository of Grey Literature 16 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Distance to nearby galaxies
Šándorová, Ivana ; Zasche, Petr (advisor) ; Wolf, Marek (referee)
Title: Distance to nearby galaxies Author: Ivana Šándorová Institute: Astronomical Institute of the Charles University Supervisor: doc. RNDr. Petr Zasche, Ph.D., Astronomical Institute of the Charles University Abstract: The present work is focused on the study of the variable stars, particularly the lumi- nosity of cepheids in The Large Magellanic Cloud. The data were obtained from photometric observations of starfield (image centre coordinates: RA: 5◦13 36 , DE: −69h 22m 42s) using the 1,54 m Danish telescope at the observatory La Silla in Chile. The aim of this work was to find the distance of Large Magellanic Cloud, which was determined by the "period - lu- minosity relation" method for cepheids. We studied 13 cepheids, which were compared with one non-variable star. We computed the average value of distance modulus as (18,42 ± 0,40) mag. The distance modulus from the latest publication (Pietrzi'nski, G. and others, 2019) is (18,477 ± 0,004 (statistic) ± 0,026 (systematic)) mag. SIPS (Scientific Image Processing System) is software for measuring and processing of images of star field and was used in this work for processing of photometric images of star field. Own program was used for creating and editing the light curves. Keywords: galaxy, variable stars, cepheids, distance modulus 1
Distance to the Magellanic clouds
Kulich, Matúš ; Zasche, Petr (advisor) ; Korčáková, Daniela (referee)
Twelve eclipsing binary systems from the region of the Large Magellanic Cloud have been studied in this thesis in order to calculate the distance. The photometric data come from the OGLE survey carried out at the Las Campanas Observatory in Chile and the spectroscopic data come from other papers where they had already been partially ana- lyzed for other purposes. From these data, the light curves and the radial velocity curves of these systems have been constructed and analyzed using the PHOEBE soft- ware, in which the physical parameters and the absolute magnitudes of their individual components have been determined by the method of synthetic curves. By comparing them to the observed apparent magnitudes in I-band deduced from the light curves and taking into account the bolometric corrections and the V-I indices, the distance modu- lus of the Large Magellanic Cloud could be determined to be 18.59 ± 0.4 mag, which fairly corresponds to the quite familiar results determined by using this and other meth- ods in various research papers. However, in order to determine the distance modulus more accurately, it would be necessary to use accurate, much more complex models of stellar atmospheres and not simply rely on the general relations of the main-se- quence stellar parameters, which exhibit quite a large variance.
Spectroscopic diagnosis of extended circumstellar regions about early type stars
Dvořáková, Nela ; Korčáková, Daniela (advisor) ; Zasche, Petr (referee)
Nela Dvořáková 19.7.2019 1 Abstract We study a representative of a diverse group of stars exhibiting the B[e] phe- nomenon, designated MWC 939. This object might be an important link be- tween the stage of the asymptotic giant branch and planetary nebula stage as it is one of a few such objects observed. Our focus is aimed at spectral analysis of the circumstellar matter around the central star. We assemble a line list for MWC 939 and observe variations of its spectrum. Electron density and temper- ature are estimated using nebular diagnostics of ratios of [S II] λλ 6716, 6731 ˚A and [O I] λλ 6300, 6364 ˚A and 5577 ˚A. These estimates are then used for detailed calculations of the structure of circumstellar envelope. 1
An analysis and solution of the light curves of the massive triple star δ Orionis
Oplištilová, Alžběta ; Harmanec, Petr (advisor) ; Zasche, Petr (referee)
This bachelor thesis deals with δ Orionis A, a triple star from the multiple star system δ Orionis (Mintaka) in the constellation of Orion. This triple star consists of an eclipsing binary with the orbital period P = 5.732436 d and a distant tertiary with an orbital period in the order of several thousands of days. Even though the spectral lines of the secondary are very weak in the optical spectrum, they can be detected using a special analysis technique in the program KOREL. This work is based on a series of photometric and spectroscopic observations of changes in the brightness. The spectroscopic data come from the Ondřejov observatory and the photometric data are from several different photometers on artificial Earth satellites: SMEI, MOST and BRITE. Using spectroscopic data analysis software suite it was possible to determine the eccentricity e = 0.07590 and the mass ratio q = 0.44963. The parameters of the eclipsing binary were determined with the help of the eclipsing binary modelling software PHOEBE 1 that can process the light curves (photometry) as well as the radial velocity curves (spectroscopy). The residuals of light curves, or the deviations between the theoretical model and observation, were separated from the local solution and using the Stellingwerf statistics, one of the Phase...
The light curves of eclipsing binaries
Korda, David ; Zasche, Petr (advisor)
New CCD photometric observations of ten short-period LMB (Low Mass Binaries) were carried out. Data were obtained using 65 cm telescope in Ondrejov in the filters I, R and V from 2014 to 2016. Light curves were analysed using the program PHOEBE. The obtained masses and radii of the stars were compared with the theoretical mass-radii relation. There arises that the short-period binaries have the radii of about 4 % larger than the theoretical prediction from the stellar evolution models. 1
Photometric analysis of CzeV371
Sedláčková, Eva ; Zasche, Petr (advisor) ; Korčáková, Daniela (referee)
The thesis focuses on the analysis of the light curve of eclipsing binary called CzeV 371 Aur by program PHOEBE. The data were collected during five years, each season is analysed separately. This binary is a detached system consisting of two main sequence stars of the spectral type K with the period of 0,90696 days. Other parameters of this system are the inclination i = 85, 19◦ or the tem- perature of the secondary component T2 = 4060 K assuming the temperature of the primary component T1 = 4200 K. This system is interesting for asym- metries on the light curve, which are changing during the years. These can be interpreted as a spot on the primary compoment. According to the character and the rate of its changes, we can say that it is probably not the same spot in all seasons, but it is rather a group of smaller short-lived spots. 1
Study of connection between period changes and spectral type in eclipsing binaries
Vyhnálková, Veronika ; Zasche, Petr (advisor) ; Wolf, Marek (referee)
Main aim was to study whether there is a correlation between the changes in the period of the eclipsing binary stars and the spectral type of their secondary components. In the course of this thesis the character of period changes based on O-C diagrams is studied. Obtaining necessary data, several diagrams were constructed, namely the dependence of the mass ratio of both components (or period) for the effective temperature of the secondary, and another for various star type and lenght of measurement. From these diagrams the absence of alterning period change of the binaries with hot secondary was not proved, but it is indicated the shift of temperature of secondaries for binaries with increase (decrease) period to higher (lower) values. Also it was showed that monotone period changes are approximately twice more frequent for β Lyrae and W UMa-type stars than for Algols.
CCD photometry of variable objects in nearby galaxies
Kára, Jan ; Wolf, Marek (advisor) ; Zasche, Petr (referee)
The work concerns the study of variable stars in the Small Magellanic Cloud with use of time series of photometric images of star field NGC 330, which were obtained by the 1,54-m Danish telescope at the observatory La Silla in Chile during years 2012 - 2016. The aim of this work is to produce light curves of variable stars a to determine their period of variability assuming the variations are periodical. For some stars data from earlier published papers were used, which led to the coverage of longer period of time and therefore to the improvement of the accuracy of the period determination. The work lists summary of some of the types of variable stars and of mechanisms causing their variability. The work focus mainly on cepheids, which can be used to determine distances in the Universe thanks to the relation between their absolute magnitude and period of pulsation.
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)
The light curves of eclipsing binaries
Korda, David ; Zasche, Petr (advisor) ; Wolf, Marek (referee)
New CCD photometric observations of ten short-period LMB (Low Mass Binaries) were carried out. Data were obtained using 65 cm telescope in Ondřejov in the filters I, R and V from 2014 to 2016. Light curves were analysed using the program PHOEBE. The obtained masses and radii of the stars were compared with the theoretical mass-radii relation. There arises that the short-period binaries have the radii of about 4 % larger than the theoretical prediction from the stellar evolution models. Powered by TCPDF (www.tcpdf.org)

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