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Abstract:
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The subject of this PhD thesis are Type II Cepheids. Type II Cepheids are pulsating Population II stars with masses of around 0.5 0.6 M⊙. Their mass determines where they are positioned on the Hertzsprung-Russell diagram (HRD), that is, their luminosity and eective temperature. These stars can be found in the Milky Way, the Magellanic Clouds, and in other distant galaxies. They occupy a narrow strip on the HRD which is called the instability strip. Here the radii and luminosity change periodically, and this change can be seen in the light curves. Because of their age, and their position on the HRD, these variables form a separate period-luminosity relation (PL relation). Using the spectral energy distribution models we determined in this thesis the eective temperatures and luminosities, and from evolutionary models the masses and radii, for Type II Cepheids and anomalous Cepheids in the Large and Small Magellanic Clouds. In the thesis, the rst period- luminosity relation was constructed using bolometric magnitude (Mbol). The thesis also presents the reclassication of Type II Cepheids from the Milky Way using the Fourier decomposition of the light curves measured in V lter. The Fourier decomposition was used to calculate the Fourier parameters, which were then used to compare the stars from the Milky Way with the sample of known Type II Cepheids and anomalous Cepheids from the OGLE-III catalogue for the Large Magellanic Cloud. From the 59 stars (taken from the General Catalogue of Variable Stars), 18 turned out to be anomalous Cepheids, 1 anomalous Cepheid pulsating in the rst overtone, 11 classical Cepheids, 2 peculiar W Virginis stars or classical Cepheids, and 7 were found not to be pulsating stars at all. |