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A study of spectral and photometric variations of the Be star V960 Tau = 120 Tau
Švrčková, Jana ; Harmanec, Petr (advisor) ; Korčáková, Daniela (referee)
The thesis is focused on analysis of spectra and photometry of Be star 120 Tau. A period of 142,4 d was found in the spectroscopy dat, which might be related to a binary character of this object. This period has to be confirmed by a set new observations. Both positive and negative correlation were present in the color-color diagram of U − B vs B − V . The explanation of this fact is the inclination of the rotational axis, which is near 60◦ . Spectral type, radius and an interval of possible rotational periods were also determined. Two more periods were found in the photometry data - 1,0375 d a 10,91 d. The shorter one is probably related to the rotation of the star. Other short periods listed in other works were not confirmed. The object's behavior is very complicated, more observations are needed to explain it. 1
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Spectroscopic and photometric investigation of selected hot stars
Oplištilová, Alžběta ; Harmanec, Petr (advisor) ; Pribulla, Theodor (referee)
To rigorously study hot stars, we need to determine their properties as accurately as possible. This thesis focuses on improving the accuracy of parameters of two hot stars and contributes to the collection of stars with more known parameters. While photometric and spectroscopic data sets on hot stars δ Ori A and ω CMa are plentiful, the former is a triple star that suffers from having a faint spectrum of the secondary, which complicates its analysis, and the latter is a Be star, the origin, formation, and long-term variability of whose gaseous envelopes (veils) remain unexplained. Using mathematical techniques (Fourier transforms) and modelling software PHOEBE 1, properties of δ Ori A are determined, and conjecture on the presence of a circumstellar envelope in δ Ori A might be true by considering the shape changes of the Hα line. A conjecture that period changes of ω CMa correlate to the mass of the circumstellar envelopes seems to be proved true by considering variations of radial velocities, V/R ratio, and determining profile line asymmetry. 1
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A new study of time variability of the Be star LQ And
Lipták, Jozef ; Harmanec, Petr (advisor) ; Korčáková, Daniela (referee)
We contradict binary nature of LQ And. Radial velocities of Hα emision are bound to changes less than 2 km/s. We were not able to detect any periodic variability in radial velocities of core and wings of Hα emision nor of line He I 6678 Å. We discus effect of telluric line movement on precision of our measurement. Detected period of 0,415 d in intensity ratio IV /IR needs aditional confirmation. The star overcome striking increase in intensity of the emission accompained by increase in overall brightness and shortening of photometric period from 0,3094 d to 0,3083 d. Our estimated interval of rotational periods of the star lies in between this photometric period and double of it, which shows that rotation might not be responsible for the photometric changes. 1
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A study of the long-term brightness and colour variations of the Be star 88 Herculis
Vitovský, Kristián ; Harmanec, Petr (advisor) ; Korčáková, Daniela (referee)
Photometric observations of the Be star 88 Herculis from 12 different sources were collected covering a period from 1968 to 2019 for the purpose of studying variations on the timescale of years to decades. All the used data was either available in or transformed into the Johnson Standard system. Since systematic photometric observations began in the 1970's the star underwent three long-term variation cycles that differ in strength and length. A quantitative description of each cycle is given. The data suggests that the star is also changing on an even longer timescale in both luminosity and colour. The photometric data was compared to the evolution of the Hα emission line and discussed in connection to possible physical models. It is shown that he object exhibits behavior that corresponds to what is described in literature as the Negative correlation. 1
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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...
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A new study of the long-term and orbital variations of the Be star V923 Aql
Steiner, Michal ; Harmanec, Petr (advisor) ; Wolf, Marek (referee)
The first part of this thesis deal with the topic of Be stars, their variability on different time scales and some of the models explaining formation of the envelope. Next part deals with software, which is used for measurement. After introduction to these programs the data analysis follows. Overall, 46 spectra from Ondřejov Observatory and Hvar photometric observations that covered time RJD=52000- 58500 has been used. Each finding were compared with already known properties of V923Aql. Most behavior patterns that were seen in the past has been seen even in the available data, but a difference between RVHα and RVM measured on metallic lines were found. Also, the length of long-term cycle seems to differ from that in the past cycles. 1
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A new spectroscopic study of the eclipsing binary V1143 Cyg
Jonák, Juraj ; Harmanec, Petr (advisor) ; Wolf, Marek (referee)
Using multiple red spectra of the eclipsing binary V1143 Cyg obtained between the years 2015 and 2017 at the Observatory of Ondřejov and in 2008 and 2009 at the Lick observatory in USA, we calculated a more recent orbital solution using the method of Fourier spectra disentangling. These new data, in addition to previous spectroscopic and photometric measurements, span an observation period of almost a hundred years. Since this binary star is remarkable due to its high orbital excentricity, along with classical, a significant relativistic apsidal motion is present. Using the software PHOEBE and available data we calculated the value of the total apsidal motion as 9,8(3).10−5 deg.d−1 , which is in good agreement with previous works. 1
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Determination of accurate fundamental stellar properties of stars via analyses of suitable binary and multiple systems
Nemravová, Jana Alexandra ; Harmanec, Petr (advisor) ; Budaj, Ján (referee) ; Stee, Philippe (referee)
Context: Binaries and multiple systems are very frequent and form large fraction of all stellar systems. In contrast to their single counterparts, studying binaries provides the possibility to accurately determine fundamental properties of their components that are needed for testing models of stellar structure and evolution. On top of that, binaries can be used for accurate distance determinations. The mass exchange in close binaries remains the only mechanism, which completely alters their evolution. Aims: The primary goal of my doctoral study was to determine orbital elements of selected systems and properties of their components - masses, radii, and ef- fective temperatures. - In case of more complicated objects (e.g. interacting multiple systems, mass-transferring binaries, . . . ) the secondary goal was to confront our results with predictions of theoretical models. Methods: Studies that I co-authored were based on three different types of ob- servations, each sensitive to partly different properties of studied systems - photometry, spectroscopy, and spectro-interferometry. The analysis was carried out through several "observation-specific" models, whose outcome was critically compared to each other and to previous studies of the object in question. Results: Throughout my study I contributed to: (i)...
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A study of binary stars with accretion disks
Chadima, Pavel ; Harmanec, Petr (advisor) ; Krtička, Jiří (referee) ; Mourard, Denis (referee)
This thesis contains spectroscopic analyses of two unusual binaries with circum- stellar disks - β Lyr and ǫ Aur. Several hundred optical spectra were processed and analyzed for both binaries which led to several original findings. For β Lyr, it was a discovery of a weak shell spectrum originating in a disk pseudophotosphere and a hidden satellite spectrum, present only during eclipses, which arise from additional absorption of the primary light passing through the gaseous envelope around the secondary. For ǫ Aur, it led to the discovery of the apparent multiperiodic line vari- ability occuring during the current eclipse with a dominant and common period of 66d .21 and to an explanation of complex Hα line profiles during the eclipse which is again caused by an additional absorption of a primary light in an atmosphere of a dark disk around a secondary. Also rich series of radial velocity measurements and photometric observations were collected and used to determine a new precise orbital solution for ǫ Aur. Further, a hydrodynamical and a radiative modeling of a discontinuous mass transfer in a close binary system was carried out which resulted in a formation of an elongated disk with a slow prograde revolution, demonstrated itself by double emission Hα line profiles that exhibit V/R variations.
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Improvement of the physical elements of the star V649 Cas
Tarics, Jan ; Harmanec, Petr (advisor) ; Zverko, Juraj (referee)
Title: Improvement of the physical elements of the star V649 Cas Author: Jan Tarics Department: Astronomical Institute of Charles University Supervisor: Prof. RNDr. Petr Harmanec, DrSc. Supervisor's e-mail address: hec@sirrah.troja.mff.cuni.cz Abstract: Analysis of new as well as previously published photometric and spectroscopic observations of V649 Cas led to a conclusive confirmation that the object is at least quadruple. Keywords: Stars:binaries, Stars:variables:eclipsing, Stars:individual V649 Cas
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