Jan Kára - personal webpage

About me

I am a postdoctoral researcher at the Astronomical Institute of the Charles University. My field of interest in astronomy are variable stars, mainly I am focused on cataclysmic variables. I am using photometric and spectroscopic observations to analyse these objects, some of the data I obtained myself during many observing nights.
In my free time I enjoy travelling, hiking, cycling, and photography. And even though I am using my camera mainly to take pictures of the places I visit, I also like to point it upwards during nights to take some pictures of the night sky. When the weather forces me to stay indoors, I enjoy reading books, mostly some from the fantasy genre and mythological stories from various cultures.

Curriculum vitae

Research

PhD thesis

Title: Cataclysmic variables
Defense: 2023
Cataclysmic variables are compact binary systems consisting of a white dwarf and a late-type star from which matter is being accreted onto the white dwarf. The transferred matter doesn’t fall directly onto the white dwarf, instead it forms accretion disc. Cataclysmic variables are the main topic of my Ph.D. study programme, during which I analysed several interesting systems. These systems include CzeV404 Her (Kára et al. 2021), SDSS J154453.60+255348.8 (Medina Rodriguez et al. 2023), AY Psc (Kára et al. 2023a), and IX Vel (Kára et al. 2023b).
You can find more information about my doctoral thesis here.

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Diploma thesis

Title: Flare stars
Defense: 2018
Abstract: The work deals with the study of the flare stars, which is a group of stars for which sudden brightening can be observed. The work focuses on a star GJ 3236, which is a low-mass eclipsing binary and on which numerous flares have been observed. For the analysis of this system spectroscopic and photometric data were used, which were obtained at various observatories. Parameters of the binary system have been determined by analysing spectroscopic and photometric data with the program PHOEBE. A total of 241 flares have been detected in the photometric data and for 190 flares, which light curves were not affected by eclipses, released energies were estimated. The set of flares was used for the study of stellar activity of the binary. The energy distribution of observed flares is similar to the flares observed on other flare stars and also on the Sun. This suggests, that the flare mechanism is the same for these stars.

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Bachelor thesis

Title: CCD photometry of variable objects in nearby galaxies
Defense: 2016
Abstract: 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.

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Publications

Refereed publications (ADS)

Wolf, M., Zasche, P., Kára, J., Zejda, M., Janík, J., Mašek, M., Lehký, M., Merc, J., Richterková, A., Hanžl, D., Mikulášek, Z., de Villiers, S. N., & Liška, J. (2024). Apsidal motion and TESS light curves of three southern close eccentric eclipsing binaries: GM Nor, V397 Pup, and PT Vel. A&A, 690, A231. 2024A&A...690A.231W
Zasche, P., Henzl, Z., Merc, J., Kára, J., & Kučáková, H. (2024). Eight new 2+2 doubly eclipsing quadruple systems detected. A&A, 687, A6. 2024A&A...687A...6Z
Krtička, J., Benáček, J., Budaj, J., Korčáková, D., Pál, A., Piecka, M., Zejda, M., Bakış, V., Brož, M., Chang, H.-K., Faltová, N., Gális, R., Jadlovský, D., Janík, J., Kára, J. , Kolář, J., Krtičková, I., Kubát, J., Kubátová, B., Kurfürst, P., Labaj, M., Merc, J., Mikulášek, Z., Münz, F., Paunzen, E., Prišegen, M., Ramezani, T., Rievajová, T., Řípa, J., Schmidtobreick, L., Skarka, M., Szász, G., Weiss, W., Zajaček, M., & Werner, N. (2024). Science with a Small Two-Band UV-Photometry Mission II: Observations of Stars and Stellar Systems. Space Science Reviews, 220, 24. 2024SSRv..220...24K
Kára, J. , Schmidtobreick, L., Pala, A. F., & Tappert, C. (2023). Structure of the accretion flow of IX Velorum as revealed by high-resolution spectroscopy. A&A, 678, A131., 2023A&A...678A.131K
Merc, J., Gális, R., Wolf, M., Dubovský, P. A., Kára, J., Sims, F., Foster, J. R., Medulka, T., Boussin, C., Coffin, J. P., Buil, C., Boyd, D., & Montier, J. (2023). Comprehensive analysis of a symbiotic candidate V503 Her. AJ, 166, 65., 2023AJ....166...65M
Zasche, P., Henzl, Z., Mašek, M., Uhlař, R., Kára, J., Merc, J., & Kučáková, H. (2023). Detection of seven 2+2 doubly eclipsing quadruple systems. A&A 675, A113., 2023A&A...675A.113Z
Kára, J. , Zharikov, S., Wolf, M., Amantayeva, A., Subebekova, G., Khokhlov, S., Agishev, A., and Merc, J. (2023). The Z Camelopardalis-type Star AY Piscium: Stellar and Accretion Disk Parameters. ApJ, 950, 47., 023ApJ...950...47K
Medina Rodriguez, A. L., Zharikov, S., Kára, J. , Wolf, M., Agishev, A., and Khokhlov, S. (2023). VY Scl-type cataclysmic variable SDSS J154453.60+255348.8: stellar and disc parameters. MNRAS 521, 5846-5859., 023MNRAS.521.5846M
Šmelcer, L., Wolf, M., Kučáková, H., Zasche, P., Kára, J. , Hornoch, K., Zejda, M., and Auer, R. F. (2023). A photometric study of NSVS 7453183: a probable quadruple system with long-term surface activity. MNRAS 520, 353-363., 023MNRAS.520..353S
Zasche, P., Henzl, Z., and Kára, J. (2022). The first study of four doubly eclipsing systems. A&A 659, A8., 022A&A...659A...8Z
Kára, J. , Zharikov, S., Wolf, M., Kučáková, H., Cagaš, P., Medina Rodriguez, A. L., and Mašek, M. (2021). The period-gap cataclysmic variable CzeV404 Her: A link between SW Sex and SU UMa systems. A&A 652, A49., 021A&A...652A..49K
Wolf, M., Kučáková, H., Zasche, P., Hornoch, K., Kára, J. , Merc, J., and Zejda, M. (2021). Possible substellar companions in dwarf eclipsing binaries. SDSS J143547.87+373338.5, NSVS 7826147, and NSVS 14256825. A&A 647, A65., 021A&A...647A..65W
Merc, J., Gális, R., Kára, J. , Wolf, M., and Vrašťák, M. (2020). The nature of the symbiotic candidate 2MASS J07363415+6538548 in the field of NGC 2403. MNRAS 499, 2116-2123., 020MNRAS.499.2116M
Zasche, P., Wolf, M., Kučáková, H., Kára, J. , Merc, J., Zejda, M., Skarka, M., Janík, J., and Kurfürst, P. (2020). First apsidal motion and light curve analysis of 162 eccentric eclipsing binaries from LMC. A&A 640, A33., 020A&A...640A..33Z
Zasche, P., Vokrouhlický, D., Wolf, M., Kučáková, H., Kára, J. , Uhlář, R., Mašek, M., Henzl, Z., and Cagaš, P. (2019). Doubly eclipsing systems. A&A 630, A128., 019A&A...630A.128Z

Telegrams

Hornoch, K., Kucakova, H., Kára, J. , Wolf, M., & Shafter, A. W. (2024). Discovery of a Probable Nova in M31. The Astronomer's Telegram 16412, 1. 2024ATel16412....1H
Hornoch, K., Scheirich, P., Srba, J., Skarka, M., Fatka, P., Henych, T., Pavelka, J., Kára, J. , Kucakova, H., and Shafter, A. W. (2023). Discovery of a Probable Nova in M31. The Astronomer's Telegram 15965, 1., 023ATel15965....1H
Hornoch, K., Carey, G., Kucakova, H., and Kára, J. (2019). Discovery of a Possible Nova in M31. The Astronomer's Telegram 13198, 1., 019ATel13198....1H