Перегляд за Автор "Udovichenko, Serhii M."

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    Gaia18aak is a new SU UMa-type dwarf nova
    (2019) Simon, A.; Pavlenko, E.; Shugarov, S.; Vasylenko, V.; Izviekova, I.; Reshetnyk, V.; Godunova, V.; Bufan, Yu.; Baransky, A.; Antonyuk, O.; Baklanov, V.; Troianskyi, V.; Udovichenko, Serhii M.; Keir, L.; Удовіченко, Сергій Миколайович; Удовиченко, Сергей Николаевич
    We report the discovery of a new SU UMa-type dwarf nova, Gaia18aak/ AT2018C, based on its optical observations, which were performed at ve observatories (Lisnyky/Kyiv, Terskol, CrAO, Mayaki/Odessa and Star a Lesn a, Slovakia) with six small telescopes. The observational campaign started just after the alert was published by ESA Gaia, DPAC and the Photomet- ric Science Alerts Team (http://gsaweb.ast.cam.ac.uk/alerts); the object was very intensely observed during the rst month. After this there was organized a four-month monitoring in order to test outburst activity of the object. We detected the 0.0647-d (or 0.0692-d) superhump period during ve nights of the superoutburst. Furthermore, we found the only possible outburst during the subsequent 100 nights.
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    Lithium-rich classical Cepheid V1033 Cyg: evolutionary status
    (Одеський національний університет імені І. І. Мечникова, 2019) Udovichenko, Serhii M.; Kovtyukh, Valery V.; Keir, L. E.; Удовиченко, Сергей Николаевич; Ковтюх, Валерій В.; Кеір, Л. Є.; Удовіченко, Сергій Миколайович
    We investigate evolutional status of cepheid V1033 Cyg in this work, its period of light variation consists 4 d .94 and the star is a real candidate on first crossing of instability stripe (IS) (as well as α of UMi). At first crossing of instability stripe, that lasts all close 1000 years, cepheids demonstrate the rapid increase of period, sometimes is a presence of strong line of lithium 6707 ˚A. Such objects knows only four in our Galaxy, one of them - V1033 Cyg. During included in a instability stripe amplitude of pulsations headily grows from a zero to some permanent size, and on leaving from (IS) - again falls to a zero. For verification this phenomenon in the Astronomical observatory of Odesa National University (Ukraine) on the 48-cm telescope AZT-3, equipped by CCD photometer with the optical sensor Sony ICX429ALL, a 1864 measuring of light V1033 Cyg were done in the filter of V and 713 in the filter R, that are partly presented in the Table. 1 and Fig. 2, and fully accessible to address http://cdsarc.ustrasbg.fr/viz-bin/cat. Considerable change of amplitude it is not got by us. The position of cepheid is certain by us in the (IS) - it appeared that star is near her center. In this phase evolutional to development and it must not be observed considerable change of amplitude (color index). The light curves, effective temperature and luminosity of V1033 Cyg are consistent with fundamental mode pulsation for a classical Cepheid on the center of the instability strip.
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    MASTER OT J172758.09+380021.5: a peculiar ER UMa-type dwarf nova, probably a missed nova in the recent past
    (2021) Pavlenko, E.; Kato, T.; Antonyuk, K.; Pit, N.; Keir, L.; Udovichenko, Serhii M.; Dubovsky, P.; Sosnovskij, A.; Antonyuk, O.; Shimansky, V.; Gabdeev, M.; Rakhmatullaeva, F.; Kokhirova, G.; Belan, S.; Simon, A.; Baklanov, A.; Kojiguchi, N.; Godunova, V.; Удовіченко, Сергій Миколайович; Удовиченко, Сергей Николаевич
    A CCD photometry of the dwarf nova MASTER OT J172758.09 +380021.5 was carried out in 2019 during 134 nights. Observations covered three superoutbursts, ve normal outbursts and quiescence between them. The available ASASSN and ZTF data for 2014 { 2020 were also examined. Spectral observations were done in 2020 when the object was in quiescence. Spectra and photometry revealed that the star is an H-rich active ER UMa-type dwarf nova with a highly variable supercycle (time interval between two successive superoutbursts) of 50 { 100 d that implies a high and variable mass-transfer rate. MASTER OT J172758.09+380021.5 demonstrated peculiar behaviour: short-lasted superoutbursts (a week); a slow superoutburst decline and cases of rebrightenings; low frequency (from none to a few) of the normal outbursts during the supercycle. In 2019 a mean period of positive superhumps was found to be 0.05829 d during the superoutbursts. Late superhumps with a mean period of 0.057915 d which lasted about 20 d after the end of superoutburst and were replaced by an orbital period of 0.057026 d or its orbital-negative superhump beat period were detected. An absence of eclipse in the orbital light curve and its moderate amplitude are consistent with the orbital inclination of about 40 found from spectroscopy. The blue peaks of the V-Ic and B-Rc colour indices of superhumps during the superoutburst coincided with minima of the light curves, while B-Rc of the late superhumps coincided with a rising branch of the light curves. We found that a low mass ratio q = 0:08 could explain most of the peculiarities of MASTER OT J172758.09+380021.5. The mass-transfer rate should be accordingly higher than what is expected from gravitational radiation only, this assumes the object is in a post-nova state and underwent a nova eruption relatively recently { hundreds of years ago. This object would provide probably the rst observational evidence that a nova eruption can occur even in CVs near the period minimum.
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    On the irregular variations in the light curves of RY Vul
    (Одеський національний університет імені І. І. Мечникова, 2018) Udovichenko, Serhii M.; Keir, L. E.; Удовиченко, Сергей Николаевич; Кеір, Л. Є.; Удовіченко, Сергій Миколайович
    In the Astronomical observatory of the Odesa National University traditionally study variable stars of different types: pulsating, double, irregular et al. By photometric observations it is possible to set the type of variable star, period of the brightness changes, spectral class, to estimate the temperature of surface. For observations variable stars there was the chosen area of star sky from by two stars Y Vul and RY Vul in the distance not more than 15 angular minutes (angular size of one frame). For these stars was got more than 5900 images during 56 nights during observant seasons 2011-2017. For all observations were got the curves of light variations. Results are for variable star Y Vul (type RR Lyr) published separately, and in this publication we bring results over of observation for star RY Vul. The star RY Vul according General Catalogue of Variable Star (GCVS) is RR Lyr variable, but period and initial epoch are unknown. To determine these parameters the photometric observations during several seasons in 2011-2017 of the variable star RY Vul on the Astronomical station near Odessa have been carried out. The 48-em telescope reflector AZT-3 equipped with CCD photometer was used. The light curves in V and R band were obtained and analyzed. It turned out that the light curves of the star is fully irregular. Therefore, the variable star RY Vul should be attribute to type "irregular variables".
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    Photometrical observations some RR Lyr type-stars with Blazhko effect
    (2019) Udovichenko, Serhii M.; Keir, L.; Удовіченко, Сергій Миколайович; Удовиченко, Сергей Николаевич
    The variability of the star was found by C. Hoffmeister in 1936. The star thoroughly was investigated by V. P. Tsessevich, which determined the primary ele- ments of period: Max. hel. J.D. = 2436047.522 + 0.6130535 E, and discovered the sophisticated shape of light variation curves, known as Bllazhko effect (40.64 day) (Tsessevich, 1961, 1966). He mentioned, that the curve of maximum height shows considerable dispersion, and it seems, that the most part of time we ob- serve the weakened maxima and only in some time intervals (short-term) we observe the maxima in the considerable heights. It indicates in modulation of a light curves by additional frequencies, and the star represents the scienti c interest for observations. Visual observations in 20 century were carried out by Hoffmeister and Tsessevich. Now V365 Her is known as RR Lyr-star type (RRab) with amplitude 12:m7 14:m0 (P), has period 0:d613138, Kholopov et al. (1985).