The results of new photometric observations of the chromospherically active star ET Dra, performed using telescopes of the Zvenigorod INASAN Observatory, the Russian-Cuban Observatory in the territory of the Republic of Cuba (Havana), and the Terskol INASAN Observatory (a total of 8 sets of observations) with the addition of archival observations of the Kamogata Wide-field Survey. Variations in the shape of the light curve caused by the rotational modulation of a star with spots on the surface, as well as studies of the long-term variability of the star’s brightness, were investigated based on the data acquired in 2018–2023. Characteristic changes in the ET Dra light curve were noted including a decrease of the stellar brightness in the V filter, its cyclic variations, and subsequent brightness increase. The shape of the phase curve and the duration of the extended minimum of brightness vary. During the HJD 245 9670–245 9715 interval, the amplitude of the star’s brightness variability reached a maximum value of more than 0.4m, as it was in 1990. The surface temperature inhomogeneities maps were calculated and estimates of the spottedness parameter S of the object were performed for each of the 8 sets of observations. Maximum value of parameter S was 32.2‒33.5

We present the results of our photometric observations of the chromospherically active star FK Com (prototype of its group of stars) acquired during the recent 5 years (2018–2023) at the INASAN observatories in Zvenigorod and Simeiz and at the Russian–Cuban observatory in Habana (Republic of Cuba). In total, we obtained 9060 estimates of the star’s brightness in the V filter between 2018 and 2023. Our measurements, as well as data from the literature and from the Kamogata Wide-field Survey (KWS) archive, were combined into a unified set containing 17 653 measurements for a time interval about 57 years long. Based on the power spectrum derived from these data, we identified possible activity cycles P_cycl , estimated by us to be 2.4, 5.63, 8, 13.6, 30, and 49 years. The dominating P_cycl is 5.63 years long. We show that the dominating cycle found by us from extensive data to be about 5.63 years (5.4–5.8 years from other sources in the literature) can also be noticed from the analysis of earlier studies. We compared our results on the activity cycles of FK Com to data on long-term variations of two other stars of the same type, HD 199178 (V1794 Cyg) and ET Dra. Data on P_cycl of other chromospherically active stars (from the literature and from our measurements) were used to analyze the log (1/P_rot)-log (P_cycl/P_rot) diagram. We make a conclusion on the compatibility of our determinations of activity cycles for stars of the FK Com type with data for RS CVn stars.

The properties of the planetary system TOI-1422, in which two planets of a neptune type orbit around a low-activity star of solar type with an age of about 5 billion years, are examined. We have previously analyzed activity of the star TOI-1422, found indications of the existence of possible activity cycles, and considered estimates of the orbital rotation period P of the star. The inner planet TOI-1422 b belongs to the hot-neptune types; it rotates with an orbit of period about 13 days and has an equilibrium temperature of Teq,b = 867 K. Calculations using a model of atmospheric loss with an energy limit for TOI-1422 b yielded 9.4·108 g/s of matter from the atmosphere. The outer planet of the system TOI-1422 c can also be regarded as a hot neptune; it has an orbital period of 29.3 days, its minimal mass, Mc sini, is 11.1M ⊕ , and the equilibrium temperature is Teq,c = 661 K. For estimating the radius of TOI-1422 c we have used an empirical M-R relation. It was found that the loss of matter from the atmosphere of the planet TOI-1422 c is 7.8·107 g/s and, given the error in the parameters, it may lie within a range from 6.1·107 g/s to 9.7·107 g/s.

Рассмотрены свойства планетной системы TOI-1422, в которой две планеты типа нептун вращаются вокруг малоактивной звезды солнечного типа около 5 млрд лет. Ранее нами был проведен анализ проявлений активности звезды TOI- 1422, найдены указания на существование возможных циклов активности и рассмотрены оценки величины периода Р вращения звезды. The properties of the TOI-1422 planetary system in which two neptune-type planets orbit around of low-activity solar-type star with the age of about 5 billion years are considered. Earlier we analyzed the activity of the star TOI-1422 and found indications of the existence of possible cycles of activity and considered estimates of the rotation period of the star.

The star KIC 2142183, which was previously noted as a rapidly rotating giant with flare activity, was studied based on the analysis of photometric observations with the Kepler space telescope. We have estimated the spottedness parameter S for KIC 2142183 (5–14% of the entire visible surface area of the star) and differential rotation (the $$\Delta \Omega $$ parameter is in the range of 0.022–0.068 rad/day). KIC 2142183 has a high flare activity: the literature contains information on 100 flares with energies log E in the range from 34.8 to 36.3. The results of the study and the data available in the literature suggest that KIC 2142183 is a likely candidate for an FK Com star. It was concluded that the characteristics (rotation, flare activity, and spot activity) of the giants KIC 2142183 and the candidate KIC 6428626 studied previously are in fairly good agreement. The area of spots on the surface of both giant stars in absolute terms not only significantly exceeds the total area of spots on the Sun, but is larger than the entire visible surface area of the Sun. Both stars have high flare activity.

Abstract—We present new results of the study of ET Dra—a star of the FK Com type—based on observations carried out at the Zvenigorod Observatory of the Institute of Astronomy of RAS with the help of the FRAM-ORM telescope of the La Palma observatory (Spain) and the broadband optical monitoring system Mini-MegaTORTORA, located on the territory of the SAO RAS. We have studied changes in the shape of the light curve caused by the rotational modulation of a star with spots on its surface and the long-term variability of the star’s brightness. An independent determination of the rotation period of $${{P}_{{{\text{phot}}}}}$$ was carried out using all sets of observations available to us. The increase in the brightness of the star near HJD 2459044 during observations with the FRAM-ORM telescope in all three filters was interpreted by us as a stellar flare. Our flare energy estimates are $$2.8 \times {{10}^{{37}}}$$ , $$1.9 \times {{10}^{{37}}}$$ , and $$1.5 \times {{10}^{{37}}}$$ erg in the $$B$$ , $$V$$ , and $$R$$ wavelength ranges, respectively. Observations with a duration of more than 2200 days, carried out at the SAO RAS, opened up the possibility of analyzing the long-term brightness variability of ET Dra. Evidence was found for the existence of cycles lasting 580 days and 810 days (1.55 and 2.23 years, respectively).

The planetary system of the star TRAPPIST-1 hosts seven exoplanets, three of which are in the habitable zone. Based on published data, we have analyzed the properties of cool dwarfs that could be considered as an analog of this object. Using the data available in the literature (Seli et al. 2021) for ultracool dwarfs similar to TRAPPIST-1, we have determined their spottedness $$S$$ (the fraction of the surface covered by cool spots) and the spot area in fractions of the solar surface area. We have found that, on average, TRAPPIST-1 rotates more slowly than most of the stars from the sample under consideration, while its spottedness is higher than that in them. We have investigated seven objects for which reliable information about their ages, rotation, and spot activity is available. The fraction of the TRAPPIST-1 surface covered by spots has been found to exceed those for other objects, including even those for younger stars with an age of 1–3 Gyr. We have identified two objects, TIC 302408306 and TIC 366567664, with characteristics (ages, rotation) close to those of TRAPPIST-1. Their ages are estimated to be 9.0 and 7.9 Gyr, respectively. These stars rotate more rapidly than TRAPPIST-1, while the surface area covered by spots in them is slightly smaller than that in TRAPPIST-1. These objects have more stable and smoother phase curves with one minimum.

We obtained a unique series of photometric data for more than a hundred years for a rapidly rotating single G5 III–IV giant HD 199178 (V1794 Cyg), belonging to FK Com type stars. The analysis of the long-term variation of the activity of this star in the filter B is based on all measurements available in literary sources. To evaluate the brightness of HD 199178 in the era preceding photoelectric and CCD-observations, the measurements of photographic plates from the SAI MSU archive were shot at the Krasnopresnenskaya Observatory of Moscow State University in Moscow (4 records shot from 1898 to 1903, and 41 records for the period from 1935 to 1958) were performed. As a result, a total of 2142 assessments of the brightness of the star in the filter B were received. They have a unique duration of 118.3 yr and cover the time interval from 1898 to July 2016. Evidence was found of the existence of long-term cycles of photometric variability lasting for about 25‒60 years. We put forward an assumption on existence of possible activity cycles of 2000, 3165, 5050, 9000, and 21 600 d (respectively, 5.5, 8.7, 16.6, 24.7, and 59.2 years). The results are compared with other estimates of activity cycles in HD 199178. The most reliable should be recognizing the existence of a cycle lasting 8.7‒9 years. It was found that in order to combine data into a single array, the convertation of B magnitudes into V magnitudes using the average value of the color index ( B – V ) is not possible due to the changes (including cyclic) of color index ( B – V ) over time.

Based on the available photometric data spanning almost 8000 days (21.9 years) of observations of a bright G5 V dwarf, solar-type star HD 4915, we carried out a study of the manifestations of its activity, probably transitioning to a state similar to the Maunder Minimum. To estimate the duration of the possible activity cycles of the star, we used three independent data sets. We obtained evidence of HD 4915 light variations, including the interval of time corresponding to a decrease in its chromospheric activity variations. Based on the constructed power spectrum, we can suggest the existence of possible cycles of the order of 1640 and 630 days (4.5 and 1.7 years) for the object’s brightness, which are comparable with the chromospheric activity cycle estimate of 4–4.2 years, significantly shorter than the duration of the magnetic activity cycle of the Sun, which is a distinguishing feature of HD 4915. Using photometric observations of the star from Kamogata Wide-field Survey, including data from the measurements taken after 2018, when it could have been starting an activity phase similar to the Maunder Minimum, we obtained indications of possible 450, 1260 and 2000 day cycles (1.23, 3.5 and 5.5 years) and made a conclusion about the presence of cyclic light variations during this supposed lower activity state of HD 4915. We discuss the probable estimate of the star’s rotation period. A consideration of the HD 4915 data available in the TESS archive for four observing sets led us to conclude that they are unsuitable for determining its rotation period.

Представлены результаты новых спектральных наблюдений хромосферно-активной звезды FK Com в 2021 и 2022 г. в Симеизской обсерватории и в обсерватории Синлонг (Xinglong, NAOC, Китай). Рассмотрена эволюция профилей линии H α в спектре FK Com. Новые наблюдения показали, что зарегистрированные нами изменения формы профилей линии H α аналогичны опубликованным ранее в литературе. По нашим спектрограммам, полученным для фаз вращения звезды близким к 0.7 с интервалом около года (в 2021 и 2022 г.) и полученным на обсерваториях KPNO (в 2000 г.) и NOT в 1998, 1999, 2001, 2003, 2004 г. для этой же фазы, установлены различия в профилях линии H α . Вероятно, изменения профилей линии H α в большей степени зависят от уровня активности звезды, чем от фазы вращения. We present the results of new spectral observations of the chromospherically active star FK Com in 2021 and 2022 at the Simeiz Observatory and the Xinglong Observatory (NAOC, China). The evolution of the pro les of the H α line in the spectrum of FK Com is considered. New observations indicate that the changes in the shape of the pro les of the H α line registered by us are similar to those previously published in the literature. According to our spectra obtained for the phases of rotation of the star close to 0.7 with an interval of about a year (in 2021 and 2022) and obtained at the KPNO (2000) and NOT observatories in 1998, 1999, 2001, 2003, 2004 for the same phase, di erences in the pro les of the H α line are established. Probably, the changes in the pro les of the H α line depend more on the level of activity of the star than on the phase of rotation.

Abstract—According to the results of analysis of the Kepler space telescope photometric observations, we studied a star KIC 5428626, which was previously noted as a rapidly rotating giant with a flare activity. We have estimated the spottedness parameters $$S$$ of this object ( $$7$$ – $$12$$ % of the area of the total visible surface of the star) and its differential rotation ( $$\Delta \Omega $$ is $$0.016$$ rad/day). The positions (longitudes) of the dominant active region on the surface of the star were found and their evolution over time was traced: cyclic variations of the positions with a characteristic time of about $$400$$ days are possible. A similar conclusion has previously been made about the existence of cyclic variations in the positions of active regions of the star FK Com—the prototype of stars under study. KIC 5428626 has a high flare activity. The literature provides data on $$143$$ flares with the energy $$\log E$$ ranging from $$34.8$$ to $$37.4$$ . Results of the study and data available in the literature allow us to consider KIC 5428626 as an attractive target for setting forth its possible belonging to the group of FK Com-type stars.

Ранее по данным наблюдений с космическим телескопом “Kepler” нами было показано, что по своим параметрам KIC 7739728 близка к звездам типа FK Com и может рассматриваться, как потенциальный кандидат для включения в число объектов этого типа. В настоящей работе мы провели анализ всех имеющихся для KIC 7739728 данных в архиве миссии TESS (14 и 26 сектора наблюдений). Показано, что кривая блеска этой звезды ярко проявляет свойства регулярной вращательной модуляции и что в период времени между 14 и 26 секторами произошло явление переключения положений долгот активных областей на поверхности звезды (флип-флоп). Рассматриваются аргументы в пользу возможной принадлежности KIC 7739728 к объектам типа FK Com. Using the observations with the Kepler space telescope we found that parameters of KIC 7739728 are close to that ones of the FK Com type stars and that the object can be considered as a potential candidate for inclusion in the number of objects of this type. In this paper we analysed all available data for KIC 7739728 in the TESS mission archive (14 and 26 sectors). It is shown that the light curve of this star clearly exhibits the properties of regular rotational modulation and that in the time interval between 14 and 26 sectors the phenomenon of switching the positions of the longitudes of the active regions on the surface of the star (flip-flop) occurred. The arguments in favour of the possible relation of KIC 7739728 to objects of the FK Com type are considered.

This article is a brief survey of our previous work devoted to searching for candidate type FK Com giant stars and an analysis of data for yet another new candidate, KIC 7732964. Establishing that KIC 7732964 belongs to this group of stars requires further study of the evolutionary status of the star (dwarf, subdwarf, or giant). The star has fast rotation and high flare activity, which are more typical of dwarf or subgiant stars. As for other candidates, in the case of KIC 7732964 additional spectral observations are required to establish the absence of binarity, refine the value of the acceleration of gravity, and its spectral classification.

Дифференциальное вращение звезд спектрального класса А - Institutional repository of Federal State Autonomous Educational Institution of Higher Professional Education Ural Federal University named after the first President of Russia B.N.Yeltsin

We present the results of our analysis of the photospheric and chromospheric activity of the star DS Tuc (DS Tuc A, HD 222259A), which is a member of the Tucana–Horologium (Tuc–Hor) group with an age of 45 Myr. The star DS Tuc may be considered as the prototype of a young Sun, while its planetary system may be considered as the prototype of a young Solar system. Using data from the archive of TESS observations, we have analyzed the activity of this star. According to our estimate, the stellar rotation period is $$P=2.85\pm 0.18$$ days, which coincides with its known estimates. The light curve has been analyzed by the method of solving the inverse problem of reconstructing the maps of surface temperature inhomogeneities. We show that there are concentrations of spots at two longitudes on these maps. The spot positions undergo changes. The fraction $$S$$ of the spotted stellar surface is about 3.3 $$\%$$. We have studied the object’s position on the $$S$$–age, $$S$$–rotation period, and $$S$$–Rossby number diagrams and concluded that it corresponds to the general pattern of the dependences established previously for young stars with planetary systems and solar-type stars. Based on All Sky Automated Survey observations, we have estimated for the first time the possible activity cycle of DS Tuc to be 1610 days (4.4 years).

Published data indicate a substantial increase in the differential rotation parameter ∆Ω of stars hotter than 6700 K. By analyzing the shape of the light curves and the presence of a specific set of peaks in their power spectra, we have found that 47 of 57 objects with T eff greater than 7500 K that were studied can be identified as pulsating stars and only 10, as stars with brightness variation owing to rotational modulation. After eliminating the pulsating variables, for the stars with T eff greater than 7500 K the average value of ∆Ω= 0.051±0.01 rad/day. This conclusion conflicts with our earlier assumption that the peaks in the power spectra for ROTD stars are caused by a possible manifestation of differential rotation. Further independent evidence for a low value of ∆Ω for stars in spectral class A has been obtained from Zeeman-Doppler charts for the star γ Gem, with an estimate for the differential rotation parameter of the star of 0.0073±0.0023 rad/day.

New observations of the RS CVn variable UX Ari were carried out using Mini-MegaTORTORA (MMT-9) wide-field optical monitoring system and robotic wide-angle observation system in Zvenigorod observatory of INASAN. We defined more accurately the cycles of the long-period variability of UX Ari and noticed considerable changes in the shape of the power spectrum. In the long-term region we find three cycles at 5, 13.2 and 30 years. It is possible that some cycles are aliases but the most promising period of 30 years is clearly seen. We suppose that P(cycle) estimations for active stars over 10-50 years intervals should made it possible to build a new family of relations on diagrams P(cycle)/P(rot) versus 1/P(rot).