We have analyzed the change in the period of the ultracompact binary system ZTF J213056.71+442046.5, a source of potentially detectable mHz gravitational waves for planned space laser interferometers. The photometric data cover a time interval of almost 6.5 years and include our own observations carried out with the RC600 telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University and data from the ZTF sky survey. The O-C diagram can be described by quadratic light elements that correspond to a rate of period decrease dP/dt=(-2.66± 0.62)× 10^-12 s s ^-1 . This value leads to an almost twofold increase in the expected signal-to-noise ratio for the observations of gravitational waves from this binary system with space laser interferometers.

The results of photometric and spectroscopic observations of supernova SN 2022prv carried out with six telescopes including the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU are presented. The dates and magnitudes at the brightness maximum and the parameters of the light curves are determined. The photometric evolution of SN 2022prv is characterized by a constant decrease in brightness after the maximum at a rate quite high for a type II supernovae. Approximately 55 days after the maximum, the rate of the decrease in brightness increased. The maximum luminosity has reached M_V=-18m.1 which is higher than average for SN II. In the pre-maximum spectra, high-excitation emission lines were observed characteristic of the ionization of the circumstellar matter by a burst during the shock wave emergence onto the surface of the star. However, approximately 20 days after the maximum, the spectrum did not differ from that typical of SN II. The rate of the envelope expansion at this stage was about 3500 km s ^-1 which is a little smaller than average for SN II values.

In the period December 12, 2022, to February 28, 2023, we performed a series of UBVRI observations of 65 asteroids, including 50 primitive-type objects, which could be observed near perihelion at that time, and calculated their approximated reflectance spectra. The observations were aimed at searching for spectral signs of sublimation-driven dust activity in the asteroids and formation of a transient dust exosphere, which are caused by the presence of Н2О ice in their interior and the highest subsolar temperature. Based on the analysis of the accuracy and shape of approximated reflectance spectra of the primitive-type asteroids, a set of which was conventionally restricted by the geometric albedo value not exceeding 0.10, we found sublimation-driven dust activity in asteroids 164 Eva, 360 Carlova, and 750 Oskar by distinct short-term variations in the reflectance of these asteroids in the U band. During one of the nights, similar spectral changes and sublimation-driven dust activity related to them were detected in asteroid 629 Bernardina; the geometric albedo of this asteroid is somewhat higher (0.14 or 0.19), which may be indicative of a heterogeneous composition of its material and, apparently, a local outcropping of water ice on its surface. Moreover, in three asteroids of a high-temperature type, 757 Portlandia, 1121 Natascha, and 1687 Glarona, noticeable variations were detected in the entire spectral range; they may be connected with ejection of submicron dust particles from the surface by some other mechanisms. To substantiate and interpret the results of observations, we numerically modeled the reflectance spectra of conditional asteroids of taxonomic types C and S (with low- and high-temperature mineralogy, respectively), which are enveloped by an optically thin dust exosphere containing aggregate or homogeneous submicron particles of different composition. On the basis of this modeling, we introduce a quantitative criterion to identify a weak sublimation-driven dust activity in primitive-type asteroids in the visible range.

We present the results of a new X-ray to near-IR photometric and spectroscopic monitoring of the changing look active galactic nucleus NGC 2617 carried out from March 2022 to March 2024. We found significant variability at all wavelengths and in the intensities and profiles of the broad Balmer lines. Reverberation mapping was carried out for three observing seasons during 2021-2024. We obtained time delays of $\sim$4 d for the response of the H ${\beta }$ line to optical continuum variations. The X-ray variations correlate well with the UV and optical, with a few days lag for longer wavelengths. The K band lagged the B band by $\sim$ 15 d during the last three seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017-2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The $HK$-band variability is governed primarily by dust. The H ${\beta }$/H ${\alpha }$ ratio variations (for broad components only) correlate with the X-ray and UV fluxes. The spectral type changed from type 1.8 to type 1.9 during 2023 October-2024 January and then a more rapid change to type 1.5 occurred in 2024 February. We interpret these changes as a combination of two factors: changes in the accretion rate as a dominant cause but also the sublimation or recovery of dust along the line of sight.

The results of photometric, polarimetric, and spectroscopic observations of the young star ZZ Tau IRS in the visible and near-infrared bands are presented. Against the continuum of an M spectral type star about 50 emission lines of allowed (H I, He I, Na I, S II) and forbidden (O I, O II, O III, N I, N II, S II, Ca II, Fe II, Ni II) transitions were identified. It was found that from the autumn of 2020 to the beginning of 2023, the brightness of the star in the visible region decreased (Δ I≈ 1m.5 ) and then began to return to the initial level. As the visible brightness of the star declined, its color indices decreased in the visible region, but increased in the near-IR bands. At light minimum, the degree of polarization in the I band reached approx 13 % , and the equivalent widths of, e.g., the H α and [S II] λ 6731 lines increased to 376 and 79 Å^∘ , respectively. Arguments are given in favor of ZZ Tau IRS being a UX Ori type star, and its variability being due to eclipses by dust clouds, which are inhomogeneities in the dusty disk wind. Forbidden lines are formed both in the disk wind and in the jet, the axis of what is oriented along PA=61^∘± 3^∘ . The jet mass-loss rate exceeds 5× 10^-10M_⊙ yr ^-1 , what is abnormally large for a star with a mass less than 0.3M_⊙ . Apparently, the disk wind of ZZ Tau IRS is not axially symmetric, probably due to the azimuthal asymmetry of the protoplanetary disk found earlier from ALMA observations.

Context. A strong global magnetic field of young low-mass stars and a high accretion rate are the necessary conditions for the formation of collimated outflows (jets) from these objects. But it is still unclear whether these conditions are also sufficient. Aims. We aim to check whether BP Tau, an actively accreting young star with a strong magnetic field, has a jet. Methods. We carried out narrowband [S II] 672 nm imaging and spectroscopic observations of BP Tau and its vicinity. Results. We find that BP Tau is a source of a Herbig-Haro flow (assigned number HH 1181), which includes two HH objects moving from the star in opposite directions and a micro- (counter-) jet of ∼1″ projected length. The flow is oriented along position angle 59 ± 1°.

ABSTRACT We present the results of multicolour UBVRCICJHK photometry, spectroscopic analysis and spectral energy distribution (SED) modelling for the post-AGB candidate IRAS 02143+5852. We detected Cepheid-like light variations with the full peak-to-peak amplitude ΔV ∼ 0.9 mag and the pulsation period of about 24.9 d. The phased light curves appeared typical for the W Vir Cepheids. The period–luminosity relation for the Type II Cepheids yielded the luminosity logL/L⊙ ∼ 2.95. From a low-resolution spectrum, obtained at maximum brightness, the following atmospheric parameters were determined: Teff ∼ 7400 K and logg ∼ 1.38. This spectrum contains the emission lines H α, ${\rm Ba\, {\small II}}$ λ6496.9, ${\rm He\, {\small I}}$λ10830, and Pa β. Spectral monitoring performed in 2019–2021 showed a significant change in the H α profile and appearance of CH and CN molecular bands with pulsation phase. The metal lines are weak. Unlike typical W Vir variables, the star shows a strong excess of infrared radiation associated with the presence of a heavy dust envelope around the star. We modelled the SED using our photometry and archival data from different catalogues and determined the parameters of the circumstellar dust envelope. We conclude that IRAS 02143+5852 is a low-luminosity analogue of dusty RV Tau stars.

The observations and comprehensive study of intermediate initial mass stars at the late stages of evolution, and after the asymptotic giant branch (AGB) in particular, are of crucial importance to identify the common properties for the stars of given group and to reveal binaries among them. This work aims to investigate photometric and spectral peculiarities of a poorly studied post-AGB candidate and infrared source IRAS 07253–2001. We present the new multicolor UBVR_CI_CYJHK photometry obtained with the telescopes of the Caucasian mountain observatory and analyse it together with the data acquired by the All Sky Automated Survey for SuperNovae. We report on the detection of multiperiod brightness variability caused by pulsations. A beating of close periods, the main one of 73 days and additional ones of 68 and 70 days, leads to amplitude variations. We have also detected a long-term sine trend in brightness with a period of nearly 1800 days. We suppose it to be orbital and IRAS 07253–2001 to be binary. Based on new low-resolution spectroscopic data obtained with the 2.5-m telescope of the Caucasian mountain observatory in 2020 and 2023 in the λ 3500–7500 wavelength range we have identified spectral lines and compiled a spectral atlas. We have found the [N II], [Ni II] and [S II] forbidden emission lines in the spectrum and discuss their origin. The H α line has a variable double-peaked emission component. We have derived preliminary estimates of the star’s parameters and detected a variation of radial velocity with a peak-to-peak amplitude of about 30 km s ^-1 .

Источник BL Lac демонстрировал повышенную активность с августа 2020 до июля 2022 г. Максимум этой активности пришелся на период июль–август 2021 г. В этот период источник достиг исторических максимумов яркости в различных энергетических диапазонах. Наблюдения этого нестандартного максимума проводились сотрудниками ГАИШ Крымской станции ГАИШ и на телескопах Кавказской горной обсерватории (КГО ГАИШ МГУ). Были получены данные фотометрических наблюдений в оптическом диапазоне и ближней инфракрасной области, а также поляриметрические данные в оптике. При исследовании корреляции оптического и гамма-излучения, оптического и ИК-излучения подтвердилась ее высокая степень с почти нулевым запаздыванием – это значит, что области излучения пространственно совпадают либо расположены очень близко друг от друга. Степень линейной поляризации в исследуемый период менялась в широких пределах, достигая значения 20 \({\%}\) , причем наблюдалась антикорреляция степени линейной поляризации с яркостью объекта. Подобный характер изменения наблюдался и в предшествующие вспышки этого объекта. Изменения направления вектора напряженности электрического поля (EVPA) показывают зависимость от скорости изменения яркости объекта. Угол вектора напряженности электрического поля сильно менялся при вспышках, а в моменты медленного изменения интенсивности менялся медленно.

The source BL Lac exhibited an enhanced activity from August 2020 to July 2022. This activity peaked in July–August 2021. In this period the source reached historic brightness maxima in various energy ranges. Observations of this nonstandard maximum were carried out by the SAI staff of the Crimean Station of SAI and with the telescopes of the Caucasus Mountain Observatory (CMO SAI MSU). Optical and near-infrared photometric data as well as optical polarimetric data were obtained. When investigating the correlation between the optical and gamma-ray fluxes and between the optical and infrared fluxes, its high degree with an almost zero lag was confirmed—this means that the emission regions spatially coincide or are very close together. The degree of linear polarization in the investigated period changed in a wide range, reaching 20 % , with an anticorrelation between the degree of linear polarization and the brightness of the object having been observed. A similar pattern of variation was also observed in the preceding flares of this object. The changes in the electric vector position angle (EVPA) show a dependence on the rate of change of the object’s brightness. The EVPA changed greatly during flares and slowly at the times of a slow change in the intensity.

— In December 2021 to February 2022, the UBVRI photometry of 29 primitive-type asteroids of the Main Belt, being near the perihelion distances, was carried out at the 0.6-meter RC600 semiautomatic telescope of the Caucasus Mountain Observatory (CMO) of the Sternberg Astronomical Institute, Moscow State University. These observations, as well as the data processing and analysis, were aimed at searching for supposed sublimation-driven dust activity on asteroids under maximal subsolar temperatures. Among the tasks to be accomplished was the comparison of the physical and dynamic parameters of active and inactive asteroids. The main result is that substantial spectral signs of quasi-simultaneous sublimation-driven dust activity were detected on six primitive-type asteroids of the Main Belt—145 Adeona, 302 Clarissa, 322 Phaeo, 435 Ella, 690 Wratislavia, and 779 Nina (on 302 Clarissa, 322 Phaeo, 435 Ella, and 690 Wratislavia—for the first time). These six asteroids represent ~21% of all bodies included in the observation program. Probable spectral manifestations of activity at a lower intensity level were detected for the first time on five more asteroids—424 Gratia, 751 Faina, 762 Pulcova, 778 Theobalda, and 859 Bouzaréah. On 145 Adeona and 779 Nina, sublimation-driven dust activity near perihelion was registered for the third time for the last ten years; this time interval corresponds to about three orbital periods of these asteroids around the Sun. We consider the circumstances due to which five of the listed asteroids possess families. General processes and conditions that could and/or can influence the portion of primitive-type asteroids that quasi-simultaneously show signs of sublimation-driven dust activity are discussed.

We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC~2617 carried out from 2016 until 2022 and covering the wavelength range from the X-ray to the near-IR. The facilities included the telescopes of the SAI MSU, MASTER Global Robotic Net, the 2.3-m WIRO telescope, Swift, and others. We found significant variability at all wavelengths and, specifically, in the intensities and profiles of the broad Balmer lines. We measured time delays of ~ 6 days (~ 8 days) in the responses of the H-beta (H-alpha) line to continuum variations. We found the X-ray variations to correlate well with the UV and optical (with a small time delay of a few days for longer wavelengths). The K-band lagged the B band by 14 +- 4 days during the last 3 seasons, which is significantly shorter than the delays reported previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises from two different emission regions: the outer part of the accretion disc and a more distant dust component. The HK-band variability is governed primarily by dust. The Balmer decrement of the broad-line components is inversely correlated with the UV flux. The change of the object's type, from Sy1 to Sy1.8, was recorded over a period of ~ 8 years. We interpret these changes as a combination of two factors: changes in the accretion rate and dust recovery along the line of sight.

We present the results of BVRI photometry for the type II-P supernova (SN) 2019edo in NGC 4162 obtained from April 29, 2019, to January 26, 2020, with several telescopes, including the 60-cm telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University. The shape of the light curves is typical for SN II-P. However, the plateau lasted for about 76 days, which is less than the typical value for SN of this class, while the luminosity rise to the peak was unusually fast. The absolute $$V$$ magnitude at maximum light was $$-16\overset{m}{.}$$ 9, which is close to the mean value for SN II-P. The brightness decline rate at the late phase is slightly higher than the expected one for the radiation due to $${}^{56}$$ Co decay. As a result of our radiation-hydrodynamics simulations of the SN explosion with the STELLA code, we have managed to consistently reproduce the initial rise and plateau phases in the light curves. The constructed SN model has the following parameters: an ejecta mass $$M_{\textrm{env}}=6.6M_{\odot}$$ , an SN progenitor radius $$R_{0}=500R_{\odot}$$ , and a mass of radioactive $${}^{56}\textrm{Ni}\approx 0.05M_{\odot}$$ . The SN progenitor was inside a cocoon, a stellar wind, with a total mass $$M_{\textrm{wind}}\approx 0.01M_{\odot}$$ and a radius $$R_{\textrm{wind}}=10^{15}$$ cm. The energy release during the explosion was $$E_{\textrm{burst}}=0.8\times 10^{51}$$ erg.

The observed characteristics of the spectral and photometric variability of SS 433 are discussed based on the data for 2018–2021 and compared with earlier results. The change in the orbital period that we discovered earlier according to $$V$$ -photometry is confirmed by the data in the $$B$$ -filter, although with less accuracy. In the observation interval from 1978 to 2021, secular changes are not observed either in the stationary or moving H $$\alpha $$ lines. However, there are breaks in the precession phase up to $$ \pm 11$$ days, which appear at time scales less than 1 year and disappear in 2–3 years.

Based on the spectroscopic observations carried out with the 2.5-m telescope at the Caucasus Mountain Observatory (CMO) of the Sternberg Astronomical Institute (SAI), we have established the symbiotic nature of the poorly studied S star CSS 1102. The Balmer jump in emission is observed in the object’s spectrum, and there are lines typical for gaseous nebulae (H I, He I, and [Ne III]). An analysis of the spectral energy distribution has shown that, apart from the nebula and the cool component of spectral type S4.5/2, excess emission in the blue and near-ultraviolet ranges that can be attributed to an accretion disk is noticeable in the spectrum of CSS 1102. The photometric monitoring performed at the 60-cm CMO SAI telescope in the $$B$$ band has revealed rapid variability on a time scale of tens of minutes and with an amplitude of several percent. This is an additional argument for the existence of an accretion disk in the system.

Abstract —NGC 225 is a young moderately populated cluster with discrepant age, distance, and color excess estimates reported by different authors. We combine our photometry with the data from large surveys (2MASS, WISE, Pan-STARRS) to derive the parameters of NGC 225 and study the extinction law in the near infrared in the direction of the cluster. We use theoretical isochrones to infer the color excess $$E(B - V) = 0.29 \pm 0.01$$ , distance $$D = 667 \pm 18$$ pc, and Age = $$100$$ – $$160$$ Myr. We fit extinction in the infrared by a power-law relation, $${{\lambda }^{{ - \alpha }}}$$ , and find $$\alpha = 2.16 \pm 0.34$$ .

Context. During its ongoing all-sky survey, the Mikhail Pavlinsky ART-XC (Astronomical Roentgen Telescope - X-ray Concentrator) telescope on board the Spectrum-Roentgen-Gamma (SRG) observatory is set to discover new X-ray sources, many of which can be transient. Here we report the discovery and multiwavelength follow-up of a peculiar X-ray source SRGA J043520.9+552226 = SRGe J043523.3+552234. This is the high-energy counterpart of the optical transient AT2019wey. Aims. Through its sensitivity and the survey strategy, the Mikhail Pavlinsky ART-XC telescope uncovers poorly studied weak transient populations. Using the synergy with current public optical surveys, we aim to reveal the nature of these transients to study their parent populations. SRGA J043520.9+552226 is the first transient detected by ART-XC that has a bright optical counterpart suitable for further studies. Methods. We used available public X-ray and optical data and observations with SRG, INTEGRAL, NuSTAR, NICER, Swift, and ground-based telescopes to investigate the spectral energy distributions of the source in different phases of the outburst. Results. Based on X-ray spectral and timing properties derived from space observations, optical spectroscopy, and photometry obtained with the 2.5 m and RC600 telescopes of the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Moscow State University, we propose that the source is a black hole in a low-mass close X-ray binary system.