DDO 68 is a star-forming (SF) dwarf galaxy residing in a nearby void. Its gas metallicity is among the lowest known in the local Universe, with the 12+log(O/H) parameter in the range of 6.96–7.3 dex. Six of its SF regions are located in or near the so-called ‘‘Northern Ring’’, in which the Hubble Space Telescope (HST) images reveal many luminous young stars. We present for these SF regions (Knots) the results of optical monitoring in 35 epochs during the years 2016–2023. The data was acquired with the 6-m (BTA) and 1-m telescopes of the Special Astrophysical Observatory, and the 2.5-m telescope of the MSU Caucasian Mountain Observatory. We complement the above results with the archival data from 10 other telescopes for 11 epochs during the years 1988–2013 and with three our BTA observations between 2005 and 2015. Our goal is to search for variability of these Knots and to relate it to the probable light variations of their brightest stars. One of them, DDO 68-V1 (in Knot 3), was identified in 2008 with a luminous blue variable (LBV) star born in the lowest metallicity environments. For Knot 3, variations of its integrated light in the previous epochs reached about 0m.8 . In the period since 2016, the amplitude of the variations in Knot 3 has reached about 0m.3 . For the rest of the Knots, due to the lower amplitudes, the manifestation of variability is less pronounced. We examine the presence of variability via the χ^2 criterion and the Robust Median Statistics and discuss the robustness of the detected variations. The variability is detected according to both criteria in the light curves of all Knots with the χ^2 confidence level at α=0.0005 . The peak-to-peak amplitudes of the variations are approximately 0m.09 , 0m.13 , 0m.11 , 0m.08 , and 0m.16 for Knots 1, 2, 4, 5, and 6, respectively. The amplitudes of the related variations of the brightest supergiants in these regions can reach about 3m.0 .

We present a study of the radio and optical properties of the high-frequency peaker (HFP) blazar PKS 1614 + 051 at z=3.21 based on the data covering the time period of 1997–2024. The radio data are represented by the instantaneous 1–22 GHz measurements from the SAO RAS RATAN-600 radio telescope, the 5 and 8 GHz data from the IAA RAS RT-32 telescopes, and the 37 GHz data from the RT-22 telescope of CrAO RAS. The optical measurements in the R band were collected with the SAO RAS 1-m Zeiss-1000 and 0.5-m AS-500/2 telescopes, and the ZTF archive data. We have found low overall variability indices (0.1–0.2) and a median spectral peak at 4.6 GHz, which is stable during the long-term period of monitoring. An analysis of the radio light curves reveals significant time delays (0.6 to 6.4 yrs) between the radio frequencies along with variability timescales ranging from 0.2 to 1.8 yrs in the source’s rest frame, which is similar to the blazars at lower redshifts. Spectral modeling suggests the presence of both synchrotron self-absorption (SSA) and free-free absorption (FFA) processes. Based on the SSA model, we provide estimates of the magnetic field strength which peaks at approximately 100 mG. A spectroscopic study with the BTA SCORPIO-1 spectrograph has found evidence of the regular motion of a neutral hydrogen envelope around the blazar center, which confirms the presence of a sufficient amount of gaseous matter to form an external FFA screen. The results highlight the importance of multi-wavelength and long-term monitoring to understand the physical mechanisms driving the variability in high-redshift blazars.

DDO68 is a star-forming (SF) dwarf galaxy residing in a nearby void. Its gas metallicity is among the lowest known in the local Universe, with parameter 12+log(O/H) in the range of 6.96-7.3 dex. Six of its SF regions are located in or near the so-called 'Northern Ring', in which the Hubble Space Telescope (HST) images reveal many luminous young stars. We present for these SF regions (Knots) the results of optical monitoring in 35 epochs during the years 2016–2023. The data was acquired with the 6m (BTA) and the 1m telescopes of the Special Astrophysical Observatory and the 2.5m telescope of the MSU Caucasian Mountain Observatory. We complement the above results with the archive data from 10 other telescopes for 11 epochs during the years 1988-2013 and with 3 our BTA observations between 2005 and 2015. Our goal is to search for variability of these Knots and to relate it to the probable light variations of their brightest stars. One of them, DDO68-V1 (in Knot 3), was identified in 2008 with a luminous blue variable (LBV) star, born in the lowest metallicity environments. For Knot 3, variations of its integrated light in the previous epochs reached 0.8 mag. In the period since 2016, the amplitude of variations of Knot 3 reached 0.3 mag. For the rest Knots, due to the lower amplitudes, the manifestation of variability is less pronounced. We examine the presence of variability via the criterion chi^2 and the Robust Median Statistics and discuss the robustness of the detected variations. The variability is detected according to the both criteria in the lightcurves of all Knots with the chi^2 confidence level of alpha = 0.0005. The peak-to-peak amplitudes of variations are 0.09, 0.13, 0.11, 0.08 and 0.16 mag for Knots 1, 2, 4, 5 and 6, respectively. The amplitudes of the related variations of the brightest supergiants in these regions can reach of 3.0 mag.

We present an optical-to-radio study of the BL Lac object S4 0954+658 observations during 1998–2023. The measurements were obtained with the SAO RAS Zeiss-1000 and AS-500/2 0.5-m telescopes in 2003–2023, with the RATAN-600 radio telescope at 1.25 (0.96, 1.1), 2.3, 4.7 (3.7, 3.9), 8.2 (7.7), 11.2, 22.3 (21.7) GHz in 1998–2023, with the IAA RAS RT-32 Zelenchukskaya and Badary telescopes at 5.05 and 8.63 GHz in 2020–2023, and with the RT-22 single-dish telescope of CrAO RAS at 36.8 GHz in 2009–2023. In this period the blazar was showing extremely high broadband activity with the variability amplitude of the flux densities up to 70–100 % both in the optical and radio domains. During the period of 2014–2023 the blazar displayed extremely high activity in the radio wavelengths, and we detected multiple radio flares of varying amplitude and duration. The large flares last on average from 0.3 to 1 year at 22–36.8 GHz and slightly longer at 5–11.2 GHz. The optical flares are shorter and last 7–50 days. The characteristic time scale τ of variation at 5–22 GHz is about 100 days in the most active epoch of 2014–2023 and about 1000 days for the state with lower activity in 2009–2014. We found a general correlation between the optical, radio, and γ -ray flux variations, which suggesting that we observe the same photon population from different emission regions. We estimated the linear size of this region as 0.5–2 pc for different conditions. A broadband radio spectrum with two components of the S4 0954+658 jet was modeled using both electrons and protons as emitting particles. The results suggest that the synchrotron radio waves in this AGN may be produced by relativistic protons.

We present the results of our optical study of the eclipsing polar Gaia23cer. We analyze the orbital brightness variability in high ( ⟨ r⟩≈ 16.5^m ) and low ( ⟨ r⟩≈ 19.2^m ) states. The system has an orbital period P_orb=102.0665± 0.0015 min and exhibits deep eclipses with a duration Δ t_ecl=401.30± 0.81 s. The spectra have a red cyclotron continuum with the Zeeman H α absorption triplet forming in a magnetic field with a strength B=15.2± 1.1 MG. The source of emission lines has a high radial velocity semi-amplitude ( K≈ 450 km s ^-1 ), and its eclipse lags behind the eclipse of the white dwarf. The mass M_1=0.79± 0.03 M_⊙ and temperature T=11 350± 650 K of the white dwarf have been estimated by modelling the spectral energy distribution. The eclipse duration corresponds to a donor mass M_2=0.10-0.13 M_⊙ and an orbital inclination i=84.3^∘-87.0^∘ . The donor temperature was estimated to be T≈ 2900 K by modelling the elliptical variability and eclipse depth.

We have performed spectroscopic and photometric studies of the poorly explored polar BM CrB. Based on ZTF survey data, we have revealed three brightness states of the polar and evidence of the transition from one-pole to two-pole accretion as the average brightness of the system increases. We show that there are a change in the longitude of the main accretion spot (by $${\approx}17^{\circ}$$ ) and an increase in its extent (by $${\approx}10^{\circ}$$ ) when passing from the low state to the high one. Zeeman H $$\alpha$$ absorptions formed in a magnetic field of strength $$B=15.5\pm 1$$ MG are present in the spectra. The cool halo extending from the accretion spot to $${\approx}{1/4}$$ of the white dwarf radius can be the source of these absorptions. Our modeling of the behavior of the H $$\alpha$$ emission line shows that the main source of the emission is the segment of the accretion stream near the Lagrange point L $${}_{1}$$ that is periodically eclipsed by the donor star. The spectra exhibit a cyclotron component forming in the accretion spot. Their modeling by a simple accretion spot model gives constraints on the magnetic field strength, $$B=15$$ –40 MG, and the temperature, $$T_{e}\gtrsim 15$$ keV.

Выполнены спектральное и фотометрическое исследования слабоизученного поляра BM CrB. На основе данных обзора ZTF выявлено три состояния блеска поляра и признаки перехода от однополюсного к двухполюсному режиму аккреции при увеличении среднего блеска системы. Показано, что при переходе от низкого состояния к высокому происходит изменение долготы главного аккреционного пятна (на \({\approx}17^{\circ}\) ) и увеличение его протяженности (на \({\approx}10^{\circ}\) ). В спектрах присутствуют зеемановские абсорбции линии H \(\alpha\) , которые формируются в магнитном поле напряженностью \(B=15.5\pm 1\) МГс. Источником этих абсорбций может быть холодное гало, простирающееся от аккреционного пятна на \({\approx}{1/4}\) радиуса белого карлика. Моделирование поведения эмиссионной линии Н \(\alpha\) показывает, что основным источником эмиссии является участок аккреционной струи вблизи точки Лагранжа L \({}_{1}\) , который периодически затмевается звездой-донором. В спектрах проявляется циклотронная компонента, формируемая в аккреционном пятне. Ее моделирование простой моделью аккреционного пятна дает ограничения на напряженность магнитного поля \(B=15\) –40 МГс и температуру \(T_{e}\gtrsim 15\) кэВ.

The active core of the galaxy AO0235+164 is monitored in the optical and radio bands at millimeter wavelengths. Using the multifrequency data obtained in gamma, optical and radio bands, the characteristics of its radiation in the active phase of 2015–2016 are studied. The cross-correlation method was used to determine the delays of the 2015 flare that took place in AO0235+164 in different bands. The analysis made it possible to establish that, in comparison with the previous flare phenomena, changes in the orientation of the emissions (jets) have occurred. The angle θ between the jets and the direction towards the observer has decreased by a factor of \(\sqrt 2 \), resulting in a twofold increase in the γ-factor. The obtained value γ ≈ 40 is the most extreme value ever observed in AO0235+164 over the entire span of observations.

The results of studies of the optics of the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) by the Shack–Hartmann (SH) method are presented. Using a Shack–Hartmann wavefront sensor (SH WFS) we have adjusted the telescope optical system by means of shifts and tilts of the secondary mirror. The procedure has significantly reduced the aberrations that appeared during the long-term instrument operation. A new method to investigate the surface quality of the mirrors of the Zeiss-1000 being applied, characteristics close to the diffraction limit are achieved. In general, the entire opto-mechanical telescope system provides an image quality of about 0.5″ at 80%energy level.