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 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.

Based on data from the ZTF photometric survey, we have revealed asynchrony of the polar SDSS J085414.02+390537.3. A beat period P_beat=24.6± 0.1 days, during which the system changes its brightness by ≈3^m , is distinguished in the light curves. Power peaks at the white-dwarf rotation period P_spin=113.197± 0.001 min and orbital period P_orb=113.560± 0.001 min are revealed in the periodograms, with the corresponding polar asynchrony being 1-P_orb/P_spin=0.3% . The photometric behavior of the polar points to a change of the main accreting pole during the beat period. Based on the Zeeman splitting of the H β line, we have estimated the mean magnetic field strength of the white dwarf to be B=28.5± 1.5 MG. The magnetic field strength near the magnetic pole has been found by modeling the cyclotron spectra to be B=34± 2 MG. The Doppler tomograms in the H β line exhibit a distribution of emission sources typical for polars in velocity space with evidence of the transition of the accretion stream from the ballistic trajectory to the magnetic one.

We report the results of photometric and spectroscopic monitoring of CI Cam within 24 years since its outburst in 1998. Over this time, we found a system component emitting in the He II 4686 Å emission line, on an elliptical orbit with a period of $$19\overset{\textrm{d}}{.}407$$ days and an eccentricity of 0.44–0.49. The variations of the optical brightness are observed with the same period and with an average amplitude of $$0\overset{\textrm{m}}{.}04$$ . The total amplitude of the He II radial velocity variations is about 380 km s $${}^{-1}$$ . The equivalent width of the line is variable on a time scale of tens of minutes as well as with the orbital period. Maximum equivalent widths of the He II line are observed when the component passes the descending node of the orbit. The intensity of the He II 4686 Å emission gradually increases with time. Slow radial velocity variations on a scale of decades were detected by means of high resolution spectroscopy in the iron emission lines and a forbidden nitrogen line formed in the circumstellar nebula. The B-type star turned out to be a pulsating variable. During the period between 2005 and 2009, pulsations were multiperiodic with the dominant periods $$0\overset{\textrm{d}}{.}5223$$ , $$0\overset{\textrm{d}}{.}41539$$ , and $$0\overset{\textrm{d}}{.}26630$$ days. However, since 2012 it has pulsated in a single mode with a variable period in the $$0\overset{\textrm{d}}{.}403{-}0\overset{\textrm{d}}{.}408$$ day range depending on the star’s luminosity. We identify the 2005–2009 pulsations as a resonance of the radial modes, and the residual stable mode as the first overtone. The pulsations are coherent on a scale of several months, and their average amplitudes are $$0\overset{\textrm{m}}{.}02{-}0\overset{\textrm{m}}{.}04$$ . The pulsation data constrain the spectral type of the main component to B0–B2 III, the distance to the system to 2.5–4.5 kpc, and the absolute visual magnitude $$M_{V}$$ to the range of $$-3\overset{\textrm{m}}{.}7$$ to $$-4\overset{\textrm{m}}{.}9$$ . The classification of the CI Cam main component as a B[e] supergiant is completely ruled out due to the observed pulsation periods. CI Cam may be a system at the stage after the first mass exchange and may be attributed to the FS CMa-type group of objects with the B[e] phenomenon.

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.

KK242 is a LV dwarf of transition type residing in the void environment. Koda et al. present clear indications on its connection with Scd galaxy NGC 6503. This implies the distance to KK242 of similar to 6.3 Mpc and its M-B = -10.5 mag. Its radial velocity, known from the Effelsberg radio telescope H i observations, reveals, however, the difference with that of NGC 6503, Delta V similar to 400 km s(-1). If real, this fact implies the substantial constraints on its origin. To clear-up the issue of KK242 radial velocity, we obtained with the SAO 6-m telescope spectra of its faint star-forming (SF) complex. H alpha and H beta emission is detected in two adjacent compact regions, the southern and northern, separated by similar to 2 arcsec (similar to 60 pc). Their mean radial velocity is V-hel = -66 km s(-1), similar to 100 km s(-1) lower than that of NGC 6503. We use the HST Legacy Archive images and photometry of individual stars from the Extragalactic Distance Database, available for KK242, to identify in the SF complex the exciting hot stars, the probable BHeB and RHeB stars and a supernova remnant. We address, based on the possible range of its gas metallicity, the probable evolutionary paths of KK242. Using package cloudy and parameters of the exciting B0V stars, we conclude that the observed flux ratio of the [S ii] doublet to H alpha is consistent with the value of 12+log (O/H) similar to 7.35 +/- 0.18 dex, expected for a stripped void dIrr galaxy.

—The paper describes Zeiss-1000, the one meter telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS), the history of the development of its observation methods and potential areas of astrophysical research. Detailed attention is paid to instruments and methods of observation which are in service nowadays.

Abstract—The article presents the results of multicolor photometry, medium and low resolution spectroscopy of the red nova V838 Mon remnant for 16 years after the 2002 outburst. We also used the archival photometry with the photographic plates of the Sonneberg and Moscow collections from 1928 to 1994. Analysis of these observational data confirmed that the progenitor of the V838 Mon explosion was a wide pair of B3V type stars of reduced luminosity. A brighter component exploded; it was 36 per cent brighter than its companion, and located on the zero-age main sequence of the Spectrum–Luminosity Diagram. Immediately after the outburst, in the fall of 2002, the remnant was a brown L-type supergiant (sgL), but in the fall of 2003 its spectrum changed to M type with a blue radiation excess appeared in the spectral energy distribution, which we interpreted as the reflection effect of the B type companion on the dust formed on the M star. In 2008, the companion was engulfed by the expanding explosion remnant, a type M supergiant (sgM). When the companion was immersing in the expanding M-star, a void was discovered under the M-star upper layer, in which the companion moved for about 200 days. Over the past 10 years, the luminosity of the M star has increased in the V filter by a factor of 10, and the spectral type has changed from M7.5 to M5.5. Based on radial velocities in the BaII 6497 Å and CaI 6572 Å lines, a deceleration of the expanding envelope of the M supergiant was detected, and in 2018, the envelope velocity approached to the heliocentric velocity of the star +71 km s−1. Quasi-periodic changes with a period of 320 days appeared then in the light curves, especially clearly expressed in I filter. We assume that the remnant has an elongated structure, and its rotation period is about 640 days. This is probably a gigantic contact system that will become a detached binary system in future development. The observations do not confirm the assumption that the explosion of one of the V838 Mon components was due to the merger of a compact binary system components located in a hierarchical triple one. Two hypotheses were proposed on the nature of the explosion of one of the V838 Mon components, directly based on the early age of this system: (1) the ignition of thermonuclear burning of hydrogen in the core after the gravitational compression of a protostar; (2) the fragmentation of the core inside a rapidly rotating star in the stage of gravitational compression of a protostar, and later, the subsequent defragmentation (merger of the core components) due to the loss of torque.

Here we present the long-term optical spectral monitoring of a changing-look active galactic nuclei (AGN) NGC 3516 that covers 22 years (from 1996 to 2018). We explore a variability in the broad lines and continuum, finding that the continuum is changing by more than a factor of 2, while the broad lines are varying by more than a factor of 10. The minimum of activity is observed in 2014, when the broad lines almost disappeared. We confirm that NGC 3516 is a changing-look AGN, and the absorption seen in the UV and X-ray may indicate that there is an obscuring region which is responsible for this. The line profiles are also changing. The mean profiles of the broad Halpha and Hbeta lines show shoulder-like structure in the wings, and enhanced peak, that may indicate a complex BLR. The rms-profiles of both lines seem to have the same shape and width of around 4200 km/s, indicating practically the same kinematics in the Halpha and Hbeta emitting regions. Measured time-lags between the continuum and Halpha and Hbeta broad-line variability are ~15 and 17 days, respectively, that in combination with the broad lines width allows us to estimate the NGC 3516 central black hole mass. We find that the black hole mass is 4.73+-1.40 x 10^7M_sun which is in agreement with previous estimates.

Abstract . We analyzed a 40-year set of multicolor photometry and a 15-year set of synoptic monitoring of SS 433 along with fragmentary spectral and radio data. This system contains a neutron star and an A3–A7 I giant. The system is found to be either close, in contact, or it has a common envelope from time to time. The A-type giant is now in transition to the dynamical mass transfer.