We have selected candidate massive stars in the galaxy IC 342 based on archival images from the Hubble Space Telescope and images from the 2 m telescope at the Natioal Astronomical Observatory Rozhen, Bulgaria. Spectral observations of 24 out of 27 selected stars are carried out with the 6 m BTA telescope at the SAO RAS and with the 3.5 m Apache Point Observatory telescope (USA) as part of the program for searching bright massive stars in galaxies outside the Local Group. Our analysis reveals that 12 objects have spectra lacking prominent features, except for the emission lines of the surrounding nebulae and are identified as single supergiants of classes O9 to F5 or spatially unresolved young compact clusters. One source with an absorption spectrum probably belongs to our Galaxy. The spectra of seven other objects show features typical of Wolf-Rayet stars or compact clusters containing Wolf-Rayet stars. Another source is a compact supernova remnant. Two other objects are tentatively classified as cold LBV candidates, and one object is classified as a B[e]-supergiant candidate.

Luminous blue variables are a class of massive, unstable stars that exhibit significant photometric variability. Their variability can be linked to their significant mass-loss rates, envelope instabilities and sometimes binarity. These factors can affect the star's brightness and spectrum. LBVs are relatively rare, so studying their variability is challenging. To understand their different types of photometric variability, continuous long-term observations are needed.In this study, we present the analysis of the optical light curves of LBV stars and LBV candidates in the galaxy IC 342. Our observations cover time interval of nearly 4 year and were taken in B and R bands with the 2m telescope at NAO Rozhen, Bulgaria. We supplement our photometry with data from the Pan-STARRS catalog DR1 to expand the light curve coverage and to study both microvariability and long-term variability.

The results of a search for massive luminous stars in the NGC 6946 galaxy are presented. Using the 6-meter telescope of the SAO RAS, spectra of 8 candidates were obtained. Two stars have the (J203455.57+601055.4 and J203448.52+601054.5) emission line spectra. Object J203455.57+601055.4 exhibits CIII+NIII and HeII lines characteristic of WR clusters, single WR stars or Luminous Blue Variables (LBVs) in a hot state. The star J203448.52+601054.5 was classified as a cool LBV candidate based on observed emission lines of hydrogen, HeI, FeII and (FeII).

Яркие голубые переменные (luminous blue variables, LBV) представляют собой редкий тип звезд высокой светимо- сти, обладающих сильной фотометрической и спектральной переменностью. Вопрос об их происхождении остается открытым, поскольку существуют две противоположные точки зрения: LBV — стадия эволюции массивной оди- ночной звезды, и LBV — результат эволюции массивных тесных двойных. Известно немногим более 50 звезд этого типа в нашей и других галактиках, в основном принадлежащих Местной группе. В работе обсуждаются различные методы поиска LBV в зависимости от расстояния, особое внимание уделено результатам поиска LBV в галактиках за пределами Местной группы по данным 6-метрового телескопа САО РАН. Luminous blue variables (LBVs) are a rare type of luminous stars with strong photometric and spectral variability. Their evolutionary status remains unclear, since there are two opposite points of view: LBV is a short stage of evolution of a massive single star, and LBV is the result of the evolution of interacting massive binaries. A little more than 50 stars of this type are known in our and other galaxies, mainly belonging to the Local Group. The paper discusses various methods for searching for LBVs depending on the distance, with special attention to the results of searching in galaxies outside the Local Group according to the data obtained with 6-m telescope SAO RAS.

We study Luminous Blue Variable (LBV) candidate J004341.84+411112.0 in the Andromeda galaxy. We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS. The candidate shows typical LBV features in its spectra: broad and strong hydrogen lines and the He i lines with P Cygni profiles. Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0. We estimate the temperature, reddening, radius and luminosity of the star using its spectral energy distribution. Obtained bolometric luminosity of the candidate (M (bol) = -10.41 +/- 0.12 mag) is quite similar to those of known LBV stars in the Andromeda galaxy. We analyzed a ten year light curve of the object in R filter. The candidate demonstrates photometric variations of the order of 0.4 mag, with an overall brightness increasing trend Delta R > 0.1 mag. Therewith, the corresponding color variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity. LBV-type variability of the object, similarity of its spectrum and estimated luminosity to those of known LBVs allow us to classify J004341.84+411112.0 as an LBV.

A search for a correlation between the luminosities of the brightest stars and luminosities of their host galaxies was carried out on archival Hubble Space Telescope (HST) $$F606W$$ or $$F555W$$ (V) and $$F814W$$ (I) images of 150 nearby galaxies. The sample contains only galaxies with ongoing star formation and with known distances we derived with the TRGB-method. We correlated the average absolute luminosities of the three brightest blue and the three brightest red stars with the luminosity of a host. We find a linear relation for both the blue and the red stars in irregular and low-mass spiral galaxies. Their scatters are sufficiently small ( $${{0.}^{{\text{m}}}}4$$ ) to make these relations useful for distance determination for low-mass galaxies. We found that all 31 dwarf galaxies $$({{M}_{B}} > - {{13}^{{\text{m}}}})$$ in our sample lack bright massive stars $$({{M}_{V}}{\text{(BS)}} < - {{7.}^{{\text{m}}}}0)$$ , probably due to the physical conditions that prevent their birth. For galaxies with higher an average luminosity in the range $$ - {{18}^{{\text{m}}}} < {{M}_{B}} < - {{13}^{{\text{m}}}}$$ , there is an asymmetry in the distribution of the number of galaxies relative to the linear dependence, indicating an increase in the fraction of galaxies with bright stars.

Two LBV candidates have been found in the galaxy IC342. Within the framework of the program for search of LBV stars in galaxies outside the Local Group, spectral and photometric observations were carried out with the 6-m telescope of SAO RAS. These objects revealed observational features characteristic of such stars. Their spectra show typical LBV emission lines: broad and strong hydrogen lines, HeI and FeII, and [FeII] lines. We have obtained estimates of the interstellar reddening and the photosphere temperatures. For one star, it was possible to build a spectral energy distribution (SED) and determine the temperature more accurately. We estimated the absolute magnitudes as $M_v \approx$ -9.3$^m$ and -10.8$^m$, which allows us to classify them as LBV candidates.

We study the luminous blue variable candidate J004229.87+410551.8 in the Andromeda Galaxy. Earlier, the star displayed a spectral anomaly: although a hot emission spectrum had been detected, it had strong CaII H and K absorption lines. Subsequently the star was assumed to be a hot hypergiant or a B[e] supergiant. For the purpose of clear star classification, we conducted spectroscopic and photometric analysis of the object and its surroundings with the 6-m telescope of SAO RAS, the 3.5-m ARC telescope of the Apache Point Observatory and the 2.5-m telescope of the Caucasus Mountain Observatory of the Sternberg Astronomical Institute. The spectrum of the star has the FeII, [FeII], [OI], and Balmer emission lines. Its spectral energy distribution shows an excess in the near-infrared range due to hot circumstellar dust. The indicated features and a high estimated value of star's luminosity (log (L/L_⊙) = 4.6± 0.2) allow us to finally classify the object as a B[e] supergiant.

We report here the first results from a 15-yr long variability monitoring of the z = 2.0 quasar QSO B1312+7837. It shows luminosity changes with a period P ∼ 6.13 yr (P ∼ 2.04 yr at rest frame) and amplitude of ∼0.2 mag, superimposed on a gradual dimming at a rate of ∼0.55 mag per 100 yr. Two false periods associated with power peaks in the data windowing function were discarded. The measured period is confirmed with a bootstrapping Monte Carlo simulation. A damped random walk model yields a better fit to the data than a sine-function model, but at the cost of employing some high-frequency variations which are typically not seen in quasars. We consider the possible mechanisms driving this variability, and conclude that orbital motion of two supermassive black holes – result from a recent galaxy merger – is a possible explanation.

This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group. To search for massive stars, we processed the results of stellar photometry from the Hubble Space Telescope (HST) images using the DAOPHOT and DOLPHOT packages. The results of such searches are demonstrated with examples of the galaxies DDO 68, M94 and NGC 1672. In the galaxy DDO 68, the LBV star changes its brightness, and massive stars in M94 can be identified by excess in the H alpha band. For the galaxy NGC 1672, we measure the distance for the first time by the TRGB method, which enabled determining the luminosities of the brightest stars, likely hypergiants, in the young star formation region. So far, we have performed stellar photometry on HST images of 320 northern sky galaxies located at a distance less than 12 Mpc. This allowed us to identify 53 galaxies with probable hypergiants. Further photometric and spectral observations of these galaxies are planned to search for massive stars.

Ultraluminous X-ray sources (ULXs) were identified as a separate class of objects in 2000 based on data from the Chandra X-Ray Observatory. These are unique objects: their X-ray luminosities exceed the Eddington limit for a typical stellar-mass black hole. For a long time, the nature of ULXs remained unclear. However, the gradual accumulation of data, new results of X-ray and optical spectroscopy, and the study of the structure and energy of nebulae surrounding ULXs led to the understanding that most of the ultraluminous X-ray sources must be supercritical accretion disks like SS 433. The discovery of neutron stars in a number of objects only increased the confidence of the scientific community in the conclusions obtained, since the presence of neutron stars in such systems clearly indicates a supercritical accretion regime. In this review, we systematize the main facts about the observational manifestations of ULXs and SS 433 in the X-ray and optical ranges and discuss their explanation from the point of view of the supercritical accretion theory.

We study five Luminous Blue Variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-meter telescope at the Apache Point Observatory and on the 6-meter telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, HeI, FeII, and [FeII] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in V band), which allows us to classify it as a LBV. The star J004415.04+420156.2 shows characteristics typical for B[e]-supergiants. The star J004411.36+413257.2 is classified as FeII star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We for the first time obtain NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in the J004341.84+411112.0. This allows us to confirm that MN112 is a LBV, which should show its brightness variability in longer time span observations.

We search for luminous blue variable (LBV) stars in galaxies outside the Local Group. Here we present a study of two bright Ha sources in the NGC247 galaxy. Object j004703.27-204708.4 (M-V = -9.08 +/- 0.15 mag) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He I with P Cyg profiles, emission lines of iron Fe II, silicon Si II, nitrogen NII and carbon CII, forbidden iron [Fe II] and nitrogen [N II] lines. The variability of the object is Delta B = 0.74 +/- 0.09 mag and Delta V = 0.88 +/- 0.09 mag, which makes it a reliable LBV candidate. The star j004702.18-204739.93 (M-V = -9.66 +/- 0.23 mag) shows many emission lines of iron Fe II, forbidden iron lines [Fe II], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [OI] and calcium [Ca II] formed in the circumstellar matter. The study of the light curve of this star did not reveal significant variations in brightness (Delta V = 0.29 +/- 0.09 mag). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes M-bol = -10.5(-0.4)(+0.5) and M-bol = -10.8(-0.6)(+0.5), which correspond to bolometric luminosities log(L-bol/L-circle dot) = 6.11(-0.16)(+0.20) and 6.24(-0.25)(+0.20) for j004703.27-204708.4 and j004702.18-204739.93, respectively. Thus, the object j004703.27-204708.4 remains a reliable LBV candidate, while the object j004702.18-204739.93 can be classified as a B[e]-supergiant.

ABSTRACT MN112 is a Galactic luminous blue variable (LBV) candidate with a circumstellar nebula. P Cygni was the first LBV discovered, and was recorded during major eruptions in the 17th century. The stars have similar spectra with strong emission hydrogen lines, He i, N ii, Si ii, and Fe iii lines. We present the results of spectroscopic analysis and modelling of MN112 spectra. We obtained the main stellar parameters and chemical abundances of MN112 and compared them with those of P Cygni. Atmosphere models were calculated using the non-local thermodynamic equilibrium radiative transfer code cmfgen. We have used spectra of MN112 obtained with the 3.5-m telescope at the Observatory of Calar Alto and 3.5-m ARC telescope at the Apache Point Observatory. P Cygni spectra were taken with the 6-m BTA telescope. We have found the best fit of the observed spectrum with the model at temperature $T_{\text{eff}}= 15\, 200$ K, clumping-corrected mass-loss rate $\dot{M}f^{-0.5}=5.74 \times 10^{-5}\, \mathrm{M}_{\odot }\text{yr}^{-1}$, filling factor f = 0.1, luminosity $L=5.77 \times 10^5\, \mathrm{L}_{\odot }$ for MN112. The ratio of helium to hydrogen He/H is 0.27 (by the number of atoms) with nitrogen overabundance (XN/X⊙ = 6.8) and an underabundance of carbon (XC/X⊙ < 0.1).