The paper presents and analyzes a summary of magnetometric studies of single white dwarfs (WD) conducted at SAO RAS jointly with a number of other observatories. The goals of the studies are to search for regular large-scale magnetic fields in these stars and to construct a probability distribution of WD occurrence depending on the strength of these fields. Based on the analysis, the WDs were determined whose magnetospheres do not change their configurations for a long time, from several tens to hundreds of years at least, and possibly more. These stars can be used as standards of circular polarization. Using data from modern surveys and SAO RAS observations, versions of the observed probability distributions of WDs by their surface magnetic fields in the range of 10^3-10^9 G were constructed. The distribution of WDs with fields from 10^6 G to 10^9 G is well described by a power-law dependence. In the region of smaller fields the dependence is violated, demonstrating a selection ‘‘dip’’. The selection is caused by the technical complexity of magnetometric studies of WDs. The paper also discusses the physical nature of the selection associated with the complication of the interaction of global magnetic fields of low intensity (less than 10 kG) with dynamic processes in the surface layers of WDs. In particular, convection is capable of destroying the global symmetry of the surface magnetic field with an intensity of several kilogauss. Based on the analysis of the obtained distributions, it is concluded that all WDs with surface fields above several tens of kilogauss are carriers of regular global fields damped on times of 10^10 years. Magnetic fields with intensities of several kilogauss and lower lose their global structure, fragmenting into spots, which complicates and even makes impossible their detection by standard spectropolarimetric methods. Confirming examples and recommendations for improving the methodology of magnetometric observations of degenerate stars with weak magnetic fields are given.

The light curves for almost 50 thousand stars with magnitudes m∈[11m.5,19m.5] have been obtained over 2.5 years at SAO RAS in the process of conducting an exoplanet survey in roughly 1∘.5 -sized fields around the white dwarfs WD 0009 + 501 and GRW + 708247. In this paper we present a catalog of variable stars that have been found in the considered regions. Periodogram analysis was used as the main variation search method. The catalog includes 150 periodic variable stars: 113 of them have been known previously, and for the remaining 37 variations have been discovered for the first time. These stars were classified according to the nature of the variations into four eclipsing variable and three pulsating types, as well as rotating stars. We present the periods and variation amplitudes in the range of P∈[0d.036,32d.14] and Δ m∈[0m.0064,1m.45] , determined from the investigated data.

We report eight new exoplanet candidates discovered at the SpecialAstrophysical Observatory of the Russian Academy of Sciences usingthe transit technique. Photometric observations were performedwith a 50-cm robotic telescope during the second half of 2020.Transits with depths of $$\Delta m=0\overset{\textrm{m}}{.}056{-}0\overset{\textrm{m}}{.}173$$ andperiods $$P=18\overset{\textrm{h}}{.}8{-}8\overset{\textrm{d}}{.}3$$ weredetected in $$m=14\overset{\textrm{m}}{.}3$$ – $$18\overset{\textrm{m}}{.}8$$ stars. All the stars considered are dwarfs with radii $$R_{*}=0.4{-}0.6R_{\odot}$$ (with an uncertainty of up to $$1.1 R_{\odot}$$ for a single star). We use simulations to estimatethe candidate radii (all are greater than 1.4 times the Jovianradius), semi-major axes of their orbits (0.012–0.035 AU), andother orbital parameters. We report the transit light curves fortwo stars obtained in 2022 based on individual observations.

Abstract—This study continues the investigation of the super-fast variability of line profiles in the spectra of stars of early spectral classes performed in 2017 and 2018. We investigated the variability of line profiles in the spectra of OBA stars with the SCORPIO multi-mode focal reducer at the 6-m SAO RAS telescope (BTA). Short-period regular variations of the H and He lines were detected in the spectra of the chemically peculiar A0Vp star α2 CVn with periods ranging from approximately 30 to 135 minutes. Using the windowed Fourier transform let us detect the transient quasi-regular variations in the Balmer-line profiles with periods of 3–6 minutes. We discuss a possible origin of fast spectral variations.

Ultraluminous X-ray sources (ULXs) that are located in external galaxies exhibit X-ray luminosities exceeding those of the brightest black holes in the Milky Way and the Local Group galaxies by hundreds or even thousands of times. New classes of objects have been discovered: ultraluminous X-ray pulsars (ULXPs) and high-velocity outflows whose X-ray-range speed is up to 0.2 c . The ULXs and ULXPs fully correspond to concepts of super-Eddington accretion. Five ULXs exhibit quasiperiodic oscillations and a flat-topped noise in the X-ray range power spectrum. Optical spectra of ULXs are very similar to those of SS433, late nitrogen stars (WNL/WR), or LBV (luminous blue variable) stars. The results obtained suggest that ULXs are systems that contain supercritical accretion disks.

We study the optical counterparts of ultraluminous X-ray sources (ULXs) NGC 4559 X-10 and NGC 4395 ULX-1. Their absolute magnitudes, after taking reddening into account, are MV ≈ −5.3 and MV ≈ −6.2, respectively. The spectral energy distribution (SED) of the NGC 4559 X-10 counterpart is well fitted by a spectrum of an A-type star, whereas NGC 4395 ULX-1 has a blue power-law spectrum. Optical spectroscopy of NGC 4395 ULX-1 has shown a broad He ii λ4686 emission, which puts this object in line with all of the other spectrally studied ULXs. Analyzing the absolute magnitudes of 16 well-studied ULX counterparts, we find that the intrinsically fainter counterparts with MV ≳ −5.5 have, on average, blackbody-like or power-law SEDs. In other ULX counterparts with MV ≲ −5.5, we may observe a power-law-like SED; the only one donor is in NGC 7793 P13 (the ULX-pulsar). One may suggest that as the original accretion rate decreases (but nevertheless remains supercritical), the optical luminosity of the wind becomes lower and the donor star might dominate. Using the Swift archival X-ray data for NGC 4395 ULX-1, we have found a period of 62.8 ± 2.3 days. The X-ray phase curve of the source is very similar to the precession curve of SS 433.

We model the evolution of massive magnetic stars in the Galaxy using our own population synthesis code. A comparison of our model magnetic field distribution with that obtained from an analysis of measurements of magnetic fields shows that both model and real distributions can be approximated by a log-normal law with a mean log(B) = 2.5. Based on this comparison we conclude that the magnetic flux variations of OBA stars on the main sequence (MS) are very slow. The shape of the magnetic field distribution for 0, B and A stars appeared to be similar. This means that the mechanisms of the generation of their magnetic field are probably identical.

This study continues our investigation of the super-fast variability of line profiles in the spectra of early-type stars. We have investigated the line-profile variability in spectra of OBA-stars with the SCORPIO multi-mode focal reducer mounted at the 6-m SAO RAS telescope. Regular short-period variations of the H and He lines in the spectra of the B1I star ρ Leo were detected with periods ranging from 2 to 90 minutes, as well as irregular line-profile variations on time intervals less than 1 minute. A possible origin of rapid spectral variations is discussed.

An ongoing SAO RAS program for the 6-m telescope to search for and study luminous blue variable (LBV) candidates in the M31 and M33 galaxies was started in 1997. This paper summarizes the results of our observations over the last 20 years. Over this time, we have a general lists of candidates and obtained photometry and spectroscopy for approximately one hundred stars from the list. A detailed study and classification of LBV candidates were carried out.We alsomonitored spectrally and photometrically the confirmed LBV stars in these galaxies. Based on these results, the spectral energy distributions (SEDs) of LBVs and LBV candidates were computed, and the interstellar extinction values, temperature, and luminosity were derived. We propose a new method of confirming the nature of LBV stars. It is based on a special property exhibited only by LBV stars—the constancy of the bolometric luminosity, with except of a rare phase of giant eruption, registered for two historical LBVs in our galaxy and about few dozen extragalactic LBVs. Using this method, we determine the fundamental parameters of these stars: temperature, radius, luminosity, and interstellar extinction. We discuss the nature of several individual LBV stars discovered by us in M33 and the classification of the LBV candidates in M31. Thus, for 20 years of observations we have found four LBV stars in M33; in the M31 galaxy with different methods, we have confirmed seven objects as a LBV class.

We present a code for the optimal extraction of long-slit 2D spectra in crowded stellar fields. Its main advantage and difference from the existing spectrum extraction codes is the presence of a graphical user interface (GUI) and a convenient visualization system of data and extraction parameters. On the whole, the package is designed to study stars in crowded fields of nearby galaxies and star clusters in galaxies. Apart from the spectrum extraction for several stars which are closely located or superimposed, it allows the spectra of objects to be extracted with subtraction of superimposed nebulae of different shapes and different degrees of ionization. The package can also be used to study single stars in the case of a strong background. In the current version, the optimal extraction of 2D spectra with an aperture and the Gaussian function as PSF (point spread function) is proposed. In the future, the package will be supplemented with the possibility to build a PSF based on a Moffat function. We present the details of GUI, illustrate main features of the package, and show results of extraction of the several interesting spectra of objects from different telescopes.