The study of fractal structures in the stellar medium of the Galaxy is one of the important problems of stellar dynamics, since it makes it possible to construct a kinetic theory of the stellar medium, which is more consistent with observational data, and to refine the basic equations of stellar dynamics for fractal stellar media. In connection of this it is studied the fractal properties of ∼ 200 000 stars of all spectral types in solar neighborhood at distance of 1 to 100 parsecs from the Sun based on GAIA DR2 data. The main stages in the development of ideas about fractal structures in the stellar medium of galaxies are considered. The analysis of spatial distribution of stars is carried out by the ‘‘mass–radius’’ method. Numerical calculations for selected ∼ 200 000 stars show that mean conditional local star density in spheres with increasing radius ‘‘ r ’’ with center in the i th star is approximated by power laws, that indicates on the presence of fractal structures in stellar medium in solar neighborhood with fractal (Hausdorff) dimension D≈ 2.41 . The data obtained for ∼ 200 000 stars are discussed and compared with previous result, received for ∼ 13 000 stars of F, G-type dwarfs in solar neighborhood based on the data of Geneva–Copenhagen Survey.

Based on the original version of the pulsating photosphere method that allows modeling the changes in the effective temperature, a revision of the physical characteristics of the unique binary Cepheid V350 Sgr was carried out. Previously published measurements of radial velocities were used, as well as new ones obtained by us, which allowed us to refine the parameters of the Cepheid orbit. The choice of the projection factor PF=1.34 allowed us to reconcile our estimates of the cycle-averaged radius ⟨R⟩_I/R_⊙≈ 41.3-41.9 , luminosity M_V≈-3m.52-3m.57 , normal color (B-V)_0≈ 0m.56± 0m.01 , effective temperature ⟨logT_eff⟩_I≈ 3.788± 0.002 , distance D≈ 992± 14 pc and color excess E(B-V)≈ 0m.35± 0m.01 with MESA theoretical evolutionary tracks for the mass 5.1M_⊙ and metallicity [Fe/H]=-0.18 dex (or mass 5.2M_⊙ , [Fe/H]≈-0.10 dex) and the PARSEC 2.0 track for the mass 5.2M_⊙ , Z≈ 0.01 . The evolutionary age of the Cepheid, which is in the phase of the third crossing of the instability strip, is estimated at 100 Myr. It is shown that the Gaia eDR3/DR3 catalogues provide a distance overestimated by approximately 25 i≈ 53^∘± 3^∘ and the orbital semi-major axes a_1≈ 1.63± 0.05 AU, a_2≈ 3.42± 0.09 AU were determined for the first time, with the relative orbit size of about 5 AU.

In this paper, we analyze the apparent surface density observations of 81 globular clusters provided by Gaia DR2. The problems of analyzing these observations and their differences from similar data obtained using the HST are discussed. Based on the results of this analysis of the quality of observational data and a number of physical considerations, we separate globular clusters into three classes and then consider the issues of modeling the apparent surface density versus distance. The values of the free parameters of the model are found by the symplectic minimization method. The free parameters including the concentration parameter are for the first time found using the 4-parameter generalized model we propose.

In this paper, we study the fractal properties of the stellar medium in the solar vicinity based on the Gaia DR2 data for 200 000 stars of all spectral types at distances from 1 to 100 pc from the Sun. We consider the main stages of the development of ideas about the fractal structure in the stellar medium of galaxies. Analysis of the spatial distribution of stars is performed using by the ‘‘mass–radius’’ method. Numerical calculations show that the mean conditional local stellar density in spheres with the increasing radius r with the center in the i -th star is approximated by power laws, which confirms the de Vaucouleurs–Mandelbrot conclusions for fractal structures in gravitating media and indicates the presence of fractal structures in the stellar medium in the solar neighborhood with the fractal dimension D≃ 2.41 . The characteristics of the fractal properties of the medium, determined from a sample of 200 000 stars, are discussed and compared with an earlier result obtained for 13 000 F and G dwarfs in the solar neighborhood according to the Geneva–Copenhagen survey.

Two new Herbig-Haro flows were found in a study of the isolated Dobashi 5006 dark cloud (l = 216°.7, b = –13°.9): one certain (HH 1179) and one presumable, associated with the infrared sources 2MASS 06082284-0936139 and 2MASS 06081525-0933490, correspondingly. Judging from their spectral energy distributions, these sources may be Class 1 objects with luminosities of order 23 L ⨀ and 3.6 L ⨀ , respectively. They are part of the poor star cluster MWSC 0739, study of which based on data from the Gaia DR3 survey has made it possible to detect 17 stars which are probably members of it. A list of them and their main parameters is given. The distance of the cluster is estimated to be 820 pc and the color excess on the path to the cluster is E(BP - RP) ≈ 1.05 mag. All of these stars are PMS-objects and most of them are optically variable. It is concluded that the newly discovered compact star-formation zone in the Dobashi 5006 cloud has an age of no more than a few million years and this process continues up to the present time.

Based on Gaia DR3 data, a new revision of the stellar content isperformed within the $$20^{\prime}$$ -radius field centered on theyoung open cluster vdB 130, which is a part of the Cyg OB1stellar association. A total of 97 stars and 39 protostars ofluminosity classes I/II/III are identified that have proper-motionbased cluster membership probabilities $$P>0.98$$ . The totalnumber of possible cluster members with membership probabilities $$P>0.50$$ is equal to about 300, and the cluster age estimated byfitting theoretical isochrones does not exceed 10 Myr. Thetrigonometric-parallax based cluster distance is $$D\approx 1670\pm 60$$  pc, and the cluster color excess, $$E(BP-RP)\approx 0\overset{\textrm{m}}{.}85\pm 0\overset{\textrm{m}}{.}02$$ withevidence for strong differential extinction.

We present observations of the vdB 130 cluster vicinity in a narrow-band filter centered at a 2.12 μm molecular hydrogen line performed at the Caucasus Mountain Observatory of the Lomonosov Moscow State University. The observations reveal an H _2 emission shell around vdB 130, coincident with a bright infrared shell, visible in all Spitzer bands. Also, numerous H _2 emission features are detected around infrared Blobs E and W and in the vicinity of a protocluster located to the east of the shell, in a tail of a cometary molecular cloud. H _2 emission in the vicinity of the vdB 130 cluster is mostly generated in well-developed H II regions and is of fluorescent nature. In the protocluster area, isolated spots are observed, where H _2 emission is collisionally excited and is probably related to shocks in protostellar outflows. Obtained results are discussed in the context of possible sequential star formation in the vicinity of the vdB 130 cluster, triggered by the interaction of the expanding supershell surrounding the Cyg OB1 association with the molecular cloud and an associated molecular filament.

We propose a new version of the (Baade–Becker–Wesselink) pulsating photospheres method based on direct spectral measurements of the effective temperatures of Cepheids carried out in different pulsation phases. By comparing the effective temperatures calculated using normal color calibrations with real spectroscopic estimates, we were able to not only determine the color excess with an accuracy of the order of $$0\mathop .\limits^{\text{m}} 01$$ mag, but also use all the measured effective temperature values to derive a new color calibration for the effective temperature of high luminosity stars, also taking into account the differences in metallicity $${\text{[Fe/H}}]$$ and surface gravity $$\log {\kern 1pt} g$$ : log Teff = 3.88 – 0.20(B – V)0 + 0.026(B –V) $$_{0}^{2}$$ + 0.009log g – 0.010(B – V)0log g – 0.051[Fe/H] + 0.051(B – V)0[Fe/H], the relative accuracy of which is approximately $$1.1\% $$ . In addition, the complete identity of the two main versions of the Baade–Becker–Wesselink method was proved: the surface brightness method (SB), first proposed by Barnes and Evans in 1976, and the maximum likelihood method (or light-curve modeling method) proposed by Balona in 1977 and later improved by Rastorguev and Dambis in 2010. This approach consists of using significantly nonlinear color calibrations for $$\log {{T}_{{{\text{eff}}}}}$$ and bolometric correction $$BC$$ and is easily applicable to the surface brightness method. This method is also applicable in studies of other types of pulsating variable stars, e.g., RR Lyrae, Mirae and $$\delta $$ Sct type variables with known effective temperature estimates.

Using the widely known simplex method of minimizing the square of the difference between the observed and theoreticaldensities, we have found the corresponding free parameters for globular clusters. As observational data we have taken mostlythe density profiles constructed by [1] based on a combination of Hubble Space Telescope and ground-based data. One ofthe free parameters of our model characterizes the concentration of stars toward the globular cluster center. Errors for freeparameters of the model are calculated.

To construct the rotation curve of the Galaxy, classical Cepheids with proper motions, parallaxes and line-of-sight velocities from the Gaia DR2 Catalogue are used in large part. Our working sample formed from literature data contains about 800 Cepheids with estimates of their age. We determined that the linear rotation velocity of the Galaxy at the solar distance is V-0 = 240 +/- 3 km s(-1). In this case, the distance from the Sun to the axis of rotation of the Galaxy is found to be R-0 = 8.27 +/- 0.10 kpc. A spectral analysis of radial and residual tangential velocities of Cepheids younger than 120 Myr showed close estimates of the parameters of the spiral density wave obtained from data both at the present time and in the past. Therefore, the value of the wavelength lambda(R, theta) is in the range [2.4-3.0] kpc, the pitch angle i(R, theta) is in the range [-13 degrees, -10 degrees] for a four-arm pattern model, and the amplitudes of the radial and tangential perturbations are f(R) similar to 12 km s(-1) and f(theta) similar to 9 km s(-1), respectively. Velocities of Cepheids older than 120 Myr currently give a wavelength lambda(R, theta) similar to 5 kpc. This value differs significantly from the one we obtained from samples of young Cepheids. An analysis of the positions and velocities of old Cepheids, calculated by integrating their orbits backward in time, made it possible to determine significantly more reliable values of the parameters of the spiral density wave: wavelength lambda(R, theta) = 2.7 kpc and amplitudes of radial and tangential perturbations f(R) = 7.9 km s(-1) and f(theta) = 5 km s(-1), respectively.

In view of the absence of a satisfactory solution to the globular cluster (GC) classification problem, we have searched for a physical parameter that admits of the GC classification and finding empirical dependences on observed physical characteristics. For this purpose, we have considered a model of the apparent density in GCs with three free parameters. Using the widely known simplex method of minimizing the square of the difference between the observed and theoretical densities, we have found the corresponding free parameters for 26 GCs. As observational data we have taken mostly the density profiles constructed by Miocchi et al. (2013) based on a combination of Hubble Space Telescope and ground-based data. One of the free parameters of our model characterizes the concentration of stars toward the GC center. We have found a number of empirical dependences of this parameter on the main physical characteristics of GCs. The derived empirical formulas can be used in determining these characteristics for other GCs via the concentration and vice versa.

ABSTRACT Two star-forming regions are studied: the young embedded open cluster vdB 130 and the protocluster neighbourhood observed in the head and tail of the cometary molecular cloud located in the wall of the expanding supershell surrounding the Cyg OB1 association. The Gaia DR2 catalogue is employed to verify the stellar composition of the vdB 130 cluster whose members were earlier selected using the UCAC4 catalogue. The new sample of vdB 130 members contains 68 stars with close proper motions (within 1 mas yr−1) and close trigonometric parallaxes (ranging from 0.50–0.70 mas). The relative parallax error is shown to increase with distance to objects and depend on their magnitude. At a distance of 1.5–2 kpc it is of about 3–7 per cent and 20–30 per cent for bright and faint stars, respectively. The cluster is not older than ∼10 Myr. New spectroscopic and photometric observations carried out on Russian telescopes are combined with Gaia DR2 to search for optical components in the protocluster region – a new starburst. An analysis of 20 stars in the vicinity of the protocluster revealed no concentration of either proper motions or parallaxes. According to spectroscopic, photometric and trigonometric estimates, the distances to these stars range from 0.4–2.5 kpc, and colour excess is shown to increase with a distance D (kpc) in accordance with the law E(B − V) ≃ 0.6 × D mag.

We studied a small comet-shape reflection nebula, located in the dark cloud SL 4 in the Vela Molecular Ridge cloud C, known as BBWo 192E (GM 1-23), and a young infrared cluster embedded into the nebula, for the evidences of recent star formation. We obtained the images of BBWo 192E in Halpha and [SII] lines and in SDSS i' with Blanco telescope at the Cerro Tololo Interamerican Observatory to discover new Herbig-Haro (HH) flows. 2MASS and WISE surveys were used for the search of the additional member stars of the cluster. We also studied proper motions and parallaxes of the cluster members with the aid of GAIA DR2. Five new groups containing at least 9 HH objects tracing several distinct outflows were revealed. A previously unreported reflection nebula and a number of probable outflow sources were found in the infrared range. The proper motions allowed selecting eight probable member stars in the visual range. Their parallaxes correspond to a mean distance 800 +/- 100 pc for this cluster. The bolometric luminosities of the brightest cluster members are 1010 L(sun) (IRAS 08513-4201,the strong source in the center of the cluster) and 2 to 6 L(sun) for the five other stars. The existence of the optical HH flows around the infrared cluster of YSOs suggests that star formation in this cloud is on-going around the more massive HAeBe star. By its morphology and other features this star-forming region is similar to the zone of star formation near CPM 19.

We present a realization of the maximum-likelihood technique, which is one of the latest modifications of the Baade–Becker–Wesselink method. Our approach is based on nonlinear calibrations of the effective temperature and bolometric correction, which take into account metallicity and surface gravity. It allows one to estimate the key Cepheid parameters, the distance modulus, and the interstellar reddening, combining photometric and spectroscopic data (including the effective temperature data). This method is applied to a sample of 44 Galactic Cepheids for which multiphase temperature measurements are available. The additional data correction is performed to subtract the impact of the component in binary/multiple systems. We also study the effect of shock waves, whose presence in the stellar atmosphere distorts the observational data and leads to systematic errors in the obtained parameters. We determine the optimal restriction on the input data to eliminate this effect. This restriction provides accurate period–radius and period–luminosity relations that are consistent with the results in previous studies. We found the following relations: log R = (0.68 ± 0.03) · log P + (1.14 ± 0.03), Mv = − (2.67 ± 0.16) · (log P − 1) − (4.14 ± 0.05).

Calibration of the period-luminosity relation (PLR) for Cepheids has always been one of the biggest goals of stellar astronomy. Among a considerable number of different approaches, the Baade-Becker-Wesselink (BBW) method stands in the foreground as one of the most universal and precise methods. We present a new realization of the BBW method which is considered to be the generalization of surface brightness (\citealt{Barnes+Evans+1976}) and \cite{Balona+1977} approaches first proposed by \cite{Rastorguev+Dambis+2010} and described in \cite{Paper1}. One of the main features of this method is using measured effective temperature variations to determine the main parameters of Cepheid, such as distance, radius, luminosity, colour excess, intrinsic colour. We apply this method to 45 Cepheids of Northern sky, for which multiphase temperature data are available. We take into account the effect of shock waves, whose presence in stellar atmosphere distorts the observational data and the calibrations used in this work. Within $0.0-0.87$ phase interval we derived PL relation $ _I=-(2.67 \pm 0.17)\cdot logP - (1.58 \pm 0.16)$. It was used to calculate the distances, rotation curve and kinematical parameters of the sample of 435 Cepheids with GAIA DR2 proper motions.

A new version of the Baade--Becker--Wesselink (hereafter BBW) method is proposed, based on direct spectroscopic measurements of effective temperatures of 45 northern Cepheids, made in different pulsating phases. By comparing the temperature estimates obtained from the calibration of effective temperature by normal color with real temperature measurements we were able not only to determine the color excess with an accuracy of 0.01 mag, but also to derive new color calibration of the effective temperature immediately for all available measurements with taking into account the differences in [Fe/H] and log g values: log Teff = 3.88 - 0.20 (B-V)o + 0.026 (B-V)o^2 + 0.009 log g - 0.010 (B-V)o log g - 0.051 [Fe/H] + 0.051 (B-V)o [Fe/H], which is accurate to about 1.1%. We also showed the complete identity of the two main versions of the BBW technique: surface brightness method proposed by Barnes and Evans (1976) and maximum likelyhood method of Balona (1977), refined later by Rastorguev and Dambis (2010).

V CVn is a red semiregular variable star with an amplitude of its V -band brightness variations of ≈2 m . An unusually high amplitude of its polarization variability, up to 6%, a noticeable inverse correlation between polarization and total flux, and relative constancy of the angle of polarization distinguish this star from other semiregular variables. To clarify the nature of these peculiarities, we have observed the object with the 2.5-m telescope at the Caucasian Observatory of the Sternberg Astronomical Institute of the Moscow State University using differential speckle polarimetry at wavelengths of 550, 625, and 880 nm. The observations were performed on 20 dates distributed over three pulsation periods. We have detected an asymmetric reflection nebula around the star at a distance of ≈35 mas. Three regions that change their brightness with the same characteristic time scale as the star, but with different phase shifts are identified in the nebula. We consider several hypotheses that could explain this behavior.

We present an analytical review of the current state of the problems of stellar astronomy. We report the results obtained by Russian astronomers by 2017.We show that the studies conducted in Russia cover all major fields of stellar astronomy, use modern observational methods and data analysis techniques, and meet high scientific standards.