Results from a study of low resolution spectra and kinematics of the star V1117 Her located at a high galactic latitude b = +33°.8 are presented. It is shown that this star has A7 IV photospheric class, luminosity L ≈ 26 Lʘ, and spectral signs of accretion activity. This confirms its previous classification as a young Ae Herbig star with photometric UX Ori type variability. In addition, the parallax

An exact explicit barometric formula is derived for an ultrarelativistic degenerate Fermi-gas governed by the Chandrasekhar equation of state.

New observational data on the last two outbursts of the EXor star V1118 Ori are presented. The combined light curve of the last outburst is derived and fitted. The dates of the start of the outburst, its maximum, and end, as well as the maximum magnitude, and the rates of increase and decrease of the brightness were determined.

The mass spectra of astronomical objects of various kinds are compared: cosmic dust, asteroids, planets, stars, star clusters, galaxies, and galactic clusters. The authors have previously noted a similarity in the (initial) mass functions for relatively massive objects (stars, galaxies, galactic clusters). In this paper the range of masses of astronomical objects is extended to the limit and covers

The equations of motion for the parametrized post-Newtonian (PPN) formalism for several S-stars close to the relativistic compact object Sgr A* at the center of the galaxy are examined. The effect of the difference in the periods of Newtonian and post-Newtonian orbits is taken into account. The period of the best approximation to the PN-orbit of the star S2 exceeds the period of the Newtonian orbit

Results from spectral observations of known emission stars in the vicinity of Cyg OB7 are presented. 64 spectra of 9 emission stars were obtained over the period 2001-2007. The equivalent widths of the most characteristic lines for T-Tau stars were obtained in all these spectra. It is noted that all the spectral lines manifest strong variations. The spectra of these stars are in the spectral range

Published data indicate a substantial increase in the differential rotation parameter ∆Ω of stars hotter than 6700 K. By analyzing the shape of the light curves and the presence of a specific set of peaks in their power spectra, we have found that 47 of 57 objects with Teff greater than 7500 K that were studied can be identified as pulsating stars and only 10, as stars with brightness variation owing

This paper is the second part of the author’s previous work. Its purpose is to illustrate the efficiency of using the previously introduced auxiliary functions known as linear images (LI) of the reflection-transmission function with simple examples of nonlinear problems for a one-dimensional purely scattering medium. First, an explicit analytic solution is obtained for the nonlinear “direct” problem

This is a theoretical study of changes in several characteristics of the spectra of early-type supergiants owing to scattering of continuum radiation. Thomson scattering on free electrons is treated as the scattering mechanism, although the approach used here is quite general. The reason for changes in the spectral class of a star with constant bolometric luminosity and surface temperature is elucidated

We report the results of broadband observations of distant blazar PKS 0537-286 (z = 3.1) using data spanning more than ten years from the Fermi Large Area Telescope together with Swift UVOT/XRT archival data taken between 2005 and 2017. In the γ -ray band, the peak flux above 100 MeV, Fγ = (6 23 ± 0 56) ∙ 10-7 photon cm-2 s-1 observed on MJD 57874 within one week, corresponds to Lγ = 2 46 ∙ 1049 erg

Results are presented from a study of the binary star ADS 7251 (STF 1321) based on a uniform series of observations on the 65-cm refractor at Pulkovo from 1962 through 2018. The errors in the yearly average positions ρ and θ are equal to 0′′.004 and 0°.02 for the photographic and 0.”003 and 0.°01 for the CCD observations. A new orbit is calculated from the found relative position and the exact parallax

Photometric studies of the SU UMa-type dwarf nova IRXS J161659.5+620014 have been made on the 2.6-m and 1.25-m telescopes at the Crimean Astrophysical Observatory during 2017 and 2018 in the quiescent state of the system, during normal outbursts, and during superoutbursts. It is found that the interval between adjacent normal outbursts was about 11 days during 2017. Observations in the quiescent state

We explore the distribution of position angles (PA) of galaxies in clusters. We selected for study the isolated clusters, since the distribution of the galaxy orientation in clusters with close neighbors could be altered by the gravitational influence of the latter. We assume that galaxies are aligned, if their number at one 90º position angle interval is more than twice higher than at the other 90º

Numerous indications that the magnetic field structures in magnetic stars do not change with age are cited. The stars rotate like a solid.

This is a study of spectral and photometric observations of the binary system with an X-ray component V725 Tauri=A0535+262. It consists of a giant star HDE 245770 of spectral class O9.7 and the pulsar A0535+26 with a pulsation period of ~103 s. Active stages of this object, accompanied by “giant” X-ray outbursts, have been observed repeatedly. The last events occurred during 2009-2011. Our studies

We present the results of X-ray spectral analysis of the Seyfert type 2 galaxy Mrk 417 ( ɀ ≈ 0.0327 ) based on data from the NuSTAR (3-60 keV) and Swift/BAT (14-150 keV) space observatories. The spectrum from the NuSTAR observatory is well described by a basic power-law model with neutral absorption and an additional reflection component from a cold neutral medium (power-law index \( \Gamma ={1.63}_{-0

This is a detailed spectral classification of 96 active galaxies from the Véron-Cetty and Véron catalog (2010, Version 13, VCV-13) of active galaxies and quasars. These objects were identified as radio sources using standard radio catalogs. Those galaxies which had radio sources in at least 6 different radio bands and had been identified spectrally in the SDSS catalog were selected. The types of activity

B3 1343 + 451 is a distant ( z = 2.534 ) and bright flat-spectrum radio quasar observed in the γ -ray band. The results from the multiwavelength observations of B3 1343 + 451 with Fermi-LAT and Swift are reported. In the γ -ray band, strong flares were observed on 05 December 2011 and on 13 December 2009 when the flux increased up to (8.78 ± 0.83)·10-7 photon cm-2 s-1. The hardest photon index Γ =

The results of observations at high temporal resolution (∆T~4 min) of the B0.5V star ε Per A on the 2-m telescope of the Terskol Observatory are reported. Regular components of variations in line profiles with periods 1.5-18 hours are recorded. Evidence of irregular variations in line profiles on time scales of minutes is detected. The nature of these variations is discussed.

The feasibility of detecting candidate slow-rotating magnetic Ap stars with periods from a few tens of days to several hundred years is considered. The question of the fraction of objects of this kind among all Ap stars is important from the standpoint of understanding the origin and evolution of magnetic stars. The search for such objects can be based on analysis of their photometric variability using

The physical conditions in the chromosphere of polar and equatorial coronal holes in the decay phase of the 24-th solar activity cycle are studied. Models of the chromosphere are constructed based on the intensities of the HeI 10830 Å and Hα lines and using a non-LTE program. The calculations showed that the temperature in equatorial coronal holes is similar to that of polar coronal holes. The temperature

The relationship between the magnetic fluxes and areas of coronal holes (CH) at mid and low latitudes |φ |< 60° and the mean magnetic field (MMF) of the sun over the period from January 19 through December 12, 2012, is studied using ultraviolet images and magnetograms obtained with the Solar Dynamics Observatory satellite. It is shown that the boundaries of the CH determined with the algorithms CHIMERA

Long-term automatic tracking of coronal bright points has made it possible to study their proper motions using data from the AIA 193 Å channel of SDO/AIA. Fits files for 95 visually long-lived bright points uniformly distributed in latitude have been chosen for processing. A specially developed program automatically fixes the heliographic coordinates of the centroid of the chosen coronal bright points

Electric currents flow in active regions of the sun. Information on the distribution of the currents is important for understanding energy release processes on the sun’s surface and in overlying layers. This is an analysis of the probability density function (PDF) of the absolute value of the density of photospheric vertical electric currents | jz | in 48 active regions from 2010 through 2015 at times

The hypothesis of two phases of charged particle acceleration in solar flares is well known, with subrelativistic electrons accelerated in the first phase and relativistic electrons and protons in the second. Both phases are distinguished in the solar proton events and their parent flares of December 26, 2001 (M7.1), November 2, 2003 (X8.3), and August 9, 2011 (X6.9), while in the interplanetary space

It is argued that, not only the blue (at the brightness maximum) but also the red (in the slow decay phase) components of the optical continuum of powerful flares on dMe stars are formed near the photosphere. The possible appearance of HeI lines in the relaxation zones for the plasma to a state of thermal equilibrium (as a result of a rise in electron temperature owing to elastic collisions of electrons

Data on solar hydrogen filaments obtained at the Abastumani Astrophysical Observatory during solar activity cycles 19-22 are used to study the characteristic periods of the solar differential rotation. In addition to the known 11-year period of solar activity, a quasi-biennial periodicity was revealed for the rotation rates of hydrogen filaments and a quasi-five-year periodicity was also found for

In the present paper, we are developing an analytical method for solving the time-dependent Kompaneets equation in its generalized form. The technique is generalizing the Dubinov and Kitayev method. In the particular case of a low photon number density, for the corresponding linear equation, the solutions are expressed in terms of Heun functions.

The fractal dimensions of cosmic microwave background (CMB) maps and other sources obtained by the “Planck” mission are investigated. It is shown that the choice of source distribution models used in data processing can significantly affect the fractal dimension of CMB.

A theoretical model of a cold and dense isolated solar prominence is presented. The thermodynamic parameters of a filament (gas pressure, density and temperature) are calculated from a specified magnetic field structure. The filament lies above the photospheric polarization separation line and its magnetic field falls off rapidly with distance from the axis, so that the total electric current along

Data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) on the components of the magnetic field vector in the photosphere for 39 active regions (AR) of the 24th solar activity cycle are used to calculate the parameters of the electric current. The time variations in the electric current parameters in the AR over the time the region is within ±35° of the central

We present deep CCD photometry (V ~ 21 mag) in BVR Johnson-Cousin filters supported with 2MASS JHKs data set for the open star cluster NGC 7790. The cluster’s parameters such as reddening, distance, metallicity and age etc… are derived using two color diagrams in optical and near-infrared bands. These parameters are EB-V = 0.512 ± 0.006, EV-R = 0.382 ± 0.005, EJ-H = 0.337 ± 0.001 and EJ-Ks = 0.505

In the present paper we use a complete set of CCD observations to model the light curves of the new W UMa systems, GSC 4835-1716 and USNO-A2.0_1275-10813091. The light curve modeling is performed by means of the W-D code where Kurucz (1993) model atmospheres are implemented. We treated the asymmetry of the observed curves using a spotted model. Physical parameters of the accepted model revealed that

This paper is a study of the spatial dynamics of microwave emission (data from the Nobeyama Radioheliograph) from two active regions NOAA 12673 and NOAA 11261 for several hours prior to powerful class M x-ray flares. The spatial distribution of the radio brightness and emission intensity in certain parts of the active region is found to be highly nonstationary. Data in the ultraviolet (AIA/SDO) are

Estimates of the integrated (SFR) and specific (sSFR) rates of star formation are given for 181 galaxies of later Sc, Scd, and Sd types seen almost face-on. Their SFRs were determined from FUV fluxes in the GALEX survey. The median values of the sSFR are: -10.66 dex for Sc, -10.44 dex for Scd, and -10.40 dex for Sd types in units of yr-1. The average value of the sSFR for these galaxies falls off smoothly

An analysis is presented of photometric observations of the intermediate polar DO Dra obtained during an epoch of significant reduction in its outburst activity for different average brightnesses of the system: 13m.6-12m.8 (2008) and 14m.7-14m.3 (2019). The observations in 2008 were made in the Johnson BVR system and in 2019, in integrated light. For the first time in quasi-simultaneous observations

This is a detailed spectral classification of 198 candidate active galactic nuclei (AGN) from a joint HRC/BHRC sample consisting of a combination of the HRC (Hamburg-ROSAT) and BHRC (Byurakan-ROSAT) catalogs. These objects have been identified as optical counterparts of ROSAT x-ray sources, but spectra for 198 of them are given in the SDSS without determinations of their spectral classification. They

This is a photometric study of the dwarf nova MN Dra made during 2012-2017 on nine telescopes over 152 nights. Overall, the observations covered 4 superoutbursts, 7 normal outbursts and the quiescent state. The interval between neighboring superoutbursts in 2017 was 65 days, and between neighboring normal bursts, 15 days. During the superoutbursts of 2012 and 2017, positive superhumps with a period

RY Sct is a unique massive binary star system in a short transitional evolutionary phase. It is an eclipsing binary where both stars have overfilled their Roche cavities, so that the system is in an “overcontact” state. It is surrounded by a young circumstellar nebula. The binary is regarded as a rare progenitor of a type WR+OB system. RY Sct is close to the Eddington luminosity limit, so that radiative

Here, we aim to determine the kinematical properties, velocity ellipsoid and Oort constants using a sample of halo red giants. The study is based mainly on the space and radial velocities of 1583 red giant stars collected from the SEGUE-1 and SEGUE-2 surveys. We divided the sample into three subsamples: the inner halo, the outer halo and the stars near the galactic plane. The fitting of the radial

In this paper, two efficient computational algorithms based on Rational and Exponential Bessel (RB and EB) functions are compared to solve several well-known classes of nonlinear Lane-Emden type models. The problems, which are define in some models of non-Newtonian fluid mechanics and mathematical physics, are nonlinear ordinary differential equations of second-order over the semi-infinite interval

The MIT quark bag model is used to determine the thermodynamic characteristics of hot strange quark matter that is opaque to neutrinos. Three different variants of the lepton content of hot quark matter are considered. The numerical calculations are done for different temperatures and lepton charge densities. It is shown that in hot (kT~100 MeV) quark matter there are roughly as many neutrinos as massive

Four active regions (AR) of the sun are studied. Observational data were obtained from directly visible (line of sight) sharp_cea_720s SDO/HMI magnetograms. The data for each AR were processed by a least squares method in an ellipse. Using a sequence of images after processing the data in all the AR, oscillations of the major and minor axes of the ellipse, as well as of the angles of inclination of

The current 24th solar activity cycle differs substantially from previous cycles in a number of parameters, especially in terms of a large asymmetry in the number of sunspots (Sp) during the second peak of its maximum. From March 2013 through December 2015. a significant predominance was observed in the number of sunspots in the southern hemisphere. The main purpose of this paper is to clarify the

In connection with a published critique, the author justifies the use of a motionless homogeneous plane layer of pure hydrogen plasma that is near local thermodynamic equilibrium (LTE) for analyzing the characteristics of the radiation from a chromospheric condensation of thickness ∆z=10 km in a gas dynamic model of stellar flares. It is shown that the shock-wave model of flares proposed by Belova

The computer program magreg in IDL language has been developed for determining the longitudinal component Bz of the magnetic field of stars. The program has been tested on observations of a number of objects at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAN) using the main stellar spectrograph of the 6-m telescope. The well studied magnetic star γ Equ is used as an

In the present paper, we obtained the first orbital solution for the newly discovered W UMa systems: GSC 3983-0544 and GSC 4502-1040. We used the most recent version of the Wilson-Devinney code to model the light curves of the two systems. The spectral type of the components of the two systems was adopted and the accepted solutions revealed some absolute parameters, which enable us to draw a preliminary

Published data on the observed properties of the filaments (chains of galaxies and groups of galaxies) which dominate the large-scale structure of the universe are collected. Some of these properties are not described in the standard ΛCDM cosmological model. It is found that the properties of galaxies depend on their position inside or near a filament. The hypothesis is advanced that in the early Universe

Data from the SDSS survey are used to study two galaxies with X-structures (UGC 501 and UGC 12253) visible from the edge. Both objects are spiral galaxies of late morphological types with extended stellar disks. The X-structures in the galaxies have different sizes and shapes. The possibility that the different observational parameters of the X-structures in UGC 501 and UGC 12253 are related to different

The extragalactic radio source OJ 287 is one of the most studied blazars. A huge amount of data has been accumulated on it (for more than 40 years in the radio range and more than 100 in the optical). Studies of the rapid variability in the radio flux and stellar magnitude of this object with characteristic times ranging from a few hours to several days are of interest in connection with the possible

Details of investigation of SBS0750+603B by providing 3D-spectroscopy are presented as part of a study of a sample of about 350 galaxies of star-formation activity. The observations were made on the 6-m telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences using the MPFS multi-pupil spectrograph. An analysis of the surface distributions of the major parameters

We carried out a survey of low-surface-brightness companions around nine luminous Local Volume galaxies using long exposures with small amateur telescopes. We found 12 low- and very low-surfacebrightness objects around the galaxies, NGC 628, NGC 2337, NGC 3368, NGC 3521, NGC 4236, NGC 4258, NGC 4594, NGC 5055, and NGC 6744, situated within 12 Mpc from us. Assuming the dwarf candidates are satellites

We counted galaxies in the area with 10 Mpc radius around 30 isolated ACO clusters at redshifts z < 0.1. We show that surface densities of galaxies around clusters regularly decrease till 10 Mpc. Separate counts of blue and red galaxies of the cluster environment revealed that at all cluster-centric distances the surface density of red galaxies are higher than that of blue ones. The surface density

Data from the second Gaia release (Gaia DR2) are used to analyze and evaluate several important parameters for 127 carbon (C) stars of which 56 are AGB stars of class N and 71 are giants of early CH classes detected in low-dispersion spectral plates from the First Byurakan Survey (FBS). For the FBS C-stars Gaia DR2 G broad – band magnitudes are in the range 9m.4 < G < 18m.2. The radial velocities RV

The triggering process for coronal mass ejections (CME) in the solar atmosphere is not fully understood. We use observations from different spacecraft at several wavelengths to detect an instability process for a prominence/filament with subsequent eruption of CME. Time series of spectral lines at 304, 171, 193, and 211 Å have been obtained with the SDO spacecraft, and at 304, 171, 195, and 284 Å with

Bright IR galaxies (LIRG, ULIRG, and HLIRG) are important for research on star formation processes in the early universe since they can be detected at large distances owing to their luminosity. High IR is indicative of active star formation and starburst (SB) processes, which are typical of HII regions. In many cases high IR is indicative of an active galactic nucleus (AGN). This raises the question

Based on published parameters of their atmospheres, the masses of 100 RR Lyrae variables (lyrids) in the field are determined using evolutionary tracks from the Dartmouth data base and the properties of lyrids with different metallicities are compared. It was found that the masses of the metal-rich ([Fe/H] > –0.5) lyrids with thin-disk kinematics lie within an interval of (0.51-0.60) M ʘ . According

The observed masses (62 stars) and metallicity (38 stars) of ejected envelopes in novae with CO and ONeMg white dwarfs are studied. The observed masses and metallicities are compared with the theoretical dependence of the mass and metallicity of an envelope on the parameter t3, which characterizes the rate of brightness decrease. The observed masses and metallicities did not have a dependence on t3

The magnetic field structures of stars with different ages are studied. No changes in the position and orientation of magnetic dipoles with age are observed. It is concluded that there are no global motions, such as differential rotation meridional circulation, etc., inside magnetic stars. Arguments are presented in favor of the assumption that magnetic stars rotate as solids. These conclusions do

Data from the Kepler Orbital Observatory are used in a statistical study of the periodic/cyclical variability of the flare frequency of 76 flare stars. Corresponding periodic functions of the flare frequency are obtained and a possible periodicity of the flare frequency with a period equal to the star’s rotation period is tested. The periodicities of the function of the flare frequency turned out to