The results of a photometric analysis of edge-on spiral galaxies in three blue fields of the Hubble Space Telescope (HDF-N, FDF-S, HUDF) are discussed. It is shown that galaxies at z ≈ 0.5 have lower values of the radial exponential scales hr of the stellar disks compared to nearby galaxies. The observed variation in the scales of the disks is consistent with a n hr ∝ (1 + z)–n law, where n ≈ 1. Indications

Studies of the magnetic fields of Herbig Ae/Be (HAeBe) stars can aid in understanding how the magnetic fields of AB stars of intermediate mass are created and evolve. It has been shown that the magnetic fields and magnetic fluxes of HAeBe stars before they emerge on the main sequence are significantly lower than for their successors, main sequence AB stars. In order to explain this mystery, the effect

We present the first photometric observations and light curve modelling of the discovered systems GSC 01870-00458 and USNO-A2.0-0975 04721840. Our modelling was carried out using a recent Windows interface version of Wilson and Devinney code based on model atmospheres provided by Kurucz. The accepted models revealed absolute and physical parameters that can be used to study the evolutionary states

The results of detailed studies of the galaxy with star-formation activity SBS 1539+597 based on panoramic spectroscopy are presented. This work was done as part of our project for the comprehensive study of ~500 galaxies in seven selected fields of the Second Byurakan Survey (SBS). The observations of SBS 1539+597 were made on the 6-m telescope at the Special Astrophysical Observatory of the Russian

Using known values of rotational and centrifugal distortion constants in conjunction with electric dipole moment of NH2CHO, we have calculated energies of rotational levels in the ground vibrational state, and the probabilities for radiative transitions between the levels. The radiative transition probabilities in conjunction with the scaled values of collisional rate coefficients are used in the Sobolev

The orbits of visual binary systems still attract the interest of many working groups in astronomy. These orbits are the most important and reliable sources of stellar masses. In the present paper, we computed the orbits and dynamical masses of some visual binaries using an independent code. We used the Kowalsky method to compute the geometrical elements, while the dynamical elements (the orbital period

This is a study of drift waves in the electron-positron plasma of the magnetosphere of a pulsar. It is shown that the nonlinear interaction of the drift waves with the plasma particles leads to the formation of small-scale structures. The cyclotron instability which develops in these structures may be the reason for the formation of the nano-outbursts discovered in the radio emission of a pulsar in

Cyanamide (NH2CN) has pyramidal equilibrium structure with two substates, denoted by 0+ and 0–. For each state of NH2CN, knowing rotational and centrifugal distortion constants in conjunction with electric dipole moment, energies for rotational levels and the probabilities for radiative transitions between the levels are calculated. The radiative transition probabilities in conjunction with scaled

In this study we continue spectral class determinations for large numbers of optically faint periodic variables taken from the Catalina Surveys Data Release 1 (CSDR1) and LINEAR data sets. Spectral classes and physical parameters are presented for 1184 periodic variables with periods P ≥ 10 days, taken from modern large sky area spectroscopic and photometric databases, including LAMOST (Large Sky Area

Non-singular Kruskal-like coordinates of some black holes space-times in f (R) gravity are presented in this research paper, and are also removed by establishing Kruskal-Szekeres coordinates for Non-extremal case. Carter-like coordinates can also be built for its extreme case.

The emission spectrum of dust undergoing substantial temperature fluctuations behind strong shocks (>100 km/s) is modeled. The model includes calculating the temperature distribution function of the dust particles owing to stochastic heating by electrons in the ambient plasma, as well as the features of the resulting spectral distribution of the emission from the dust. As the surrounding plasma cools

In this paper, we have studied Friedmann-Robertson-Walker space-time in the presence of domain walls in the framework of f(G) theory of gravitation. We propose the generalization of linearly varying deceleration parameter. It is observed that the universe is accelerating and expanding. The values of state finder parameters are close to ΛCDM model. Some physical parameters of the obtained models are

Solar activity of an explosive character during the 23rd and 24th cycles is analyzed. X-ray observations from the GOES-15 satellite during flares and observations during coronal mass ejections (CME) with the SOHO/LASCO coronagraph are used. The delay intervals between the onset of a flare and the onset of a Halo-type CME associated the same active region were analyzed. It is shown that the time interval

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