Photometric observations of Cepheids from the ASAS-3 catalog: Photoelectric <Emphasis Type="Italic">BV I</Emphasis><Subscript>c</Subscript> observations of 46 low-amplitude Cepheids

From December 2006 to January 2008, we performed 1699 BV I _c observations for 46 low-amplitude Cepheids discovered in the course of the ASAS project using the 76-cm telescope of the South-African Astronomical Observatory (SAAO). We provide the tables of observations and V light and B-V and V-I _c color curves. These new observations, along with data from the ASAS-3 catalog, have been used to improve the elements of the light variations. Our data allow the number of known Galactic low-amplitude Cepheids to be almost doubled. This makes it possible to increase the number of distance indicators suitable for studying the structure of the inner Galactic arms by almost 15%.     

Optical observations of type-IIP supernova 2004dj: Evidence for asymmetry of the <Superscript>56</Superscript>Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The ⁵⁶Ni mass in the envelope of SN 2004dj was estimated from the light curve to be ≈0.02M_⊙. This estimate is confirmed by modeling the Hα luminosity. The Hα emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of ?1600 km s^?1 at the early nebular phase. A similar asymmetry was found in the Hβ, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric ⁵⁶Ni ejecta. The Hα profile and its evolution are reproduced in the model of an asymmetric bipolar ⁵⁶Ni structure for a spherical hydrogen distribution. The mass of the front ⁵⁶Ni jet is comparable to that of the central component and twice that of the rear ⁵⁶Ni jet. We point out that the asymmetric bipolar structure of ⁵⁶Ni ejecta is also present in SN 1999em, a normal type-IIP supernova.     

CCD BVI c observations of Cepheids

In 2008–2013, we obtained 11333 CCD BVI _c frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Católica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 0?05 in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids.     

Analysis of the Z distribution of young objects in the Galactic thin disk

We have obtained new estimates of the Sun’s distance from the symmetry plane Z _⊙ and the vertical disk scale height h using currently available data on stellar OB associations, Wolf–Rayet stars, HII regions, and Cepheids. Based on individual determinations, we have calculated the mean Z _⊙ = ?16 ± 2 pc. Based on the model of a self-gravitating isothermal disk for the density distribution, we have found the following vertical disk scale heights: h = 40.2 ± 2.1 pc from OB associations, h = 47.8 ± 3.9 pc from Wolf–Rayet stars, h = 48.4 ± 2.5 pc from HII regions, and h = 66.2 ± 1.6 pc from Cepheids. We have estimated the surface, Σ = 6 kpc^?2, and volume, D(Z _⊙) = 50.6 kpc^?3, densities from a sample of OB associations. We have found that there could be ～5000 OB associations in the Galaxy.     

Kinematics of the galaxy from Cepheids with proper motions from the Gaia DR1 catalogue

A sample of classical Cepheids with known distances and line-of-sight velocities has been supplemented with proper motions from the Gaia DR1 catalogue. Based on the velocities of 260 stars, we have found the components of the peculiar solar velocity vector (U, V, W)_⊙ = (7.90, 11.73, 7.39) ± (0.65, 0.77, 0.62) km s^?1 and the following parameters of the Galactic rotation curve: Ω₀ = 28.84 ± 0.33 km s^?1 kpc^?1, Ω′₀ = ?4.05 ± 0.10 km s^?1 kpc^?2, and Ω″₀ = 0.805 ± 0.067 km s^?1 kpc^?3 for the adopted solar Galactocentric distance R ₀ = 8 kpc; the linear rotation velocity of the local standard of rest is V ₀ = 231 ± 6 km s^?1.     

FG Sge at the stage of dust shell ejection

New photometric observations of the variable star FG Sge, a rapidly evolving planetary nebula nucleus, were performed in 2003–2008. On 230 nights, we obtained 86 UBV and 155 BV RI (or R _c , I _c ) magnitude estimates. The maximum amplitude of the V-band light variations was >8 ^m . Six deep minima and four high maxima were observed. Analysis of the light curve has shown that the pulsation period of the star remained constant since 1991 and was P = 115 days. We have studied the wavelength dependence of the extinction at various phases of the light curve. The blueing of the B-V color at deep minima is interpreted as the result of light scattering in the circumstellar dust shell of the star formed by preceding dust ejections since 1992. Our spectroscopic observations performed on nine nights in 2003–2007 with the 125-cm telescope at the Crimean Station of the Sternberg Institute have confirmed the previously detected intensity variations of the Swan bands and the sodium doublet with brightness. It is noted that the Swan bands originate in the upper atmosphere, the star’s extended envelope, while the sodium doublet originates mainly in the circumstellar shell of FG Sge. We suggest that the star is currently located in the temperature-luminosity diagram at the turning point of the horizontal track of cooling in the direction of hot stars—evolution caused by the last helium shell flash at the planetary nebula stage.     

The <Emphasis Type="Italic">z</Emphasis> distribution of hydrogen clouds and masers with kinematic distances

Data on HII regions, molecular clouds, and methanol masers have been used to estimate the Sun’s distance from the symmetry plane z _⊙ and the vertical disk scale height h. Kinematic distance estimates are available for all objects in these samples. The Local-arm (Orion-arm) objects are shown to affect noticeably the pattern of the z distribution. The deviations from the distribution symmetry are particularly pronounced for the sample of masers with measured trigonometric parallaxes, where the fraction of Local-arm masers is large. The situation with the sample of HII regions in the solar neighborhood is similar. We have concluded that it is better to exclude the Local arm from consideration. Based on the model of a self-gravitating isothermal disk, we have obtained the following estimates from objects located in the inner region of the Galaxy (R ≤ R ₀): z _⊙ = ?5.7 ± 0.5 pc and h ₂ = 24.1 ± 0.9 pc from the sample of 639 methanol masers, z _⊙ = ?7.6±0.4 pc and h ₂ = 28.6±0.5 pc from 878HII regions, z _⊙ = ?10.1 ± 0.5 pc and h ₂ = 28.2 ± 0.6 pc from 538 giant molecular clouds.     

Determining the Absolute Magnitudes of Galactic-Bulge Red Clump Giants in the <Emphasis Type="Italic">Z</Emphasis> and <Emphasis Type="Italic">Y</Emphasis> Filters of the Vista Sky Surveys and the <Emphasis Type="Italic">IRAC</Emphasis> Filters of the Spitzer Sky Surveys

The properties of red clump giants in the central regions of the Galactic bulge are investigated in the photometric Z and Y bands of the infrared VVV (VISTA/ESO) survey and the [3.6], [4.5], [5.8], and [8.0] μm bands of the GLIMPSE (Spitzer/IRAC) Galactic plane survey. The absolute magnitudes for objects of this class have been determined in these bands for the first time: M _Z = ?0.20 ± 0.04, M _Y = ?0.470 ± 0.045, M_[3.6] = ?1.70 ± 0.03, M_[4.5] = ?1.60 ± 0.03, M_[5.8] = ?1.67 ± 0.03, and M_[8.0] = ?1.70 ± 0.03. A comparison of the measured magnitudes with the predictions of theoretical models for the spectra of the objects under study has demonstrated good mutual agreement and has allowed some important constraints to be obtained for the properties of bulge red clump giants. In particular, a comparison with evolutionary tracks has shown that we are dealing predominantly with the high-metallicity subgroup of bulge red clump giants. Their metallicity is slightly higher than has been thought previously, [M/H] ? 0.40 (Z ? 0.038) with an error of [M/H] ? 0.1 dex, while the effective temperature is 4250± 150 K. Stars with an age of 9–10 Gyr are shown to dominate among the red clump giants, although some number of younger objects with an age of ~8 Gyr can also be present. In addition, the distances to several Galactic bulge regions have been measured, as D = 8200–8500 pc, and the extinction law in these directions is shown to differ noticeably from the standard one.     

Further photometric observations of the X-ray binary A0535+26/V725 Tau: A new activity cycle

We performed new photoelectric U BV observations of the X-ray binary A0535+26 at the Crimean Station of the Sternberg Astronomical Institute in 1998–2003. After the brightness stabilized at a minimum of about 500 days in duration, a new brightness rise steeper than that observed previously began: the brightness increased over two seasons of observations by a total amplitude of \(0\mathop .\limits^m 5\). The physical parameters (T _e , n _e ) of the additional emission that caused this brightening match, within the error limits, were obtained from the averaged over 15 years, data, that include both the ascending and descending branches of the light curve. We found a delay of the variations in the Hα line relative to the continuum, which is no more than one year.     

Parameters of the classical type-IIP supernova SN 1999em

Based on observations of SN 1999em, we determined the physical parameters of this supernova using hydrodynamic calculations including nonequilibrium radiative transfer. Taking the distance to SN 1999em estimated by the expanding photosphere method (EPM) to be D = 7.5 Mpc, we found the parameters of the presupernova: radius R = 450R_⊙, mass M = 15M_⊙, and explosion energy E = 7 × 10⁵⁰ erg. For the distance D = 12 Mpc determined from Cepheids, R, M, and E must be increased to the following values: R = 1000R_⊙, M = 18M_⊙, and E = 10⁵¹ erg. We show that one cannot restrict oneself to using the simple analytical formulas relating the supernova and presupernova parameters to obtain reliable parameters for type-IIP presupernovae.     

Thermonuclear X-ray burst of MXB 1658-298 with <Emphasis Type="Italic">NuSTAR</Emphasis>

MXB 1658-298 is a transient Low-Mass X-ray Binary (LMXB), which shows eclipses, dips and bursts in its light curve. This source has undergone three active periods separated by long quiescent phases. The latest phase of enhanced X-ray emission was observed during 2015–2016. We have analysed broadband data from Swift/XRT and NuSTAR observations carried out in 2015. During NuSTAR observation, one thermonuclear X-ray burst took place. The X-ray emission during the burst was brighter by a factor of \(\sim 200\), compared to the pre-burst emission. This work focuses on the spectral analysis of MXB 1658-298 during the persistent and the burst phases using NuSTAR observation of 2015. We have also determined the temperature and radius evolution during the burst using the time-resolved spectroscopy. The burst phase shows mild Photospheric Radius Expansion (PRE).     

Fundamental parameters and intrinsic colors of F,G, and K supergiants and classical cepheids

We used high-resolution echelle spectra with high signal-to-noise ratio to determine with a high degree of accuracy some atmospheric parameters (T _eff, log g and [Fe/H]) for 68 non-variable supergiants of types F, G, and K and 26 classical Cepheids in 302 pulsation phases. Very accurate effective temperatures, with errors of only 10–30 K, were determined by the line-depth ratio method. We found that the observed intrinsic color indices (B ? V)₀ can be related to these parameters: (B ? V)₀ = 57.984? 10.3587(log T _eff)² + 1.67572(log T _eff)³ ? 3.356 log g+ 0.321 V _t + 0.2615[Fe/H] + 0.8833log g(log T _eff). With this empirical relation, the intrinsic colors of individual supergiants and classical Cepheids of spectral types F0-K0 and of luminosity classes I and II can be estimated with an accuracy as high as 0.05 ^m , which is comparable to the accuracy of the most elaborate photometric procedures. In view of large distances to supergiants, the method we propose here allows a large-scale mapping of interstellar extinction with an accuracy of 0.1–0.2 ^m in a quite large region of the Galaxy.     

Plane Symmetric Dark Energy Models in the Form of Wet Dark Fluid in <Emphasis Type="Italic">f</Emphasis> (<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">T</Emphasis>) Gravity

In this paper, we have investigated the plane symmetric space-time with wet dark fluid (WDF), which is a candidate for dark energy, in the framework of f (R,T) gravity Harko et al. 2011, Phys. Rev. D, 84, 024020), where R and T denote the Ricci scalar and the trace of the energy–momentum tensor respectively. We have used the equation of state in the form of WDF for the dark energy component of the Universe. It is modeled on the equation of state p = ω(ρ ? ρ ^?). The exact solutions to the corresponding field equations are obtained for power-law and exponential volumetric expansion. The geometrical and physical parameters for both the models are studied. Also, we have discussed the well-known astrophysical phenomena, namely the look-back time, proper distance, the luminosity distance and angular diameter distance with red shift.     

Catalog of candidates for quasars at 3 &lt; <Emphasis Type="Italic">z</Emphasis> &lt; 5.5 selected among X-Ray sources from the 3XMM-DR4 survey of the XMM-Newton observatory

We have compiled a catalog of 903 candidates for type 1 quasars at redshifts 3 < z < 5.5 selected among the X-ray sources of the “serendipitous” XMM-Newton survey presented in the 3XMMDR4 catalog (the median X-ray flux is ≈5 × 10^?15 erg s^?1 cm^?2 in the 0.5–2 keV energy band) and located at high Galactic latitudes |b| > 20° in Sloan Digital Sky Survey (SDSS) fields with a total area of about 300 deg². Photometric SDSS data as well infrared 2MASS and WISE data were used to select the objects. We selected the point sources from the photometric SDSS catalog with a magnitude error δ _mz′ < 0.2 and a color i′ ? z′ < 0.6 (to first eliminate the M-type stars). For the selected sources, we have calculated the dependences χ²(z) for various spectral templates from the library that we compiled for these purposes using the EAZY software. Based on these data, we have rejected the objects whose spectral energy distributions are better described by the templates of stars at z = 0 and obtained a sample of quasars with photometric redshift estimates 2.75 < z _phot < 5.5. The selection completeness of known quasars at z _spec > 3 in the investigated fields is shown to be about 80%. The normalized median absolute deviation (Δz = |z _spec ? z _phot|) is σ _Δz /(1+z _spec) = 0.07, while the outlier fraction is η = 9% when Δz/(1 + z _спек.) > 0.2. The number of objects per unit area in our sample exceeds the number of quasars in the spectroscopic SDSS sample at the same redshifts approximately by a factor of 1.5. The subsequent spectroscopic testing of the redshifts of our selected candidates for quasars at 3 < z < 5.5 will allow the purity of this sample to be estimated more accurately.     

Evolution of the structure of the H<Subscript>2</Subscript>O supermaser outburst region in Orion KL

During the period 1979–1999, we investigated the hyperfine structure of the H₂O supermaser region located in the core of the molecular cloud OMC-1 in Orion KL. The angular resolution is 0.1 mas, which corresponds to 0.045 AU. The detected structure, which consists of a central object, an accretion disk, a bipolar outflow, and an envelope, corresponds to the initial formation stage of a low-mass star. The accretion disk is at the stage of separation into groups of concentric rings. The bipolar outflow is a neutral, highly collimated jet of accreted material that includes H₂O molecules and dust grains in the icy envelope. The injector is a bright compact source with a size <0.05 AU and a brightness temperature T_b≈10¹⁷ K. The velocity of the bipolar outflow is v≈10 km s^?1. The rotation velocity of the jet is v_rot≈1.5 km s^?1. The jet has the shape of a conical helix due to the precession of the rotation axis. Occasionally, dense blobs (comet-shaped bullets) are ejected. The envelope amplifies the radio emission from the structures in a ～0.5 km s^?1 maser window band with velocities v≈7.65 km s^?1 by more than two orders of magnitude.     

Catalog of equatorial coordinates and <Emphasis Type="Italic">B</Emphasis>-magnitudes of stars of the Kitab part of the FON project

The processing of the plates of the Kitab part of the FON project has been completed. In total, 1963 plates were processed. The catalog of equatorial coordinates α, δ, and B-magnitudes for 13 413268 stars and galaxies up to B ≤ 17.5 ^m for the epoch 1984.97 is compiled. The Epson Expression 10000XL scanner with a 1200 dpi scanning mode and a plate size of 30 × 30 cm or 13000 × 13000 pel was used to digitize astronegatives. Coordinates of stars and galaxies are obtained in the Tycho-2 catalog system and B-magnitudes are obtained in the photovoltaic system. The catalog internal accuracy for all objects is σ_α,δ = 0.23" and σ _B = 0.15 ^m (for stars in the range B = 5 ^m …14 ^m , errors are σ_α,δ = 0.085" and σ _B = 0.054 ^m ) for equatorial coordinates and stellar B-magnitudes, respectively. Convergence between the calculated and reference positions is σ_α,δ = 0.042", and convergence between photoelectric B-magnitudes is σ _B = 0.16 ^m . Coordinate errors with respect to the UCAC-4 catalog are σ_α,δ = 0.26" (9892697 or 73.75% of stars and galaxies were identified).     

A photometric study of faint galaxies in the field of GRB 000926

We present our B, V, R_c, and I_c observations of a \(3'.6 \times 3'\) field centered on the host galaxy of GRB 000926 (α_2000.0=17^h04^m11^s, \(\delta _{2000.0} = + 51^ \circ 47'9\mathop .\limits^{''} 8\)). The observations were carried out on the 6-m Special Astrophysical Observatory telescope using the SCORPIO instrument. The catalog of galaxies detected in this field includes 264 objects for which the signal-to-noise ratio is larger than 5 in each photometric band. The following limiting magnitudes in the catalog correspond to this limitation: 26.6 (B), 25.7 (V), 25.8 (R), and 24.5 (I). The differential galaxy counts are in good agreement with previously published CCD observations of deep fields. We estimated the photometric redshifts for all of the cataloged objects and studied the color variations of the galaxies with z. For luminous spiral galaxies with M(B)z～1.     

Results of a long-term monitoring of the multiple system SZ Cam

We present the results of the reduction of our photometric and spectroscopic observations for the eclipsing binary SZ Cam performed with the telescopes at the Astronomical Observatory of the Ural Federal University and the Special Astrophysical Observatory of the Russian Academy of Sciences in 1996–2014. Based on an 11-year-long photometric monitoring of SZ Cam, we have obtained new elements of its photometric orbit and parameters of its components. We have detected low-amplitude periodic light variations in SZ Cam that are possibly related to the ellipsoidal shape of the components of the spectroscopic binary third body. Based on published data and our new spectroscopy, we have found new values for the mass ratio, q = 0.72 ± 0.01, and parameters of the radial velocity curves of the components, V ₀ = ?3.6 ± 1.7 km s^?1, K ₁ = 190.2 ± 1.9 km s^?1, and K ₂ = 263.0 ± 2.4 km s^?1. The component masses have been estimated to be M ₁ = 16.1 M _⊙ and M ₂ = 11.6 M _⊙. We have obtained new light elements and parameters of the radial velocity curves for the third body, V ₀ ^3b = 4.2 ± 0.6 km s^?1 and K ₁ ^3b = 26.6 ± 0.8 km s^?1. We have improved the period of the relative orbit of SZ Cam and the third body, P _orb = 55.6 ± 1.5 yr.     

Fisher Matrix-based Predictions for Measuring the <Emphasis Type="Italic">z</Emphasis> = 3.35 Binned 21-cm Power Spectrum using the Ooty Wide Field Array (OWFA)

We use the Fisher matrix formalism to predict the prospects of measuring the redshifted 21-cm power spectrum in different k-bins using observations with the upcoming Ooty Wide Field Array (OWFA) which will operate at 326.5 MHz. This corresponds to neutral hydrogen (HI) at z = 3.35, and a measurement of the 21-cm power spectrum provides a unique method to probe the large-scale structures at this redshift. Our analysis indicates that a 5σ detection of the binned power spectrum is possible in the k range 0.05 ≤ k ≤ 0.3 Mpc^?1 with 1000 hours of observation. We find that the signal- to-noise ratio (SNR) peaks in the k range 0.1?0.2 Mpc^?1 where a 10σ detection is possible with 2000 hours of observations. Our analysis also indicates that it is not very advantageous to observe beyond 1000 h in a single field-of-view as the SNR increases rather slowly beyond this in many of the small k-bins. The entire analysis reported here assumes that the foregrounds have been completely removed.     

Dwarf-to-giant galaxy ratio in superclusters and in the field at 0.02 &lt; <Emphasis Type="Italic">z</Emphasis> &lt; 0.05

We report the results of the study of red-sequence (RS) galaxies in 47 galaxy clusters (0.023 < z < 0.047) located in different environments: in the superclusters Hercules and Leo, and in the field, based on the SDSS catalog data. In the

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interval, the number of bright RS dwarf galaxies in galaxy clusters increaseswith the X-ray luminosity of the cluster as logN ∝ log _X ^0.64 . The dwarf-to-giant ratio (DGR) does not depend on the surroundings, mass, or richness of the cluster. This ratio is seen to increase for galaxy clusters with log L _X > 43.5 erg/s or σ > 520 km/s. The compositeDGR of galaxy clusters, determined both from the membership in different structures and the X-ray luminosity along the radius R ₂₀₀, is minimum in the central regions of the clusters (about 0.6 ± 0.06), reaches a maximum within 0.3–0.9R ₂₀₀ (about 0.9 ± 0.10), and decreases approximately to 0.7 ± 0.03 upon reaching the radius 1.4 R ₂₀₀.