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Publisher: Springer-Verlag (Total: 2352 journals)

 Astronomy Letters   [SJR: 0.58]   [H-I: 30]   [20 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1562-6873 - ISSN (Online) 1063-7737    Published by Springer-Verlag  [2352 journals]
• A Deep Extragalactic Survey with the ART-XC Telescope of the Spectrum-RG
Observatory: Simulations and Expected Results
• Authors: I. A. Mereminskiy; E. V. Filippova; R. A. Burenin; S. Yu. Sazonov; M. N. Pavlinsky; A. Yu. Tkachenko; I. Yu. Lapshov; A. E. Shtykovskiy; R. A. Krivonos
Pages: 67 - 80
Abstract: To choose the best strategy for conducting a deep extragalactic survey with the ART-XC X-ray telescope onboard the Spectrum–Röntgen–Gamma (SRG) observatory and to estimate the expected results, we have simulated the observations of a 1.1° × 1.1° field in the 5–11 and 8–24 keV energy bands. For this purpose, we have constructed a model of the active galactic nuclei (AGN) population that reflects the properties of the X-ray emission from such objects. The photons that “arrived” from these sources were passed through a numerical model of the telescope, while the resulting data were processed with the standard ART-XC data processing pipeline. We show that several hundred AGNs at redshifts up to z ≈ 3 will be detected in such a survey over 1.2 Ms of observations with the expected charged particle background levels. Among them there will be heavily obscured AGNs, which will allow a more accurate estimate of the fraction of such objects in the total population to be made. Source confusion is expected at fluxes below 2 × 10−14 erg s−1 cm−2 (5–11 keV). Since this value can exceed the source detection threshold in a deep survey at low particle background levels, it may turn out to be more interesting to conduct a survey of larger area (several square degrees) but smaller depth, obtaining a sample of approximately four hundred bright AGNs as a result.
PubDate: 2018-02-01
DOI: 10.1134/s1063773718020044
Issue No: Vol. 44, No. 2 (2018)

• Geometric Aspects and Testing of the Galactic Center Distance
Determination from Spiral Arm Segments
• Authors: I. I. Nikiforov; A. V. Veselova
Pages: 81 - 102
Abstract: We consider the problem of determining the geometric parameters of a Galactic spiral arm from its segment by including the distance to the spiral pole, i.e., the distance to the Galactic center (R0). The question about the number of points belonging to one turn of a logarithmic spiral and defining this spiral as a geometric figure has been investigated numerically and analytically by assuming the direction to the spiral pole (to the Galactic center) to be known. Based on the results obtained, in an effort to test the new approach, we have constructed a simplified method of solving the problem that consists in finding the median of the values for each parameter from all possible triplets of objects in the spiral arm segment satisfying the condition for the angular distance between objects. Applying the method to the data on the spatial distribution of masers in the Perseus and Scutum arms (the catalogue by Reid et al. (2014)) has led to an estimate of R0 = 8.8 ± 0.5 kpc. The parameters of five spiral arm segments have been determined from masers of the same catalogue. We have confirmed the difference between the spiral arms in pitch angle. The pitch angles of the arms revealed by masers are shown to generally correlate with R0 in the sense that an increase in R0 leads to a growth in the absolute values of the pitch angles.
PubDate: 2018-02-01
DOI: 10.1134/s1063773717120039
Issue No: Vol. 44, No. 2 (2018)

• Searching for Binary Systems Among Nearby Dwarfs Based on Pulkovo
Observations and SDSS Data
• Authors: M. Yu. Khovrichev; A. A. Apetyan; E. A. Roshchina; I. S. Izmailov; D. A. Bikulova; A. P. Ershova; I. A. Balyaev; A. M. Kulikova; V. V. Petyur; A. A. Shumilov; K. I. Os’kina; L. A. Maksimova
Pages: 103 - 118
Abstract: Our goal is to find previously unknown binary systems among low-mass dwarfs in the solar neighborhood and to test the search technique. The basic ideas are to reveal the images of stars with significant ellipticities and/or asymmetries compared to the background stars on CCD frames and to subsequently determine the spatial parameters of the binary system and the magnitude difference between its components. For its realization we have developed a method based on an image shapelet decomposition. All of the comparatively faint stars with large proper motions (V >13 m , μ > 300 mas yr−1) for which the “duplicate source” flag in the Gaia DR1 catalogue is equal to one have been included in the list of objects for our study. As a result, we have selected 702 stars. To verify our results, we have performed additional observations of 65 stars from this list with the Pulkovo 1-m “Saturn” telescope (2016–2017). We have revealed a total of 138 binary candidates (nine of them from the “Saturn” telescope and SDSS data). Six program stars are known binaries. The images of the primaries of the comparatively wide pairs WDS 14519+5147, WDS 11371+6022, and WDS 15404+2500 are shown to be resolved into components; therefore, we can talk about the detection of triple systems. The angular separation ρ, position angle, and component magnitude difference Δm have been estimated for almost all of the revealed binary systems. For most stars 1.5′′ < ρ < 2.5′′, while Δm <1.5m.
PubDate: 2018-02-01
DOI: 10.1134/s1063773718010024
Issue No: Vol. 44, No. 2 (2018)

• Simulations of the Dynamics of the Debris Disks in the Systems Kepler-16,
Kepler-34, and Kepler-35
• Authors: T. V. Demidova; I. I. Shevchenko
Pages: 119 - 125
Abstract: We investigate the long-term dynamics of planetesimals in debris disks in models with the parameters of the binary star systems Kepler-16, Kepler-34, and Kepler-35 with planets. Our calculations show that the formation of a stable ring coorbital with the planet is possible for Kepler-16 and Kepler-35. In Kepler-34 significant orbital eccentricities of the binary system and the planet can prevent the formation of such a structure. The detection of circumbinary ring-like structures in observations of binary star systems can be evidence for the existence of planets retaining coorbital rings of dust and planetesimals.
PubDate: 2018-02-01
DOI: 10.1134/s1063773718010012
Issue No: Vol. 44, No. 2 (2018)

• Tropospheric Delay from VLBI and GNSS Measurements
• Authors: V. S. Gubanov
Pages: 126 - 138
Abstract: Using an updated version of the QUASAR software package developed at the Institute of Applied Astronomy of the Russian Academy of Sciences, we have processed the VLBI observations within the international CONT14 program (May 6–20, 2014), in which a global network of 17 stations was involved (a total of ~250 000 observations). The package update concerned the optimization of data structure and the refinement of stochastic models for the random variations in wet tropospheric delay and atomic clock difference. The main goal of this paper is to compare the VLBI determinations of the tropospheric delay with its independent determinations using global navigation satellite systems (GNSS). We show that both these determinations agree well between themselves only in the case of a global analysis of the VLBI observations, where the VLBI station coordinates are also refined, along with the tropospheric delay and the clock synchronization and Earth orientation parameters. If, alternatively, the station coordinates are insufficiently accurate and are not refined from VLBI observations, then it is appropriate not to determine the tropospheric delay from these observations, but to take it from the publicly accessible independent GNSS data. However, this requires that the VLBI and GNSS techniques operate simultaneously at a common observing site. We have established the shortcomings of the universally accepted method of stabilizing the global solution associated with the absence of a criterion for choosing reference stations and radio sources. Two ways of their elimination are proposed: (i) introducing a coordinated list of weight factors for the errors in the coordinates of such stations and sources into the stabilization algorithm and (ii) adopting a coordinated list of stations and sources the refinement of whose coordinates is not required at all for a certain time.
PubDate: 2018-02-01
DOI: 10.1134/s1063773718020032
Issue No: Vol. 44, No. 2 (2018)

• Relative Contribution of the Hydrogen 2 s Two-Photon Decay and Lyman- α
Escape Channels during the Epoch of Cosmological Recombination
• Authors: J. A. Rubiño-Martin; R. A. Sunyaev
Pages: 1 - 7
Abstract: We discuss the evolution of the ratio in number of recombinations due to 2s two photon escape and due to the escape of Lyman-α photons from the resonance during the epoch of cosmological recombination, within the width of the last scattering surface and near its boundaries. We discuss how this ratio evolves in time, and how it defines the profile of the Lyman-α line in the spectrum of CMB. One of the key reasons for explaining its time dependence is the strong overpopulation of the 2p level relative to the 2s level at redshifts z ≲ 750.
PubDate: 2018-01-01
DOI: 10.1134/s1063773718010036
Issue No: Vol. 44, No. 1 (2018)

• Stellar Mass—Halo Mass Relation and Star Formation Efficiency in
High-Mass Halos
• Authors: A. V. Kravtsov; A. A. Vikhlinin; A. V. Meshcheryakov
Pages: 8 - 34
Abstract: We study relation between stellar mass and halo mass for high-mass halos using a sample of galaxy clusters with accurate measurements of stellar masses from optical and ifrared data and total masses from X-ray observations. We find that stellar mass of the brightest cluster galaxies (BCGs) scales as M *,BCG ∝ M 500 αBCG with the best fit slope of α BCG ≈ 0.4 ± 0.1. We measure scatter of M *,BCG at a fixed M 500 of ≈0.2 dex. We show that stellar mass-halo mass relations from abundance matching or halo modelling reported in recent studies underestimate masses of BCGs by a factor of ∼2−4. We argue that this is because these studies used stellar mass functions (SMF) based on photometry that severely underestimates the outer surface brightness profiles of massive galaxies. We show that M * −M relation derived using abundance matching with the recent SMF calibration by Bernardi et al. (2013) based on improved photometry is in a much better agreement with the relation we derive via direct calibration for observed clusters. The total stellar mass of galaxies correlates with total mass M 500 with the slope of ≈0.6 ± 0.1 and scatter of 0.1 dex. This indicates that efficiency with which baryons are converted into stars decreases with increasing cluster mass. The low scatter is due to large contribution of satellite galaxies: the stellar mass in satellite galaxies correlates with M 500 with scatter of ≈0.1 dex and best fit slope of αsat ≈ 0.8 ± 0.1. We show that for a fixed choice of the initial mass function (IMF) total stellar fraction in clusters is only a factor of 3−5 lower than the peak stellar fraction reached in M ≈ 1012 M ⊙ halos. The difference is only a factor of ∼1.5−3 if the IMF becomes progressively more bottom heavy with increasing mass in early type galaxies, as indicated by recent observational analyses. This means that the overall efficiency of star formation in massive halos is only moderately suppressed compared to L * galaxies and is considerably less suppressed than previously thought. The larger normalization and slope of the M *−M relation derived in this study shows that feedback and associated suppression of star formation in massive halos should be weaker than assumed in most of the current semi-analytic models and simulations.
PubDate: 2018-01-01
DOI: 10.1134/s1063773717120015
Issue No: Vol. 44, No. 1 (2018)

• Spotted Surface Structure of the Active Giant PZ Mon
• Authors: Yu. V. Pakhomov; K. A. Antonyuk; N. I. Bondar’; N. V. Pit’; I. V. Reva; A. V. Kusakin
Pages: 35 - 48
Abstract: Based on our photometric observations in 2015–2016 and archival photometric data for the active red giant PZ Mon, we have found the main characteristics of the stellar surface: the unspotted surface temperature T eff = 4730 K, the spot temperature T s = 3500 K, and the relative spot area from 30 to 40%. The best agreement with the observations has been achieved in our three-spot model including a cool polar spot with a temperature of ~3500 K as well as large and small warm spots with a temperature of ~4500 K. The stable polar spot is responsible for the long-period brightness variations. Its presence is confirmed by an analysis of the TiO 7054 Å molecular band. The small-amplitude 34-day variability is attributable to the warm spots located on the side of the secondary component, which determine the relatively stable active longitude.
PubDate: 2018-01-01
DOI: 10.1134/s1063773717120040
Issue No: Vol. 44, No. 1 (2018)

• On the Dynamical Foundations of the Lidov–Kozai Theory
• Authors: V. I. Prokhorenko
Pages: 49 - 66
Abstract: The Lidov–Kozai theory developed by each of the authors independently in 1961–1962 is based on qualitative methods of studying the evolution of orbits for the satellite version of the restricted three-body problem (Hill’s problem). At present, this theory is in demand in various fields of science: in the field of planetary research within the Solar system, the field of exoplanetary systems, and the field of high-energy physics in interstellar and intergalactic space. This has prompted me to popularize the ideas that underlie the Lidov–Kozai theory based on the experience of using this theory as an efficient tool for solving various problems related to the study of the secular evolution of the orbits of artificial planetary satellites under the influence of external gravitational perturbations with allowance made for the perturbations due to the polar planetary oblateness.
PubDate: 2018-01-01
DOI: 10.1134/s1063773717120052
Issue No: Vol. 44, No. 1 (2018)

• Type I X-ray Bursts Detected by the JEM-X Telescope Onboard the INTEGRAL
Observatory in 2003–2015
• Authors: I. V. Chelovekov; S. A. Grebenev; I. A. Mereminskiy; A. V. Prosvetov
Pages: 781 - 795
Abstract: We present the results of our analysis of the JEM-X/INTEGRAL data obtained from January 2003 to January 2015 aimed at searching for type I X-ray bursts from known and new bursters. Such bursts are caused by thermonuclear explosions on the surface of a neutron star. We have searched for bursts in the records of the count rate of the JEM-X detectors in the 3–20 keV energy band. We have separately reconstructed and analyzed the light curves of 104 X-ray bursters known to date based on the JEM-X data. A similar search for bursts was previously carried out in the 15–25 keV data from the IBIS/ISGRI telescope onboard the INTEGRAL observatory obtained in 2003–2009. We have continued to analyze the data from this telescope up until the observations in January 2015. The joint catalog of bursts detected by the two instruments includes 2201 events; their basic parameters are given. The large size of the sample of bursts makes it one of the most representative of the existing one and allows various statistical studies of bursts to be performed. In particular, we have constructed the dependence of the mean rate of type I bursts from bursters on the luminosity (accretion rate), revealed an appreciable burst rate from sources with a near-Eddington luminosity, and investigated the population of multiple bursts with a recurrence time much shorter than the time it takes for a critical mass of matter required for the initiation of an explosion to be accumulated on the neutron star surface. Almost all of the detected bursts are associated with already known bursters,we have found only one previously unknown burster, IGRJ17380-3749, in the archival data, and one more known, but poorly studied source, AX J1754.2-2754, has been identified as a burster. Several similar sources have previously been identified as bursters directly during the INTEGRAL observations.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717120076
Issue No: Vol. 43, No. 12 (2017)

• Fine Structure of the Core of the Blazar OJ 287-I
• Authors: L. I. Matveyenko; S. S. Sivakon’
Pages: 796 - 811
Abstract: The fine structure of the active region, the bulge, of the blazar OJ 287 has been investigated with a resolution of 20 μas (0.1 pc) at a wavelength of 7 mm, the epochs of 2007–2017. The structure and kinematics correspond to a vortex nature. The surrounding matter, the plasma, is transferred to the center along two arms from opposite directions. The emerging excess angular momentum is carried away along the rotation axis by bipolar outflows, rotating coaxial tubes, in a direction X ≈ −120◦ in the plane of the sky as it is accumulated. The central high-velocity bipolar outflow has a helical shape. The diameters of the low-velocity flows are ø1 ≈ 0.3 and ø2 ≈ 0.65 mas, or 1.4 and 3 pc, respectively. Ring currents whose tangential directions are observed as parallel chains of components are excited in the flow walls. The peak brightness temperature of the nozzle reaches Tb ≈ 1012−1013 K. A “disk” with a diameter ø ≈ 0.5 mas (≈2.2 pc) is observed by the absorption of synchrotron radiation. The disk is inclined to the plane of the sky at an angle of 60◦ in the jet direction. The fragments are seen from a distance of ∼0.2 mas outside the absorption zone. The jet sizes exceed considerably the counterjet ones. An enhanced supply of plasma from the northern arm gives rise to an independent vortex 0.2 mas away from the central one in the NW direction. As in the first case, the helical central bipolar outflow is surrounded by a low-velocity component ø ≈ 0.28 mas in diameter with built-in ring currents. The jet is ejected in the direction X = −50◦ in the plane of the sky. The jet orientation changes, X = −130◦ at a distance of 1 mas. A high activity of the central and two side nozzles spaced 0.22 mas apart in the direction X = −40◦ is occasionally observed simultaneously. The active region of the blazar is observed through an ionized medium, a screen, whose influence is significant even at a wavelength of 7 mm. The absorption and refraction of the transmitted emission in the screen affect the apparent brightness relative to the positions of the fragments.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717120027
Issue No: Vol. 43, No. 12 (2017)

• SDSS J170745+302056: A low-surface-brightness galaxy in a group
• Authors: V. P. Reshetnikov; S. S. Savchenko; A. V. Moiseev; O. V. Egorov
Pages: 812 - 819
Abstract: Based on SDSS data and spectroscopic observations with the 6-m BTA telescope at SAO RAS, we have studied the galaxy SDSS J170745+302056. By the set of its characteristics— an exponential brightness distribution, a central stellar disk surface brightness μ0(B) = 23m. 25/—, blue colors, a low metallicity, and a moderate star formation rate—this galaxy belongs to typical low-surfacebrightness spiral galaxies. The exponential scale length of the galaxy’s disk is ≈3 kpc, while its optical diameter exceeds 20 kpc. SDSS J170745+302056 is a member of a group of five galaxies and possibly interacts with the galaxy UGC 10716. The existence of a large low-surface-brightness galaxy in such a dense environment is very unusual.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717120064
Issue No: Vol. 43, No. 12 (2017)

• Heating of the polar caps of old radio pulsars
• Authors: A. I. Tsygan
Pages: 820 - 830
Abstract: The X-ray luminosity and temperature of the polar cap heated by the back flux of positrons from a radio pulsar with a period P ∼ 1 s and a magnetic field B ~ 1012 G have been estimated. An additional source of X-ray emission—a thin, hotter semiring on the polar-cap periphery—is shown to also exist. It is heated by the back flux of electrons from the light cylinder. Furthermore, the electric field near the hot semiring accelerates the ions of the surface layer that leave the neutron-star magnetosphere. The semiring area is smaller than the polar-cap area approximately by a factor of 100, i.e., at the same luminosity the temperature is higher by a factor of 3. The observed X-ray emission from old radio pulsars is the emission from thin hot polar-cap semirings. The emission from the polar caps themselves is strongly attenuated by interstellar absorption.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717110056
Issue No: Vol. 43, No. 12 (2017)

• A search for photometric and spectroscopic evolutionary changes in the
young planetary nebula Vy 2-2
• Authors: V. P. Arkhipova; M. A. Burlak; V. F. Esipov; N. P. Ikonnikova; G. V. Komissarova
Pages: 831 - 843
Abstract: The results of long-term photometric and spectroscopic observations of the young compact planetary nebula Vy 2-2 (PNG 045.4-02.7) are presented. The UBV photometry in 1990–2016 has revealed a slight brightness trend in the yearly averaged data, most pronounced in the V band. We have measured the relative fluxes of optical emission lines on the spectrograms taken with the 1.25-m telescope at the Southern Station of the SAI MSU in 1999–2016, estimated the absolute flux in the Hβ line to be F(Hβ) = (2.1 ± 0.4) × 10−12 erg cm−2 s−1, and determined the interstellar extinction constant c(Hβ) = 1.8. The electron temperature and density in the nebula have been estimated from diagnostic line ratios: Te = (10−12) × 103 K and Ne ≥ 105 cm−3. To detect any possible evolutionary changes, we have compared the new observations with the archival data obtained over the entire history of spectroscopic observations of Vy 2-2. No significant changes in the relative intensities of the strongest emission lines and the integrated flux in the Hβ line exceeding the observational errors have been found. We have revealed a tendency for the intensity ratio F(λ4363)/F(λ4959) to decrease with time, which may be related to a decrease in the electron density in the nebula. Based on our photometric and spectroscopic data, we have estimated the luminosity of the central star of Vy 2-2, which corresponds to the evolutionary tracks for the most massive post-AGB stars of the O-rich sequence.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717110019
Issue No: Vol. 43, No. 12 (2017)

• On searching for observational manifestations of Alfvén waves in
solar faculae
• Authors: N. I. Kobanov; S. A. Chupin; A. A. Chelpanov
Pages: 844 - 853
Abstract: In an effort to detect torsional oscillations, we have studied the periodic half-width variations for several spectral lines in solar faculae. The duration of the series being analyzed was from 40 to 150 min. We have determined the dominant frequencies and amplitudes of the half-width oscillations and considered their phase relations to the intensity and line-of-sight velocity oscillations. Five-minute profile halfwidth oscillations with a peak-to-peak amplitude of ∼10 m ˚A are recorded with confidence in the upperphotospheric Si I 10 827 ˚A line in faculae. The chromospheric He I 10 830 A˚ and Hα line profiles shows ∼40–60 m ˚A variations in two frequency bands, 2.5–4 and 1–1.9 mHz. No center-to-limb dependence that, according to the theory, must accompany the torsional oscillations has been revealed in the behavior of the oscillation amplitudes. According to present views, these variations cannot be caused by periodic temperature and magnetic field changes. Our observations do not allow us to explain these variations by the sausage mode action either, which should manifest itself at the double frequency.
PubDate: 2017-12-01
DOI: 10.1134/s1063773717110044
Issue No: Vol. 43, No. 12 (2017)

• A beam of particles in ultrahigh-energy cosmic rays'
• Authors: G. F. Krymsky; M. I. Pravdin; I. E. Sleptsov
Pages: 703 - 705
Abstract: Three particles with energies of 36, 35, and 58 EeV arrived from one sky region were recorded by two EAS arrays during a day. The events are assumed to have been produced by the beam of particles that resulted from the interaction of cosmic rays with a relativistic shock front.
PubDate: 2017-11-01
DOI: 10.1134/s1063773717100048
Issue No: Vol. 43, No. 11 (2017)

• Radius of the neutron star magnetosphere during disk accretion
• Authors: E. V. Filippova; I. A. Mereminskiy; A. A. Lutovinov; S. V. Molkov; S. S. Tsygankov
Pages: 706 - 729
Abstract: The dependence of the spin frequency derivative $$\dot \nu$$ of accreting neutron stars with a strongmagnetic field (X-ray pulsars) on the mass accretion rate (bolometric luminosity, L bol) has been investigated for eight transient pulsars in binary systems with Be stars. Using data from the Fermi/GBM and Swift/BAT telescopes, we have shown that for seven of the eight systems the dependence $$\dot \nu$$ (L bol) can be fitted by the model of angular momentum transfer through an accretion disk, which predicts the relation $$\dot \nu$$ ∼ L 6/7 bol. Hysteresis in the dependence $$\dot \nu$$ (L bol) has been confirmed in the system V 0332+53 and has been detected for the first time in the systems KS 1947+300, GRO J1008-57, and 1A 0535+26. Estimates for the radius of the neutron star magnetosphere in all of the investigated systems have been obtained. We show that this quantity varies from pulsar to pulsar and depends strongly on the analytical model and the estimates for the neutron star and binary system parameters.
PubDate: 2017-11-01
DOI: 10.1134/s1063773717110020
Issue No: Vol. 43, No. 11 (2017)

• Properties of the Tycho-2 catalogue from Gaia data release
• Authors: V. V. Vityazev; A. S. Tsvetkov; S. D. Petrov; D. A. Trofimov; V. I. Kiyaev
Pages: 730 - 750
Abstract: Based on the measurements performed in the first 14 months of Gaia operation, we have solved the problem of obtaining the systematic differences between the stellar positions and proper motions of the TGAS (Tycho–Gaia Astrometric Solution) and Tycho-2 catalogues. By dividing the common stars from the TGAS and Tycho-2 catalogues into three G-magnitude groups for mean values of $$10\underset{\raise0.3em\hbox{\(\smash{\scriptscriptstyle\cdot}$$}}{m} 5,11\underset{\raise0.3em\hbox{$$\smash{\scriptscriptstyle\cdot}$$}}{m} 5,and13\underset{\raise0.3em\hbox{$$\smash{\scriptscriptstyle\cdot}$$}}{m} 0,\) we have obtained the systematic differences between the stellar equatorial coordinates and proper motions of both catalogues in the form of a decomposition into vector spherical harmonics by taking into account the magnitude equation. The systematic components have been extracted from the individual differences with a probability of 0.977–0.999. The constructed model of systematic differences allows any position measurements performed using Tycho-2 as a reference catalogue to be transformed to the TGAS frame. An important fact is the existence of a magnitude equation in the systematic differences: when passing from bright (G = 10 m ) to faint (G = 13 m ) stars, the systematic position differences change within the range from approximately −40 to 15 mas, while the systematic proper motion differences change from −3 to 3 mas yr−1. The orientation and mutual rotation parameters of the Tycho-2 and TGAS frames have also been found to be different for stars of different magnitudes: when passing from bright to faint stars, the rotation angle of the Tycho-2 frame relative to TGAS changes from 3.51 to 5.63 mas, while the angular velocity of rotation changes from 0.35 to 1.22 mas yr−1. Based on the developed method that allows the extent to which the systematic errors in the equatorial propermotions of stars affect the results of a kinematic analysis of the Galactic proper motions to be estimated within the Ogorodnikov–Milne model, we have shown that the slope of the Galactic rotation curve and the Oort parameter C are most sensitive to the transition from the Tycho-2 frame to the TGAS one. Their relative changes after the transformation to the TGAS frame reach 56 and 100%, respectively. At the same time, the changes in the estimates of the Oort parameters A and B as well as the linear velocity of the Sun relative to the Galactic center, the Galactic rotation period, the ratio of the epicyclic frequency to the angular velocity of Galactic rotation, and the mass of the Galaxy within the Galactocentric distance of the Sun are not so large, being 2−10%.
PubDate: 2017-11-01
DOI: 10.1134/s106377371711007x
Issue No: Vol. 43, No. 11 (2017)

• Spectroscopic studies of the unique yellow supergiant α Aqr in the
Cepheid instability strip
• Authors: I. A. Usenko; A. S. Miroshnichenko; S. Danford
Pages: 751 - 767
Abstract: Based on 21 spectra with resolutions from 12 000 to 42 000 taken in 1997–2016 for the yellow supergiant α Aqr (which is believed to be nonvariable in the Cepheid instability strip), we have determined its effective temperature T eff and radial velocities from metal and hydrogen absorption lines. Blue and red components that account for 20–25% of the total number of lines used have been detected in the profiles of these lines. The effective temperature and radial velocities estimated from metal lines and their components do not show any noticeable variations, while the radial velocities determined from hydrogen lines show variations that are largest for the Hα line, with an amplitude of more than 10 km s−1. These variations resemble periodic (∼100 days) and sporadic ones. The presence of variable red components in the hydrogen line cores confirms that there is a circumstellar envelope around the supergiant. The radial velocities of these components exhibit a behavior similar to that of the hydrogen lines but with larger amplitudes (it is twice that for the R component of the Hα line). Such an unusual variability as well as the presence of blue components in metal lines and the star’s position at the red edge of the Cepheid instability strip can be explained by a possible residual pulsational activity in the upper atmospheric layers of the star, which “swings” the envelope with a larger amplitude when passing into a less dense medium. The multicomponent structure of the Na I D doublet lines and their variations over long time intervals may be indicative of a chromospheric activity and a change in the stellar wind intensity. These processes can affect the sporadic variations of the radial velocities in the upper atmospheric layers of the star and its envelope. We raise the question about a revision of the classification of α Aqr as a yellow nonvariable supergiant.
PubDate: 2017-11-01
DOI: 10.1134/s1063773717110068
Issue No: Vol. 43, No. 11 (2017)

• Structure and physical conditions in the Hα loops of an M7.7 solar
flare
• Authors: N. M. Firstova; V. I. Polyakov
Pages: 768 - 779
Abstract: The M7.7 solar flare on July 19, 2012, is the most dramatic example of a “Masuda” flare with a well-defined second X-ray above-the-loop-top source. The behavior of the system of loops accompanying this flare has been studied comprehensively by Liu et al. based on Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) data. We have performed spectroscopic and filter observations of the Hα loops in this flare with the Large Solar Vacuum Telescope. The basic physical parameters in the loops of this peculiar flare generally coincide with the known data in Hα loops. However, the electron density, 1011 cm−3, and the integrated disk-center continuum intensity, 12%, are quite high, given that the observations were obtained almost 3 h after the flare onset.We have estimated the ascending velocity of the loop arcade (~3.5 km s−1) and the height difference between the Hα and 94 Å loops (~2 × 104 km).
PubDate: 2017-11-01
DOI: 10.1134/s1063773717110032
Issue No: Vol. 43, No. 11 (2017)

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