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Publisher: Springer-Verlag (Total: 2350 journals)

 Astrophysics   Journal Prestige (SJR): 0.243   Citation Impact (citeScore): 11   Number of Followers: 23           Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1573-8191 - ISSN (Online) 0571-7256    Published by Springer-Verlag  [2350 journals]
• Dust-Corrected Star Formation Rates in Galaxies with Outer Rings
• Authors: I. Kostiuk; O. Silchenko
Pages: 1 - 8
Abstract: The star formation rates SFR, as well as the SFR surface densities ΣSFR and absolute stellar magnitudes MAB, are determined and corrected for interinsic dust absorption for 34 disk galaxies of early morphological types with an outer ring structure and ultraviolet emission from the ring. These characteristic are determined for the outer ring structures and for the galaxies as a whole. Data from the space telescopes GALEX (in the NUV and FUV ultraviolet ranges) and WISE (in the W4 22 μm infrared band) are used. The average relative deviation in the corrected SFR and ΣSFR derived from the NUV and FUV bands is only 19.0%, so their averaged values are used for statistical consideration. The relations between the dust-corrected SFR characteristics, UV colours, the galaxy morphological type, absolute magnitude are illustrated.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9510-4
Issue No: Vol. 61, No. 1 (2018)

• Spectral Variability of the Herbig Ae/Be Star HD 37806
• Authors: M. A. Pogodin; S. E. Pavlovskiy; O. V. Kozlova; N. G. Beskrovnaya; I. Yu. Alekseev; G. G. Valyavin
Pages: 9 - 21
Abstract: Results are reported from a spectroscopic study of the Herbig Ae/Be star HD 37806 from 2009 through 2017 using high resolution spectrographs at the Crimean Astrophysical Observatory and the OAN SPM Observatory in Mexico. 72 spectra of this object near the Hα, Hβ, HeI 5876 and D NaI lines are analyzed. The following results were obtained: 1. The type of spectral profile of the Hα line can change from P Cyg III to double emission and vice versa over a time scale on the order of a month. 2. Narrow absorption components are observed in the profiles of the Hα and D NaI lines with radial velocities that vary over a characteristic time on the order of a day. 3. On some days, the profiles of the Hβ, HeI 5876, and D NaI lines show signs of accretion of matter to the star with a characteristic lifetime of a few days. A possible interpretation of these phenomena was considered. The transformation of the Hα profile may be related to a change in the outer latitudinal width of the boundary of the wind zone. The narrow variable absorption lines may be caused by the rotation of local azimuthal inhomogeneities in the wind zone owing to the interaction of the disk with the star’s magnetosphere in a propeller regime. Several current theoretical papers that predict the formation of similar inhomogeneous wind structures were examined. It is suggested that the episodes with signs of accretion in the spectral line profiles cannot be a consequence of the modulation of these profiles by the star’s rotation but are more likely caused by sudden, brief changes in the accretion rate. These spectral observations of HD 37806 should be continued in a search for cyclical variability in the spectral parameters in order to identify direct signs of magnetospheric accretion and detect possible binary behavior in this object.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9511-3
Issue No: Vol. 61, No. 1 (2018)

• On Quasi-Periodic Brightness Variations of P Cygni
• Authors: N. Kochiashvili; S. Beradze; R. Natsvlishvili; I. Kochiashvili; M. Vardosanidze; A. Pannicke
Pages: 22 - 29
Abstract: Until recent decades, it was considered that all Luminous Blue Variables are single massive and high luminosity stars. Now for several of them a companion has been found. The opinion exists that P Cygni also has a companion with an orbital period of about seven years. In accordance with this hypothesis, a known powerful eruption occurred near the periastron point. P Cygni, as well as several other well-known Luminous Blue Variable (LBV) stars, is a so-called "Supernova Impostor" because it survived after a powerful outburst. However, there were cases during the last decade when a LBV star survived after a powerful giant eruption, and then after a few years, explode as a supernova. Because the real reason for the great eruption and characteristic light variability of LBV, including P Cygni, is not established yet, any kind of photometric and spectral observational data is very significant. We present the results of analysis of the long-term photometric observations of hypergiant P Cygni. On the basis of these data, different quasi-periodic brightness changes of the star were revealed.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9512-2
Issue No: Vol. 61, No. 1 (2018)

• Photospheric Spots and Flare on the Active Dwarf Star FR Cnc
• Authors: A. V. Kozhevnikova; V. P. Kozhevnikov; I. Yu. Alekseev
Pages: 30 - 40
Abstract: We perform analysis of new BVRI photometry of young active dwarf star FR Cnc (K7V), obtained at Kourovka astronomical observatory of Ural Federal University with the help of multichannel electrophotometer in February 2010. The lightcurve displays sinusoidal rotation modulation with the amplitude of 0m.15 in V band. Reddening of the brightness at the photometric minimum confirms that this modulation is caused by cold photospheric spots. An analysis of the spottedness distribution in terms of a zonal model based on our own and published data shows that the spots are localized at lower and middle latitudes from 47° to 56°, occupy 10-21% of the star’s area, and are colder than the photosphere by 1650 K. A flare was detected on February 3, 2010, at a time corresponding to HJD=2455231. 3136. A maximum amplitude of 0m.11 was observed in the B band, the amplitudes in the V, R, and I bands were 0m.04, 0m.03, and 0m.02, respectively, and the duration of the flare was 32.5 min. It was noted that the flare occurred near the maximum spottedness of the star. The calculated total energy of the flare was 2.4·1033 and 1.3·1033 erg in the B and V bands, respectively. The flare was found to have an afterglow, with an overall increase in the star’s brightness by 0m.02 in the B band after the flare compared to the pre-flare level.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9513-1
Issue No: Vol. 61, No. 1 (2018)

• Abundance of Chemical Elements in RR Lyrae Variables and their Kinematic
Parameters
• Authors: M. L. Gozha; V. A. Marsakov; V. V. Koval’
Pages: 41 - 49
Abstract: A catalog of the chemical and spatial-kinematic parameters of 415 RR Lyrae variables (Lyrids) in the galactic field is compiled. Spectroscopic determinations of the relative abundances of 13 chemical elements in 101 of the RR Lyrae variables are collected from 25 papers published between 1995 and 2017. The data from different sources are reduced to a single solar abundance scale. The mean weighted chemical abundances are calculated with coefficients inversely proportional to the reported errors. An analysis of the deviations in the published relative abundances in each star from the mean square values calculated from them reveals an absence of systematic biases among the results from the various articles. The rectangular coordinates of 407 of the RR Lyrae variables and the components of the three-dimensional (3D) velocities of 401 of the stars are calculated using data from several sources. The collected data on the abundances of chemical elements produced by various nuclear fusion processes for the RR Lyrae variables of the field, as well as the calculated 3D velocities, can be used for studying the evolution of the Galaxy.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9514-0
Issue No: Vol. 61, No. 1 (2018)

• New Variable Stars in the KP2001 Catalog from the Data Base of the
Northern Sky Variability Survey
• Authors: G. V. Petrosyan
Pages: 50 - 63
Abstract: The optical variability of stars in the KP2001 catalog is studied. Monitor data from the automatic Northern Sky Variability Survey (NSVS) are used for this purpose. Of the 257 objects that were studied, 5 are Mira Ceti variables (mirids), 33 are semiregular (SR), and 108 are irregular variables (Ir). The light curves of the other objects show no noticeable signs of variability. For the first time, 11 stars are assigned to the semiregular and 105 stars to the irregular variables. Of the irregular variables, the light curves of two, No. 8 and No. 194, are distinct and are similar to the curves for eclipsing variables. The periods and amplitudes of the mirids and semiregular variables are determined using the “VStar” program package from AAVSO. The absolute stellar magnitudes M K and distances are also estimated, along with the mass loss for the mirids. The behavior of stars from KP2001 in 2MASS and WISE color diagrams is examined.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9515-z
Issue No: Vol. 61, No. 1 (2018)

• NY Ser: Outburst Activity and Multiperiodic Processes in its Various
Stages During 2014 and 2016
• Authors: A. S. Sklyanov; E. P. Pavlenko; O. I. Antonyuk; A. A. Sosnovskij; V. P. Malanushenko; N. V. Pit’; K. A. Antonyuk; A. N. Khairutdinova; Yu. V. Babina; A. I. Galeev
Pages: 64 - 82
Abstract: Results from observation campaigns for the dwarf nova NY Ser during 2014 and 2016 are presented. Data were obtained on a total of 126 nights in 2014 that include 20 normal outbursts and one superoutburst and on 22 nights in 2016 that include 5 normal outbursts. The shape of the curves for the normal outbursts indicated the existence of “outside-in” and “inside-out” outbursts in this system. In different stages of outburst activity (quiescent state, outburst, and superoutburst) NY Ser manifests brightness oscillations with different periods. In the quiescent state and in normal outbursts, the orbital period 0d.097558(6) predominated. During the superoutburst we identified two stages in the evolution of superhumps: a stage in which the tidal instability of the accretion disk increases (A) and a stage with developed superhumps (B). Stage A for NY Ser has been identified for the first time, but its duration and period are not uniquely determined. In stage B, positive superhumps with an average period of 0d.10464(9) and a period excess of ε = 0.072 were recorded and negative superhumps with an average period of 0d.0938(1) and a period deficit of ε = -0.038 were detected for the first time.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9516-y
Issue No: Vol. 61, No. 1 (2018)

• New Asymptotic Giant Branch Carbon Stars in the Galactic Halo
• Authors: N. Mauron; K. S. Gigoyan; G. R. Kostandyan
Pages: 83 - 90
Abstract: For the first time the data on the eight confirmed or candidate carbon (C) stars found mainly from objective-prism plates are presented. By using the Catalina database of lightcurves, we find that all these stars are pulsating, allowing a distance to be estimated through the K-band Period-Luminosity (PL) relation. This relation does not depend on spectral type (M or C) and distances are reliable even for C candidates. Seven stars are more than 10 kpc from the galactic plane, suggesting they do not belong to the galactic disk. We also find one star located at about 180 kpc from the Sun, being one of the most distant star in the Galaxy. Many of these new C stars are relatively blue. Some comments are also provided on seven other known halo carbon stars for which either a pulsation period is obtained, or because they were not included in previous works on halo C stars.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9517-x
Issue No: Vol. 61, No. 1 (2018)

• Ultraviolet Spectral Evolution of V1974 Cyg Using IUE Low Resolution
Spectra
• Authors: G. M. Hamed; M. R. Sanad; A. Essam; S. Yousef
Pages: 91 - 100
Abstract: We investigated the spectral evolution of some normalized UV emission lines through different stages of the outburst of the classical nova V1974 Cyg using International Ultraviolet Explorer (IUE) low resolution short wavelength spectra. The emission line fluxes were calculated and used to estimate the ultraviolet luminosity of the emitting region, and the latter is used to determine the average mass accretion rate during the post-nova phase. We found an average value of the ultraviolet continuum luminosity L cont  ∼ 4.6 ± 0.4 × 1035 erg s-1 and the average mass accretion rate $${\overset{\cdot }{M}}_{acc}\sim 6.6\pm 0.6\times {10}^{-10}{M}_{\astrosun}\kern0.5em {yr}^{\hbox{-} 1}$$ . We used the fitted continuum luminosity to estimate the temperature of the central white dwarf, and we found an average value of ~ 3×105 K. The spectral behavior is attributed to the variation in the opacity, temperature, and density of the ejecta during the different phases of the outburst. Our results are consistent with the theoretical ONe classical nova models.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9518-9
Issue No: Vol. 61, No. 1 (2018)

• Stability of Nonstationary Cooling of Pure Hydrogen Gas with Respect to
the Number of Discrete Levels Taken into Account
• Authors: O. M. Belova; K. V. Bychkov
Pages: 101 - 112
Abstract: The effect of the number K of atomic hydrogen levels taken into account on the cooling of the gas behind a shock front is studied. The calculations are done for the conditions in the atmospheres of long-period Mira Ceti type variables. K ranges from 2 to 25. The electron temperature Te(t; K) and ionization state x(r,K) asymptotically approach limiting functions Te(t) and x(t) that are independent of K. After the maximum electron temperature is reached, a partial equilibrium phase sets in, during which the populations of the highly excited discrete levels with principal quantum numbers ≥ 8 obey the Saha equation for the instantaneous electron temperature and density.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9519-8
Issue No: Vol. 61, No. 1 (2018)

• Magnetic Field Generation in Hybrid Stars
• Authors: D. M. Sedrakian; M. V. Hayrapetyan; D. S. Baghdasaryan
Pages: 113 - 121
Abstract: The mechanism for magnetic field generation in hybrid neutron stars (containing “npe,” hadron, “2SC” and “CFL” quark phases) is discussed. It is assumed that the rotational vortices in “npe” and “CFL” phases with a quantum of circulation h/2m also continue in the “2SC” phase. Since the superconducting components in the “npe” and “2SC” phases are charged, entrainment currents develop around the vortices and generate a magnetic field. The average magnetic field in the quark phase is on the order of 5·1015 G and exceeds the field in the “npe” phase by 2-3 orders of magnitude. The magnetic field penetrates into the “CFL” phase by means of magnetic vortices with a flux 2Φ0 and it can partially destroy the proton superconductivity in the “npe” phase. On the star’s surface, the magnetic field reaches 5·1014 G, a level comparable to the magnetic field of magnetars. Magnetars may, therefore, contain quark matter.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9520-2
Issue No: Vol. 61, No. 1 (2018)

• Accelerated Expansion of the Early and Late Universe in Terms of the
Scalar-Tensor Theory of Gravitation. II
• Authors: R. M. Avagyan; G. H. Harutyunyan
Pages: 122 - 133
Abstract: The cosmological dynamics of a quasi-de Sitter model is described in an “Einstein” representation of the modified Jordan theory using a qualitative theory of dynamic systems. An inflationary picture of the expansion is obtained for a range of the dimensionless acceleration parameter from one to zero.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9521-1
Issue No: Vol. 61, No. 1 (2018)

• LRS Bianchi Type-I Bulk Viscous Cosmological Models in f ( R, T ) Gravity
• Authors: P. Sahoo; R. Reddy
Pages: 134 - 143
Abstract: We have studied the locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f (R, T) gravity (R is the Ricci scalar and T is the trace of the stress energy tensor) with bulk viscous fluid as matter content. The model is constructed for the linear form f (R, T) = R + 2f (T). The exact solution of the field equations is obtained by using a time varying deceleration parameter q for a suitable choice of the function f (T). In this case, the bulk viscous pressure $$\overline{\mathrm{p}}$$ is found to be negative and the energy density ρ is found to be positive. The obtained model is anisotropic, accelerating, and compatible with the results of astronomical observations. Also, some important features of physical parameters of this model have been discussed.
PubDate: 2018-03-01
DOI: 10.1007/s10511-018-9522-0
Issue No: Vol. 61, No. 1 (2018)

• Search for Variability in Young Planetary Nebulae
• Authors: L. N. Kondratyeva; E. K. Denissyuk; M. A. Krugov
Pages: 497 - 506
Abstract: Data from long-term spectral observations of two young planetary nebulae are presented. A significant enhancement of the radiation fluxes in all emission lines and a higher degree of ionization of the gas are detected in the spectrum of M1-46. The opposite effect is observed in the spectrum of M1-65. Over 10 years (2005-2015) the radiative fluxes in the emission lines fell by a factor of 2-3, after which they began to increase. The cause of the observed variability may be a change in the temperature of the central star or a change in the inhomogeneous structure of the nebula through which the ionizing radiation passes.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9501-x
Issue No: Vol. 60, No. 4 (2017)

• Improved Orbit and Mass of the Binary Star 61 Cyg Based on Photographic
Observations at Pulkovo
• Authors: N. A. Shakht; D. L. Gorshanov; O. O. Vasilkova
Pages: 507 - 519
Abstract: Observations of stars close to the sun which, in terms of their physical properties, are possible objects for space missions aimed at searching for planetary components, are made at the Pulkovo Observatory. In this paper we present new orbital elements for the binary star 61 Cyg derived from long-term series of observations at Pulkovo including current data on this star.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9502-9
Issue No: Vol. 60, No. 4 (2017)

• Photometric Studies of Stars in the Vicinity of Cyg OB7
• Authors: N. D. Melikian; J. Gomez
Pages: 520 - 531
Abstract: Results of BVRI photometric studies of 131 stars in the stellar association Cyg OB7 are presented. Observational data were obtained with the 2.6-m telescope at the Byurakan Observatory during 2000, 2002, 2004, and 2011 using the ByuFOSC-2 and SCORPIO spectral cameras. Observations made in 2007 on the 182-cm telescope (Asiago, Italy) at the Padova Astronomical Observatory with the AFOSC (Asiago Faint Object Spectrograph and Camera) detector system are also used. Variations with amplitudes ranging from 0m.2 to 2m.16 are detected in 42 of the stars. Variability is observed for the first time in 31 of the 42 stars. The brightness of 32 of the stars was essentially unchanged during the time of our measurements. All of the 42 variables lie very close to the T Tau type stars on a two-color diagram.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9503-8
Issue No: Vol. 60, No. 4 (2017)

• Possibilities for Estimating Horizontal Electrical Currents in Active
Regions on the Sun
• Authors: Yu. A. Fursyak; V. I. Abramenko
Pages: 544 - 552
Abstract: Part of the “free” magnetic energy associated with electrical current systems in the active region (AR) is released during solar flares. This proposition is widely accepted and it has stimulated interest in detecting electrical currents in active regions. The vertical component of an electric current in the photosphere can be found by observing the transverse magnetic field. At present, however, there are no direct methods for calculating transverse electric currents based on these observations. These calculations require information on the field vector measured simultaneously at several levels in the photosphere, which has not yet been done with solar instrumentation. In this paper we examine an approach to calculating the structure of the square of the density of a transverse electrical current based on a magnetogram of the vertical component of the magnetic field in the AR. Data obtained with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO) for the AR of NOAA AR 11283 are used. It is shown that (1) the observed variations in the magnetic field of a sunspot and the proposed estimate of the density of an annular horizontal current around the spot are consistent with Faraday’s law and (2) the resulting estimates of the magnitude of the square of the density of the horizontal current $${j}_{\perp}^2$$ = (0.002− 0.004) A2/m4 are consistent with previously obtained values of the density of a vertical current in the photosphere. Thus, the proposed estimate is physically significant and this method can be used to estimate the density and structure of transverse electrical currents in the photosphere.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9505-6
Issue No: Vol. 60, No. 4 (2017)

• Is EG 50 a White or Strange Dwarf'
• Authors: G. S. Hajyan; Yu. L. Vartanyan
Pages: 553 - 562
Abstract: The time dependences of the luminosity of a white dwarf and four strange dwarfs with masses of 0.5 M (the mass of the white dwarf EG 50 with a surface temperature of 2.1·104 K) are determined taking neutrino energy losses into account. It was assumed that these configurations radiate only at the expense of thermal energy reserves. It is shown that the sources of thermal energy owing to nonequilibrium b-processes and the phenomenon of crystallization of electron-nuclear matter are insignificant in determining the cooling time of white and strange dwarfs with masses of 0.5 M⨀. It is shown that in this approximation the time dependences of the luminosity of white and strange dwarfs with masses of 0.5 M⨀ differ significantly only for surface temperatures TR≥7·104 K, so it is impossible to determine whether EG 50 is a white or strange dwarf based on the cooling time.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9506-5
Issue No: Vol. 60, No. 4 (2017)

• Some Consequences of the Expansion of the Universe on Small Scales
• Authors: H. A. Harutyunian
Pages: 572 - 581
Abstract: The possibility of detecting the accelerated expansion of the universe at all its points is examined. Observational data indicative of Hubble expansion on small scales are adduced for this purpose. The validity of current opinion on the equilibrium of systems of cosmic objects is also discussed. It is noted that this opinion is a simple consequence of the unproved Kant-Laplace hypothesis on the formation of cosmic objects and systems of them. It is proposed that a system attached to the cosmological horizon be used as a reference system. It is noted that all points on this sphere are an initial point from which expansion of the observed universe of the given observer began. The numerical value of the acceleration obtained in this way is almost the same as the anomalous acceleration found by space probes.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9508-3
Issue No: Vol. 60, No. 4 (2017)

• Effect of the Kerr Metric on Photosperic Radius Expansion in X Ray Burst
• Authors: S. Kalita; A. Barman
Pages: 582 - 591
Abstract: The main objective of this paper is to study general relativistic effects on the photospheric radius expansion during an X-ray burst. We examine how the Kerr metric causes a shift in the effective temperature and radiation flux with respect to the Schwarzschild values during mass accretion onto a neutron star or a black hole resulting in the X-ray burst. The spin of the compact object is used up to the maximal Kerr limit χ = 0.99 with different latitudes of accretion emission. The amplitude of temperature shift relative to the Schwarzschild case is found to be δT/T ≈  − (10−3 − 10−4) for the range χ = 0.1 − 0.99 at latitudes θ = 0o , 30o, 45o and 88o. The ratio of emission flux in the Kerr metric to that in the Schwarzschild metric, F(K)/F(S), is found to be less than unity. It goes up to a maximum of 0.9 for the lowest nonzero value of the spin parameter (i.e., 0.1). For the maximal Kerr limit, χ = 0.99 , it saturates near 0.8. This effect is more prominent towards the pole. This reduction in temperature and flux is found to be consistent with the absence of photospheric radius expansion in the X Ray burst LMXB 4U 1608-52, observed by NuSTAR. Although this is not uniquely ascribed to the metric, it is believed that the spacetime metric effect in the burst phenomena can be used as a probe for testing general relativity. Also, the shift in temperature or the radiation flux might have an observable signature in the element synthesis processes in such environments.
PubDate: 2017-12-01
DOI: 10.1007/s10511-017-9509-2
Issue No: Vol. 60, No. 4 (2017)

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