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Publisher: Springer-Verlag   (Total: 2329 journals)

 Astronomy Letters   [SJR: 0.58]   [H-I: 30]   [19 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 1562-6873 - ISSN (Online) 1063-7737    Published by Springer-Verlag  [2329 journals]
• Diffusion of elements in the interstellar medium in early-type galaxies
• Authors: P. S. Medvedev; S. Yu. Sazonov; M. R. Gilfanov
Pages: 285 - 303
Abstract: The role of diffusion in the redistribution of elements in the hot interstellar medium of earlytype galaxies is considered. It is well known that gravitational sedimentation can affect significantly the abundances of helium and heavy elements in the hot intergalactic gas of massive galaxy clusters. The universal temperature profile in cool-core clusters and the theoretical mass–temperature relation suggest that the maximum effect of sedimentation must take place in the most massive virialized objects in the Universe. However, observational data from the Chandra and XMM-Newton observatories demonstrate more complex scaling relations between the masses of early-type galaxies and other parameters, such as the mass fraction and temperature of the interstellar gas. An important fact is that the radial temperature profile can have both falling and rising patterns. We have calculated the diffusion based on the observed gas density and temperature distributions for 13 early-type galaxies that have different envelope types and cover a wide range of X-ray luminosities. To estimate the maximum effect of sedimentation and thermal diffusion, we have solved the full set of Burgers equations for a non-magnetized interstellar plasma. The results obtained demonstrate a considerable increase of the He/H ratio within one effective radius for all galaxies of our sample. For galaxies with a falling or constant temperature profile the average increase of the helium abundance is 60% in one billion years of diffusion. The revealed effect can introduce a significant bias into the metal abundance estimate based on X-ray spectroscopy and can affect the evolution of stars that could be formed from a gas with a high helium abundance.
PubDate: 2017-05-01
DOI: 10.1134/s1063773717050024
Issue No: Vol. 43, No. 5 (2017)

• Vertical distribution and kinematics of planetary nebulae in the milky way
• Authors: V. V. Bobylev; A. T. Bajkova
Pages: 304 - 315
Abstract: Based on published data, we have produced a sample of planetary nebulae (PNe) that is complete within 2 kpc of the Sun. We have estimated the total number of PNe in the Galaxy from this sample to be 17 000±3000 and determined the vertical scale height of the thin disk based on an exponential density distribution to be 197 ± 10 pc. The next sample includes PNe from the Stanghellini–Haywood catalog with minor additions. For this purpose, we have used ~200 PNe with Peimbert’s types I, II, and III. In this case, we have obtained a considerably higher value of the vertical scale height that increases noticeably with sample radius. We have experimentally found that it is necessary to reduce the distance scale of this catalog approximately by 20%. Then, for example, for PNe with heliocentric distances less than 4 kpc the vertical scale height is 256 ± 12 kpc. A kinematic analysis has confirmed the necessity of such a reduction of the distance scale.
PubDate: 2017-05-01
DOI: 10.1134/s1063773717040028
Issue No: Vol. 43, No. 5 (2017)

• New orbits of wide visual double stars
• Authors: O. V. Kiyaeva; L. G. Romanenko; R. Ya. Zhuchkov
Pages: 316 - 331
Abstract: Based on photographic and CCD observations with the Pulkovo 26-inch refractor, radial velocity measurements with the 1.5-m RTT-150 telescope (TUBITAK National Observatory, Turkey), and highly accurate observations published in the WDS catalog, we have obtained the orbits of ten wide visual double stars by the apparent motion parameter method. The orientation of the orbits in the Galactic coordinate system has been determined. For the outer pair of the multiple star HIP 12780 we have calculated a family of orbits with a minimum period P = 4634 yr. Two equivalent solutions with the same period have been obtained for the stars HIP 50 (P = 949 yr) and HIP 66195 (P = 3237 yr). We have unambiguously determined the orbits of six stars: HIP 12777 (P = 3327 yr), HIP 15058 (P = 420 yr), HIP 33287 (P = 1090 yr), HIP 48429 (P = 1066 yr), HIP 69751 (P = 957 yr), and HIP 73846 (P = 1348 yr). The orbit of HIP 55068 is orientated perpendicularly to the plane of the sky, P >1000 yr. The star HIP 48429 is suspected to have an invisible companion.
PubDate: 2017-05-01
DOI: 10.1134/s1063773717040041
Issue No: Vol. 43, No. 5 (2017)

• A joined model for solar dynamo and differential rotation
• Authors: L. L. Kitchatinov; A. A. Nepomnyashchikh
Pages: 332 - 343
Abstract: A model for the solar dynamo, consistent in global flow and numerical method employed with the differential rotation model, is developed. The magnetic turbulent diffusivity is expressed in terms of the entropy gradient, which is controlled by the model equations. The magnetic Prandtl number and latitudinal profile of the alpha-effect are specified by fitting the computed period of the activity cycle and the equatorial symmetry of magnetic fields to observations. Then, the instants of polar field reversals and time-latitude diagrams of the fields also come into agreement with observations. The poloidal field has a maximum amplitude of about 10 Gs in the polar regions. The toroidal field of several thousand Gauss concentrates near the base of the convection zone and is transported towards the equator by the meridional flow. The model predicts a value of about 1037 erg for the total magnetic energy of large-scale fields in the solar convection zone.
PubDate: 2017-05-01
DOI: 10.1134/s106377371704003x
Issue No: Vol. 43, No. 5 (2017)

• The speckle polarimeter of the 2.5-m telescope: Design and calibration
• Authors: B. S. Safonov; P. A. Lysenko; A. V. Dodin
Pages: 344 - 364
Abstract: The speckle polarimeter is a facility instrument of the 2.5-mSAIMSU telescope that combines the features of a speckle interferometer and a polarimeter. The speckle polarimeter is designed for observations in several visible bands in the following modes: speckle interferometry, polarimetry, speckle polarimetry, and polaroastrometry. In this paper we describe the instrument design and the procedures for determining the angular scale of the camera and the position angle of the camera and the polarimeter. Our measurements of the parameters for the binary star HD 9165 are used as an example to demonstrate the technique of speckle interferometry. For bright objects the accuracy of astrometry is limited by the error of the correction for the distortion caused by the atmospheric dispersion compensator. At zenith distances less than 45◦ the additional relative measurement error of the separation is 0.7%, while the additional error of the position angle is 0.3°. In the absence of a dispersion compensator the accuracy of astrometry is limited by the uncertainty in the scale and position angle of the camera, which are 0.15% and 0.06°, respectively. We have performed polarimetric measurements of unpolarized stars and polarization standards. The instrumental polarization at the Cassegrain focus in the V band does not exceed 0.01%. The instrumental polarization for the Nasmyth focus varies between 2 and 4% within the visible range; we have constructed its model and give a method for its elimination from the measurements. For stars with an intrinsic polarization of less than 0.2% during observations at the Cassegrain focus the error is determined mainly by the photon and readout noises and can reach 5 × 10−5.
PubDate: 2017-05-01
DOI: 10.1134/s1063773717050036
Issue No: Vol. 43, No. 5 (2017)

• Preheating of the early universe by radiation from high-mass X-ray
binaries
• Authors: S. Yu. Sazonov; I. I. Khabibullin
Pages: 211 - 220
Abstract: Using a reliablymeasured intrinsic (i.e., corrected for absorption effects) present-day luminosity function of high-mass X-ray binaries (HMXBs) in the 0.25–2 keV energy band per unit star formation rate, we estimate the preheating of the early Universe by soft X-rays from such systems. We find that X-ray irradiation, mainly executed by ultraluminous and supersoft ultraluminous X-ray sources with luminosity L X > 1039 erg s−1, could significantly heat (T >T CMB, where T CMB is the temperature of the cosmic microwave background) the intergalactic medium by z ~ 10 if the specific X-ray emissivity of the young stellar population in the early Universe was an order of magnitude higher than at the present epoch (which is possible due to the low metallicity of the first galaxies) and the soft X-ray emission from HMXBs did not suffer strong absorption within their galaxies. This makes it possible to observe the 21 cm line of neutral hydrogen in emission from redshifts z < 10.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040077
Issue No: Vol. 43, No. 4 (2017)

• Active zone of the nucleus of the quasar 3C 273
• Authors: L. I. Matveyenko; S. V. Seleznev
Pages: 221 - 232
Abstract: The superfine structure of the quasar 3C 273 has been investigated at wavelengths λ = 2 and 6 cm with angular resolutions up to φ = 20 μas for epochs 2005–2014. We have identified a nozzle and a bipolar outflow: a jet and a counterjet consisting of coaxial high- and low-velocity components. The separation between the nozzles in the plane of the sky is Δρ = 0.84 ± 0.16 pc; the flow ejection velocity is v ≤ 0.1c. The nozzle brightness temperature reaches T b ≈ 45 × 1012 K, φ = 20 μas, λ = 2 cm. The ejected electrons radiatively cool at a distance up to ≤4 pc. However, the jet afterglow is observed at a 8% level at a distance up to ρ ≈ 16 pc; the acceleration compensates for the radiative losses. The reduction in the emission level of the central flow at large distances determines the jet bifurcation. The counterjet shape is a mirror reflection of the initial part of the jet, suggesting a symmetry and identity of the ejected flows. The counterjet and jet nozzles are in the near and remote parts of the active region, respectively. The emission from the nozzles is absorbed by a factor of 2 and 15, respectively. The absorption decreases with increasing distance and the brightness of the jet fragments rises to its maximum at 0.5 pc from the nozzle. Arclike structures, arm fragments, are observed in the region of the nozzles. The relativistic plasma comes to the nozzles and is ejected. The brightness temperature of the arclike structures reaches 10% of the peak value, which is determined by the a smaller optical depth, the visibility in the transverse direction. The central high-velocity flow is surrounded by low-velocity components, hollow tubes being ejected as an excess angular momentum is accumulated. The remainder of the material flows along the arms toward the disk center until the next accumulation of an excess angular momentum and the process is repeated. The diameter of the outer nozzle is Ø = 25 pc and, further out, decreases exponentially; Ø n ≈ 80 exp(−1.15n) pc. The flow kinematics, collimation, and acceleration have a vortical nature. Ring currents producing magnetic fields, which accelerate and stabilize the processes, are generated in the rotating flows (tubes). The tangential directions of the currents are observed as parallel chains of components.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040053
Issue No: Vol. 43, No. 4 (2017)

• Study of the nuclear activity of the Seyfert galaxy NGC 7469 over the
period of observations 2008–2014
• Authors: L. S. Ugol’kova; B. P. Artamonov; E. V. Shimanovskaya; V. V. Bruevich; O. Burkhonov; Sh. A. Egamberdiev; N. V. Metlova
Pages: 233 - 240
Abstract: We present the results of our multicolor UBV RI observations of NGC 7469, a type 1 Seyfert galaxy (SyG 1), in 2008–2014 at the Maidanak Observatory. Analysis of the long-term variability of NGC 7469 for two observing periods, 1990–2007 and 2008–2014, has shown the existence of yet another activity cycle of the slow component in 2009–2014 with an activity maximum in 2011–2012. We have studied the slow variability component in 2009–2014 and constructed the color–color (U − B), (B − V) diagrams for the variability maxima and minima of NGC 7469 in various apertures and for the blackbody gas radiation modeling the accretion disk radiation. It can be seen from the color–color diagram that the color of the nuclear part of NGC 7469 becomes bluer at maximum brightness, suggesting a higher temperature of the accretion disk. We have analyzed the X-ray variability of NGC 7469 in 2008 and 2009 in comparison with the activity minimum in 2003. The optical–X ray correlation coefficient in 2008 is close to 0.5. The weak correlation is explained by the influence of an SN 1a explosion in the circumnuclear part of NGC 7469, which manifests itself in the optical band but does not change the pattern of X-ray variability. Comparison of the variability data for 2009 shows an optical–X ray (U band–7–10 keV) correlation with a correlation coefficient of about 0.93. The correlation coefficient and the lag depend on the wavelength in the optical and X-ray bands. The lag between the X-ray and optical fluxes in 2009 is observed to a lesser extent in 2003.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040089
Issue No: Vol. 43, No. 4 (2017)

• Refinement of the parameters of three selected model Galactic potentials
based on the velocities of objects at distances up to 200 kpc
• Authors: V. V. Bobylev; A. T. Bajkova; A. O. Gromov
Pages: 241 - 251
Abstract: This paper is a continuation of our recent paper devoted to refining the parameters of threecomponent (bulge, disk, halo) axisymmetric model Galactic gravitational potentials differing by the expression for the dark matter halo using the velocities of distant objects. In all models the bulge and disk potentials are described by the Miyamoto–Nagai expressions. In our previous paper we used the Allen–Santillán (I), Wilkinson–Evans (II), and Navarro–Frenk–White (III) models to describe the halo. In this paper we use a spherical logarithmic Binney potential (model IV), a Plummer sphere (model V), and a Hernquist potential (model VI) to describe the halo. A set of present-day observational data in the range of Galactocentric distances R from 0 to 200 kpc is used to refine the parameters of the listed models, which are employed most commonly at present. The model rotation curves are fitted to the observed velocities by taking into account the constraints on the local matter density ρ⊙= 0.1 M ⊙pc−3 and the force K z=1.1/2πG = 77M ⊙pc−2 acting perpendicularly to the Galactic plane. The Galactic mass within spheres of radius 50 and 200 kpc are shown to be, respectively, M 50 = (0.409 ± 0.020) × 1012 M ⊙ and M 200 = (1.395 ± 0.082) × 1012 M ⊙ in model IV, M 50 = (0.417 ± 0.034) × 1012 M ⊙ and M 200 = (0.469 ± 0.038) × 1012 M ⊙in model V, and M 50 = (0.417 ± 0.032) × 1012 M ⊙ and M 200 = (0.641 ± 0.049)× 1012 M ⊙ in model VI. Model VI looks best among the three models considered here from the viewpoint of the achieved accuracy of fitting the model rotation curves to the measurements. This model is close to the Navarro–Frenk–White model III refined and considered best in our previous paper, which is shown using the integration of the orbits of two globular clusters, Lynga 7 and NGC 5053, as an example.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040016
Issue No: Vol. 43, No. 4 (2017)

• Investigation of the dependence of rare-earth element abundances on the
effective temperature and magnetic field in the atmospheres of chemically
peculiar (Ap) stars
• Authors: T. A. Ryabchikova; A. M. Romanovskaya
Pages: 252 - 264
Abstract: We have derived the abundances of the rare-earth elements (REEs) Ce, Pr, Nd, and Eu in the atmospheres of 26 magnetic peculiar (Ap) stars in the range of effective temperatures 7000–10 000 K from spectra with resolutions R = 48 000 and 80 000 and investigated the dependence of the CePrNdEu anomalies (the difference in the element abundances determined separately from lines of the first and second ionization stages) on the effective temperature. The REE anomaly is shown to decrease with increasing effective temperature virtually to the point of disappearance for all of the investigated elements, except Eu. For the best-studied element Nd the Nd anomaly has also been found to decrease with increasing magnetic field strength for cool stars. For hot stars there is no Nd anomaly in a wide range of magnetic field strengths. Since the presence of anomalies in cool Ap stars is associated with the REE concentration in the upper atmospheric layers, the lower boundary of the REE layer apparently sinks into deeper layers with increasing effective temperature and magnetic field, causing the anomalies to disappear. We have detected an anticorrelation between the abundances of iron-peak elements and rare-earth elements, which serves as additional evidence for different stratification of these elements in the atmospheres of Ap stars.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040065
Issue No: Vol. 43, No. 4 (2017)

• Spectroscopic studies of yellow supergiants in the Cepheid instability
strip
• Authors: I. A. Usenko
Pages: 265 - 283
Abstract: High-resolution spectra of nine yellow nonvariable supergiants (NVSs) located within the canonical Cepheid instability strip from Sandage and Tammann (1969) (α Aqr, ϵ Leo, μ Per, ω Gem, BD+60 2532, HD 172365, HD 187299, HD 190113, and HD 200102) were taken with the 1-m Zeiss and 6-m BTA telescopes at the Special Astrophysical Observatory of the Russian Academy of Sciences in the 1990s. These have been used to determine the atmospheric parameters, chemical composition, radial velocities, reddenings, luminosities, distances, and radii. The spectroscopic estimates of T eff and the luminosities determined from the Hipparcos parallaxes have shown eight of the nine program NVSs on the T eff−log(L/L ⊙) diagram to be outside the canonical Cepheid instability strip. When the edges of the Cepheid instability strip from Bono et al. (2000) are used, out of the NVSs from the list on the diagram one is within the Cepheid instability strip but closer to the red edge, two are at the red edge, three are beyond the red edge, two are at the blue edge, and one is beyond the blue edge. The evolutionary masses of the objects have been estimated. The abundances of α-elements, r- and s-process elements for all program objects have turned out to be nearly solar. The СNO, Na, Mg, and Al abundance estimates have shown that eight of the nine NVSs from the list have already passed the first dredge-up. Judging by the abundances of the key elements and its position on the T eff−log(L/L ⊙) diagram, the lithium-rich supergiant HD 172365 is at the post-main-sequence evolutionary stage of gravitational helium core contraction and moves toward the first crossing of the Cepheid instability strip. The star ϵ Leo should be assigned to bright supergiants, while HD 187299 and HD 190113 may have already passed the second dredge-up and move to the asymptotic branch.
PubDate: 2017-04-01
DOI: 10.1134/s1063773717040090
Issue No: Vol. 43, No. 4 (2017)

• Optical spectroscopy of candidates for quasars at 3 < z < 5.5 from
the XMM-newton X-ray survey. A distant X-ray quasar at z = 5.08
• Authors: G. A. Khorunzhev; R. A. Burenin; S. Yu. Sazonov; A. L. Amvrosov; M. V. Eselevich
Pages: 135 - 145
Abstract: We present the results of optical spectroscopy for 19 quasar candidates at photometric redshifts z phot ≳ 3, 18 of which enter into the Khorunzhev et al. (2016) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. We have performed spectroscopy for a quasi-random sample of new candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory. The spectra at AZT-33IK were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. Fourteen of the 18 candidates actually have turned out to be quasars; 10 of them are at spectroscopic redshifts z spec > 3. The high purity of the sample of new candidates suggests that the purity of the entire K16 catalog of quasars is probably 70–80%. One of the most distant (z spec = 5.08) optically bright (i′ ≲ 21) quasars ever detected in X-ray surveys has been discovered.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717030045
Issue No: Vol. 43, No. 3 (2017)

• Spatial environment of polar-ring galaxies from the SDSS
• Authors: S. S. Savchenko; V. P. Reshetnikov
Pages: 146 - 151
Abstract: Based on SDSS data, we have considered the spatial environment of galaxies with extended polar rings. We used two approaches: estimating the projected distance to the nearest companion and counting the number of companions as a function of the distance to the galaxy. Both approaches have shown that the spatial environment of polar-ring galaxies on scales of hundreds of kiloparsecs is, on average, less dense than that of galaxies without polar structures. Apparently, one of the main causes of this effect is that the polar structures in a denser environment are destroyed more often during encounters and mergers with other galaxies.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717020050
Issue No: Vol. 43, No. 3 (2017)

• Kinematics of the galaxy from Cepheids with proper motions from the Gaia
DR1 catalogue
• Authors: V. V. Bobylev
Pages: 152 - 158
Abstract: 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.
PubDate: 2017-03-01
DOI: 10.1134/s106377371703001x
Issue No: Vol. 43, No. 3 (2017)

• Kinematics of the galaxy from OB stars with proper motions from the Gaia
DR1 catalogue
• Authors: V. V. Bobylev; A. T. Bajkova
Pages: 159 - 166
Abstract: We consider two samples of OB stars with different distance scales that we have studied previously. The first and second samples consist of massive spectroscopic binaries with photometric distances and distances determined from interstellar calcium lines, respectively. The OB stars are located at heliocentric distances up to 7 kpc. We have identified them with the Gaia DR1 catalogue. Using the proper motions taken from the Gaia DR1 catalogue is shown to reduce the random errors in the Galactic rotation parameters compared to the previously known results. By analyzing the proper motions and parallaxes of 208 OB stars from the Gaia DR1 catalogue with a relative parallax error of less than 200%, we have found the following kinematic parameters: (U, V)⊙ = (8.67, 6.63)± (0.88, 0.98) km s−1, Ω0 = 27.35 ± 0.77 km s−1 kpc−1, Ω′0 = −4.13 ± 0.13 km s−1 kpc−2, and Ω″0 = 0.672 ± 0.070 km s−1 kpc−3, the Oort constants are A = −16.53 ± 0.52 km s−1 kpc−1 and B = 10.82 ± 0.93 km s−1 kpc−1, and the linear circular rotation velocity of the local standard of rest around the Galactic rotation axis is V 0 = 219 ± 8 km s−1 for the adopted R 0 = 8.0 ± 0.2 kpc. Based on the same stars, we have derived the rotation parameters only from their line-of-sight velocities. By comparing the estimated values of Ω′0, we have found the distance scale factor for the Gaia DR1 catalogue to be close to unity: 0.96. Based on 238 OB stars of the combined sample with photometric distances for the stars of the first sample and distances in the calcium distance scale for the stars of the second sample, line-of-sight velocities, and proper motions from the Gaia DR1 catalogue, we have found the following kinematic parameters: (U, V, W)⊙ = (8.19, 9.28, 8.79)± (0.74, 0.92, 0.74) km s−1, Ω0 = 31.53 ± 0.54 km s−1 kpc−1, Ω′0 = −4.44 ± 0.12 km s−1 kpc−2, and Ω″0 = 0.706 ± 0.100 km s−1 kpc−3; here, A = −17.77 ± 0.46 km s−1 kpc−1, B = 13.76 ± 0.71 km s−1 kpc−1, and V 0 = 252 ± 8 km s−1.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717030021
Issue No: Vol. 43, No. 3 (2017)

• The outburst of the X-ray nova GRS 1739-278 in September 2016
• Authors: I. A. Mereminskiy; E. V. Filippova; R. A. Krivonos; S. A. Grebenev; R. A. Burenin; R. A. Sunyaev
Pages: 167 - 174
Abstract: During the scanning observations of the Galactic center region in late August–September 2016 we detected a new (third) outburst of the historical X-ray nova GRS 1739-278, a presumed black hole in a low-mass X-ray binary. This was reported in the Astronomer’s Telegrams (Mereminskiy et al. 2016). In this paper we present the results of INTEGRAL and Swift observations of the outburst development. According to these observations, the flux from the source in the hard X-ray band (20–60 keV) rose from ~11 (September 3) to ~30 mCrab (September 14), was at the attained level for ~8 days, and then returned to ~15 mCrab. The spectrum of the source taken at its peak brightness in the energy range 0.5–150 keV could be fitted by a single power law with a photon index of 1.86 ± 0.07 distorted only by photoabsorption corresponding to the hydrogen column density log10 (N H) = 22.37 under the assumption of a solar abundance. This means that the source at this time was in the low/hard state. Infrared observations with the RTT-150 telescope near the X-ray brightness peak of the source revealed no emission down to $$22_ \cdot ^m 0$$ (in the r’ band) and $$20_ \cdot ^m 9$$ (in the i’ band). At the time of writing the paper we do not yet know whether this outburst ended or only its initial stage was observed. If it ended, then based on the light curve and spectra, we can state that it was a “failed” outburst, i.e., the amount of accreted matter in this episode was insufficient to reach the high or very high state with a soft blackbody component in the spectrum characteristic of developed outbursts.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717030057
Issue No: Vol. 43, No. 3 (2017)

• NuSTAR observations of the X-ray pulsar LMC X-4: A constraint on the
magnetic field and tomography of the system in the fluorescent iron line
• Authors: A. E. Shtykovsky; A. A. Lutovinov; V. A. Arefiev; S. V. Molkov; S. S. Tsygankov; M. G. Revnivtsev
Pages: 175 - 185
Abstract: We present the results of the spectral and timing analysis of the X-ray pulsar LMC X-4 based on data from the NuSTAR observatory in the broad X-ray energy range 3–79 keV. Along with a detailed analysis of the source’s averaged spectrum, high-precision spectra corresponding to different phases of the neutron star spin cycle have been obtained for the first time. The Comptonization model is shown to describe best the source’s spectrum, and the evolution of its parameters as a function of the pulse phase has been traced. For all spectra (the averaged and phase-resolved ones) in the energy range 5–55 keV we have searched for the cyclotron absorption line. The derived upper limit on the optical depth of the cyclotron line τ ~ 0.15 (3σ) points to the absence of this feature in the given energy range, which provides a constraint on the magnetic field of the neutron star: B <3 × 1011 or >6.5 × 1012 G. The latter constraint is consistent with the magnetic field estimate obtained by analyzing the pulsar’s power spectrum, B ≅ 3 × 1013 G. Based on our analysis of the phase-resolved spectra, we have determined the delay between the emission peaks and the equivalent width of the fluorescent iron line. This delay depends on the orbital phase and is apparently associated with the travel time of photons between the emitting regions in the vicinity of the neutron star and the region where the flux is reflected (presumably in the inflowing stream or at the place of interaction between the stream and the outer edge of the accretion disk).
PubDate: 2017-03-01
DOI: 10.1134/s1063773717030069
Issue No: Vol. 43, No. 3 (2017)

• Change in the orbital period of a binary system due to dynamical tides for
main-sequence stars
• Authors: S. V. Chernov
Pages: 186 - 201
Abstract: We investigate the change in the orbital period of a binary system due to dynamical tides by taking into account the evolution of a main-sequence star. Three stars with masses of one, one and a half, and two solar masses are considered. A star of one solar mass at lifetimes t = 4.57 × 109 yr closely corresponds to our Sun. We show that a planet of one Jupiter mass revolving around a star of one solar mass will fall onto the star in the main-sequence lifetime of the star due to dynamical tides if the initial orbital period of the planet is less than P orb ≈ 2.8 days. Planets of one Jupiter mass with an orbital period P orb ≈ 2 days or shorter will fall onto a star of one and a half and two solar masses in the mainsequence lifetime of the star.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717030033
Issue No: Vol. 43, No. 3 (2017)

• Change in the activity character of the coronae of low-mass stars of
various spectral types
• Authors: B. A. Nizamov; M. M. Katsova; M. A. Livshits
Pages: 202 - 209
Abstract: We study the dependence of the coronal activity index on the stellar rotation velocity. This question has been considered previously for 824 late-type stars on the basis of a consolidated catalogue of soft X-ray fluxes. We carry out a more refined analysis separately for G, K, and M dwarfs. Two modes of activity are clearly identified in them. The first is the saturation mode, is characteristic of young stars, and is virtually independent of their rotation. The second refers to the solar-type activity whose level strongly depends on the rotation period. We show that the transition from one mode to the other occurs at rotation periods of 1.1, 3.3, and 7.2 days for stars of spectral types G2, K4, and M3, respectively. In light of the discovery of superflares on G and K stars from the Kepler spacecraft, the question arises as to what distinguishes these objects from the remaining active late-type stars. We analyze the positions of superflare stars relative to the remaining stars observed by Kepler on the “amplitude of rotational brightness modulation (ARM)—rotation period” diagram. The ARM reflects the relative spots area on a star and characterizes the activity level in the entire atmosphere. G and K superflare stars are shown to be basically rapidly rotating young objects, but some of them belong to the stars with the solar type of activity.
PubDate: 2017-03-01
DOI: 10.1134/s1063773717020049
Issue No: Vol. 43, No. 3 (2017)

• Influence of the magnetic field on the density distribution of solar wind
protons and cometary ions in the shock layer ahead of cometary ionospheres

• Authors: V. B. Baranov; D. B. Alexashov
Pages: 126 - 133
Abstract: The “mass loading” of the solar wind by cometary ions produced by the photoionization of neutral molecules outflowing from the cometary nucleus plays a major role in the interaction of the solar wind with cometary atmospheres. In particular, this process leads to a decrease in the solar wind velocity with a transition from supersonic velocities to subsonic ones through the bow shock. The so-called single-fluid approximation, in which the interacting plasma flows are considered as a single fluid, is commonly used in modeling such an interaction. However, it is occasionally necessary to know the distribution of parameters for the components of the interacting plasma flows. For example, when the flow of the cometary dust component in the interplanetary magnetic field is considered, the dust particle charge, which depends significantly on the composition of the surrounding plasma, needs to be known. In this paper, within the framework of a three-dimensional magnetohydrodynamic model of the solar wind flow around cometary ionospheres, we have managed to separately obtain the density distributions of solar wind protons and cometary ions between the bow shock and the cometary ionopause (in the shock layer). The influence of the interplanetary magnetic field on the position of the point of intersection between the densities with the formation of a region near the ionopause where the proton density is essentially negligible compared to the density of cometary ions is investigated. Such a region was experimentally detected by the Vega-2 spacecraft when investigating Comet Halley in March 1986. The results of the model considered below are compared with some experimental data obtained by the Giotto spacecraft under the conditions of flow around Comets Halley and Grigg–Skjellerup in 1986 and 1992, respectively. Unfortunately, our results of calculations on Comet Churyumov–Gerasimenko are only predictive in character, because the trajectory of the Rosetta spacecraft, which manoeuvred near its surface for several months, is complex.
PubDate: 2017-02-01
DOI: 10.1134/s1063773717020013
Issue No: Vol. 43, No. 2 (2017)

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