Spectral investigations of stellar objects from the second Byurakan sky survey. I. The fields centered on α=08h00m, δ=+59°00′ and α=09h47m, δ=+51°00′

Byurakan Astrophysical Observatory; Special Astrophysical Observatory, USSR Academy of Sciences. Translated from Astrofizika, Vol. 33, No. 1, pp. 89–105, July–August, 1990.     

Astrometric Observations of the Galilean Moons of Jupiter at the Pulkovo Normal Astrograph in 2016−2017

We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2016?2017. We obtained 761 positions of the Galilean moons of Jupiter in the system of the Gaia DR1 catalog (ICRF, J2000.0) and 854 differential coordinates of the satellites relative to each other. The mean errors in the satellites’ normal places and the corresponding root-mean-square deviations are ε_α = 0.0020′′, ε_δ = 0.0027′′, σ_α = 0.0546′′, and σ_δ = 0.0757′′. The equatorial coordinates of the moons are compared to the motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are less than 0.031′′. The best agreement with observations is achieved by a combination of the EPM2015 and V. Lainey-V.2.0|V1.1 motion theories, which yields the average (O–C) residuals of approximately 0.02″. Peculiarities in the behavior of the (O–C) residuals and error values in Ganymede have been noticed.     

Low resolution spectroscopy of selected Algol systems

The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries.     

Nonlinear model to study filamentation instability of circularly polarized dispersive Alfvén waves in solar wind plasmas

This paper examines the small-scale solar wind turbulence driven in view of the Alfvén waves subjected to ponderomotive nonlinearity. Filamentation instability is known to take place for the case of dispersive Alfvén wave (DAW) propagating parallel to the ambient magnetic field. The ponderomotive force associated with DAW is responsible for wave localization and these webs of filaments become more intense and irregular as one proceeds along the spatial domain. The ponderomotive force associated with pump changes with pump parameters giving rise to different evolution patterns. This paper studies in detail the nonlinear evolution of filamentation instability introduced by dispersive Alfven waves (DAWs) which becomes dispersive on account of the finite frequency of DAW i.e., pump frequency is comparable to the ion cyclotron frequency. We have explicitly obtained the perturbation dynamics and then examined the impact of pump magnitude on the driven magnetic turbulence using numerical simulation. The results show steepening at small scales with increasing pump amplitude. The compressibility associated with acoustic fluctuations may explain the variation in spectral scaling of solar wind turbulence as observed by Alexandrova et al. (Astrophys. J. 674:1157, 2008).     

X-ray emission from accretion disks in active galactic nuclei

We constructed a grid of relativistic models for standard high-relative-luminosity accretion α-disks around supermassive Kerr black holes (BHs) and computed X-ray spectra for their hot, effectively optically thin inner parts by taking into account general-relativity effects. They are known to be heated to high (～10⁶–10⁹ K) temperatures and to cool down through the Comptonization of intrinsic thermal radiation. Their spectra are power laws with an exponential cutoff at high energies; i.e., they have the same shape as those observed in active galactic nuclei (AGNs). Fitting the observed X-ray spectra of AGNs with computed spectra allowed us to estimate the fundamental parameters of BHs (their mass and Kerr parameter) and accretion disks (luminosity and inclination to the line of sight) in 28 AGNs. We show that the Kerr parameter for BHs in AGNs is close to unity and that the disk inclination correlates with the Seyfert type of AGN, in accordance with the unification model of activity. The estimated BH masses M_x are compared with the masses M_rev determined by the reverberation mapping technique. For AGNs with luminosities close to the Eddington limit, these masses agree and the model under consideration may be valid for them. For low-relative-luminosity AGNs, the differences in masses increase with decreasing relative luminosity and their X-ray emission cannot be explained by this model.     

Increase of the Magnetic Flux From Polar Zones of the sun in the Last 120 Years

Lockwood, Stamper, and Wild (1999) argued that the average strength of the magnetic field of the Sun has doubled in the last 100 years. They used an analysis of the geomagnetic index aa. We calculated the area of polar zones of the Sun, A _pz, occupied by unipolar magnetic field on H synoptic magnetic charts, following Makarov (1994), from 1878 to 2000. We found a gradual decrease of the annual minimum latitude of the high-latitude zone boundaries, _2m, of the global magnetic field of the Sun at the minimum of activity from 53° in 1878 down to 38° in 1996, yielding an average decrease of 1.2° per cycle. Consequently the area of polar zones A _pz of the Sun, occupied by unipolar magnetic field at the minimum activity, has risen by a factor of 2 during 1878–1996. This means that the behavior of the index aa and consequently the magnetic flux from the Sun may be explained by an increase of the area of polar caps with roughly the same value of the magnetic field in this period. The area of the unipolar magnetic field at the poles (A _pz) may be used as a new index of magnetic activity of the Sun. We compared A _pz with the aa, the Wolf number W and A^* -index (Makarov and Tlatov, 2000). Correlations based on `11-year' averages are discussed. A temperature difference of about 1° between the Maunder Minimum and the present time was deduced. We have found that the highest latitude of the polar zone boundaries of the large-scale magnetic field during very low solar activity reaches about 60°, cf., the Maunder Minimum. It is supposed that the _2m-latitude coincides with the latitude where _r=0, with (r,) being the angular frequency of the solar rotation. The causes of the waxing and waning of the Sun's activity in conditions like Maunder Minimum are discussed.     

Existence and amount of intergalactic dust

The existence of intergalactic dust has been proved by the following observational facts: the decrease of the numbers of distant galaxies and clusters of galaxies behind the central regions of near clusters of galaxies; the different distributions of RR Lyrae stars and galaxies near ι Microscopii (Hoffmeister's cloud); the dependence of colour excesses of galaxies on supergalactic coordinates as well as on the surface density of bright galaxies; the colour index vs redshift correlation of quasistellar objects. The densities of intergalactic dust are estimated to be between 5×10^?30 g cm^?3 (near the centers of clusters of galaxies) and 2×10^?34 g cm^?3 (in general intergalactic space). The grains may be formed either in the early phases of the Universe (25相似文献   

Collisional heating of interplanetary gas: Fokker-Planck treatment

Interstellar gas streaming through the solar system undergoes both elastic collisions with solar wind ions and destructive, ionizing processes. The Boltzmann equation is set up, with linear Fokker-Planck terms describing the glancing elastic collisions. Solutions combining the dynamical effects of the central force field and the diffusion in velocity space are derived, appropriate to cool gas.For the He component of the streaming gas, if initially at 100 K, the collisional heating dominates inside 2 a.u. upstream and 5 a.u. downstream. A modified formula is given for the density in the downstream wake, as enhanced by gravitational focussing. Calculations of the helium resonant radiation backscatter require substantial modification.     

Discovery of the 'missing' mode in HR 1217 by the Whole Earth Telescope

HR 1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals  1.5×33.3 μHz)  to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multisite photometric campaign on the rapidly oscillating Ap star HR 1217 using the 'Whole Earth Telescope'. While a complete analysis of the data will appear in a later paper, one outstanding result from this run is the discovery of a newly detected frequency in the pulsation spectrum of this star, at the frequency predicted by Cunha.     

On the global solution of the N-body problem

In connection with the publication (Wang Qiu-Dong, 1991) the Poincaré type methods of obtaining the maximal solution of differential equations are discussed. In particular, it is shown that the Wang Qiu-Dong'sglobal solution of the N-body problem has been obtained in Babadzanjanz (1979). First the more general results on differential equations have been published in Babadzanjanz (1978).