HeII <Emphasis Type="Italic">λ</Emphasis>304 emission above sunspot umbrae

Observations of sunspot umbrae in the HeII λ304 Å and HeI λ10830 Å lines are analyzed and compared. Spectral observations in the HeI λ10830 line obtained on the Large Non-Eclipse Solar Coronograph of the Sayan Solar Observatory are used, together with HeII λ304 data obtained with the SOHO/EIT and CORONAS-f spacecraft. The contrast in the HeII λ304 line was chosen as an indicator of the UV flux. The dependences of the contrast in the HeII λ304 line and the parameters of the HeI λ10830 IR triplet on the sunspot area are obtained. The sunspot areas were determined using white-light images. A division of the dependences of the parameters of the HeI λ10830 and HeII λ304 lines on the sunspot area into two branches can be distinguished for leading and trailing sunspots. Possible origins of this behavior of the line parameters are discussed.     

Horizontal magnetic fields in the solar photosphere

Two-dimensional simulations of time-dependent solar magnetogranulation are used to analyze the horizontal magnetic fields and the response of the synthesized Stokes profiles of the IR FeI λ1564.85 nm line to the magnetic fields. The 1.5-h series of MHD models used for the analyses reproduces a region of the magnetic network in the photosphere with an unsigned magnetic flux density of 192 G at the solar surface. According to the magnetic-field distribution obtained, the most probable absolute strength of the horizontal magnetic field at an optical depth of τ ₅ = 1(τ ₅ denotes τ at λ = 500 nm) is 50 G, while the mean value is 244 G. On average, the horizontal magnetic fields are stronger than the vertical fields to heights of about 400 km in the photosphere due to their higher density and the larger area they occupy. The maximum factor by which the horizontal fields are greater is 1.5. Strong horizontal magnetic flux tubes emerge at the surface as spots with field strengths of more than 500 G. These are smaller than granules in size, and have lifetimes of 3–6 min. They form in the photosphere due to the expulsion of magnetic fields by convective flows coming from deep subphotospheric layers. The data obtained qualitatively agree with observations with the Hinode space observatory.     

A study of the supergiant 89 Her

We have used spectrograms taken with a dispersion of 8–12 Å per mm and Kurucz model atmospheres to study the supergiant 89 Her (F2Ibe).We find the effective temperature and gravity T _eff = 6300 ± 150 K and log g = 0.5 ± 0.2. We have analyzed the microturbulence in the star’s atmosphere based on FeI, FeII, and TiII lines, deriving ξ _t = 7.0 ± 0.5 km/s for the FeI and TiII lines and ξ _t = 8.0 ± 0.5 km/s for the FeII lines. Abundances were determined for 23 elements. The elemental abundances in the atmosphere of 89 Her show deficiencies compared to the solar chemical composition, except for sodium, which is overabundant relative to the Sun.     

Comparison of the magnetic properties of leading and following spots and the overlying ultraviolet emission

SDO/HMI and SDO/AIA data for the 24th solar-activity cycle are analyzed using a quicker and more accurate method for resolving π ambiguities in the transverse component of the photospheric magnetic field, yielding new results and confirming some earlier results on the magnetic properties of leading and following magnetically connected spots and single spots. The minimum inclination of the field lines to the positive normal to the solar surface α _min within umbrae is smaller in leading than in following spots in 78% of the spot pairs considered; the same trend is found for the mean angle 〈α〉 in 83% of the spot pairs. Positive correlations between the α _min values and the 〈α〉 values in leading and following spots are also found. On average, in umbrae, the mean values of 〈B〉, the umbra area S, and the angles α _min and 〈α〉 decrease with growth in the maximum magnetic field B _max in both leading and following spots. The presence of a positive correlation between B _max and S is confirmed, and a positive correlation between 〈B〉 and S in leading and following spots has been found. Themagnetic properties of the umbrae of magnetically connected pairs of spots are compared with the contrast of the He II 304 emission above the umbrae, C ₃₀₄. Spots satisfying certain conditions display a positive correlation between C _304?L and 〈α _L 〉 for the leading (L) spots, and between C _304?L /C _304?F and l _L /l _F , where l _L (l _F ) are the lengths of the field lines connecting leading (L) or following (F) spots from the corresponding spot umbrae to the apex of the field line.     

Geometry of solar prominences and magnetic fields in the corona

The spatial location of the surface at which most of the prominence mass is concentrated is compared with the location of the “neutral surface” where B _r = 0 (B _r is the magnetic field) calculated in a potential approximation using photospheric data. More than fifty prominences (filaments) observed in 1999–2003 are studied. The vertical deviations of the prominences (predominantly toward the west) correspond well to the inclination of the neutral surface. The results provide evidence for the magnetic support of filaments of opposite polarities (the magnetic-rope model).     

Pre-flare changes in the turbulence regime for the photospheric magnetic field in a solar active region

Observations of the total magnetic field in the active region NOAA 6757 have been used to study the turbulence regime from 2.5 h before the onset of a 2B/X1.5 flare until two minutes after its maximum. The curvature of the exponent ζ(q) for the structure functions of the B _z field increases monotonically before the flare (i.e., the multifractal character of the B _z field becomes more complex) but straightens at the flare maximum and coincides with a linear Kolmogorov dependence (implying a monofractal structure for the B _z field). The observed deviations of ζ(q) from a Kolmogorov line can be used for short-term forecasting of strong flares. Analysis of the power spectra of the B _z field and the dissipation of magnetic-energy fluctuations shows that the beginning of the flare is associated with the onset of a new turbulence regime, which is closer to a classical Kolmogorov regime. The scaling parameter (cancellation index) of the current helicity of the magnetic field, k _h , remains at a high level right up until the last recording of the field just before the flare but decreases considerably at the flare maximum. The variations detected in the statistical characteristics of the turbulence can be explained by the formation and amplification of small-scale flux tubes with strong fields before the flare. The dissipation of magnetic energy before the flare is primarily due to reconnection at tangential discontinuities of the field, while the dissipation after the flare maximum is due to the anomalous plasma resistance. Thus, the flare represents an avalanche dissipation of tangential discontinuities.     

Parameters of V404 Cyg—A black-hole binary

We present the results of spectroscopic observations of the X-ray binary V404 Cyg obtained on the 6-m telescope of the Special Astrophysical Observatory in 2001–2002. We have used a statistical approach to interpret the radial-velocity curve of V404 Cyg. We derived the dependence of the mass of the X-ray emitting component m_x on the mass of the optical component m_v via an analysis of the radial-velocity curve based on profiles of the CaI 6439.075 Å absorption line synthesized in a Roche model. Using the orbital inclination estimated from the ellipticity of the optical component, i=54°–64°, and the component-mass ratio q=m_x/m_v=16.7 found from the rotational broadening of the spectral lines, we obtain m _s =10.65±1.95M_⊙ for the mass of the black hole.     

The Wolf–Rayet star HD 192163 as a possible evolutionary progenitor of a low-mass X-ray binary

We have used 46 high-resolution echelle spectra of the Wolf-Rayet star HD 192163 taken in 2005–2009 at the Cassegrain focus of the 2-m Zeiss-2000 telescope of the Shamakha Astrophysical Observatory to study profiles of the five strongest emission lines (HeII 4859, HeII 5411, CIV 5808, HeI 5875, (HeII + Hα) 6560). We also obtained four echelle spectrograms of the Wolf-Rayet star HD 191765 for a comparative study of the NaI 5890 (D₂) and NaI 5896 (D₁) interstellar absorption lines. The echelle spectrograms were reduced using the DECH20 code. We determined the equivalent widths, radial velocities, central intensities, and half-widths of the emission lines. We detected variations in the violetwing of the (HeII + Hα) 6560 emission band (between λ ～ 6496 Å and λ ～ 6532 Å). Our statistical analysis of the radial velocities available for the (HeII + Hα) 6560 emission band reveals a peak at the ～1% level at the frequency ν = 0.195 d^?1, corresponding to the period P = 5.128^d. We also studied the NaI 5890 (D₂) and NaI 5896 (D₁) interstellar absorption lines, which are important for understanding the nature of the nebula NGC 6888, whose origin is related to HD 192163. Asymmetric profiles were found for the NaI 5890 and NaI 5896 interstellar absorption lines, interpreted as reflecting a contribution from NGC 6888 to these lines. We suggest that the detected profile variations of the (HeII + Hα) 6560 emission band and the periodic variations of its Doppler shifts (P = 5.128^d) are due to the existence of a low-mass K-M star companion to the Wolf-Rayet star. HD 192163 is a possible evolutionary progenitor of a low-mass X-ray binary.     

Effect of 2-D Random Field Discretization on Failure Probability and Failure Mechanism in Probabilistic Slope Stability

This paper investigates, using the random field theory and Monte Carlo simulation, the effects of random field discretization on failure probability, p _f, and failure mechanism of cohesive soil slope stability. The spatial sizes of the discretized elements in random field Δx, Δy in horizontal and vertical directions, respectively, are assigned a series of combinational values in order to model the discretization accuracy. The p _f of deterministic critical slip surface (DCSS) and that of the slope system both are analyzed. The numerical simulation results have demonstrated that both the ratios of Δy/λ _y (λ _y  = scale of fluctuation in vertical direction) and Δx/λ _x (λ _x  = scale of fluctuation in horizontal direction) contribute in a similar manner to the accuracy of p _f of DCSS. The effect of random field discretization on the p _f can be negligible if both the ratios of Δx/λ _x and Δy/λ _y are no greater than 0.1. The normalized discrepancy tends to increase at a linear rate with Δy/λ _y when Δx/λ _x is larger than 0.1, and vice versa for p _f of DCSS. The random field discretization tends to have more considerable influence on the p _f of DCSS than on that of the slope system. The variation of p _f versus λ _x and λ _y may exhibit opposite trends for the cases where the limit state functions of slope failure are defined on DCSS and on the slope system as well. Finally, the p _f of slope system converges in a more rapid manner to that of DCSS than the failure mechanism does to DCSS as the spatial variability of soil property grows from significant to negligible.     

Assessing the vegetation canopy influences on wind flow using wind tunnel experiments with artificial plants

Wind erosion causes serious problems and considerable threat in most regions of the world. Vegetation on the ground has an important role in controlling wind erosion by covering soil surface and absorbing wind momentum. A set of wind tunnel experiments was performed to quantitatively examine the effect of canopy structure on wind movement. Artificial plastic vegetations with different porosity and canopy shape were introduced as the model canopy. Normalized roughness length (Z ₀/H) and shear velocity ratio (R) were analyzed as a function of roughness density (λ). Experiments showed that Z ₀/H increases and R decreases as λ reaches a maximum value, λ _max, while the values of Z ₀/H and R showed little change with λ value beyond as λ _max.     

Magnetic field models for HD 116458 and HD 126515

We have modeled the magnetic fields of the slowly rotating stars HD 116458 and HD 126515 using the “magnetic charge” technique. HD 116458 has a small angle between its rotation axis and dipole axis (β = 12°), whereas this angle is large for HD 126515 (β = 86°). Both stars can be described with a decentered-dipole model, with the respective displacements being r = 0.07 and r = 0.24 in units of the stellar radius. The decentered-dipole model is able to satisfactorily explain the phase relations for the effective field, B_e(P), and the mean surface field, B_s(P), for both stars, along with the fact that the B_e(P) phase relation for HD 126515 is anharmonic. We discuss the role of systematic measurement errors possibly resulting from instrumental or methodical effects in one or both of the phase relations. The displacement of the dipole probably reflects real asymmetry of the stellar field structure, and is not due to measurement errors. Using both phase relations, B_e(P) and B_s(P), in the modeling considerably reduces the influence of the nonuniform distribution of chemical elements on the stellar surface.     

Earthquake hazard and risk assessment based on unified scaling law for earthquakes: Altai–Sayan Region

We apply the general concept of seismic risk analysis based on morphostructural analysis of the territory, pattern recognition of earthquake-prone nodes, and the Unified Scaling Law for Earthquakes, USLE, in another seismic region of Russia to the west from Lake Baikal, i.e., Altai–Sayan Region. The USLE generalizes the empirical Gutenberg–Richter relationship making use of apparently fractal distribution of earthquake sources of different size: \( \log_{10} N\left( {M,L} \right)\, = \,A\, + \,B \cdot \left( {5\, - \,M} \right)\, + \,C \cdot \log_{10} L, \) where N (M, L) is the expected annual number of earthquakes of a certain magnitude M within an seismically prone area of linear dimension L. The local estimates of A, B, and C allow determination of the expected maximum credible magnitude in a given time interval and the associated spread around ground shaking parameters (e.g., peak ground acceleration, PGA, or macroseismic intensity, I₀). Compilation of the corresponding seismic hazard map of Altai–Sayan Region and its rigorous testing against the available seismic evidences in the past is used to model regional maps of specific earthquake risks for population, cities, and infrastructures.     

The initial trajectories of eruptive solar prominences

Trajectories of eruptive prominences are compared with the shapes of coronal neutral surfaces calculated in a potential approximation using photospheric measurements. Space-based Solar Dymamics Observatory and STEREO observations carried out at different viewing angles enable a precise determination of a prominence’s position at successive times during its eruption. In the initial segments of their trajectories, eruptive prominences move along neutral surfaces (B_r = 0) of the potential coronal magnetic field. This can be used to predict the directions of subsequent coronal mass ejections and to estimate their geoefficiency.     

The pulsar J1852+0040 in Kes 79 and the nature of central compact objects in supernova remnants

A possible model for the pulsar PSR J1852+0040 associated with the supernova remnant Kes 79 and detected in place of a central compact object in this remnant is discussed. The main observational properties of the pulsar can be understood as consequences of its weak surface magnetic field (B _s < 3 × 10¹¹ G) and short rotational period (P ～ 0.1 s). Its X-ray emission is thermal, and is generated in a small region near the surface of the neutron star due to cooling of the surface as the surface accretes matter from a relict disk surrounding the pulsar. The radio emission is generated in the outer layers of the pulsar magnetosphere by the synchrotron (cyclotron) mechanism. The optical luminosity of J1852+0040 is estimated to be L _opt < 10²⁸ erg/s. If the spectral features in another central compact object, 1E 1207.4+5209, are interpreted as electron cyclotron lines, this provides evidence for a weak surface magnetic field for this neutron star as well (B < 6 × 10¹⁰ G). The hypothesis that all central compact objects have weak surface fields makes it possible to explain the number of detected central compact objects, the absence of pulsar-wind nebulae associated with these objects, and the fact that no pulsar has yet been detected at the position of SN 1987a. We suggest that, after the supernova remnant has dissipated, the central compact object becomes a weak X-ray source (XDINS), whose weak emission is also due to the weakness of its magnetic field.     

Global solar magnetology and reference points of the solar cycle

The solar cycle can be described as a complex interaction of large-scale/global and local magnetic fields. In general, this approach agrees with the traditional dynamo scheme, although there are numerous discrepancies in the details. Integrated magnetic indices introduced earlier are studied over long time intervals, and the epochs of the main reference points of the solar cycles are refined. A hypothesis proposed earlier concerning global magnetometry and the natural scale of the cycles is verified. Variations of the heliospheric magnetic field are determined by both the integrated photospheric i(B _r )_ph and source surface i(B _r )_ss indices, however, their roles are different. Local fields contribute significantly to the photospheric index determining the total increase in the heliospheric magnetic field. The i(B _r )_ss index (especially the partial index ZO, which is related to the quasi-dipolar field) determines narrow extrema. These integrated indices supply us with a “passport” for reference points, making it possible to identify them precisely. A prominent dip in the integrated indices is clearly visible at the cycle maximum, resulting in the typical double-peak form (the Gnevyshev dip), with the succeeding maximum always being higher than the preceding maximum. At the source surface, this secondary maximum significantly exceeds the primary maximum. Using these index data, we can estimate the progression expected for the 23rd cycle and predict the dates of the ends of the 23rd and 24th cycles (the middle of 2007 and December 2018, respectively).     

Mean absolute strength of the solar magnetic field in 1968–2006

Measurements of the mean magnetic field of the Sun as a star (the line-of-sight component of the magnetic field of the visible hemisphere for a given day) carried out at six observatories are used to compile a catalog of the mean magnetic field for 1968–2006 (containing about 18 000 daily values). The cataloged data are compared with direct daily measurements of the absolute line-of-sight field made at the Kitt Peak Observatory in 2003–2006 (original data with a resolution of 1″ averaged over the solar disk). The true absolute mean field strength averaged over the visible solar hemisphere is determined for 1968–2006 to be B ₀ = 7.7 ± 0.2 G. This figure exceeds previous estimates by almost a factor of four. B ₀ exhibits no appreciable slow trend over the entire 39-year interval, but varies substantially with the cycle. The period of this variation is 10.5 ± 0.7 yr, and its harmonic amplitude is 1.7 G. The magnetic flux of spots and active regions makes B ₀ almost twice the field strength in the “normal” photosphere at the solar minimum, i.e., for the “quiet” Sun.     

Probabilistic seismic hazard assessment in the Constantine region,Northeast of Algeria

This paper presents a seismic hazard evaluation and develops an earthquake catalogue for the Constantine region over the period from 1357 to 2014. The study contributes to the improvement of seismic risk management by evaluating the seismic hazards in Northeast Algeria. A regional seismicity analysis was conducted based on reliable earthquake data obtained from various agencies (CRAAG, IGN, USGS and ISC). All magnitudes (M _l, m _b) and intensities (I ₀, I _MM, I _MSK and I _EMS) were converted to M _s magnitudes using the appropriate relationships. Earthquake hazard maps were created for the Constantine region. These maps were estimated in terms of spectral acceleration (SA) at periods of 0.1, 0.2, 0.5, 0.7, 0.9, 1.0, 1.5 and 2.0 s. Five seismogenic zones are proposed. This new method differs from the conventional method because it incorporates earthquake magnitude uncertainty and mixed datasets containing large historical events and recent data. The method can be used to estimate the b value of the Gutenberg-Richter relationship, annual activity rate λ(M) of an event and maximum possible magnitude M _max using incomplete and heterogeneous data files. In addition, an earthquake is considered a Poisson with an annual activity rate λ and with a doubly truncated exponential earthquake magnitude distribution. Map of seismic hazard and an earthquake catalogue, graphs and maps were created using geographic information systems (GIS), the Z-map code version 6 and Crisis software 2012.     

Development of a technique for IR spectroscopic determination of nitrogen content and aggregation degree in diamond crystals

A technique for IR spectroscopic determination of the total nitrogen content N _S in the form of A-and B ₁-defects is suggested. It provides for the computer processing and decomposition of IR spectra into constituent bands, calculation of the total absorption band area S _N and individual areas S _A and S _B1 and their normalization with respect to the total area of the diamond intrinsic absorption S ₀, with the normalization coefficients K _S , K _A , and K _B1 being calculated. Based on the analysis of the IR spectra of 60 octahedral diamond crystals from the Mir and Yubileinaya pipes (Sakha-Yakutiya), the empirical functions N _S = 911.85 K _S ^0.9919 ppm (R ² = 0.9859), N _A = 1185.6 K _A ^1.1511 ppm (R ² = 0.8703), and N _B1 = 911.85 K _S ^0.9919 ? 1185.6 K _A ^1.1511 ppm have been defined.     

Polarization of radiation in turbulent magnetized atmospheres

Multiple scattering of radiation in a semi-infinite electron atmosphere in the absence of true absorption (the Milne problem) is considered. The electron plasma is assumed to be turbulent, i.e., the magnetic field B has a regular B ₀ and a stochastic B′ component (B = B ₀ + B′). Faraday rotation of the plane of polarization (s8 λ² B ₀ cos gJ) due to the field B ₀ depolarizes the outcoming radiation due to the superposition of rays with different polarization-angle rotations, corresponding to different paths traveled before they left the atmosphere. Stochastic Faraday rotation due to isotropic fluctuations, B′, efficiently decreases the amplitude of the polarization of each individual beam as it travels through the turbulent atmosphere. This effect is proportional to λ⁴ 〈(B′)²〉, and becomes the dominant factor at large λ. We use the Ambartsumian-Chandrasekhar invariance principle, which results in six nonlinear equations (for the field B ₀ perpendicular to the surface of the medium). We also compute the degree of polarization for the cases B ₀ = 0, B′ ≠ 0, and B′ = 0, B ₀ ≠ 0, and for a number of versions of the general case, B ₀ ≠ 0, B′ ≠ 0. The spectra of the degree of polarization (for the case B ₀ = 0) are presented for optical (λ = 0 ? 1 μm), infrared (λ = 1?5 μm), and X-ray (1–50 keV) wavelengths.     

Effect of the pulsar-tube radius on the gamma-ray curvature radiation from the polar regions of radio pulsars with non-dipolar magnetic fields

The effect of the radius of the tube of open magnetic-field lines on the gamma-ray curvature radiation from the polar regions of a radio pulsar with a non-dipolar magnetic field is analyzed. The pulsar is considered in a polar-cap model with free electron emission from the neutron-star surface. The effect of the non-dipolar magnetic field on the radius of curvature of the field lines and the field intensity is taken into account. In connection with the creation of electron-positron pairs, we take into account only the birth of pairs by curvature radiation in the magnetic field. The small non-dipolarity of the field enables the radio pulsar not to turn off, even after a considerable decrease in the pulsar-tube radius. For instance, with a 20% non-dipolarity (ν = 0.2), a pulsar with B = 10¹³ G and P = 0.5 s can still operate even for a fivefold decrease in the pulsar-tube radius. A maximum is observed in the dependence of the electrostatic potential in the diode on the non-dipolarity parameter ν at ν ～ 0.5–0.7. The pulse profile in non-thermal X-ray emission for ν ～ 0.5–0.7 may look virtually the same as for ν ～ 0.1–0.2. Decreases in the pulsar-tube radius could be due to a structure of currents in the magnetosphere that results in the pulsar diode on the neutron-star surface occupying only a small fraction of the pulsar tube, with the remainder of the tube containing an outer annular gap. The pulsar-tube size is also affected by the presence of a circum-pulsar disk. A change in the pulsar-tube radius could also be due to an external magnetic field, associated with either a magnetic white dwarf or a circum-pulsar disk.