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.     

Formation of accretion disks in close-binary systems with magnetic fields

We have developed a three-dimensional numerical model and applied it to simulate plasma flows in semi-detached binary systems whose accretor possesses a strong intrinsic magnetic field. The model is based on the assumption that the plasma dynamics are determined by the slow mean flow, which forms a backdrop for the rapid propagation of MHD waves. The equations describing the slow motion of matter were obtained by averaging over rapidly propagating pulsations. The numerical model includes the diffusion of magnetic field by current dissipation in turbulent vortices, magnetic buoyancy, and wave MHD turbulence. A modified three-dimensional, parallel, numerical code was used to simulate the flow structure in close binary systems with various accretor magnetic fields, from 10⁵ to 10⁸ G. The conditions for the formation of the accretion disk and the criteria distinguishing the two types of flow corresponding to intermediate polars and polars are discussed.     

Numerical simulation of a solar flare produced by the emergence of new magnetic flux

A scenario for the production of a current sheet above an active region during the emergence of new magnetic flux is considered. The formation of a current sheet is demonstrated via a numerical solution of a system of MHD equations with dissipative terms. The flare energy is stored in the magnetic field of the current sheet. The decay of the current sheet can account for a number of solar-flare phenomena, including the observed divergence of H _α ribbons.     

The presence of a magnetic field on the pulsating subdwarf Balloon 090100001. Observations of 2012

New polarization observations of the subdwarf Bal 09 are analyzed. Bal 09 belongs to the group of hybrid sdB stars, which display both short- and long-period pulsations. Explaining certain properties of Bal 09 that were previously unknown in relation to subdwarfs (variations of the amplitude of the fundamental pulsation mode, rotational splitting of line multiplets and variation of this splitting) requires invoking information about the magnetic field of the star. According to estimates made in 2010, the longitudinal component of the magnetic field of Bal 09 is 34±63 G. This value is significantly lower than the fields found earlier for six other hot subdwarfs. New observational data for the longitudinal magnetic field of Bal 09 was obtained on July 27, 2012, using the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory (SAO). The longitudinal component of the magnetic field 〈B _z 〉 was found via a regression analysis. When applied to the star HD 210762 with a zero total magnetic field, this method yielded the value 〈B _z 〉 = ?12 ± 9 G. The observations also included measurements of 〈B _z 〉 for the well-studied magnetic star γ Equ, which is used at the SAO for calibration and testing of the polarimetric instruments. The estimate obtained for γ Equ is 〈B _z 〉 = ?546±16G, consistentwith the general variations of the longitudinal magnetic-field component of this star. This new study, based on data obtained on July 27, 2012, leads to a similar estimate of the longitudinal magnetic field, 〈B _z 〉 = ?23±53 G. This estimate of 〈B _z 〉 was obtained for the full analyzed spectral range (4400–4958 Å). The corresponding “limited” solution yielded ?32±63 G. The regression analysis for the individual spectral sub-bands and for bands containing characteristic spectral features, did not provide firm evidence of the presence of a magnetic field, with a strength exceeding the error in 〈B _z 〉. The data analysis leads to the conclusion that the errors of the measurements made in 2010 and 2012 are in good agreement. This testifies to the reliability of the method applied and of the resulting observational material. In addition, the estimates are in good agreement among themselves and with estimates obtained earlier, in 2010. The results unambiguously confirm the earlier conclusion that the subdwarf Bal 09 does not have magnetic field with a strength comparable to those detected earlier for six sdB and sdO stars. Estimates of 〈B _z 〉 for hot subdwarfs that have appeared in the literature since the 2010 study also provide trustworthy evidence for the absence of magnetic fields ～ 1 kG in these objects.     

Long-term variations in the asymmetry of the magnetic field of the sun and heliosphere

The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of B _z together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of B _z . Time intervals, in which negative values of the B _z component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability.     

The signature of the interplanetary magnetic field components on the low latitude geomagnetic field disturbance

The signature of the interplanetary magnetic field componentB _y andB _z and their effects on the low lattitude field are studied for Alibag station. It has been found that the direction and magnitude of theB _y component of IMF have their signatures on the low latitude geomagnetic field, varying with the time of the day and season.     

The outer turbulence scale in the interstellar plasma

The structure function for phase fluctuations on spatial scales from 10⁶ to 10¹⁷ m is constructed using data on diffractive and refractive scintillation of pulsars, scattering angles, variations in pulse arrival times, and differences in dispersion measures observed for close pairs of pulsars in globular clusters. For distances R>1 kpc (a sample of pulsars with DM≥30 pc/cm³), the fluctuations in the interstellar electron density on scales from 10⁶ to 10¹⁴ m are well described by a Kolmogorov spectrum with index 11/3. Analysis of variations in the dispersion measures for close pairs of pulsars in globular clusters indicates an outer turbulence scale of L ₀=10¹⁵ m. The relative level of turbulent fluctuations is determined for the interstellar plasma, and the important role of turbulence in the energy balance is demonstrated.     

Parameters of the turbulent magnetic field in the solar photosphere: Power spectrum of the line-of-sight field

Ground-based (Big Bear Solar Observatory) and extra-atmospheric (SOHO/MDI) measurements of the photospheric line-of-sight magnetic field of one active and two quiet regions are used to calculate power spectra of the field, taking into account the characteristic function for the diffraction limit of the telescope resolution. At high frequencies, the physically meaningful linear interval in the spectrum extends to a wave number of k=4.6 Mm^?1 (spatial scale l=1.4 Mm) for the quiet regions and k=3.35 Mm^?1 (l=1.9 Mm) for the active region. A high-frequency spectral break at k≥3 Mm^?1 is associated with the characteristic telescope function; the position of the break and the spectral slope beyond the break do not reflect the turbulent state of the field. As the field recording improves, the break shifts toward higher frequencies. The spectral indices in the physically meaningful linear interval are substantially different for the active and quiet regions: in the active region (NOAA 8375), the spectrum behaves as E(k)≈k ^?1.7 (very close to the Kolmogorov index, ?5/3) in the interval 0.78≤k≤3.35 Mm^?1, while in the quiet regions E(k)≈k ^?1.3 for 0.77≤k≤4.57 Mm^?1. This difference can be explained by the additional effect of a small-scale turbulent dynamo in the unperturbed photosphere. In this case, this mechanism can generate at least 6% of the magnetic energy of the photospheric line-of-sight field in quiet regions.     

Evolution of the H<Subscript>2</Subscript>O and OH Maser Emission in W75 N

The results of a study of H₂O and OH maser emission in the complex region of active star formation W75 N are presented. Observations were obtained using the 22-m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) and the Nan3ay radio telescope (France). Flaring H₂O maser features may be identified with maser spots associated with the sources VLA 1 and VLA 2. Themain H₂O flares occurred in VLA 1. The flare emission was associated with either maser clusters having closely spaced radial velocities and sizes up to ~2 AU or individual features. The maser emission is generated in a medium where turbulence on various scales is present. Analysis of the line shapes during flare maxima does not indicate the presence of the simplest structures—homogeneous maser condensations. Strong variability of the OH maser emission was observed. Zeeman splitting of the 1665-MHz line was detected for several features of the same cluster at a radial velocity of +5.5 km/s. The mean line-of-sight magnetic field in this cluster is ~0.5 mG, directed away from the observer. Flares of the OH masers may be due to gas compression at a shock or MHD wave front.     

Twist of magnetic fields in solar active regions

We study the twist properties of photospheric magnetic fields in solar active regions using magnetographic data on 422 active regions obtained at the Huairou Solar Observing Station in 1988–1997. We calculate the mean twist (force-free field α_f) of the active regions and compare it with the mean current-helicity density of these same active regions, h _c =B _∥·(?×B)_∥. The latitude and longitude distributions and time dependence of these quantities is analyzed. These parameters represent two different tracers of the α effect in dynamo theory, so we might expect them to possess similar properties. However, apart from differences in their definitions, they also display differences associated with the technique used to recalculate the magnetographic data and with their different physical meanings. The distributions of the mean α_f and h _c both show hemispherical asymmetry—negative (positive) values in the northern (southern) hemisphere—although this tendency is stronger for h _c. One reason for these differences may be the averaging procedure, when twists of opposite sign in regions with weak fields make a small contribution to the mean current-helicity density. Such transequatorial regularity is in agreement with the expectations of dynamo theory. In some active regions, the average α_f and h _c do not obey this transequatorial rule. As a whole, the mean twist of the magnetic fields α_f of active regions does not vary significantly with the solar cycle. Active regions that do not follow the general behavior for α_f do not show any appreciable tendency to cluster at certain longitudes, in contrast to results for h _c noted in previous studies. We analyze similarities and differences in the distributions of these two quantities. We conclude that using only one of these tracers, such as α_f, to search for signatures of the α effect can have disadvantages, which should be taken into account in future studies.     

The magnetic field of the pulsating subdwarf Balloon 090100001

We have analyzed polarization observations of the subdwarf Bal 09, which is one of a group of hybrid sdB stars that display simultaneously both short- and long-period pulsations. Certain properties previously unknown for subdwarfs have been established for Bal 09, such as variations of the pulsation amplitude of the main oscillation mode, rotational splitting of multiplets, and variations of this splitting. Information about the stellar magnetic field must be considered if we wish to explain these properties. New observational data enabling estimation of the longitudinal magnetic field of Bal 09 have been obtained on the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory. Studies of the longitudinal component of the magnetic field 〈B _z 〉 were carried out using a regression analysis. This method simultaneously yields estimates of the uncertainty in 〈B _z 〉. Test measurements of 〈B _z 〉 were carried out using the same method. For the star HD 158974, which has zero total magnetic field, the estimated longitudinal magnetic field is 〈B _z 〉 = −4 ± 5 G. The standard magnetic field for the Ap star α ²CVn was measured to be −363 ± 17 G, in very good agreement with measurements in the literature. The estimated longitudinal magnetic field for Bal 09 is 34 ± 63G—appreciably lower than values established earlier for six subdwarfs, ≈1.5 kG. The results of the regression analysis for both individual spectral subranges and for intervals containing characteristic spectral features did not indicate reliable detections of a magnetic field exceeding the uncertainties in 〈B _z 〉. The uncertainty in 〈B _z 〉, which was 60–80 G for the entire spectral range and 140–200 G for selected spectral intervals, leads to an estimated upper limit on the longitudinal magnetic field 〈B _z 〉 for Bal 09. This estimate for 〈B _z 〉 can place observational constraints on theoretical explanations for the amplitude variations of the pulsations, rotational splitting of multiplets, and possible variations of the internal structure of the star.     

The magnetic-field structure in a stationary accretion disk

The magnetic-field structure in regions of stationary, planar accretion disks around active galactic nuclei where general-relativistic effects can be neglected (from 10 to 200 gravitational radii) is considered. It is assumed that the magnetic field in the outer edges of the disk, which forms in the magnetosphere of the central black hole during the creation of the relativisitic jets, corresponds to the field of a magnetic dipole perpendicular to the plane of the disk. In this case, the azimuthal field component B_φ in the disk arises due to the presence of the radial field B_ρ and the azimuthal velocity component U_φ. The value of the magnetic field at the inner radius of the disk is taken to correspond to the solution of the induction equation in a diffusion approximation. Numerical solutions of the induction equation are given for a number of cases.     

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.     

Variability of the spectrum and spatial structure of the H<Subscript>2</Subscript>O maser in W75N-VLA 1

A model of the source associated with VLA 1 in W75N is constructed based on monitoring of the H₂O maser carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory and NRAO VLA maps of the source at epochs 1992, 1996, 1998, and 1999. The source has a complex hierarchical structure. Individual maser spots form compact clusters in the form of filaments or chains, as well as more extended arc-like clusters. There are radial-velocity gradients in the chains and filaments. All these structures are arranged in a very elongated disk. This complex configuration could arise due to various-scale turbulent motions of the emitting material, from microturbulence to large-scale turbulence. The strong elongation could be due to an outflow of material from the star. No radial motions of individual clusters of spots with respect to the central source in VLA 1 have been found. The presence of these spots at various epochs could be due to the passage of MHD waves, which excite the maser emission in corresponding zones of the maser source. This process could have a cyclic character, and be associated with the flare activity of the central star.     

The turbulence spectrum of the interstellar plasma toward the pulsars PSR B0809+74 and B0950+08

The interstellar scintillation of the pulsars PSR B0809+74 and B0950+08 have been studied using observations at low radio frequencies (41, 62, 89, and 112 MHz), and the characteristic temporal and frequency scales for diffractive scintillations at these frequencies determined. A comprehensive analysis of the frequency and temporal structure functions reduced to a single frequency shows that the spectra of the inhomogeneities of the interstellar plasma toward both pulsars are described by a power law. The index of the interstellar plasma fluctuation spectrum toward PSR B0950+08 (n = 3.00 ± 0.05) differs appreciably from the Kolmogorov index. The spectrum toward PSR B0809+74 is a power law with index n = 3.7 ± 0.1. Strong angular refraction has been detected toward PSR B0950+08. Analysis of the distribution of inhomogeneities along the line of sight indicates that the scintillations of PSR B0950+08 take place in a turbulent layer with an enhanced electron density localized approximately 10 pc from the observer. The distribution of inhomogeneities for PSR B0809+74 is quasi-uniform. The mean square fluctuations of the electron density are estimated for inhomogeneities with characteristic scale ρ ₀ = 10⁷ m along the directions toward four pulsars. The local turbulence in the 10-pc layer is a factor of 20 higher on this scale than in the extended region responsible for the scintillations of PSR B0809+74.     

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.     

区域可持续发展指标的相关性分析及降维模型研究——以中国省级区域为例

增大指标的覆盖面与减少指标的信息重复是可持续发展指标选取中面临的一对矛盾。在通常情况下指标数量越多，指标的覆盖面就越大，但指标的信息重复就越多。分析了近年来有关文献通常采用的指标，并结合中国省级区域可持续发展指标的可获取性，选取46个指标对其相关性进行分析。分析结果表明这些指标之间绝大多数呈现不同程度的相关关系，即指标间含有大量的重复信息。应用统计分析技术建立基于主成分分析的指标降维模型，得到 8个彼此独立的综合指标。根据综合指标得分，对中国31个省级区域（不包括港澳台）的可持续发展状况进行了排序。     

57Fe Mössbauer spectroscopy and magnetization of cation deficient Fe2TiO4 and FeCr2O4. Part II: Magnetization data

Magnetic properties are reported for synthetic cation deficient Fe₂TiO₄ and FeCr₂O₄ particles (<1 μm). Cation deficiency, achieved by oxidation, is characterized by the oxidation parameter z which represents the fraction of Fe²⁺ ions converted to Fe³⁺ in the spinel lattice (0≤z≤1). Fe₂TiO₄ (z=0.85) has a Curie temperature T _c that can only approximately be given with a value in the range 400–700 K and it has a magnetic moment per formula unit M≈0.50 μ_B (μ_B=Bohr's magneton) at 4.2 K, for FeCr₂O₄ it is T _c≥520 K and M (4.2 K) ≈0.16 μ_B. Magnetic hysteresis parameters at various temperatures show in part characteristic features due to relaxation phenomena. In the Ti-spinel, the latter are caused by a superposition of superparamagnetism and spin relaxation and in the Cr-spinel by superparamagnetism, in agreement with Mössbauer data (part I of this paper). The cation and vacancy distribution and magnetic coupling are discussed in both compositions with respect to magnetic moment data considering magnetic dilution by incorporated vacancies, and in the Ti-spinel also by non magnetic Ti⁴⁺.     

Origin of prolonged X-ray flares on active late-type stars

Soft X-ray data for prolonged flares in subgiants in RS CVn binary systems and some other active late-type stars (AB Dor, Algol) are analyzed. During these nonstationary events, a large amount of hot plasma with temperatures exceeding 10⁸ K exists for many hours. Numerical simulations of gas-dynamical processes in the X-ray source—giant loops—can yield reliable estimates of the plasma parameters and flare-source size. This confirms that such phenomena exist while considerable energy is supplied to the top part of a giant loop or system of loops. Refined estimates of the flare energy (up to 10³⁷ erg) and scales contradict the widely accepted idea that prolonged X-ray flares are associated with the evolution of local magnetic fields. The energy of the current component of the large-scale magnetic field arising during the ejection of magnetic field by plasma jets or stellar wind is estimated. Two cases are considered: a global stellar field and fields connecting regions with oppositely directed unipolar magnetic fields. The inferred energy of the current component of the magnetic field associated with distortion of the initial MHD configuration is close to the total flare energy, suggesting that large-scale magnetic fields play an important role in prolonged flares. The flare process encompasses some portion of a streamer belt and may propagate along the entire magnetic equator of the star during the most powerful prolonged events.     

On the hydrodynamics of flotation machines

Flotation is realized under highly turbulent flow conditions, so that turbulence may be process-determining, too. Because the principles of turbulent multi-phase flow have still not been fully worked out, one needs integral quantities to characterize the state of turbulence indirectly.To show the hydrodynamic conditions diagrams are introduced in which the power intensity $\text{P}\text{V}{}_{\mathrm{<mtext>t</mtext>}}$ is a function of air flow number c_L; impeller rotational speed n and specific air rate q_L are additional parameters. Diagrams of this kind are also useful for the characterization of the optimum operation conditions. For the flotation of different particle sizes the realization of closely defined power inputs is an important condition to obtain an optimum recovery.