Numerical simulation of the electron capture process in a magnetar interior

In a superhigh magnetic field, direct Urca reactions can proceed for an arbitrary proton concentration. Since only the electrons with high energy E (E>Q, Q is the threshold energy of inverse β-decay) at large Landau levels can be captured, we introduce the Landau level effect coefficient q and the effective electron capture rate Γ _eff . By using Γ _eff , the values of L _X and L _ν are calculated, where L _X and L _ν are the average neutrino luminosity of AXPs and the average X-ray luminosity of AXPs L _X , respectively. The complete process of electron capture inside a magnetar is simulated numerically.     

Periodic motions of a small body in the Newtonian field of a regular polygonal configuration of ν+1 bodies

We study the simple periodic orbits of a particle that is subject to the gravitational action of the much bigger primary bodies which form a regular polygonal configuration of (ν+1) bodies when ν=8. We investigate the distribution of the characteristic curves of the families and their evolution in the phase space of the initial conditions, we describe various types of simple periodic orbits and we study their linear stability. Plots and tables illustrate the obtained material and reveal many interesting aspects regarding particle dynamics in such a multi-body system.     

Plasma wave properties of the Schwarzschild magnetosphere in a Veselago medium

We re-formulate the 3+1 GRMHD equations for the Schwarzschild black hole in a Veselago medium. Linear perturbation in rotating (non-magnetized and magnetized) plasma is introduced and their Fourier analysis is considered. We discuss wave properties with the help of wave vector, refractive index and change in refractive index in the form of graphs. It is concluded that some waves move away from the event horizon in this unusual medium. We conclude that for the rotating non-magnetized plasma, our results confirm the presence of Veselago medium while the rotating magnetized plasma does not provide any evidence for this medium.     

Automated Detection of Oscillating Regions in the Solar Atmosphere

Recently observed oscillations in the solar atmosphere have been interpreted and modeled as magnetohydrodynamic wave modes. This has allowed for the estimation of parameters that are otherwise hard to derive, such as the coronal magnetic-field strength. This work crucially relies on the initial detection of the oscillations, which is commonly done manually. The volume of Solar Dynamics Observatory (SDO) data will make manual detection inefficient for detecting all of the oscillating regions. An algorithm is presented that automates the detection of areas of the solar atmosphere that support spatially extended oscillations. The algorithm identifies areas in the solar atmosphere whose oscillation content is described by a single, dominant oscillation within a user-defined frequency range. The method is based on Bayesian spectral analysis of time series and image filtering. A Bayesian approach sidesteps the need for an a-priori noise estimate to calculate rejection criteria for the observed signal, and it also provides estimates of oscillation frequency, amplitude, and noise, and the error in all of these quantities, in a self-consistent way. The algorithm also introduces the notion of quality measures to those regions for which a positive detection is claimed, allowing for simple post-detection discrimination by the user. The algorithm is demonstrated on two Transition Region and Coronal Explorer (TRACE) datasets, and comments regarding its suitability for oscillation detection in SDO are made.     

Physical State of the Photosphere at the Onset Phase of a Two-Ribbon Solar Flare

We study the physical state of the photosphere at about 30 minutes before and at the onset of a 2N/M2 two-ribbon solar flare. Semiempirical photospheric models are obtained for two Hα-kernels with the help of the SIR inversion code described by Ruiz Cobo and del Toro Iniesta (Astrophys. J. 398, 375, 1992). The models derived from the inversion reproduce spectral observations in seven Fraunhofer lines. The inferred models show variations in all photospheric parameters both before and at the onset of the flare relative to the quiet-Sun model. The temperature enhancement in the upper photospheric layers is found in the atmospheres in both kernels. The dynamical structure in the models reveals the variations at the onset of the flare relative to the preflaring ones. The inferred atmospheres show some difference in the thermodynamical parameters of two kernels.     

Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere

A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ～?15?R _⊙. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15?–?240?R _⊙), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity.     

Evolution of the Electron Distribution Function in the Whistler Wave Turbulence of the Solar Wind

The electron distribution functions from the solar corona to the solar wind are determined in this paper by considering the effects of the external forces, of Coulomb collisions and of the wave – particle resonant interactions in the plasma wave turbulence. The electrons are assumed to be interacting with right-handed polarized waves in the whistler regime. The acceleration of electrons in the solar wind seems to be mainly due to the electrostatic potential. Wave turbulence determines the electron pitch-angle diffusion and some characteristics of the velocity distribution function (VDF) such as suprathermal tails. The role of parallel whistlers can also be extended to small altitudes in the solar wind (the acceleration region of the outer corona), where they may explain the energization and the presence of suprathermal electrons.     

Charged particles’ areas of three-dimensional motions in a system of two magnetic stars

We study the parametric evolution of the regions where three-dimensional motions of a charged particle are allowed in the combined electromagnetic field produced by two rotating magnetic stars. We discuss the changes in the topology of the zero-velocity surfaces, as well as in the trapping regions of the particle motion for various values of the dipoles’ magnetic moments.     

The Minimum Activity Epoch as a Precursor of the Solar Activity

This paper considers the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields and polar activity. Such indices include: dipole–octopole index, area and average latitude of the field with dominant polarity in each hemisphere, polar activity seen in polar faculae and Ca?ii K line bright points, coronal emission line intensity (5303?Å) and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle. The obtained relationships allow us to presume that the polar field is formed from the sources of both preceding and the current activity cycles during the decay phase and at the activity minimum. The balance in these sources would therefore determine the features of the following sunspot cycle. The prediction for the 24th activity cycle using these results leads to W=102±13.     

Manifestations of the North – South Asymmetry in the Photosphere and in the Green Line Corona

The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2 months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed by numerical tests performed by selecting different numerical values of the used parameters.     

A new law emerging from the recurrences of the ‘critical-acceleration’ of MOND, suggesting a clue to unification of fundamental forces

Keeping apart the problem, whether Modified Newtonian Dynamics [MOND] can replace ‘dark matter’, this letter considers seven different theoretical recurrences of ‘critical acceleration’ of MOND noticed by Sivaram in various physical situations; adds five more observational recurrences to the list; and arrives at a set of laws which seem to be followed by all the systems bound by different fundamental forces; suggesting a clue to unification of fundamental forces. This attempt proposes a general explanation for ‘flattening of galaxies’ rotation-curves’ as well as the ‘expansion of the universe’.     

On the gravitational instability of a medium in non-uniform rotation and magnetic field

The effect of a non-uniform magnetic field on the gravitational instability for a non-uniformly rotating, infinitely extending axisymmetric cylinder in a homogeneous medium has been studied. The Bel and Schatzman criterion of gravitational instability for a non-uniformly rotating medium is modified under the effect of a non-uniform/uniform magnetic field acting along the tangential and axial directions. As a consequence the stabilizing and destabilizing effect of the non-uniform magnetic field is obtained, a new criterion for the magneto-gravitational instability is deduced in terms of Alfven’s wave velocity; and it is also found that the Jeans criterion determines the gravitational instability in the absence of rotation and when the non-uniform/uniform magnetic field acts along the axis of the cylinder.     

Plasma magnetosphere of rotating magnetized neutron star in the braneworld

Plasma magnetosphere surrounding rotating magnetized neutron star in the braneworld has been studied. For the simplicity of calculations Goldreich-Julian charge density is analyzed for the aligned neutron star with zero inclination between magnetic field and rotation axis. From the system of Maxwell equations in spacetime of slowly rotating star in braneworld, second-order differential equation for electrostatic potential is derived. Analytical solution of this equation indicates the general relativistic modification of an accelerating electric field and charge density along the open field lines by brane tension. The implication of this effect to the magnetospheric energy loss problem is underlined. It was found that for initially zero potential and field on the surface of a neutron star, the amplitude of the plasma mode created by Goldreich-Julian charge density will increase in the presence of the negative brane charge. Finally we derive the equations of motion of test particles in magnetosphere of slowly rotating star in the braneworld. Then we analyze particle motion in the polar cap and show that brane tension can significantly change conditions for particle acceleration in the polar cap region of the neutron star.     

Dark mammoth trunks in the merging galaxy NGC 1316 and a mechanism of cosmic double helices

NGC 1316 is a giant, elliptical galaxy containing a complex network of dark, dust features. The morphology of these features has been examined in some detail using a Hubble Space Telescope, Advanced Camera for Surveys image. It is found that most of the features are constituted of long filaments. There also exist a great number of dark structures protruding inwards from the filaments. Many of these structures are strikingly similar to elephant trunks in H ii regions in the Milky Way Galaxy, although much larger. The structures, termed mammoth trunks, generally are filamentary and often have shapes resembling the letters V or Y. In some of the mammoth trunks the stem of the Y can be resolved into two or more filaments, many of which showing signs of being intertwined. A model of the mammoth trunks, related to a recent theory of elephant trunks, is proposed. Based on magnetized filaments, the model is capable of giving an account of the various shapes of the mammoth trunks observed, including the twined structures.     

An Interpretation of the Coronal Holes’ Visibility in the Millimeter Wavelength Range

Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsähovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 10⁶ K). This can explain both the LTRs and HTRs associated with coronal holes.     

Smooth models of overshooting at the base of the solar convective zone

A set of smoothed temperature gradient profiles around overshooting layers at the solar convective zone bottom is considered. In classical local theories of convection the one point defined according to the Schwarzschild criterion is enough to describe a convective boundary. To get a sophisticated picture of the overshooting we use four points to compute the transition overshooting functions. Analyzing the transition gradient profiles we found that the overshooting convective flux may be either positive or negative. A negative overshooting flux appears in nonlocal convective theories and causes a steep temperature gradient profile. But we propose an evenly smoothed gradient which corresponds to a convective flux positive everywhere. To outline the effect of the temperature gradient on the solar oscillations the squared Brunt–Väisälä frequency N ² is calculated. In local convective theories the N ² profile shows the discontinuity of the first derivative at the convective boundary, while all smoothed profiles eliminate the break.     

Relative Kinematics of the Leading Edge and the Prominence in Coronal Mass Ejections

We present a statistical analysis of the relationship between the kinematics of the leading edge and the eruptive prominence in coronal mass ejections (CMEs). We study the acceleration phase of 18 CMEs in which kinematics was measured from the pre-eruption stage up to the post-acceleration phase. In all CMEs, the three part structure (the leading edge, the cavity, and the prominence) was clearly recognizable from early stages of the eruption. The data show a distinct correlation between the duration of the leading edge (LE) acceleration and eruptive prominence (EP) acceleration. In the majority of events (78%) the acceleration phase onset of the LE is very closely synchronized (within ± 20 min) with the acceleration of EP. However, in two events the LE acceleration started significantly earlier than the EP acceleration (> 50 min), and in two events the EP acceleration started earlier than the LE acceleration (> 40 min). The average peak acceleration of LEs (281 m s⁻²) is about two times larger than the average peak acceleration of EPs (136 m s⁻²). For the first time, our results quantitatively demonstrate the level of synchronization of the acceleration phase of LE and EP in a rather large sample of events, i.e., we quantify how often the eruption develops in a “self-similar” manner.     

What determines the mass of the most massive star cluster in a galaxy: statistics, physics or disruption?

In many different galactic environments the cluster initial mass function (CIMF) is well described by a power law with index ?2. This implies a linear relation between the mass of the most massive cluster (M _max?) and the number of clusters. Assuming a constant cluster formation rate and no disruption of the most massive clusters it also means that M _max? increases linearly with age when determining M _max? in logarithmic age bins. We observe this increase in five out of the seven galaxies in our sample, suggesting that M _max? is determined by the size of the sample. It also means that massive clusters are very stable against disruption, in disagreement with the mass-independent disruption (MID) model. For the clusters in M51 and the Antennae galaxies, the size-of-sample prediction breaks down around 10⁶ M_⊙, suggesting that this is a physical upper limit to the masses of star clusters in these galaxies. In this method there is a degeneracy between MID and a CIMF truncation. We show how the cluster luminosity function can serve as a tool to distinguish between the two.     

Constraining the gravitational redshift of a neutron star from the Σ-meson well depth

The effect of the Σ-meson well depth on the gravitational redshift is examined within the framework of relativistic mean field theory for the baryon octet system. It is found that, for a stable neutron star, the gravitational redshift increases with the central energy density increase or with the mass increase but decreases as the radius increases. Considering a change of U_S^(N)U_{\Sigma}^{(N)} from −30 MeV to 30 MeV, for a stable neutron star the gravitational redshift near to the maximum mass increases. In addition, it is also found that the growth of the U_S^(N)U_{\Sigma}^{(N)} makes the gravitational redshift as a function of M _max/R increase, the higher the U_S^(N)U_{\Sigma}^{(N)} the less the change in the gravitational redshift.