Quasi-thermal Noise Spectra Measured by a Dipole Antenna in the Upper Hybrid frequency band

Quasi-thermal noise (QTN) spectroscopy is one of the most effective tools for in situ diagnostics in space plasmas (Meyer-Vernet et al., 1998; Meyer-Vernet and Perche, 1989; Chugunov and Trakhtengerts, 1978). This method produces routine measurements of the bulk electron density and temperature; recently it has been extended to measure the ion bulk speed. Among the advantages of the method its immunity to spacecraft potential and photoelectron perturbations should be noted. Quasi-thermal noise spectroscopy is used particularly on Ulysses and Wind. However for the interpretation of QTN data the calculation of the noise voltage induced on antennas under different conditions is necessary. This question is especially complicated and so far insufficiently studied in magnetized plasmas. In the present paper we calculate the spectrum of the noise voltage induced on a dipole antenna in the upper hybrid frequency range. The computations are adapted to the interpretation of data acquired on the Ulysses and Wind spacecraft. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analytical Approach to the Secular Behaviour of Exoplanetary Systems

We analyse the secular interactions of two coplanar planets which are not in mean motion resonances. The analysis is based on a high order (order 12) expansion of the perturbative potential in powers of the eccentricities. The model depends on only two parameters (the ratio of semi-major axis and the mass ratio of the planets) and can be reduced to a one degree of freedom system, allowing for an exhaustive parametric analysis. Following Pauwels [Pauwels T.: 1983, Celet. Mech. & Dyn. Astro. 30, 229–247] we map the phase space on a sphere, avoiding in this way the artificial singularities introduced by other mappings. We show that the 12 order expansion is able to describe correctly most of the exosolar planetary systems discovered so far, even if the eccentricities of these planets are considerably larger than the eccentricities of our own solar system. The expansion is even able to reproduce, at moderate eccentricities, the secular resonances discovered numerically by Michtchenko and Malhotra [Michtchenko, T. A. and Malhotra, R.: 2004, Icarus 168, 237–248] at moderate to large eccentricities. FNRS Research Fellow.     

Spectrum of Fluctuations of Solar Noise Storms

The calculation of the Fourier transform of noise storm (NS) fluctuations showed that the power spectrum was adequately described by the expression G(F)∼1/F. Our results rule out the possibility that NS radiation is formed from random, short-term bursts (so-called type I bursts), since the spectrum of the sum of random short fluctuations is flat, but the real NS has a hyperbolic spectrum. This spectrum is monotonic and does not contain any components that exceed the level of the statistical fluctuations (i.e., the results of observations do not reveal the presence of periodic or resonant properties of the emission source). The hyperbolic shape of the spectrum shows that the main energy of a NS is contained in the slower temporal fluctuations.     

Analytical Approach to the Motion of a Lunar Artificial Satellite

The canonical equations of motion of an artificial lunar satellite are formulated including the effects of the asphericity of the Moon comprising the harmonics J ₂, J ₂₂, J ₃, J ₃₁, J ₄ andJ ₅, the oblateness of the Earth up to the second zonal harmonic, as well as the disturbing function due to the attractions of the Earth and of the Sun (terms are retained up to order 10^-6 for the higher orbits and 10^-8 for the lower orbits). This revised version was published online in July 2006 with corrections to the Cover Date.     

功率谱噪声改正和斑点全息术象复原

简要地介绍了斑点全息术的原理，分析了存在于实际数据中的各种噪声对功率谱造成的严重影响，讨论了消除噪声偏差的方法，最后报导了用斑点全息术对两双星的高分辨率象复原结果。     

一种频率源噪声频谱拟合方法的研究

在分析频率源的噪声特性的时候,经常需要由Allan方差或功率谱计算频率源的五种噪声强度系数的值,通常采用人工分析的方法,求出噪声系数,这严重阻碍了自动化处理的应用。给出的一种自动拟合算法可以满足这方面的需要。在最小均方误差意义下,这种算法能自动完成对噪声类别的判定、噪声区间的划分以及噪声系数确定,所有这些无须人工参予。最后,对模拟数据和实测的几种频率源的功率谱曲线进行拟合,实验研究的结果表明这种方法拟合的相对误差不超过11％。     

处理相关光变时间延迟的新方法

时间延迟相关函数(Time Delay Correlation Function,TDCF)方法是一种可以计算时间序列时间延迟的新方法,利用该方法计算blazar天体0316+413(NGC 1275)3个射电波段(4.8 GHz、8 GHz和14.5 GHz)的时间延迟并进行另外7个blazar源的多波段相关分析.对0316+413的计算结果表明:4.8 GHz光变延迟8 GHz光变410 d,即τ_(4.8-8)=410 d;4.8 GHz光变延迟14.5 GHz光变440 d,τ_(4.8-14.5)=440 d;8 GHz光变延迟14.5 GHz光变30 d,即τ_(8-14.5)=30 d;通过7个blazar天体的多波段相关分析,和离散相关函数(Discrete Correlation Function,DCF)方法相比,利用TDCF方法获得时间延迟是更加合理的.     

利用Jacobi多项式计算倾角函数

研究了一种利用Jacobi多项式计算倾角函数的方法,该方法表达式非常简单,不存在k和l是否同奇偶和计算非整数阶乘的问题,也不存在k＜0和k≥0的转换问题,递推公式可使用标准的Jacobi多项式的递推公式.而且,计算精度和适应阶数可与Gooding方法相当,计算时间比Gooding方法省9％.     

A Method to Calculate Inclination Function with Jacobi Polynomials

In this paper, a method to calculate the inclination function with Jacobi polynomials is studied, the formulation of this method is very simple, it needs not to concern about whether k and l have the same parity, and to calcu- late the non-integral factorials, nor to concern about the conversion between the case of k < 0 and the case of k ≥ 0, and the recurrent formula can be the stan- dard recurrent formula for Jacobi polynomials. In addition, its computational accuracy and applicable order-numbers are equivalent to those of the Gooding method, but its calculating time is shorter than that of the Gooding method for 9%.     

An Analytical Model for the Current Structure of the Magnetosheath Boundary in a Collisionless Plasma

Astronomy Letters - We have constructed an analytical model of a quasi-stationary current sheet in a collisionless plasma that describes the boundary of the magnetosheath formed by the solar...     

Evolution of Wide Star Pairs Owing to Irregular Forces

The dynamic evolution of wide star pairs (separated by 10⁴ AU for typical galactic conditions) under the influence of random interactions with background stars during transits is studied theoretically. Transits which form a roughly equilateral triangle at some time are considered. The combined effect of many transits can be separated into systematic heating of the pair plus random diffusion over the Kepler elements a and e. The corresponding Fokker-Planck equation is derived and its range of validity indicated. A steady state distribution over a and e is obtained.     

Electromagnetic Ion Cyclotron Waves in Multi-Ions Hot Anisotropic Plasma in Auroral Acceleration Region-Particle Aspect Approach

Using particle aspect approach, the effect of multi-ions densities on the dispersion relation, growth rate, perpendicular resonant energy and growth length of electromagnetic ion cyclotron wave with general loss-cone distribution function in hot anisotropic multi-ion plasma is presented for auroral acceleration region. It is observed that higher He⁺ and O⁺ ions densities enhance the wave frequency closer to the H⁺ ion cyclotron frequency and growth rate of the wave. The differential heating of He⁺ ions perpendicular to the magnetic field is enhanced at higher densities of He⁺ ions. The waves require longer distances to achieve observable amplitude by wave-particle interactions mechanism as predicted by growth length. It is also found that electron thermal anisotropy of the background plasma enhances the growth rate and reduces the growth length of multi-ions plasma. These results are determined for auroral acceleration region.     

精密时钟噪声的按噪声分量分解与白噪声中f^—1随机过程的最优估计

对于任何精密时钟来说,其五种噪声分量的幂律谱系数不存在固定的比例关系,因而在对精密时钟进行最优综合时需要对其噪声进行按噪声分量分解。通过探讨白噪声中ｆ＾－１随机过程的最优估计,提出了一种分层次地对精密时钟噪声进行按噪声分量分解的方法。     

Analytical approach to subhalo population in dark matter haloes

In the standard model of cosmic structure formation, dark matter haloes form by gravitational instability. The process is hierarchical: smaller systems collapse earlier, and later merge to form larger haloes. The galaxy clusters, hosted by the largest dark matter haloes, are at the top of this hierarchy and representing the largest as well as the last structures formed in the Universe, while the smaller and first haloes are those Earth-sized dark subhaloes that have been both predicted by theoretical considerations and found in numerical simulations, though there do not exist any observational hints of their existence. The probability that a halo of mass m at redshift z will be part of a larger halo of mass M at the present time can be described in the frame of the extended Press & Schecter theory making use of the progenitor (conditional) mass function. Using the progenitor mass function, we calculate analytically, at redshift zero, the distribution of subhaloes in mass, formation epoch and rarity of the peak of the density field at the formation epoch. That is done for a Milky Way size system, assuming both a spherical and an ellipsoidal collapse model. Our calculation assumes that small progenitors do not lose mass due to dynamical processes after entering the parent halo, and that they do not interact with other subhaloes. For a Λ cold dark matter power spectrum, we obtain a subhalo mass function  d n /d m   proportional to   m ^−α  with a model-independent  α∼ 2  . Assuming that the dark matter is a weakly interacting massive particle, the inferred distributions are used to test the feasibility of an indirect detection in the γ-ray energy band of such a population of subhaloes with a Gamma-ray Large Area Space Telescope like satellite.     

阵列量子器件的信噪比与处理

本文讨论了影响照相底片、光电倍增管，直到ＣＣＤ等探测器信噪比的因素。并导出了阵列量子器件的总信噪比与其单个象素的信噪比之间的关系表达式。在此基础上，着重讨论了将阵列量子器件用于天文观测时，信噪比关系式对观测和资料处理的指导意义     

Degradation due to Quantization Noise in Radio Astronomy Phased Arrays

In this article, a model is developed for determining the probability distribution of the output of a digital adder in case of 2-, 3- and 4-level quantization before summation. This probability distribution is then used to determine the efficiency of a system which determines the total power of the signal at the output of the digital adder.The sum-signal is also used in a VLBI correlation mode where the sum-signal is correlated with the signal from a VLBI partner. The efficiency, expressed in so-called Degradation Factors, is determined for 1- and 2-bit correlation and 2-, 3- and 4-level quantization before summation.Furthermore, the application of the calculated values (Total Power Detector Efficiencies and Degradation Factors) is illustrated.     

Metallicity of Young and Old Stars in Irregular Galaxies

Based on archived images obtained with the Hubble Space Telescope, stellar photometry for 105 irregular galaxies has been conducted. We have shown the red supergiant and giant branches in the obtained Hertzsprung-Russel diagrams. Using the TRGB method, distances to galaxies and metallicity of red giants have been determined. The color index (V ? I) of the supergiant branch at the luminosity level M_I = ?7 was chosen as the metallicity index of red supergiants. For the galaxies under study, the diagrams have been built, in which the correlation can be seen between the luminosity of galaxies (M_B) and metallicity of red giants and supergiants. The main source of variance of the results in the obtained diagrams is, in our opinion, uncertainty inmeasurements of galaxy luminosities and star-forming outburst. The relation between metallicity of young and old stars shows that main enrichment of galaxies with metals has taken place in the remote past. Deviations of some galaxies in the obtained relation can possibly be explained with the fall of the intergalactic gas on them, although, this inconsiderably affects metallicities of the stellar content.     

Solar Plasma Density and Spectrum of Accelerated Particles Derived From the 2.223-Mev Line of a Solar Flare

The time profile of the neutron capture line of 2.223 MeV for the flare of 16 December 1988 (its third peak) is analyzed. The enhancements of plasma density in the deep photospheric layers of the Sun under the flare region (an effect of density enhancement) have been deduced by the SINP calculation code. These enhancements are studied based on several modified models of the lower chromosphere, photosphere, and convection zone. Additionally, the case has been examined when the neutron source is placed at the top of the photosphere. The energy spectrum of accelerated particles (protons) is shown to evolve with time. Assuming a stochastic mechanism of acceleration and a Bessel function for the spectrum, we find the spectral index α T to increase from 0.005 to 0.1 during the decay phase of the burst; i.e., the proton spectrum becomes harder. Density enhancements found in the flare of 16 December 1988 are consistent with our previous results on the density enhancement effects deduced for two other flares, 6 November 1997 and 22 March 1991. It is suggested that density enhancements in the deep layers of the photosphere may be rather common features of powerful solar flares. B.M. Kuzhevskij is deseased.     

Relativist ic Corrections to the Thermal Sunyaev-Zel''''dovich Power Spectrum

We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v < 100 GHz, but become non-negligible at high frequencies v > 350 GHz. Moreover, the corrections appear to be slightly smaller at higher l or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology.