Rotational modes in a slowly and uniformly rotating star

A perturbation method is derived forr-modes in a slowly and uniformly rotating star. In contrast to previous studies, the perturbation of the gravitational potential is included in the perturbation method.On the assumption that the effects of the centrifugal force are taken into account in the equilibrium model up to the second order in the angular velocity, an eigenvalue problem of sixth-order in the radial coordinate is derived that allows one to determine the zeroth-order toroidal displacement field and the third-order term in the expansion of the eigenfrequency. Furthermore, another eigenvalue problem is derived that governs the first-order toroidal displacement field and the fourth-order term in the expansion of the eigenfrequency. This second eigenvalue problem is also of the sixth-order in the radial coordinate.It is shown that the third-order term in the expansion of the eigenfrequency is real, and that the fourth-order term is zero.     

Kinetic equilibrium of nonlinear electromagnetic waves in electron-positron-ion magnetoplasmas

The problem of a one-dimensional, nonlinear, circularly polarized wave in a collisionless plasma is solved for the case in which the group velocity of the localized wave is zero relative to the plasma frame.For an electron-positron plasma the ponderomotive potential is repulsive, and both small and large amplitude waves in the presence of reflected and transmitted particles is discussed.The inclusion of an external magnetic field such that the cyclotron frequency is smaller than the wave frequency does not alter qualitatively the results of the fieldless case, except for the fact that an electrostatic potential is generated.For the case in which the cyclotron frequency is larger than the wave frequency, the resulting potential is attractive, and it is shown that no localized waves can coexist with confined and transmitted particles. If, however, an ionic component is presnt in the electron-positron plasma, such as may be the case in pulsar magnetospheres, localized waves may again be possible.     

Comparison of parallel group velocity of ECH waves with electron resonant velocity: Implication for electron diffusion by ECH waves

We have investigated the role of group velocity in the calculation of pitch-angle diffusion coefficients by electron cyclotron harmonic (ECH) waves in planetary magnetospheres. The assumption which is generally made that the parallel group velocity can be neglected in comparison with particle parallel velocity is examined in detail. It is found that for lowest harmonic band this assumption is quite good. It is found that in general it is not possible to ignore the parallel group velocity. However, for lowest harmonic band this assumption is quite good at low electron temperatures.     

The seasonal variation of the thermal structure of the atmosphere of Neptune

Previous work on the atmosphere of Uranus is extended to Neptune. The variation of effective temperature with latitude and season is evaluated within the approximations that the redistribution of internal heat in the interior results in the temperature at fixed pressure near the top of the convective region being independent of latitude and time, and that the transport of heat in the atmosphere is by means of radiation and convection. Meridional heat transport in the atmosphere is neglected. It is found that as the absorbed solar flux varies with season the flux of internal heat varies in the opposite sense such that the variation in the sum of the two is much smaller than the variation in either. The resulting variation in the flux radiated out the top of the atmosphere, which responds to the sum of the internal and absorbed solar fluxes, is substantially smaller than for Uranus because of the much larger flux of internal heat. For Neptune, the time-averaged effective temperature at the pole is ≈0.2°K greater than at the equator and the seasonal variation in the polar effective temperature is ≈0.8°K.     

SOUSA: the Swift Optical/Ultraviolet Supernova Archive

This paper studies the motion of an infinitesimal mass in the framework of Robe’s circular restricted three-body problem in two cases; the first case is when the hydrostatic equilibrium figure of the first primary is an oblate spheroid, the shape of the second primary is considered as an oblate spheroid with oblateness coefficients up to the second zonal harmonic, while the first primary is a Roche ellipsoid in the second case and the full buoyancy of the fluid is taken into account. In case one; it is observed that there are two axial libration points on the line joining the centres of the primaries, points on the circle within the first primary are also libration points under certain conditions. It is further found that the first axial point is stable, while the second one is conditionally stable, and the circular points are unstable. It is found in case two that there is exist only one libration point (0,0,0) this point is stable.     

Time-dependent heating of the solar corona

The problem of how the corona is heated is of central importance in solar physics research. Here it is assumed that the heating occurs in a regular time-dependent manner and the response of the plasma is investigated. If the magnetic field is strong then the dynamics reduces to a one-dimensional problem along the field. In addition if the radiative time in the corona is much longer than the sound travel time then the plasma evolvesisobarically. The frequency with which heat is deposited in the corona is investigated and it is shown that there is a critical frequency above which a hot corona can be maintained and below which the plasma temperature cools to chromospheric values. An evaluation of the isobaric assumption to the solar corona and the implications of time-dependent heating upon the forthcoming SOHO observations are also presented.     

De Sitter背景时空中NUT-Kerr-Newman黑洞的玻色子熵

众所周知，一般黑洞的欧拉示性数都为2(或者为0)，而NUT—Kerr—Newman黑洞是个例外，其欧拉示性数大于2.因此计算NUT—Kerr—Newman黑洞的玻色子熵有特殊的意义．运用在brick-wall方法的基础上发展起来的膜模型计算了NUT-Kerr—Newman黑洞在de Sitter时空背景下的玻色子熵．结果表明，在选取适当的截断因子的情况下，该黑洞的熵仍满足Bekenstein—Hawking面积定律．     

Evidence for objects of lunar mass in the early solar system and for capture as a general process for the origin of satellites

The problem of the accumulation of the Moon is discussed on the assumption that the Moon is a captured object. If it is such, it is highly improbable that it is the only object of this kind present in the early solar system. Evidence indicating that other massive objects were present at that time is presented. Also, it is pointed out that the interior of the Moon must contain normal solar proportions of the elements of intermediate volatility in the lunar interior, if the Moon accumulated in a gas sphere.     

The librational dynamics of deformable bodies

The volume average of the strain tensor in a body moving in an inverse-square force field is evaluated. The calculation is carried out assuming the satellite to be an isotropic elastic body whose center of mass moves in a planar orbit. An approximate expression, in terms of its volume and elastic properties, is presented for the strain energy in the satellite. Using this expression the equation of planar librational motion is written explicity. This equation is discussed for both circular and elliptic orbits and is modified to include the effects of energy dissipation in the body. It is shown that the concept of Adiabatic Invariants allows one to analyze the influence of slow changes in the material volume and elasticity.This work was supported by NASA Grant No. NGR 05-010-020.     

太阳光谱望远镜鬼线强度测量方法及初步结果

介绍了云台太阳光谱望远镜光栅鬼线强度测量方法。给出了２ 级光谱罗兰鬼线强度的初步测量结果, 为母线强度的０ ．０４９ ％ 。结果表明光栅的质量优良, 鬼线对光谱测量的影响非常小, 一般情况下在光谱资料处理中可以不必考虑鬼线强度的改正     

Classification of Stellar Spectra with Fuzzy Minimum Within-Class Support Vector Machine

Classification is one of the important tasks in astronomy, especially in spectra analysis. Support Vector Machine (SVM) is a typical classification method, which is widely used in spectra classification. Although it performs well in practice, its classification accuracies can not be greatly improved because of two limitations. One is it does not take the distribution of the classes into consideration. The other is it is sensitive to noise. In order to solve the above problems, inspired by the maximization of the Fisher’s Discriminant Analysis (FDA) and the SVM separability constraints, fuzzy minimum within-class support vector machine (FMWSVM) is proposed in this paper. In FMWSVM, the distribution of the classes is reflected by the within-class scatter in FDA and the fuzzy membership function is introduced to decrease the influence of the noise. The comparative experiments with SVM on the SDSS datasets verify the effectiveness of the proposed classifier FMWSVM.     

Evidence for objects of lunar mass in the early solar system

The problem of the accumulation of the Moon is discussed on the assumption that the Moon is a captured object. If it is such, it is highly improbable that it is the only object of this kind present in the early solar system. Evidence indicating that other massive objects were present at that time is presented. Also, it is pointed out that interior of the Moon must contain normal solar proportions of the elements of intermediate volatility in the lunar interior, if the Moon accumulated in a gas sphere.     

Long nonlinear waves in a compressible magnetically structured atmosphere

The Hohlov-Zabolotskaja equation with an additional boundary condition is shown to describe long nonlinear small-amplitude fast sausage surface waves in a magnetic slab embedded in magnetic environment. It is proved that the obtained boundary problem has no solutions in the form of solitary waves. Approximate solution in the form of nonlinear stationary wave is found with the use of expansion in the power series of small amplitude. Second harmonic generation by a sinusoidal wave is studied. The law of energy conservation is obtained. Results of numerical computations are presented. They show that a sinusoidal disturbance does not overturn. The possibility of transmission of wave energy into corona along a magnetic slab is discussed in connection with these results.     

Magnetogravitational stability of self-gravitating plasma with thermal conduction and finite Larmor radius through porous medium

The problem of incipient fragmentation of interstellar matter to form condensation is investigated taking into account the porosity, viscosity, thermal conductivity, and effect of finite ion-Larmor radius (FLR) on the self-gravitating plasma having a uniform magnetic field acting in vertical direction. Relevant linearized equations are stated and dispersion relation is obtained. Wave propagation in longitudinal and transverse direction to the magnetic field is considered. Stability and instability of the medium is discussed. It is found that if the Jeans's instability condition is not fulfilled the medium must remain stable. Magnetic field, FLR and porosity do not affect the Jeans's criterion of instability in longitudinal direction but in transverse direction, the magnetic field and FLR have stabilizing effect which is reduced due to porosity of the medium. Thermal conductivity destabilizes the medium in both the directions. In transverse direction contribution of FLR on the Jeans's expression for instability is not observed in thermally conducting medium.     

On the potential–density relation for Stäckel discs

The general form of the surface density of an infinitely thin disc is given that generates a Sta¨ckel potential in the disc only, using formulae for the potential of elliptic and hyperbolic strings. This is useful for problems in which a simple form for the potential is important, while the corresponding surface density need only be known to check (numerically) that it is positive. A simple potential with a positive surface density is given. Also, formulae are given to calculate the surface density of such a Sta¨ckel disc, in the case in which the rotation curve is given and all the mass is concentrated in the disc.     

Cosmological models reconstructed from jerk: A thermodynamic analysis

The thermodynamic viability of some dark energy models reconstructed through the cosmological jerk parameter is investigated. Some models, already available in the literature, are picked up for the purpose. The models are broadly classified in two categories, depending on whether there is an interaction in the dark sector or not. The validity of the Generalized Second law of Thermodynamics (GSL) is used as the diagnostics. Hayward–Kodama temperature is considered in place of Hawking temperature in order to account for the dynamical nature of the spacetime. It is found that depending on the parametrization ansatz for jerk, the total entropy is increasing with time, so it is quite possible to find viable models. This holds even with an interaction in the dark sector.     

时间尺度的分域递推模型

建立时间尺度是时间测量的目的之一．实时原子时则要求对时间尺度进行必要的预测．小波分析是近年来迅速发展起来的一门学科,它可以对信号在不同的分辨率下进行分析,凡是传统的Fourier分析可以应用的地方,小波分析都可以得到应用．基于小波分析建立了一种时间尺度分域递推模型,这种方法既不同于ARMA（p,q）模型,又有别于卡尔曼滤波方法．ARMA模型要求过程是平稳随机的,而卡尔曼滤波方法虽然不要求过程是平稳的,但它预测的精度有限．分城递推模型将信号在不同的频率尺度进行正交分解,在各个尺度上对小波变换系数进行建模．最后根据陕西天文台守时实验室的实测数据,验证了分域递推模型,ARMA模型一步预测误差10ns,而分域递推模型五步预测误差平均为4．5ns．结果表明这种方法简单而切实可行,分域递推模型的预测精度优于其它方法．     

Equilibrium problems in a rotating convection zone

This paper is a continuation of the author's work on stellar convection (Vandakurov, 1975a; hereafter referred to as Paper I). The approximate equations for convective perturbations in Paper I are somewhat corrected and generalized to include both nonlinear terms and possible variations in molecular weight. A crude estimate of the nonlinear terms is given by means of an expansion of the solution in powers of the perturbation amplitude. We assume that only the most rapidly growing unstable modes are of significance and that the initial kinetic energy of each independent mode is the same. An expansion in powers of the angular velocity is also performed. (This means that some upper stellar layers with small, but not very small, superadiabaticity are considered.) It is shown that an azimuth-averaged azimuthal force is created by the unstable perturbations. In particular, it is most likely that in the upper part of any stellar convection envelope the rigid rotation is nonequilibrious. A simple formula for the above azimuthal force is derived in the case of a latitudedependent angular velocity and a small viscosity of the medium. If the perturbed characteristic scaleheight is sufficiently small, the azimuthal force created by the most unstable modes is equivalent to a viscous force, but with a negative viscosity coefficient. In the approximation under consideration, the heat flux is spherically symmetric.     

中国古代彗星记录的证认

对中国古代彗星记录的研究状况进行了全面论述,讨论了古代彗星名称、记录和轨道的确定,以事实说明,据这些彗星记录不可能得垤精确的轨道;回顾了古代彗星证认的历史发展,着重分析进行短周期彗得证认时可能出现的问题和解决方法;总结了古代彗星证认的意义：一是有助于短周期彗星长期演化的研究,二是有助于历史年代的确定。     

Some exact analytic self-similar solution in the theory of flare-UPS in novae

A stellar model in which density in the undisturbed gas is assumed to obey power law is considered. An exact analytic self-similar solution for shock velocity, pressure and density is obtained under the assumption of isothermal conditions in the rear flow field. An expression to study analytically the extent of vacuum in the inner core of the gaseous sphere is deduced for any explosion problem and is applied here to obtain the extent of the inner vacuum analytically.