共查询到20条相似文献，搜索用时 31 毫秒
1.
Recently a method has been suggested to analyze the chaotic behaviour of a conservative dynamical system by numerical analysis of the fundamental frequencies. Frequencies and amplitudes are determined step by step. As the frequencies are not generally orthogonal, a Gramm-Schmidt orthogonalization is made and for each new frequency the old amplitudes of previously determined frequencies are corrected. For a chaotic trajectory variations of the frequencies and amplitudes determined over different time periods are expected. The change of frequencies in such a calculation is a measure of the chaoticity of the trajectory. While amplitudes are corrected, the frequencies (once determined) are constant. We suggest here simple linear corrections of frequencies for the effect of other close frequencies. The improvement of frequency determination is demonstrated on a model case. This method is applied to the first fifty numbered asteroids. 相似文献
2.
Lazarus E. Kopilovich 《Experimental Astronomy》2010,28(1):1-9
Estimates for the maximum number of elements of non-redundant configurations on integer square and hexagonal grids of given
sizes are derived (a “non-redundant” configuration implies that the vector differences between its elements are all distinct).
When projecting a large 2-D interferometer or a telescope, such an estimate can be used as a guide for evaluating the maximum
possible number of antennas in a non-redundant configuration that can be arranged within a given area. The suggested estimates
are empirical and based on the available data. They are obtained by reducing the problem to the linear case and by generalizing
the method applied therein. Examples of applying the method are presented. 相似文献
3.
A. M. Mickaelian 《Astrophysics》2004,47(3):361-377
Results of spectral observations of 66 objects from the BIG (Byurakan IRAS Galaxies) sample made with the 1.93 m telescope at the Observatoire de Haute Provence (OHP, France) are presented. Emission lines are observed from 64 of the galaxies. The red shifts are determined, the radial velocities, distances, and absolute stellar magnitudes are calculated, the spectrum line parameters are determined, diagnostic diagrams are constructed, the objects are classified according to activity type, and their IR and far-IR luminosities are calculated. Of the 66 objects (corresponding to 61 IRAS sources), 6 are Sy2, 2 are LINERs, 8 are AGN (Sy2 or LINER), 10 are composite, 34 are HII, and 4 are Em of undetermined type. It is calculated that IRAS 07479+7832= BIG d141a is a ultraluminous IR galaxy (ULIG), and 21 are LIG. Spectra of several of the galaxies being studied are presented. 相似文献
4.
TRACE observations from 15 April 2001 of transverse oscillations in coronal loops of a post-flare loop arcade are investigated. They are considered to be standing fast kink oscillations. Oscillation signatures such as displacement amplitude, period, phase and damping time are deduced from 9 loops as a function of distance along the loop length. Multiple oscillation modes are found with different amplitude profile along the loop length, suggesting the presence of a second harmonic. The damping times are consistent with the hypothesis of phase mixing and resonant absorption, although there is a clear bias towards longer damping times compared with previous studies. The coronal magnetic field strength and coronal shear viscosity in the loop arcade are derived. 相似文献
5.
讨论满足约束条件的月球卫星飞行轨道的设计问题，将约束条件分类为只与太阳，月球，地球，飞行器和观测站之间的相对位置有关的运行学约束条件以及涉及到飞行器轨道运行的动力学约束条件，在考虑月球卫星轨道的受力情况后，给出一种准确快速地计算和设计满足约束条件的标准飞行轨道的方法，并应用于不同约束条件下月球卫星的轨道预设计，初步讨论了轨道设计的误差分析，轨道跟踪及实时精密定轨等正在进行的其它相关工作。 相似文献
6.
Beata Mazur Janusz Kaluzny Wojciech Krzemi&#;ski 《Monthly notices of the Royal Astronomical Society》1999,306(3):727-735
We report the results of a CCD search for short-period variables in the field of a southern globular cluster NGC 6362. We identified 19 new candidate variables, five of which are cluster RR Lyraes, four are probable SX Phe-type stars and eight are eclipsing binaries. Of the discovered binaries, three are EA-type systems, two of which are located on the cluster CMD in the turn-off region and the third 1 mag above the turn-off point, in the yellow straggler region. Five other systems are of W UMa type, three of which are foreground objects and two are likely cluster members. The remaining two candidates exhibit a modulation of the brightness level with an amplitude of 0.1–0.2 mag; further observations are needed to reveal the nature of their variability. Phased VI light curves for 20 variables (18 RR Lyrae stars and two blue stragglers) located in the central region of the cluster are presented. 相似文献
7.
David Stevenson 《Icarus》1974,22(4):403-415
The origin and maintenance of planetary magnetic fields are discussed. The discussion is not limited to dynamo theories although these are almost universally favored. Thermoelectric currents are found to be a possible alternative for Jupiter. Two energy sources for dynamos are considered: convection and precessionally induced fluid flow. The earth is the most favorabl planet for a precessionally driven dynamo, although Neptune is a possibility. Jupiter is likely to have a convectionally driven dynamo, as may Saturn, but the relevant properties of Saturn are not yet well known. Conclusions for each planet are given. 相似文献
8.
TRACE observations from 15 April 2001 of transverse oscillations in coronal loops of a post-flare loop arcade are investigated. They are considered to be standing fast kink oscillations. Oscillation signatures such as displacement amplitude, period, phase and damping time are deduced from 9 loops as a function of distance along the loop length. Multiple oscillation modes are found with different amplitude profile along the loop length, suggesting the presence of a second harmonic. The damping times are consistent with the hypothesis of phase mixing and resonant absorption, although there is a clear bias towards longer damping times compared with previous studies. The coronal magnetic field strength and coronal shear viscosity in the loop arcade are derived. 相似文献
9.
The planet Jupiter possesses a magnetic field and is surrounded by a magnetosphere. The occurrence of auroral and polar cap phenomena similar to those found on earth is very likely. In this work auroral and polar cap emissions in a model Jovian atmosphere are determined for proton precipitation. The incident protons, which are characterized by representative spectra, are degraded in energy by applying the continuous slowing down approximation. All secondary and higher generation electrons are assumed to be absorbed locally and their contributions to the total emissions are included. Volume emission rates are calculated from the total direct excitation rates with corrections for cascading applied. Results show that most molecular hydrogen and helium emissions for polar cap precipitation are below the ambient dayglow values. Charge capture by precipitating protons is an important source of Lyman α and Balmer α emissions and offers a key to the detection of large fluxes of low energy protons. 相似文献
10.
Konstantin V. Kholshevnikov 《Celestial Mechanics and Dynamical Astronomy》2008,100(3):169-179
Several metric spaces of Keplerian orbits and a set of their most important subspaces, as well as a factor space (not distinguishing
orbits with the same longitudes of nodes and pericentres) are constructed. Topological and metric properties of them are established.
Simple formulae to calculate the distance are deduced. Applications to a number of problems of Celestial Mechanics are discussed. 相似文献
11.
12.
Anthony R. Martin 《Planetary and Space Science》1974,22(1):121-141
The interaction of a conducting body moving through the ionosphere with the surrounding plasma is treated numerically. The Poisson and Vlasov equations are solved using computer techniques to give information about the redistribution of charged particles in the wake behind the body and the perturbation of the electric potential sheaths around the body. Three cases of interest are studied: body size less than, equal to, and greater than the Debye length in the surrounding plasma. A range of body potentials and ion Mach numbers are considered which are typical of conditions found in the ionosphere. Wake features, such as ion-free wake lengths and angles of propagation of disturbances in the wakes, are investigated for these conditions. Physical pictures of the mechanisms of wake formation behind a plate and a disc are built up for the three classes of body size, and differences due to geometry or size are explained. The smaller bodies are comparable in size to instrument booms, diagnostic probes, antennae, etc. and the larger bodies approach the dimensions of ionospheric satellites and space probes. 相似文献
13.
Richard P. Binzel 《Icarus》1985,63(1):99-108
Photoelectric observations of asteroid 1220 Crocus (an Eos family member) show evidence for two distinct periods in its light variation: 30.7 days and 7.90 hr. The lightcurve amplitudes are 0.87 and 0.15 mag, respectively. The shorter period variation appears to be modulated over the longer period. Two periods are possible for a rigid body only if it is in a state of precession. The observations are shown to be compatible with a body in a forced precession state. This result leads us to hypothesize the existence of a satellite of Crocus as the source of the external torque. Calculations are presented which show that there are in fact dynamically possible “binary asteroid” solutions consistent with the observations. More photoelectric and perhaps direct (space telescope) observations are needed to resolve the true nature of this asteroid. 相似文献
14.
Y. C. Whang 《Solar physics》1983,88(1-2):343-358
A one-fluid model is employed to study the global expansion of the solar wind from a two-hole corona, under the assumptions that the holes are confined to polar caps within 30° of heliographic colatitude, the flow is steady and axisymmetric, and the geometry of streamlines is prescribed. The boundary conditions are adjusted in such a way that the calculated solar wind properties at 1 AU are in a reasonable agreement with observational results. A series of numerical solutions are obtained, the series produces a maximum terminal speed of 829 km s?1 at the pole. The calculated solar wind speeds are strongly latitude dependent and are positively correlated with local divergence factor of a stream tube. The solutions imply that most plasma properties are highly inhomogeneous at the polar caps. The flow velocity, the temperature, the proton number flux and the conduction heat flux all increase towards the hole center. 相似文献
15.
The orbits of over 10000 stars are integrated in a steady-state model of the Galaxy for a time 6.0×108 yr. Initially, the stars are placed randomly inside spheres of 500 pc and 50 pc radius and are given random velocities, such that the sample has a Maxwellian or a spheroidal velocity distribution. The spheres are placed at the Sun's distance from the galactic centre (10 kpc) and are given a circular velocity of 250 km s?1. The mean velocities and dispersions of stars within 1 kpc of an ‘observer’ moving at the circular velocity are calculated as functions of time. The quantities show a strong time-dependence with oscillations of period 108 yr. The oscillations are independent of the mass model and occur also in an inverse square force field. A vertex deviation of the velocity ellipsoid, an asymmetric drift and aK-effect occur as natural consequences of the oscillations. Attempts to apply the Oort method for density determinations in the galactic plane are also influenced by the oscillations. Spiral density waves appear to have a small effect on the motions of the test stars. 相似文献
16.
The Navier-Stokes equations are solved by introducing a statistical model of density and a distinct temperature model. The non-linear terms of inertia and the viscous term are not included. The computations have been made for equinoctial conditions at a height of 300 km and at different latitudes.The results are presented in the form of a global wind pattern. The most important features are: the existence of transequatorial winds by night, the asymmetrical structure of the wind pattern and the agreement of the computed velocities with observations. 相似文献
17.
Przemysław Bartczak Sławomir Breiter Przemysław Jusiel 《Celestial Mechanics and Dynamical Astronomy》2006,96(1):31-48
Simple models of potential based on material points and material segments are confronted with a homogeneous ellipsoid potential.
A spheroid is approximated with a pair of material points or with one material segment. The segment model proves to be more
accurate. For a triaxial ellipsoid, two models are considered: one with five material points and one with two material segments
and a point. When their parameters are determined with the fourth sectorial harmonic ignored, both simple models have a similar
approximation error. Numerical tests indicate that the approximate models of a triaxial ellipsoid are 5 to 10 times faster
than exact formulation, whereas for a spheroid the approximate models are at most twice as fast as the exact formulae. 相似文献
18.
最近的多普勒观测表明恒星HD 12661周围存在两颗中等偏心率轨道上运行的行星,内行星的最小质量为2．3木星质量,轨道周期为263．6天;外行星的最小质量为1．57木星质量,轨道周期为1444．5天．该系统的稳定性要求两颗行星处在平运动轨道共振．用数值方法研究了该系统形成初期在恒星气体盘作用下的轨道迁移与稳定性,计算了行星在迁移中被平运动共振俘获的概率．发现这两颗行星目前很可能正处在11:2平运动共振边缘,且运动是混沌的,从而澄清了关于系统目前构形的不同说法,并且很可能在系统形成后行星迁移到目前构形时,气体盘几乎消失了． 相似文献
19.
M. M. Zakirov 《Astronomy Letters》2001,27(6):379-385
Photoelectric (UBVR) observations of the eclipsing variable EQ Ori are presented. The ephemerides of primary minima are refined, and the range of the star’s light variations is determined. All light curves are solved by Lavrov’s direct method, and highly accurate photometric orbital elements are obtained for the system. The magnitudes and colors of each component are calculated and analyzed in two-color (U-B)-(B-V) and (U-B)-(V-R) diagrams. The system’s primary component is classified as a metallic-line Am star. The absolute parameters of the components are estimated, and the binary is classified as a detached system with a subgiant: A0 V and K2 IV. EQ Ori has a faint physical companion, which causes the epochs of primary minimum to be systematically displaced with a period of about 30 years. The expected parameters of the distant companion are estimated. The system’s components are at a pre-ZAMS evolutionary stage, with their age being 2×106 years. EQ Ori is thought to be a member of the Ori I association. 相似文献