共查询到20条相似文献，搜索用时 796 毫秒
1.
Juan Getino José M. Farto José M. Ferrándiz 《Celestial Mechanics and Dynamical Astronomy》1998,71(2):95-108
In this paper, the mathematical algorithm elaborated by González, Getino and Farto (1998) is applied to four different nonrigid Earth models, in order to obtain the analytical expressions of the corresponding free frequencies. The solutions are studied, and the contributions of the different considered effects are evaluated. A numerical integration is also carried out, showing the validity of the obtained analytical solutions. 相似文献
2.
E. Piña 《Celestial Mechanics and Dynamical Astronomy》1999,74(3):163-174
The motion of three particles, interacting by gravitational forces, is studied in a new coordinate system given by the principal
axes of inertia, as determined by Euler angles, and using the inertia principal moments and an auxiliar angle as coordinates.
The solution to the particular Lagrange case of the three‐body problem is reviewed and solved in these new coordinates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Some asteroids in Earth‐crossing orbits avoid close approaches by entering in a mean motion resonance whenever the distance between the two orbits is small. These orbits are ‘Toro class’ according to the classification of (Milani et al., 1989). This protection mechanism can be understood by a semi‐averaged model, in which the fast variables are removed and the dynamical variables are the critical argument and the semimajor axis, with dependence upon a slow parameter. The adiabatic invariant theory can be applied to this model and accounts for all the qualitative features of the orbits in this class, including the onset of the libration when the orbit distance is small. Because of the neglected perturbations by the other planets, this theory is approximate and the adiabatic invariant is conserved only with low accuracy moreover, the Toro state can be terminated by a close approach to another planet (typically Venus). “Would you tell me, please, which way I ought to go from here?” “That depends a good deal on where you want to get to,” said the Cat. Alice in Wonderland, L. Carroll 相似文献
4.
In the free‐fall three‐body problem, distributions of escape, binary, and triple collision orbits are obtained. Interpretation
of the results leads us to the existence of oscillatory orbits in the planar three‐body problem with equal masses. A scenario
to prove their existence is described.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
L. Benet T. H. Seligman D. Trautmann 《Celestial Mechanics and Dynamical Astronomy》1998,71(3):167-189
We study the scattering motion of the planar restricted three‐body problem for small mass parameters μ. We consider the symmetric
periodic orbits of this system with μ = 0 that collide with the singularity together with the circular and parabolic solutions
of the Kepler problem. These divide the parameter space in a natural way and characterize the main features of the scattering
problem for small non‐vanishing μ. Indeed, continuation of these orbits yields the primitive periodic orbits of the system
for small μ. For different regions of the parameter space, we present scattering functions and discuss the structure of the
chaotic saddle. We show that for μ < μc and any Jacobi integral there exist departures from hyperbolicity due to regions of
stable motion in phase space. Numerical bounds for μc are given.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
The orbits of planetcrossing asteroids (and comets) can undergo close approaches and collisions with some major planet. This introduces a singularity in the Nbody Hamiltonian, and the averaging of the equations of motion, traditionally used to compute secular perturbations, is undefined. We show that it is possible to define in a rigorous way some generalised averaged equations of motion, in such a way that the generalised solutions are unique and piecewise smooth. This is obtained, both in the planar and in the threedimensional case, by means of the method of extraction of the singularities by Kantorovich. The modified distance used to approximate the singularity is the one used by Wetherill in his method to compute probability of collision. Some examples of averaged dynamics have been computed; a systematic exploration of the averaged phase space to locate the secular resonances should be the next step.'Alice sighed wearily. I think you might do something better with the time she said, than waste it asking riddles with no answers(Alice in Wonderland, L. Carroll) 相似文献
7.
G. Tancredi 《Celestial Mechanics and Dynamical Astronomy》1998,70(3):181-200
The dynamics of two families of minor inner solar system bodies that suffer frequent close encounters with the planets is
analyzed. These families are: Jupiter family comets (JF comets) and Near Earth Asteroids (NEAs).
The motion of these objects has been considered to be chaotic in a short time scale,and the close encounters are supposed
to be the cause of the fast chaos. For a better understanding of the chaotic behavior we have computed Lyapunov Characteristic
Exponents (LCEs) for all the observed members of both populations. LCEs are a quantitative measure of the exponential divergence
of initially close orbits. We have observed that most members of the two families show a concentration of Lyapunov times (inverse
of LCE) around 50–100yr. The concentration is more pronounced for JF comets than for NEAs, among which a lesser spread is
observed for those that actually cross the Earth's orbit (mean perihelion distance q < 1.05 AU). It is also observed that
a general correspondence exists between Lyapunov times and the time between consecutive encounters.
A simple model is introduced to describe the basic characteristics of the dynamical evolution. This model considers an impulsive
approach, where the particles evolve unperturbedly between encounters and suffer ‘kicks’ in semimajor axis at the encounters.
It also reproduces successfully the short Lyapunov times observed in the numerical integrations and is able to estimate the
dynamical lifetimes of comets during a stay in the Jupiter family in correspondence with previous estimates.
It has been demonstrated with the model that the encounters with the largest effect on the exponential growth of the distance
between initially nearby orbits are neither the infrequent deep encounters, nor the frequent and far ones; instead, the intermediate
approaches have the most relevant contribution to the error growth. Such encounters are at a distance a few times the radius
of the Hill's sphere of the planet (e.g. 3).
An even simpler model allows us to get analytical estimates of the Lyapunov times in good agreement with the values coming
from the model above and the numerical integrations.
The predictability of the medium‐term evolution and the hazard posed to the Earth by those objects are analysed in the Discussion
section.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Claudio Vidal 《Celestial Mechanics and Dynamical Astronomy》1998,71(1):15-33
We consider four bodies in space with same masses forming two binaries, each one symmetric with respect to a fixed axis and
moving under Newtonian gravitation in opposite directions about this axis. It is given a direct proof that all singularities
of this model are due to collisions, and it is proved that the singularities due to simultaneous double collisions are regularizable.
The set of equilibrium points on the total collision manifold is studied as well as the possible connections among them. We
show that the set of initial conditions on a given energy surface going to quadruple collision is a union of twenty submanifolds:
twelve of them have dimension 2 and the others have dimension 3. Similarly for ejection orbits from quadruple collision.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
By Hamiltonian manipulation we demonstrate the existence of separable time‐transformed Hamiltonians in the extended phase‐space.
Due to separability explicit symplectic methods are available for the solution of the equations of motion. If the simple leapfrog
integrator is used, in case of two‐body motion, the method produces an exact Keplerian ellipse in which only the time‐coordinate
has an error. Numerical tests show that even the rectilinear N‐body problem is feasible using only the leapfrog integrator.
In practical terms the method cannot compete with regularized codes, but may provide new directions for studies of symplectic
N‐body integration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
Florin Diacu 《Celestial Mechanics and Dynamical Astronomy》1999,75(1):1-15
We consider two‐body problems in which the drag is proportional to the velocity divided by the square of the distance and
whose radial and tangential components have distinct coefficients. For all parameters, we study the flow of the system obtained
by suitable coordinate and time transformations and draw conclusions about the qualitative behavior of solutions. In each
case, we examine the existence of collision–ejection, collision–escape, capture–collision, capture–escape, and oscillatory
rectilinear orbits, study the motion near collision, and show that if periodic orbits exist they must be limit cycles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We present the pattern of the polar magnetic reversal for cycle 23 derived from H synoptic charts and have also included the reversals of the earlier cycles 18–22 for comparison. At the beginning of a new cycle (i.e., soon after the polar reversal) the zonal boundaries of unipolar magnetic regions of opposite polarities (seen as filament bands on the synoptic charts) appear close to and on either side of the equator continuing through the years of minimum indicating the onset of the cancellation of flux at these low latitudes. The cycle thus starts with cancellation of flux close to the equator and ends with the polar reversal or flux cancellation near the poles. The filament bands just below the polemost ones migrate and reach latitudes 35°–45° by the time of polar reversal and become the polemost, once the polar reversal has taken place. During the years of minimum that follow, these filament bands remain more or less stagnant at the latitudes 35°–45° except for occasional slow migration towards the equator. The migration to the poles starts at a low speed of 3 m s–1 only when the spot activity has risen to a significant level and then it accelerates to 30 m s–1 at the peak of the activity. It takes 3–4 years for the polemost bands to reach the poles moving at these high speeds. We quantify this possible cause and effect phenomenon by introducing the concept of the `strength of the solar cycle' and represent this by either of a set of three parameters. We show that the velocity of poleward migration is a linear function of the `strength of the solar cycle'. 相似文献
12.
《天文和天体物理学研究(英文版)》2017,(10)
XB 1254–690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254–690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254–690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M_2 = 0.42 ± 0.04 M_⊙for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 M_⊙. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking. 相似文献
13.
G. S. Kurbasova 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):82-86
The appearance of features with cusp points on the diagrams of changes in the coordinates of the Earth’s instantaneous pole
(polhodes) is considered as the result of mapping onto the plane of its displacement over the surface during the Earth’s rotational-translational
motion. The results of qualitative and quantitative analyses of the data on the coordinates of the Earth’s instantaneous pole
are discussed. The basic principles of the theory of Whitney singularities and their application for explaining the bifurcations
of the equilibrium positions for the Zeeman catastrophe machine (Arnold 1990) are used in the analyses. 相似文献
14.
L. Zaninetti 《中国天文和天体物理学报》2006,6(4):387-395
The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2,3),-2D cut of 3D Voronoi diagram-are explored, with the single-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2,3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size. 相似文献
15.
Joseph A. Nuth III 《Earth, Moon, and Planets》2008,102(1-4):435-445
Is there an asteroid type or meteorite class that best exemplifies the materials that went into the Earth? Carbonaceous chondrites were once the objects of choice, and in the minds of many this choice is still valid. However, the origin of primitive chondritic meteorites is unclear. At the extremes they could either be fragments of very small parent bodies that never became hot enough to undergo geochemical modification other than mild lithification, or remnants of the uppermost layers of a body that had undergone a significant degree of internal differentiation, while the top layers remained cool due to radiative heat loss or loss of volatiles to space. This latter case is problematic if one considers these objects as precursors to the Earth since the timescale for the evolution of such a small body could be longer than the timescale for the accretion of the Earth. Large-scale circulation of materials in the primitive solar nebula could greatly increase the diversity of materials near 1 AU while also making the entire inner solar system both more homogeneous and much wetter than previously expected. The total mass of the nebula is an important, but poorly constrained factor controlling the growth of planetesimals. There is also a selection effect that dominates our sampling of the planetesimals that may have existed 4.5 billion years ago; namely, small fragile bodies are more likely to be lost from the system or ground down by collisions between small bodies, yet these are precisely those that may have dominated the population from which the Earth accreted. The composition of these aggregates could have played a very important role in the early chemical evolution of the Earth. In particular, the Earth may have been much wetter and richer in hydrocarbons and other reducing materials than previously suspected. 相似文献
16.
S.-I. Akasofu 《Planetary and Space Science》1979,27(7):1039-1041
When the interplanetary parameter exceeds the amount that can be dissipated by the ionosphere in terms of the Joule heat production, the excess energy is absorbed by the ring current belt, resulting in abnormal growth of the Dst index. 相似文献
17.
V. G. Kornilov M. V. Kornilov N. I. Shatsky O. V. Vozyakova I. A. Gorbunov B. S. Safonov S. A. Potanin D. V. Cheryasov V. A. Senik 《Astronomy Letters》2016,42(9):616-630
Based on the measurements performed from 2007 to 2015 at the summit of Mount Shatdzhatmaz adjacent to the 2.5-m telescope at the Caucasus Observatory of the SAI MSU, we have determined the statistical characteristics of basic meteorological parameters: the ambient air temperature, the ground wind speed, and the relative humidity. The stability of these parameters over the entire period of our measurements and their variations within an annual cycle have been studied. The median temperature on clear nights is +3.2°C, although there are nights with a temperature below ?15°C. The typical ground wind speed is 3 m s?1; the probability of a wind stronger than 10 m s?1 does not exceed 2%. The losses of observing time due to high humidity are maximal in the summer period but, on the whole, are small over a year, less than 10%. We have estimated the absolute water vapor content in the atmosphere, which is especially important for infrared observations. Minimum precipitablewater vapor is observed in December–February; the median value over these months is 5 mm. We additionally provide the wind speeds at various altitudes above the ground (from 1 to 16 km) that we obtained when measuring the optical turbulence. We present the results and technique of our measurements of the annual amount of clear night astronomical time, which is, on average, 1320 h, i.e., 45% of the possible one at the latitude of the observatory. The period from mid-September to mid-March accounts for about 70% of the clear time. A maximum of clear skies is observed in November, when its fraction reaches 60% of the possible astronomical night time. 相似文献
18.
The emergence and evolution of large granules shows thegranular dynamics particularly well. We therefore investigate the time dependence of the convective flows within a regular and an exploding granule. The observational material for this study was taken at the center of the solar disk with the German VTT in Izaña (Tenerife, Spain) during an observing campaign in the year 1994. It consists of series of spectrograms of high spatial resolution, which were digitized and processed with wavelet techniques. Among other features, our data show the dynamical portrait of a regular and an exploding granule. We can follow their temporal evolution over more than 12 min. Using absorption lines of different strength we are able to see the dynamical change of both granules at several heights within the first 200 km above 5000=1. The observations reveal significant changes of the convective flow of both granules over time as well as over height, which are discussed in detail. 相似文献
19.
Poincaré surface of section technique is used to study the evolution of a family ‘f’ of simply symmetric retrograde periodic orbits around the smaller primary in the framework of restricted three-body problem for a number of systems, actual and hypothetical, with mass ratio varying from 10−7 to 0.015. It is found that as the mass ratio decreases the region of phase space containing the two separatrices shrinks in size and moves closer to the smaller primary. Also the corresponding value of Jacobi constant tends towards 3. 相似文献
20.
B. P. Kondratyev 《Solar System Research》2012,46(5):341-351
The effect of the Earth??s compression on the physical libration of the Moon is studied using a new vector method. The moment of gravitational forces exerted on the Moon by the oblate Earth is derived considering second order harmonics. The terms in the expression for this moment are arranged according to their order of magnitude. The contribution due to a spherically symmetric Earth proves to be greater by a factor of 1.34 × 106 than a typical term allowing for the oblateness. A linearized Euler system of equations to describe the Moon??s rotation with allowance for external gravitational forces is given. A full solution of the differential equation describing the Moon??s libration in longitude is derived. This solution includes both arbitrary and forced oscillation harmonics that we studied earlier (perturbations due to a spherically symmetric Earth and the Sun) and new harmonics due to the Earth??s compression. We posed and solved the problem of spinorbital motion considering the orientation of the Earth??s rotation axis with regard to the axes of inertia of the Moon when it is at a random point in its orbit. The rotation axes of the Earth and the Moon are shown to become coplanar with each other when the orbiting Moon has an ecliptic longitude of L ? = 90° or L ? = 270°. The famous Cassini??s laws describing the motion of the Moon are supplemented by the rule for coplanarity when proper rotations in the Earth-Moon system are taken into account. When we consider the effect of the Earth??s compression on the Moon??s libration in longitude, a harmonic with an amplitude of 0.03?? and period of T 8 = 9.300 Julian years appears. This amplitude exceeds the most noticeable harmonic due to the Sun by a factor of nearly 2.7. The effect of the Earth??s compression on the variation in spin angular velocity of the Moon proves to be negligible. 相似文献