A new treatment of the albedo radiation pressure in the case of a uniform albedo and of a spherical satellite

The purpose of this paper is to present a model for the radiation pressure acceleration of a spherical satellite, due to the radiation reflected by a planet with a uniform albedo. A particular choice of variables allows one to reduce the surface integrals over the lit portion of the planet visible to the satellite to one-dimensional integrals. Exact analytical expressions are found for the integrals corresponding to the case where the spacecraft does not "see" the terminator. The other integrals can be computed either numerically, or analytically in an approximate form. The results are compared with those of Lochry (1966). The model is applied to Magellan, a spacecraft orbiting Venus.     

Coupled thermal-orbital evolution of the early Moon

Coupled thermal-orbital histories of early lunar evolution are considered in a simple model. We consider a plagioclase lid, overlying a magma ocean, overlying a solid mantle. Tidal dissipation occurs in the plagioclase lid and heat transport is by conduction and melt migration. We find that large orbital eccentricities can be obtained in this model. We discuss possible consequences of this phase of large eccentricities for the shape of the Moon and geochronology of lunar samples. We find that the orbit can pass through the shape solution of Garrick-Bethell et al. (Garrick-Bethell, I., Wisdom, J., Zuber, M. [2006]. Science 313, 652), but we argue that the shape cannot be maintained against elastic deformation as the orbit continues to evolve.     

On some aspects of the albedo effect application to the ERS-1 satellite

Some aspects of the perturbative influence of radiation reflected by the Earth's surface on the motion of an artificial satellite are discussed. We concentrate on consequences of the extreme models with anisotropic reflection on the Earth's surface (specular reflection, clouds with anisotropic phase function). The possible effects of Lála's modification of the Earth's albedo nominal value are investigated. The role of the satellite surface optical properties is pointed out in the context of the albedo effect. All mentioned models are purely numerical. The whole message of the paper can be summarized in the following items

-It is very doubtful that the 10^?8 ÷ 10^?9 m s^?2 level is reached when determining the perturbing accelerations caused by the albedo effect in the case of the ERS-1 satellite due to poorly defined optical characteristics of the Earth's atmosphere, the Earth and the satellite's surface.

-In the general case this albedo effect uncertainty level is about 50% with respect to the averaged values, and probably as high as 100% with respect to the instantaneous values of the perturbing accelerations.

     

Estimation of surface albedo increase during the eighties Sahel drought from Meteosat observations

The devastating drought in the Sahel during the 70s and the 80s is among the most undisputed and largest recent climate event recognized by the research community. This dramatic climate event has generated numerous sensitivity analyses on land-atmosphere feedback mechanisms with contradicting conclusions on surface albedo response to precipitation changes. Recent improvements in the calibration and quantitative exploitation of archived Meteosat data for the retrieval of surface albedo have permitted to compare surface albedo of 1884, the driest year of the 80s, with year 2003 which had similar precipitation rate than conditions prevailing prior to the 80s drought. This analysis reveals detailed information on the geographical extension and magnitude of the surface albedo increase during from the 80s drought. A mean zonal increase in broadband surface albedo of about 0.06 between 1984 and 2003 has been estimated from the analysis of Meteosat observations. Regions particularly affected by the 1980s drought are essentially located into a narrow band of about 2° width along 16°N running from 18°W up to 20°E. Within this geographical area, surface albedo changes are not homogeneous and largest differences might locally exceed 0.15 whereas other places remained almost unaffected. The variety of previously published results might be explained by these important spatial variations observed around 16°N.     

Asymmetry of compton scattering by relativistic electrons with an isotropic velocity distribution: Astrophysical implications

The angular distribution of low-frequency radiation after a single scattering by relativistic electrons with an isotropic velocity distribution differs markedly from the Rayleigh angular function. In particular, the scattering by an ensemble of ultrarelativistic electrons is described by the law p=1?cosα, where α is the scattering angle. Thus, photons are mostly scattered backward. We discuss some consequences of this fact for astrophysical problems. We show that a hot atmosphere of scattering electrons is more reflective than a cold one: the fraction of incident photons reflected after a single scattering can be larger than that in the former case by up to 50%. This must affect the photon exchange between cold accretion disks and hot coronae (or advective flows) near relativistic compact objects, as well as the rate of cooling (through multiple inverse-Compton scattering of the photons supplied from outside) of optically thick clouds of relativistic electrons in compact radio sources. Scattering asymmetry also causes the spatial diffusion of photons to proceed more slowly in a hot plasma than in a cold one, which affects the shapes of Comptonization spectra and the time delay in the detection of soft and hard radiation from variable X-ray sources.     

Solar and planetary destabilization of the Earth-Moon triangular Lagrangian points

In the restricted circular three-body problem, two massive bodies travel on circular orbits about their mutual center of mass and gravitationally perturb the motion of a massless particle. The triangular Lagrange points, L₄ and L₅, form equilateral triangles with the two massive bodies and lie in their orbital plane. Provided the primary is at least 27 times as massive as the secondary, orbits near L₄ and L₅ can remain close to these locations indefinitely. More than 2200 cataloged asteroids librate about the L₄ and L₅ points of the Sun-Jupiter system, and five bodies have been discovered around the L₄ point of the Sun-Neptune system. Small satellites have also been found librating about the L₄ and L₅ points of two of Saturn's moons. However, no objects have been discovered around the Earth-Moon L₄ and L₅ points. Using numerical integrations, we show that orbits near the Earth-Moon L₄ and L₅ points can survive for over a billion years even when solar perturbations are included, but the further addition of the far smaller perturbations from other planets destabilize these orbits within several million years. Thus, the lack of observed objects in these regions cannot be used as a constraint on Solar System formation, nor on the tidal evolution of the Moon's orbit.     

On the singular points of the Abelian integral transformation in the GPS/LEO occultation technique

In the inversion terrestrial atmosphere technique the inversion of theAbelian integral is one of the most often used methods for deriving the refractive index profile of the terrestrial atmosphere from GPS/LLEO radio occultation data. There exists the problem of singular point in the Abelian integral. Different methods for solving this problem are discussed and a method of finding an analytic solution of the Abelian integral after a variable transformation is proposed. The accuracies of the various methods are compared by means of simulation calculations.     

Finding the trigger to Iapetus’ odd global albedo pattern: Dynamics of dust from Saturn’s irregular satellites

The leading face of Saturn’s moon Iapetus, Cassini Regio, has an albedo only one tenth that on its trailing side. The origin of this enigmatic dichotomy has been debated for over 40 years, but with new data, a clearer picture is emerging. Motivated by Cassini radar and imaging observations, we investigate Soter’s model of dark exogenous dust striking an originally brighter Iapetus by modeling the dynamics of the dark dust from the ring of the exterior retrograde satellite Phoebe under the relevant perturbations. In particular, we study the particles’ probabilities of striking Iapetus, as well as their expected spatial distribution on the Iapetian surface. We find that, of the long-lived particles (?5 μm), most particle sizes (?10 μm) are virtually certain to strike Iapetus, and their calculated distribution on the surface matches up well with Cassini Regio’s extent in its longitudinal span. The satellite’s polar regions are observed to be bright, presumably because ice is deposited there. Thus, in the latitudinal direction we estimate polar dust deposition rates to help constrain models of thermal migration invoked to explain the bright poles (Spencer, J.R., Denk, T. [2010]. Science 327, 432-435). We also analyze dust originating from other irregular outer moons, determining that a significant fraction of that material will eventually coat Iapetus—perhaps explaining why the spectrum of Iapetus’ dark material differs somewhat from that of Phoebe. Finally we track the dust particles that do not strike Iapetus, and find that most land on Titan, with a smaller fraction hitting Hyperion. As has been previously conjectured, such exogenous dust, coupled with Hyperion’s chaotic rotation, could produce Hyperion’s roughly isotropic, moderate-albedo surface.     

Detailed prediction for the BYORP effect on binary near-Earth Asteroid (66391) 1999 KW4 and implications for the binary population

A previous theory by the authors for detailed modeling of the binary YORP effect is reviewed and expanded to accommodate doubly-synchronous binary systems, as well as a method for non-dimensionalizing the coefficients for application to binary systems where a shape model to compute its own coefficients is not available. The theory is also expanded to account for the effects of primary J₂ and the Sun’s 3rd body perturbation on the secular orbit evolution. The newly expanded theory is applied to the binary near-Earth Asteroid 1999 KW4, for which a detailed shape model is available. The result of simulation of the secular evolutionary equations shows that the KW4 orbit will be double in size in approximately 22,000 years, and will reach the Hill radius in approximately 54,000 years. The simulation also shows that the eccentricity will alternate growing and shrinking in magnitude, depending on the location of the solar node in the body-fixed frame. Therefore the eccentricity is not fixed to evolve in the opposite sign as the semi-major axis unless the circulation of the node (with a period of 500 years) is averaged out as well. The current orbit expansion rate for KW4 of 7 cm per year is shown to be detectable with observations of the mean anomaly which grows quadratically in time with an expanding orbit. Finally, the KW4 results are scaled for application to a number of other binary systems for which detailed shape models are not available. This application shows that the orbits considered can expand to their Hill radius in the range of 10⁴-10⁶ years. This implies rapid formation of binary systems is necessary to support the large percentage of binaries observed in the NEA population.     

Cepheus OB3巨分子云复合体成块性质的研究

根据文[1]中图1（a）和图1（b），分别对CepB和CepF进行成图处理，得到了它们的强度分布图和速度分段积分等高图，通过对这些强度分布图和速度分段积分等高图的分析和研究，也得到了CegheusOB3巨分子云复合体是成块的，并且这些块是没有被自引力束缚的，同时还得到了CepB和CepF的外流的动力学时标。     

A general model of the planetary radiation pressure on a satellite with a complex shape

The purpose of this paper is to present a general model for the acceleration exerted on a spacecraft by the radiation coming from a planet. Both the solar radiation reflected by the planet and the thermal emission associated with its temperature are considered. The planet albedo and the planet emissive power are expanded in spherical harmonics with respect to an equatorial reference frame attached to the planet. The satellite external surface is assumed to consist of a juxtaposition of planar surfaces. A particular choice of variables allows to reduce the surface integrals over the lit portion of the planet visible to the satellite to one-dimension integrals.     

On the possible observational manifestation of the impact of a supernova shock on the neutron star magnetosphere

The impact of a supernova explosion on the magnetosphere of a neutron star in a massive binary system is considered. The supernova shock impact on a plasma-filled neutron star magnetosphere can give rise to a long magnetospheric tail with a considerable store of magnetic energy. Magnetic reconnection in the formed current sheet can transform the magnetic energy stored in the tail into the kinetic energy of charged particles. The plasma instabilities excited by beams of accelerated relativistic particles can lead to the formation of a short pulse of coherent radio emission with parameters similar to those measured for the bright extragalactic millisecond radio burst detected in 2007.     

Numerical simulations of very large impacts on the Earth

Vertical impacts on the Earth of asteroids 500-3000 km in diameter at 15 km/s have been numerically modelled using the hydrodynamic SOVA code. This code has been modified for the spherical system of coordinates well suited for simulations of very large impacts when the entire Earth is involved in motion. The simulations include cratering process, upward motion of deep mantle layers, fall of ejecta on the Earth, escape of matter to space, and formation of rock vapour atmospheres. The calculations were made for the period preceding disappearance of rock vapour atmospheres caused by radiation several years after the largest impacts. For very large vertical impacts at 15 km/s, escaping masses proved to be negligibly small. Quantities of kinetic, internal, potential, and radiated away energies are obtained as functions of time and space. After the impacts, a global layer of condensed ejecta covers the whole of the Earth's surface and the ejecta energy is sufficient to vaporise an ocean 3 km deep. The mass of rock vapour atmosphere is 10-23% of the impactor mass. This atmosphere has a greater mass than the water atmosphere if impactor is 2000 km in diameter or larger.     

Relativistic corrections to the multiple scattering effect on the Sunyaev–Zel'dovich effect in the isotropic approximation

We extend the formalism for the calculation of the relativistic corrections to the Sunyaev–Zel'dovich effect for clusters of galaxies and include the multiple scattering effects in the isotropic approximation. We present the results of the calculations by the Fokker–Planck expansion method as well as by the direct numerical integration of the collision term of the Boltzmann equation. The multiple scattering contribution is found to be very small compared with the single scattering contribution. For high-temperature galaxy clusters of     the ratio of both the contributions is −0.2 per cent in the Wien region. In the Rayleigh–Jeans region the ratio is −0.03 per cent. Therefore the multiple scattering contribution is safely neglected for the observed galaxy clusters.     

Comparison of the large-scale clustering in the APM and the EDSGC galaxy surveys

We present the results of a numerical study of the fluid f, p and the gravitational w modes for increasingly relativistic non-rotating polytropes. The results for f and w modes are in good agreement with previous data for uniform density stars, which supports an understanding of the nature of the gravitational wave modes based on the uniform density data. We show that the p modes can become extremely long-lived for some relativistic stars. This effect is attributed to the change in the perturbed density distribution as the star becomes more compact.     

回旋同步辐射自吸收的特性

详细研究了高能电子产生的回旋同步辐射自吸收的特性,并用磁偶极子场的 射电微波源模型计算了它的光学厚度.发现: (1)自吸率Kv随谐波数s的增加迅速地 下降,以致只有低次谐波(s<5)上的自吸收才会对微波爆发谱产生实质性的影响; (2) 自吸率κv随暗波数s下降的陡度还随高能电子的能谱指数δ的增加和其低能截止能量 E0的下降而迅速增加; (3)κv值还随传播角的增大而增加,并在70°至75°范围内达到 极值; (4)假设高能电子数密度为103cm-3,则在2≤s≤5范围内的自吸收的光学厚 度τvself在101-10-2之间变化,这些值约比回旋共振吸收的光学厚度τvgyro小3至4 个数量级.τvself在均匀磁场情况下可能被高估.只有当被加速的高能电子的数密度大于 104cm-3时,自吸收的光学厚度才开始能与回旋共振吸收的光学厚度相比较.