原子钟时域频率稳定度分析中等效自由度的计算与分析

该文基于标准化自协方差函数的组合算法计算了阿仑方差、哈达玛方差的重叠和非重叠形式以及改进阿仑方差、时间方差的等效自由度,并用经验公式计算了总方法估计的等效自由度,在此基础上对各种方差估计不同噪声情况下的等效自由度进行了比较分析,得出如下结论,总方法估计的等效自由度大于相应非总方法估计的等效自由度,重叠和非重叠阿仑方差估计的等效自由度大于相应哈达玛方差估计的等效自由度;对非重叠估计而言,噪声的频率越低,其等效自由度越大;而相应的重叠估计和总方法估计与之相反,噪声的频率越高,其等效自由度越大,这也说明重叠估计和相应的总方法估计对高频噪声等效自由度的提高优于低频噪声.     

Relative Equilibria for General Gravity Fields in the Sphere-Restricted Full 2-Body Problem

Equilibrium conditions for a mutually attracting general mass distribution and point mass are derived and their stability computed. The equilibrium conditions can be reduced to six equations in six unknowns, plus the existence of four integrals of motion consisting of the total angular momentum and energy of the system. The equilibrium conditions are further reduced to two independent equations, and their theoretical properties are studied. We derive three distinct conditions for a relative equilibrium which can be used to derive robust algorithms for solving these problems for non-symmetric gravity fields: a set of necessary conditions, a set of sufficient conditions, and a set of necessary and sufficient conditions. Each of these conditions is well suited for the computation of certain classes of equilibria. These equations are solved for non-symmetric gravity fields of interest, using a real asteroid shape model for the general gravity fields. Explicit conditions for the spectral and energetic stability of the resulting equilibria are also derived and computed for the shape of interest.     

Calculation of meteoroid impacts on moon and earth

Concise derivations are given for the expected flux of meteoroids to the surfaces of the earth and the moon. Contrary to other published results, we find an accretion rate which is lower for the near side of the moon than for the far side and which is lower for the moon than for the earth, for all earth-moon distances.     

Collective resonant phenomena on small bodies in the solar system

For both asteroids and meteor streams, and also for comets, resonances play a major role for their orbital evolutions but on different time scales. For asteroids both mean motion resonances and secular resonances not only structure the phase space of regular orbits but are mainly at the origin for the inherent chaos of planet crosser objects.For comets and their chaotic routes temporary trapping into orbital resonances is a well known phenomenon. In addition for slow diffusion through the Kuiper belt resonances are the only candidates for originating a slow chaos.Like for asteroids, resonances with Jupiter play a major role for the orbital evolution of meteor streams. Crossing of separatrix like zones appears to be crucial for the formation of arcs and for the dissolution of streams. In particular the orbital inclination of a meteor stream appears to be a critical parameter for arc formation. Numerical results obtained in an other context show that the competition between the Poynting-Robertson drag and the gravitational interaction of grains near the 2/1 resonance might be very important in the long run for the structure of meteor streams.     

Survey and evaluation of eucrite bulk compositions

Abstract— The purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting, fractional crystallization and magma ocean theories for the eucrite parent body. In order to evaluate bulk elemental abundances for the eucrites, 296 peer-reviewed articles, monographs, theses or books and 143 abstracts dating from 1938 to 1997 were surveyed. Of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature, 20 were selected for in-depth examination. The selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist. The mean bulk elemental abundance, 1σ standard deviation, and the percent deviation were calculated for each element in a given eucrite. In order to evaluate the quality of the mean abundances, the elements were then grouped according to availability of data and percent deviations. Possible reasons for the different deviations in the different groups are briefly discussed. From the major element abundances, the normative (CIPW) composition, the molar compositions of pyroxene, olivine and plagioclase, and the bulk densities were calculated and compared to petrographic observations. The calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not. Possible reasons for this are discussed. Unfortunately, analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty. Therefore, future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites, especially those of key elements used for planetary modeling.     

Mapping monthly quantiles of ionospheric electron content and foF2

Monthly quantiles of ionization parameters are important information for system planning and to assess one aspect of ionospheric variability. For ionosonde parameters the data base is probably large enough to allow mapping of deciles. For electron content the situation is not so good: at least for Europe the data base only allows to construct maps for the upper and and the lower monthly quartiles.We present mapping procedures and maps for monthly quartiles of electron content and of foF2 based on experiences with mapping procedures for monthly medians. It turned out that for the lower quartiles it is necessary to to use more coefficients for the quartile maps than for the median maps.We discuss possibilities to gain decile information for electron content from foF2. For a few selected months and locations deciles can be gained from the Faraday effect on the signals of geostationary satellites. These selected cases are used to check on procedures to use foF2 experience to construct electron content deciles.     

Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars?? satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) ?teins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.     

On the mixing rules for astrophysical inhomogeneous grains

We present the computation of effective refractive coefficients for inhomogeneous two-component grains with three kinds of inclusions with   m _incl= 3.0 + 4.0i, 2.0 + 1.0i, 2.5 + 0.0001i  and a matrix with   m_m = 1.33 + 0.01i  for 11 volume fractions of inclusions from 0 to 50 per cent and wavelengths  λ= 0.5  , 1.0, 2.0 and 5.0 μm. The coefficients of extinction for these grains have been computed using a discrete dipole approximation. Computation of the extinction by the same method for grains composed of a matrix material with randomly embedded inclusions has been carried out for different volume fractions of inclusions. A comparison of extinction coefficients obtained for both models of grain material allows one to choose the best mixing rule for a mixture. In cases of inclusions with   m _incl= 2.0 + 1.0i  and 2.5 + 0.0001i the best fit for the whole wavelength range and volume fractions of inclusions from 0 to 50 per cent has been obtained for the Lichtenecker mixing rule. In the case of   m _incl= 3.0 + 4.0i  the fit for the whole wavelength range and volume fractions of inclusions from 0 to 50 per cent is not very significant but the best fit has been obtained for the Hanai rule. For volume fractions of inclusions from 0 to 15 per cent a very good fit has been obtained for the whole wavelength range for Rayleigh and Maxwell-Garnett mixing rules.     

Linear MHD Sausage Waves in Compressible Magnetically Twisted Flux Tubes

Oscillations of magnetic flux tubes are of great importance as they contain information about the geometry and fine structure of the flux tubes. Here we derive and analytically solve in terms of Kummer’s functions the linear governing equations of wave propagation for sausage surface and body modes (m=0) of a magnetically twisted compressible flux tube embedded in a compressible uniformly magnetized plasma environment in cylindrical geometry. A general dispersion relation is obtained for such flux tubes. Numerical solutions for the phase velocity are obtained for a wide range of wavenumbers and for varying magnetic twist. The effect of magnetic twist on the period of oscillations of sausage surface modes for different values of the wavenumber and vertical magnetic field strength is calculated for representative photospheric and coronal conditions. These results generalize and extend previous studies of MHD waves obtained for incompressible or for compressible but nontwisted flux tubes. It is found that magnetic twist may change the period of sausage surface waves of the order of a few percent when compared to counterparts in straight nontwisted flux tubes. This information will be most relevant when high-resolution observations are used for diagnostic exploration of MHD wave guides in analogy to solar-interior studies by means of global eigenoscillations in helioseismology.     

New set of geometrical and physical elements of the two variable stars SW lacertae and OO aquilae

Photoelectric observations of the two eclipsingvariables, were obtained in UBV standard system, for SWLac and, inVB standard system for OOAql.A new set of geometrical and physical elements for thesystems were obtained from both minima, through theirmagnitude variation during the observation time using themethod of: Fourier Analysis Techniques in-Frequency-domain for thelight curve changes. The two eclipsing variables are contact, the firstcontact angle was 48.1^° for SW Lac and 47.7^° for OO Aql.Absolute elements and effective temperatures of the twocomponents for both systems are derived.     

Computation of elliptic Hansen coefficients and their derivatives

The problem of computation of elliptic Hansen coefficients and their derivatives is considered for constructing a motion theory of an artificial Earth satellite with large eccentricity. An algorithm for analytical and numerical computation of these coefficients and their derivatives is described. The recurrence relations for derivatives of the first and second order and initial values for recurrences are obtained. As an example, numerical values of some elliptic Hansen coefficients are given for the orbit with eccentricityk=0.74.     

The role of some collisional processes in AGNs: Rate coefficients needed for modeling

The importance of some atom hydrogen collisions in AGN has been investigated. The results are useful for better estimation of the hydrogen Balmer lines fluxes, which usage for effective temperature diagnostics in astrophysical plasma is limited by errors from the line formation models. The data could be also useful for modeling cooler and denser parts of AGN BLR clouds, as well as for the investigation of Rydberg states of hydrogen and for the study of their influence during the cosmological recombination epoch. The results of the present work suggest that the investigated processes are of interest for the research and modeling of such media.     

Inelastic cross section for antihelium on nuclei: an empirical formula for use in the experiments to search for cosmic antimatter

An empirical formula for the cross section for inelastic hadronic interaction of antihelium with nuclei for the projectile energy range from 0.3 GeV/n to 80 GeV/n and target atomic mass number A from 4 to 120 has been developed. It is based on the available experimental data of nucleon (antinucleon) — nucleus and helium — nucleus inelastic cross sections. Such a formula is needed by experiments designed to search for antihelium in cosmic rays. With this formula one can estimate the efficiency of antihelium detection and correct for antihelium attenuation in the atmosphere for the balloon-borne experiments. A byproduct of this work is an empirical formula for antiproton-nucleus inelastic cross.     

中高轨卫星广播星历精度分析

GPS广播星历参数具有物理意义明确、参数少、精度高等优点,可以考虑将它应用于其他卫星导航系统。但是GPS系统的卫星构成比较单一,而其他卫星导航系统可能包含中地球轨道 (MEO)、倾斜地球同步轨道(IGSO)和地球静止轨道(GEO)等多种不同类型的中高轨卫星。分析了采用GPS广播星历参数时,MEO、IGSO和GEO卫星的广播星历拟合精度,特别讨论了轨道倾角接近于0的GEO卫星的广播星历拟合精度,并给出了相应的改进措施。计算表明,对于 MEO卫星,2 h的广播星历拟合精度(三维位置)可达厘米级;对于IGSO卫星和轨道倾角较大的GEO卫星,4 h的广播星历拟合精度约为0．1 m,径向位置误差在厘米量级;而对于轨道倾角接近于0的GEO卫星,若不采取特殊措施,由于轨道倾角和升交点经度统计相关,其广播星历拟合精度很差,为此提出了一种坐标转换方法。采用此方法后的广播星历拟合精度可达0．1 m,径向位置误差为厘米量级。     

Application of Chebyshev collocation method for relocating of spacecrafts in Hill’s frame

In this study, the Chebyshev collocation method is used for solving the spacecraft relative motion of equations in Hill’s frame. Three different models of governing equations of relative motion (M1, M2, and M3) are considered and the maneuver cost required moving the spacecraft from one state to another is computed in the form of delta velocity at the first terminal point as a function of time of flight (TOF) and inter-satellite distance (ISD). A quantitative as well as qualitative difference is observed in the maneuver cost with the inclusion of radial and/or out of plane separation in along track separation of chaser. Also, a relative comparison of path profiles is made by considering M1, M2 and M3 models. Path profiles for M3 model are found close to M2 model for short intervals for a fixed ISD, whereas path profiles for M2 and M3 do not match even for small values of ISD for a fixed but long TOF. Path profiles for M1 models match to M2 model for very low values of target orbit eccentricities.     

埃文斯目视日晕光度计测量原理研究

埃文斯目视日晕光度计（Evans Visual Sky Photometer,EVSP）是应用于日冕仪选址的重要仪器,从20世纪40年代一直使用至今,它为现代日晕光度计的定标提供了参考标准。通过使用云南天文台现存的一架EVSP研究了它的工作原理,并重点介绍了所利用的简易定标方法。给出了国际现有的多台EVSP日晕亮度定标曲线。由于EVSP内部光学元件反射率和透过率,以及中性渐变光楔的光学密度等存在未知的时间缓变特点,因此利用这种新定标手段可以高效经济地获得各自的定标曲线。     

Heterogeneity of the population of open star clusters in the Galaxy

Based on published data, we have compiled a catalogue of fundamental astrophysical parameters for 593 open clusters of the Galaxy. In particular, the catalogue provides the Galactic orbital elements for 500 clusters, the masses, central concentrations, and ellipticities for 424 clusters, the metallicities for 264 clusters, and the relative magnesium abundances for 56 clusters. We describe the sources of initial data and estimate the errors in the investigated parameters. The selection effects are discussed. The chemical and kinematical properties of the open clusters and field thin-disk stars are shown to differ. We provide evidence for the heterogeneity of the population of open star clusters.     

Discrete Virial Theorem

We reexamine the classical virial theorem for bounded orbits of arbitrary autonomous Hamiltonian systems possessing both regular and chaotic orbits. New and useful forms of the virial theorem are obtained for natural Hamiltonian flows of arbitrary dimension. A discrete virial theorem is derived for invariant circles and periodic orbits of natural symplectic maps. A weak and a strong form of the virial theorem are proven for both flows and maps. While the Birkhoff Ergodic Theorem guarantees the existence of the relevant time averages for both regular and chaotic orbits, the convergence is very rapid for the former and extremely slow for the latter. This circumstance leads to a simple and efficient measure of chaoticity. The results are applied to several problems of current physical interest, including the Hénon–Heiles system, weak chaos in the standard map, and a 4D Froeschlé map.     

Relationship between Infrared and Radio Emission of Galaxies of the Liner Type

The relationships among the monochromatic luminosities at 0.408, 1.4, and 4.85 GHz and the integrated luminosity in the far-infrared (IR) range for galaxies of the liner type (galaxies with low-ionization, narrow-emission regions) are investigated. At all the frequencies there is a close correlation between radio luminosity and IR luminosity for liners. The character of the relationship between the radio and IR luminosities of spiral liners differs from that for spiral normal and spiral Seyfert galaxies. For the latter this relationship is linear in a wide radio range. For spiral liners it may have a nonlinear character. The scatter (standard deviation) around the regression line for the relationship between radio and IR luminosities is considerably larger for spiral liners. The ratio of the emission fluxes in the far-IR range and in the radio range is larger, on the average, for spiral liners than for normal and Seyfert spiral galaxies.     

Kepler accuracy model for co-periodic satellite separation extrema

Accuracy measures are derived for the proper relative extrema in the separation distance function for co-periodic Kepler orbits. The conventional approach involves two numerical iterative processes: the method for solving Kepler’s equation for the eccentric anomaly, and the Newton–Raphson method for identifying times of the extrema. The sensitivity of the accuracy of the solution to the conditioning of the case is determined for stress tests including sequences of cases approaching a constant, then vanishing, separation. Invariance under interchanged satellite labels, single- and double-precision codes, and condition number estimates are compared to determine the number of justifiable digits.