LEO卫星轨道设计中的主要摄动源影响评估

对地球低轨道卫星（LEO）轨道设计中的摄动力模型进行了分析，并估计了其量级。然后针对用于GPS无线电掩星的LEO卫星轨道设计对掩星地面测点稳定性的要求，对力学模型进行了取舍，同时估计了各摄动力模型对轨道设计目标的影响。     

非圆轨道GPS/LEO掩星反演地球大气参数的算法及讨论

在非圆轨道GPS和LEO卫星条件下，给出一种较为直接的GPS／LEO掩星反演地球大气参数技术中弯曲角序列的迭代算法，并在理论上对该迭代法的收敛性进行了严格的数学证明．利用GPS掩星反演模拟程序，定量估算了卫星圆轨道假设对GPS／LEO掩星反演地球大气参数的影响，并验证了在非圆轨道条件下各种迭代法的一致性．指出了文献中给出的级数展开迭代算法的不足之处．     

上海天文台GPS掩星技术研究现状

简要地介绍了GPS/LEO卫星无线电掩星技术的基本原理、意义以及国际上的最近动态 ,列举了几个主要的LEO卫星计划 ;重点分析了GPS掩星探测地球大气技术中需要注意的若干问题 ,并推出可能采取的改进方案和相应的技术路线。上海天文台在GPS/LEO空基气象学中已经成功地提出 :通过通约LEO/GPS轨道方法 ,实现掩星地面观测点控制的新思路。作为一个应用实例 ,针对东中国海洋上空大气状况对中国东部经济发达的地区特别是上海地区的天气有着重要影响的背景 ,提出利用通约LEO/GPS卫星可对该地区大气实施监控。为了充分利用GPS/LEO掩星观测资源 ,上海天文台开展了振幅反演的计算方法研究 ;提出了在振幅反演中存在着无线电信号几何衰减和物理衰减两种不同的衰减机制 ,并考虑了它们的数学模型以及对反演结果的影响。简要地叙述了掩星质量因子的定义和计算方法。作为国内天文地球动力学研究中心 ,上海天文台将与国内外一些合作单位考虑建立GPS/LEO掩星技术观测处理的软件系统。作为空基GPS气象学的推广 ,还考虑进行山基和飞机载掩星观测实验 ,论证用这些方法监测局部大气剖面的可行性以及它们在国民经济和科学研究上的作用     

上海天文台GPS掩星技术研究现状

简要地介绍了GPS／LEO卫星无线电掩星技术的基本原理、意义以及国际上的最近动态，列举了几个主要的LEO卫星计划；重点分析了GPS掩星探测地球大气技术中需要注意的若干问题，并推出可能采取的改进方案和相应的技术路线。上海天台在GPS／LEO空基气象学中已经成功地提出：通过通约LEO／GPS轨道方法，实现掩星地面观测点控制的新思路。作为一个应用实例，针对东中国海洋上空大气状况对中国东部经济发达的地区特别是上海地区的天气有着重要影响的背景，提出利用通约LEO／GPS卫星可对该地区大气实施监控。为了充分利用GPS／LEO掩星观测资源，上海天台开展了振幅反演的计算方法研究；提出了在振幅反演中存在着无线电信号几何衰减和物理衰减两种不同的衰减机制，并考虑了它们的数学模型以及对反演结果的影响。简要地叙述了掩星质量因子的定义和计算方法。作为国内天地球动力学研究中心，上海天台将与国内外一些合作单位考虑建立GPS／LEO掩星技术观测处理的软件系统。作为空基GPS气象学的推广，还考虑进行山基和飞机载掩星观测实验，论证用这些方法监测局部大气剖面的可行性以及它们在国民经济和科学研究上的作用。     

GPS掩星折射率剖面一维变分同化

近年来,GPS／LEO(全球定位系统／低地球轨道)卫星无线电掩星技术给出了地球大气探测的新途径．从LEO卫星观测到的掩星数据可以反演的地球大气的气压、水汽、温度等剖面;它们对气象和大气科学研究,是具有潜在价值的数据资源．掩星数据资料的同化技术可以有效地改进这些气象参数的剖面,从而改进目前的数值天气预报模式．在当前采用的一维变分同化反演技术中,可以用掩星观测资料的大气折射率或弯曲角剖面进行同化,来反演大气水汽和温度剖面以及海平面压强．作为独立自主开发的GPD／LEO掩星技术系统的一部分,以欧洲中尺度天气预报分析(ECMWF)资料为背景场,CHAMP 掩星观测得到的折射率剖面为观测值,采用Levenberg—Marquardt方法实行GPS掩星资料一维变分同化．在讨论中,用掩星观测点附近相应的探空气球资料来检验CHAMP掩星资料变分同化的结果．     

GPS/LEO掩星方法中的电离层延迟量对太阳射电辐射流量的响应

对无线电信号在电离层中的传播路径进行了数值模拟;针对掩星观测中的五组实际卫星轨道数据(包括GPS和LEO卫星),给出了在太阳射电辐射流量(FLUX)分别为0,70,160和240等几种情况下的电离层延迟量对10.7cm波长的太阳辐射流量的响应结果;这分别对应着无太阳辐射、太阳射电辐射处于活动低谷、平静期和高峰期等几种情形。从中可以发现,掩星观测中电离层延迟量对10.7cm波长的太阳射电辐射流量的响应表现为如下特性:电离层延迟同参数FLUX的大小有明显的对应关系,即FLUX越大,则掩星观测中的电离层延迟越大;对于上升掩星情况而言,掩星观测中电离层延迟量起先逐渐增加,然后达到某一峰值,其后逐渐下降;在掩星观测的初期和中期,太阳射电辐射处于活动低谷、平静期和高峰期等几种情形之间的电离层延迟量差异都较为显著,而在掩星观测的后期,几种情形相互间电离层延迟量的差异都比较小。     

卫星圆轨道假设对GPS无线电掩星反演地球大气参数的影响

给出GPS无线电掩星反演地球大气参数过程中计算大气折射角的解析表达式，以圆轨道假设下的大气折射角计算值为先验约束，采用迭代法对不引入圆轨道假设情况的大气折射角进行归算，在此基础，利用反演方法得到了引入和不引入圆轨道假定两种情况下大气参数（气压和温度）的差分序列，结果表明：卫星圆轨道假设对GPS无线电掩星反演大气参数的影响，在气压方面为1mbar左右，而在气温方面为1K左右，这一结果支持了目前无线电掩星定性误差估计研究中通常引入卫星圆轨道假设这个近似处理方法的合理性，同时也表明：若在高精度反演地球大气参数时，摒弃圆轨道是必要的。     

火星电离层无线电掩星探测仿真研究

对中俄联合火星星-星电离层掩星技术体制进行了分析和介绍,采用三维射线追踪方法对电离层掩星事件的电波观测值进行了模拟计算,并利用模拟的掩星观测数据进行了电子密度廓线反演,结果说明仿真算法可靠.利用仿真的方法,分别对掩星电波相位观测误差和卫星轨道误差等带来的反演误差进行了个例计算和分析,结果得到:5%周的相位测量误差对白天电离层掩星探测结果的影响可以忽略,而夜间电子密度测量的绝对误差小于4×108 m-3;卫星轨道误差对掩星的主要影响是导致电离层高度抬升或下降.结果表明,中俄联合火星电离层掩星探测技术体制先进,可望获得高精度的电子密度廓线;其技术体制也可以用于月球电离层环境的探测.     

GPS／LEO掩星方法中的电离层延迟量对太阳射电辐射流量的响应

对无线电信号在电离层中的传播路径进行了数值模拟；针对掩星观测中的五组实际卫星轨道数据(包括GPS和LEO卫星)，给出了在太阳射电辐射流量(FLUX)分别为0，70，160和240等几种情况下的电离层延迟量对10．7cm波长的太阳辐射流量的响应结果；这分别对应着无太阳辐射、太阳射电辐射处于活动低谷、平静期和高峰期等几种情形。从中可以发现，掩星观测中电离层延迟量对10．7cm波长的太阳射电辐射流量的响应表现为如下特性：电离层延迟同参数FLUX的大小有明显的对应关系，即FLUX越大，则掩星观测中的电离层延迟越大；对于上升掩星情况而言，掩星观测中电离层延迟量起先逐渐增加，然后达到某一峰值，其后逐渐下降；在掩星观测的初期和中期，太阳射电辐射处于活动低谷、平静期和高峰期等几种情形之间的电离层延迟量差异都较为显著，而在掩星观测的后期，几种情形相互间电离层延迟量的差异都比较小。     

小倾角LEO多星天基平台光学跟踪GEO精密定轨

针对地基卫星测控系统(Tracking Telemetry and Command, TT&C)系统对地球静止轨道(Geostation-\lk ary Earth Orbit, GEO)卫星在空间和时间覆盖上的局限性, 提出小倾角低地球轨道(Low Earth Orbit, LEO)多星组网天基平台对GEO卫星进行跟踪定轨的方法. 根据空间环境和光学可视条件对仿真数据进行筛选以模拟真实的观测场景, 利用光学测角数据, 使用数值方法对GEO卫星的轨道进行确定. 结果与参考轨道进行重叠对比, 在平台轨道精度5 m、测量精度5rq\rq、 定轨弧长12 h的情况下, 两颗LEO卫星对GEO卫星进行跟踪定轨的精度可达到千米量级, 4颗LEO卫星对GEO目标进行跟踪定轨的精度可达到百米量级. 随着LEO组网卫星数量的增加, 定轨精度得到了较大的提高.     

A survey of orbits of co-orbitals of Mars

Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF₃₁, were discovered, librating about the L₅ Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ₇, to be a Trojan, associated with the L₄ Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND₄₃) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW₁₅ and 2000 TG₂, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion.     

Equation of state and anisotropy of pressure of magnetars

Magnetars are the neutron stars with the highest magnetic fields up to 10¹⁵–10¹⁶ G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars.     

Estimation of the Time Scale of Merging of the Components of Contact Binaries of the W UMa Type

Time scales of the transition from contact binary systems of the W UMa type to single stars of the blue straggler type are estimated. A model of one-way mass transfer from the primary component to the companion inside a common envelope (Eggen et al.) and a model of a contact binary lying on the zero-age main sequence with a companion that is losing mass (F. van't Veer) are used to calculate these scales. The merging times of components were calculated for 304 contact systems of the W UMa type from the Catalog of Approximate Photometric and Absolute Elements of Eclipsing Variable Stars on a scale of loss of mass and orbital angular momentum due to magnetic braking, under the assumption of synchronization of the axial rotation and orbital revolution. On the basis of the resulting statistics, the characteristic merging scales are 0.4-0.6 and 0.5-0.7 Gyr, respectively, for the above two models. The results of a comparison with the work of other authors are discussed.     

淮河洪水的可公度性分析

分析了上两个世纪发生在淮河的洪水事件的可公度性，根据其可公度值及其黄金分割点指出1991年与2003年淮河洪水的不可避免，最后讨论了可公度性的局限及淮河洪水可公度值的可能机制。     

Modeling of lightcurves of binary asteroids

We present a numerical method for inverting long-period components of lightcurves of asynchronous binary asteroids. Data of five near-Earth binary asteroids, (175706) 1996 FG₃, (65803) Didymos, (66391) 1999 KW₄, (185851) 2000 DP₁₀₇ and (66063) 1998 RO₁, for two of them from more than one apparition, were inverted. Their mutual orbits' poles and Keplerian elements, size ratios, and ellipsoidal shape axial ratios were estimated via this inversion. The pole solutions and size ratios for 1999 KW₄ and 2000 DP₁₀₇ are in a good agreement with independent estimates from radar measurements. We show that uncertainties of estimates of bulk densities of binary systems can be large, especially when observed on short arcs.     

Investigation of Times of Minima of Selected Early-Type Eclipsing Binaries

New precise times of minimum light for several early-type eclipsing binaries were obtained at three observatories. The changes of period of the following measured binaries are discussed: V1182 Aql, LY Aur, SZ Cam, FZ CMa, QZ Car, LZ Cen, V606 Cen, AH Cep and TU~Mus.     

Flattening of galaxies of different morphological types in subclusters of Coma

This paper deals with the observed variation in the flattening of galaxies with the density of galaxies in the subclusters of Coma surrounding NGC 4889, NGC 4874, and NGC 4839 based on data from the Abastumani Combined Catalog of Galaxies. The mean values of the observed ratios of the diameters of the galaxies, as well as histograms of their distributions, indicate that in the central, dense regions of the subclusters within a volume of 0.5h ₇₅ ⁻¹ Mpc³, E and S0 type galaxies are close to spheroidal. A significant reduction in the mean values of the diameters of the galaxies in the subclusters is noted, regardless of their morphology relative to the galaxies in the halo of the Coma cluster. In the subclusters, spiral galaxies are found with a hydrogen deficit that is more than 5 times the hydrogen deficit in spirals within the halo of the cluster. According to their 3-D coordinates, most of the galaxies with a hydrogen deficit are located closer to the south-east edge of the subcluster surrounding NGC 4874 near an extended gas filament in the x-ray region. This may indicate that the subcluster is moving toward a central condensation of faint galaxies in the Coma cluster and a possible merger with it. __________ Translated from Astrofizika, Vol. 50, No. 3, pp. 355–368 (August 2007).     

Influence of Neutron Star Parameters on Evolutions of Different Types of Pulsar

Influences of the mass, moment of inertia, rotation, absence of stability in the atmosphere and some other parameters of neutron stars on the evolution of pulsars are examined. It is shown that the locations and evolutions of soft gamma repeaters, anomalous X-ray pulsars and other types of pulsar on the period versus period derivative diagram can be explained adopting values of B < 10¹⁴ G for these objects if they have smaller mass (e.g. about 0.5 Solar mass) compared to the conventionally adopted values of mass. This approach gives the possibility to explain many properties of different types of pulsar.     

On the application of optimization methods to the determination of members of families of periodic solutions

The techniques used for the numerical computation of families of periodic orbits of dynamical systems rely on predictor-corrector algorithms. These algorithms usually depend on the solution of systems of approximate equations constructed from the periodicity conditions of these orbits. In this contribution we transform the root finding procedure to an optimization one which is applied on an objective function based on the exact periodicity conditions. Thus, the determination of periodic solutions and families of such orbits can be accomplished through unconstrained optimization. In this paper we apply and compare some well-known minimization methods for the solution of this problem. The obtained results are promising. This revised version was published online in July 2006 with corrections to the Cover Date.