Dynamics of shock waves in a contracting cloud

The contraction of an interstellar cloud is followed. The results indicates that there are shock waves appear during contraction. In order to study the effect of shock waves, two models have been studied. The post-shock temperature for the two models are, respectively, 3006 K and 2984 K. The density increases by more than three orders of magnitude. The gas is generally cooled by atoms, molecules, and grains. The dominant cooling process changes according to the chemical composition and the temperature of the gas. The thermal equilibrium depends on the existing physical conditions.     

新发现的X射线选活动星系核、白矮星和激变变星

为了研究ROSATX射线选亮近类星体巡天的选择判据 ,从 1 995年 4月至 1 996年 1 0月期间 ,利用北京天文台 2 .1 6米望远镜进行了试验观测 ,发现了 73个类星体、2 7个赛弗特星系、1个BLLac候选体、1个白矮星和 1个激变变星     

Active nuclei of galaxies

The parameters of fifteen active nuclei are determined from spectroscopic and photometric observations. The values of bolometric luminosity, gas volume and mass, kinetic energy, characteristic dimension and kinematic time-scale are given. The fluxes of radiative and mechanical energy of the gas envelope are compared. A steady-state model of the nucleus is proposed with the kinetic energy of the envelope being balanced by the light pressure. The life-time of the nucleus appears to be of the same order of magnitude as the life-time of the surrounding galaxy. The broad emission lines suggest to be caused by the gravitational potential of the nucleus. The masses of the central bodies are calculated on this basis. The typical central body mass of an active nucleus is about 10⁸ solar masses. The mass-luminosity relation is constructed. The steady-state model seems to explain the optical variability process. Collaps to the center of separate gas clouds, as results of Rayleigh-Taylor instability, leads to the flares, amplitudes and time-scales being in agreement with observations.     

Secular influence of change in the heliocentric gravitation constant <Emphasis Type="Italic">GM</Emphasis><Subscript>⊙</Subscript> on evolution of orbits of Meteor Streams

The Secular influence of the change in the heliocentric gravitational constant on the evolution of orbits of Meteor Streams is examined by using the method of celestial mechanics with variable mass and variable gravitational constant. The change in the heliocentric gravitational constant includes the combined changes in the sun’s mass and gravitational constant obtained from the modern observation of planets and spacecraft. The perturbation equations are solved by expanding series with mean anomaly. The solutions of the secular and periodic variation of orbital elements are derived. The theoretical results for the secular variables of the semi-major axes, solar distances at perihelion and orbital periods are given for three Meteor Streams: Dracorids, Quadrantids, and Ursids. The numerical results are shown in Table 2. The discussion and conclusion are drawn.     

The radiometric performances of the Planetary Fourier Spectrometer for Mars exploration

The Planetary Fourier Spectrometer (PFS) is a Fourier transform interferometer, operating in the range 1.2–45 μm. The instrument, previously included in the payload of the failed mission Mars ′96, is proposed for the future space mission Mars Express, under study by ESA. The present paper is aimed at presenting the radiometric performances of PFS. The two channels (LW and SW) forming PFS were analysed and characterised in terms of sensitivity and noise equivalent brightness. To cover the wide spectral range of PFS, different blackbodies were used for calibration. The built-in blackbodies, needed for the in-flight calibrations, were also characterised. The results show that the LW channel is comparable with IRIS Mariner 9 in terms of noise equivalent brightness. The SW channel performances, while satisfactorily, could be improved by lowering the sensor operative temperature. A simple model of the Mars radiance is used in order to calculate the signal-to-noise ratio on the spectra in typical observation conditions. The computed signal-to-noise ratio for the LW channel varies between 430 and 40, while for the SW channel it ranges from 150 to 30. The radiometric analyses confirm that PFS performances are compliant with the design requirements of the instrument. PFS is fully validated for future remote exploration of the atmosphere and the surface of Mars.     

电离氢区S140,S141和S142的红外发射研究

本文使用红外天文卫星（IRAS）巡天数据的最新版本IRAS天空巡天图（ISSA），经过进一步处理，得到了S140S141和S142SharplessHII区－分子云复合体的红外发射强度、温度及其光深的分布．在此基础上对各HII区的一些物理参量进行了统计分析，得到了分子云复合体的红外发射总光度以及复合体中尘埃的分布情况，对小尺度尘埃（VSG）的丰度进行了分析．并对各恒星形成区中的致密团块进行了研究，揭示出其中一些可能的恒星形成区域．同时，对S140区中的有关红外点源作出了能谱分析，并对S141区的激发星进行了讨论．     

Stars and substars nearest to the Sun: A study review

The structure of the solar neighborhood and its position in the galaxy, including the galactocentric distances, are analyzed. Catalogues are examined of near-sun stars and substars, which are compiled from ground and space based observations in the optical and infrared spectral regions. The problem of classifying celestial bodies in the galaxy by astrophysical and cosmogonic criteria is discussed. The problem of determining the main characteristics of the nearest stars and substars is analyzed. The statistical relationships are investigated between the main characteristics of stars and substars on the basis of their physical evolutionary models. The physical sense of these relationships is discussed. The calculated differential distribution functions of the astrophysical properties of stars and substars are examined.     

The orbit of asteroid (99942) Apophis as determined from optical and radar observations

The results of improving the orbit accuracy for the asteroid Apophis and the circumstances of its approach to Earth in 2029 are described. Gravitational perturbations from all of the major planets and Pluto, Ceres, Pallas, and Vesta are taken into account in the equations of motion of the asteroid. Relativistic perturbations from the Sun and perturbations due to the oblateness of the Sun and Earth and due to the light pressure are also included in the model. Perturbations from the Earth and Moon are considered separately. The coordinates of the perturbing bodies are calculated using DE405. The phase correction and the gravitational deflection of light are taken into account. The numerical integration of the equations of motion and equations in variations is performed by the 15th-order Everhart method. The error of the numerical integration over the 2005–2029 interval, estimated using forward and backward computations, is not more than 3 × 10^?11 AU. Improved coordinates and velocities at epoch JD2454200.5 (April 10, 2007) were obtained applying the weighted leastsquares fit. For the period from March 15, 2004, to August 16, 2006, 989 optical and 7 radar observations were used. The resulting system represents the optical observations with an error of 0.37 (66 conditional equations were rejected). The residuals of the radar observations are an order, or more, smaller than their errors. The system of Apophis’ elements and the estimates of their precision obtained in this study are in perfect agreement with the results published by other authors. The minimum Apophis-Earth distance is about 38 200 km on April 13, 2029. This estimate agrees to within 20 km with those calculated based on other published systems of elements. The effect of some model components on the minimum distance is estimated.     

A unified state model of orbital trajectory and attitude dynamics

The trajectory and attitude dynamics of an orbital spacecraft are defined by a unified state model, which enables efficient and rapid machine computation for mission analysis, orbit determination and prediction, satellite geodesy and reentry analysis. The state variables are momenta — a general form for attitude, and a parametric form for orbital motion. The orbital parameters are the velocity state characteristics of the orbital hodograph. The coordinate variables are sets of four Euler parameters, which define the rotation transformation by the quaternion algebra. The unified state model possesses many analytical properties which are invaluable for dynamical system synthesis, numerical analysis and machine solution: regularization, unified matrix algebra, state graphs and transforms. The analytic partials of position and velocity with the state and coordinate variables are presented, as well as representative perturbation functions such as air drag, gravitational potential harmonics, and propulsion thrust.     

Rayleigh-Taylor instability of ionized viscous fluids with FLR-corrections and surface-tension

The problem of Rayleigh-Taylor instability of superposed viscous magnetized fluids through porous medium is investigated in a partially-ionized medium. The fluid has ionized and neutralized particle components interacting with collisions. The effect of surface tension on R-T instability is also included in the present problem. The magnetohydrodynamic equations are modified for finite-Larmor radius corrections which is in the form of tensor. The equations of problem are linearized and using appropriate boundary condition, general dispersion relation is derived for two superposed fluids separated by horizontal boundary. The first part of the dispersion relation gives stable mode and condition is investigated using Hurwitz conditions. The second part of the dispersion relation shows that the growth rate of unstable system is reduced due to FLR corrections, viscosity, and collisional frequency of the neutrals. The role of surface tension on the system is also discussed.     

SMART-1 mission description and development status

SMART-1 is the first of the Small Missions for Advanced Research in Technology of the ESA Horizons 2000 scientific programme. The SMART-1 mission is dedicated to testing of new technologies for future cornerstone missions, using Solar-Electric Primary Propulsion (SEPP) in Deep Space. The chosen mission planetary target is the Moon. The target orbit will be polar with the pericentre close to the South-Pole. The pericentre altitude lies between 300 and 2000 km, while the apocentre will extend to about 10,000 km. During the cruise phase, before reaching the Moon, the spacecraft thrusting profile allows extended periods for cruise science. The SMART-1 spacecraft will be launched in the spring of 2003 as an auxiliary passenger on an Ariane 5 and placed into a Geostationary Transfer Orbit (GTO). The expected launch mass is about 370 kg, including 19 kg of payload. The selected type of SEPP is a Hall-effect thruster called PPS-1350. The thruster is used to spiral out of the GTO and for all orbit maneuvers including lunar capture and descent. The trajectory has been optimised by inserting coast arcs and the presence of the Moon's gravitational field is exploited in multiple weak gravity assists.The Development Phase started in October 1999 and is expected to be concluded by a Flight Acceptance Review in January 2003. The short development time for this high technology spacecraft requires a concerted effort by industry, science institutes and ESA centres. This paper describes the mission and the project development status both from a technical and programmatic standpoint.     

The James Webb Space Telescope and its Infrared Detectors

The James Webb Space Telescope (JWST) was conceived as the scientific successor to the Hubble Space Telescope (HST) and Spitzer Space Telescope. The instrument suite provides broad wavelength coverage and capabilities aimed at four key science themes: 1) The end of the dark ages: first light and reionization, 2) The assembly of galaxies, 3) The birth of stars and protoplanetary systems, and 4) Planetary systems and the origins of life. To accomplish these ambitious goals, JWST's detectors provide state-of-the-art performance spanning the λ = 0.6–28 μm wavelength range. In this paper, we describe JWST with an emphasis on its infrared detectors.     

用周期图谱分析方法计算Blazar天体的光变周期

对适用于等间隔时间序列的周期图谱分析方法进行了研究,用模拟信号进行了检验,证实了它适用于有噪声的时间序列.并把这种方法应用到类星体3C 279、3C 345,BL Lac天体OJ 287、ON 231的光变周期分析中,得到它们的光变周期分别为7.14年、10.00年、11.76年、6.80年.结果表明用周期图谱分析方法得到的结论和其他文献用Jurkevich方法得到的结论一致.获得的周期对进一步研究Blazar天体的物理机制很有帮助.还分析了窗函数的影响,指出它们的优缺点,便于在实际工作中做出正确选择.     

关于北斗G2卫星的溯往追终

2022年1月,失效的北斗G2卫星被实践21号卫星从地球静止轨道拖入了坟墓轨道.为了这项捕获任务的安全实施,需要预先确定北斗G2的旋转状态.基于过去10 yr的测光观测数据展示了北斗G2卫星自转的演化过程.根据北斗G2的自转速度和轨道的演化,确认了在过去的10 yr里发生的6次异常事件.据推测, 2012年的小碎片碰撞事件,是随后几年燃油泄漏的导火索. 2017年之后剩余燃油完全释放,再也没有出现转速异常.将2014年太阳能帆板损坏和2016年的解体事件后建立的旋转动力学模型外推1 yr,转轴的标准偏差小于3°,转速标准偏差为0.11°·s^-1,能够有效地满足捕获任务时刻旋转状态的精度要求.     

自转对恒星物理量的影响

自转本身是恒星的基本物理量之一，同时影响恒星的其它许多物物量，包括对恒星半径、形状和体积的影响；对光度、包指数、谱线轮廓、等值宽度、偏振度等观测量的影响；对引力加速度、元素丰度的影响；对恒星内部结构，如中心压力、温度、密度的影响。这些将会影响到恒星在Ｈ—Ｒ图上的位置，演化路径以及年龄和寿命等。因此，无论是理论模型还是实测研究，对自转快的恒星应该进行自转影响的修正。     

The System of Spurs in Ecliptic Coordinates

The system of spurs (radio loops I-IV) is organically inscribed in the ecliptic coordinate system (ECS). It defines one of the equators of the triaxial Local System (S). The Gould, Vaucouleurs-Dolidze, and other Belts in the role of meridians are orthogonal to S. The axis of another equator coincides with the equinoctial line. The ECS connects the structures and kinematics of three hierarchical levels: the solar system, the Local System, and the Galaxy.     

Physical properties of the Yaxcopoil‐1 deep drill core,Chicxulub impact structure,Mexico

Abstract– The Chicxulub structure in Mexico, one of the largest impact structures on Earth, was formed 65 Ma by a hypervelocity impact that led to the large mass extinction at the K‐Pg boundary. The Chicxulub impact structure is well preserved, but is buried beneath a sequence of carbonate sediments and, thus, requires drilling to obtain subsurface information. The Chicxulub Scientific Drilling Program was carried out at Hacienda Yaxcopoil in the framework of the International Continental Scientific Drilling Program in 2001–2002. The structure was cored from 404 m down to 1511 m, through three intervals: 794 m of postimpact Tertiary sediments, a 100 m thick impactite sequence, and 616 m of preimpact Cretaceous rocks thought to represent a suite of megablocks. Physical property investigations show that the various lithologies, including the impactite units and the K‐Pg boundary layer, can be characterized by their physical properties, which depend on either changes in fabric or on mineralogical variations. The magnetic properties show mostly dia‐ or paramagnetic behavior, with the exception of the impactite units that indicate the presence of ferromagnetic, probably hydrothermally deposited magnetite and pyrrhotite. The magnetic fraction contributes mainly to enhanced magnetization in the impactite lithologies and, in this way, to the observed magnetic anomalies. The shape and orientation of the magnetic grains are varied and reflect inhomogeneous fabric development and the influence of impact‐related redeposition and hydrothermal activity. The Chicxulub impact occurred at the time of the reverse polarity geomagnetic chron 29R, and this finding is consistent with the age of the K‐Pg boundary.     

Characterization of terrestrial exoplanets based on the phase curves and albedos of Mercury, Venus and Mars

The empirically derived phase curves of terrestrial planets strongly distinguish between airless Mercury, cloud-covered Venus, and the intermediate case of Mars. The function for Mercury is steeply peaked near phase angle zero due to powerful backscattering from its surface, while that for Venus has 100 times less contrast and exhibits a brightness excess near 170° due to Mie scattering from droplets in the atmosphere. The phase curve of Mars falls between those of Mercury and Venus, and there are variations in luminosity due to the planet’s rotation, seasons, and atmospheric states. The phase function and geometric albedo of the Earth are estimated from published albedos values. The curves for Mercury, Venus and Mars are compared to that of the Earth as well as theoretical phase functions for giant planets. The parameters of these different phase functions can be used to characterize exoplanets.     

Eruptive instability of cylindrical prominences

The stability of prominences and the dynamics of an eruption are studied. The prominence is represented by an uniformly twisted, curved, magnetic tube, anchored at both ends in the photosphere. Several stages of the eruption are analyzed, from the pre-eruptive phase and the onset of the instability, up to the late phases of the process. Before the eruption, the prominence evolves through a series of equilibrium states, slowly ascending either due to an increase of the electric current or to mass loss. The eruption starts when the ratio of the current to the total mass attains a critical value after which no neighbouring equilibrium exists. The linearized equation of motion was used to obtain the instability threshold, which is presented in a form enabling comparison with the observations. The height at which the prominence erupts depends on the twist, and is typically comparable with the footpoint half-separation. Low-lying prominences are stable even for large twists. The importance of the external field reconnection below the filament, and the mass loss through the legs in the early phases of the eruption is stressed. The oscillations of stable prominences with periods on the Alfvén time-scale are discussed. The results are compared with the observations.     

Correlations Between Color Gradients and Structural Parameters of Disks in Late-type Spiral Galaxies

From the second group of the data released by the Sloan numerical patrol survey (SDSS DR2), 395 face-on late-type spiral galaxies brighter than 15-th magnitude in the waveband r are selected as the sample. The relations between the color gradients and structural parameters of disks are studied. The results indicate the following: (1) The color gradient is independent of the absolute magnitude (mass) of the disk. (2) The color gradient of disk is concerned with the size of disk. The larger the disk, the steeper the color gradient. (3) The color gradient of disk is concerned with the color of disk. The bluer the disk color, the steeper the gradient. (4) The color gradient of disk is related with the surface brightness of disk. The brighter the disk, the steeper the color gradient. Moreover, the historical constraint formed by the relations between the color gradients of disks and various structural parameters is briefly discussed.