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.     

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.     

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     

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.     

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.     

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.     

Fine Structure of the Core of the Blazar OJ 287-I

The fine structure of the active region, the bulge, of the blazar OJ 287 has been investigated with a resolution of 20 μas (0.1 pc) at a wavelength of 7 mm, the epochs of 2007–2017. The structure and kinematics correspond to a vortex nature. The surrounding matter, the plasma, is transferred to the center along two arms from opposite directions. The emerging excess angular momentum is carried away along the rotation axis by bipolar outflows, rotating coaxial tubes, in a direction X ≈ ?120? in the plane of the sky as it is accumulated. The central high-velocity bipolar outflow has a helical shape. The diameters of the low-velocity flows are ø1 ≈ 0.3 and ø2 ≈ 0.65 mas, or 1.4 and 3 pc, respectively. Ring currents whose tangential directions are observed as parallel chains of components are excited in the flow walls. The peak brightness temperature of the nozzle reaches Tb ≈ 1012?1013 K. A “disk” with a diameter ø ≈ 0.5 mas (≈2.2 pc) is observed by the absorption of synchrotron radiation. The disk is inclined to the plane of the sky at an angle of 60? in the jet direction. The fragments are seen from a distance of ～0.2 mas outside the absorption zone. The jet sizes exceed considerably the counterjet ones. An enhanced supply of plasma from the northern arm gives rise to an independent vortex 0.2 mas away from the central one in the NW direction. As in the first case, the helical central bipolar outflow is surrounded by a low-velocity component ø ≈ 0.28 mas in diameter with built-in ring currents. The jet is ejected in the direction X = ?50? in the plane of the sky. The jet orientation changes, X = ?130? at a distance of 1 mas. A high activity of the central and two side nozzles spaced 0.22 mas apart in the direction X = ?40? is occasionally observed simultaneously. The active region of the blazar is observed through an ionized medium, a screen, whose influence is significant even at a wavelength of 7 mm. The absorption and refraction of the transmitted emission in the screen affect the apparent brightness relative to the positions of the fragments.     

Interaction of the X-ray source radiation with the atmosphere of the normal star in close binary systems

The structure of the stellar atmosphere irradiated by an X-ray source is calculated. On the basis of these numerical calculations an approximate theory of the X-ray reprocessing is formulated. The interaction of X-rays with the stellar atmosphere induces a considerable stellar wind. However, the main part of the X-ray energy is reemitted.The optical appearances of the close binary system including an X-ray source are discussed. The light curve of such a system is obtained. The mass-loss rate of a star with the size close to that of its Roche lobe is evaluated in the isothermal approximation. Most likely, the accretion of matter on to a neutron star, or a black hole, is the cause of the X-ray luminosity. The accreting matter is supplied with the mass outflow from the normal component induced by X-rays. The X-ray luminosity is shown to have an upper limit stipulated by the outflow saturation.The model of HZ Her=Her X1 system is constructed which accounts for the observed light curve. The optical appearances of the system are due to the X-ray heating of the face of the X-ray source area of the normal star. The radiation of this hot area is partly reflected by the surface of the disc around the X-ray source. The thin disc is formed by the accretion of matter by the X-ray source. The effective reflection of hard X-rays (hv15–30 keV) by the stellar surface is considered. This phenomenon makes it possible to detect those X-ray pulsars whose beam does not intercept the Earth.The model of Sco X1 as a black hole in a close binary system is discussed.     

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.     

Geomorphologic analysis of some Martian surface images from the Mars 4 and 5 automatic stations

The paper deals with the results of geomorphological analysis of some photographs taken by the Mars 4 and 5 probes. The area studied (700 × 900 km, centered at 32°S, 35°W) covers part of Mare Erythraeum. The main landforms of the area are craters which are sorted into four morphological classes. Fluvial, eolian, and tectonic processes as well as downslope displacement of material are identified with different degrees of certainty.The valleys, which are probably of fluvial origin, exhibit a characteristic hierarchical pattern. The main valley in the area, provisionally named Uzboi, extends from Holden crater to Hale crater. The relations between the present surface elevations and the probable fluvial origin appear to indicate tectonic uplift of some parts of the area in the past. The tectonic movements have broken a hypothetical large valley into a number of fragments, one of which is Ladon valley and another of which is Uzboi valley, although another possible explanation of the observed pattern also exists. An attempt is made to divide the geologic history of the area into stages. The probable fluvial processes seem to have started before the end of the intensive impact cratetring stage. They appear to have continued, though not so intensely, almost to the recent stage. A geomorphological map of the area shownin Fig. 3.     

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.     

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.     

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．     

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.     

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.     

Kinematics and age of 15 stars-photometric solar analogs

The radial and space velocities are inferred for 15 stars that are photometric analogs of the Sun. The space velocity components (U, V, W) of most of these stars lie within the 10–60 km/s interval. The star HD 225239, which in our previous papers we classified as a subgiant, has a space velocity exceeding 100 km/s, and belongs to the thick disk. The inferred fundamental parameters of the atmospheres of solar analogs are combined with published evolutionary tracks to estimate the masses and ages of the stars studied. The kinematics of photometric analogs is compared to the data for a large group of solar-type stars.     

1986年2月4日耀斑与电流环合并不稳定性

本文收集了１９８６年２月４日大耀斑的Ｈα、微波、Ｘ射线和γ射线全波段的观测资料。利用暗条电流环模型分析了该耀斑的物理过程，测量了活动暗条的上升运动，求解了动量方程和能量方程。结果表明：（１）１９８６年２月４日的３Ｂ／Ｘ３耀斑可能是由暗条电流环之间的合并不稳定性所致；（２）电阻撕裂摸不稳定性是一种有效的耀斑前预热机制；（３）耀斑的高能观测资料进一步表明了电流环合并不稳定性是引起该大耀斑期间所有高能粒     

The Morávka meteorite fall: 3. Meteoroid initial size,history, structure,and composition

Abstract— The properties and history of the parent meteoroid of the Morávka H5–6 ordinary chondrites have been studied by a combination of various methods. The pre‐atmospheric mass of the meteoroid was computed from fireball radiation, infrasound, seismic signal, and the content of noble gases in the meteorites. All methods gave consistent results. The best estimate of the pre‐atmospheric mass is 1500 ± 500 kg. The fireball integral bolometric luminous efficiency was 9%, and the acoustic efficiency was 0.14%. The meteoroid cosmic ray exposure age was determined to be (6.7 ± 1.0) × 10⁶ yr. The meteorite shows a clear deficit of helium, both ³He and ⁴He. This deficit can be explained by solar heating. Numerical backward integration of the meteoroid orbit (determined in a previous paper from video records of the fireball) shows that the perihelion distance was probably lower than 0.5 AU and possibly as low as 0.1 AU 5 Ma ago. The collision which excavated Morávka probably occurred while the parent body was on a near‐Earth orbit, as opposed to being confined entirely to the main asteroid belt. An overview of meteorite macroscopic properties, petrology, mineralogy, and chemical composition is given. The meteorites show all mineralogical features of H chondrites. The shock level is S2. Minor deviations from other H chondrites in abundances of trace elements La, Ce, Cs, and Rb were found. The ablation crust is enriched with siderophile elements.     

Structural peculiarities of the AGN object 1803+784

The structure of the AGN object 1803+784 has been investigated at a wavelength of 7 mm with a limiting angular resolution reaching 20 μas. The ejector nozzle surrounded by a ring structure, an accretion disk, has been identified. The nozzle size is ∼0.1 pc, the diameter of the ring structure is ∼1.4 pc, and its width is ∼0.25 pc. The reaction of the plasma flow produces a multimode precession responsible for the conical helical structure of the jet with a variable step and a curved axis. The viewing angle of the flow ejection is ∼40°. The central part of the ejected flow moving along the axis accelerates to a relativistic velocity. The apparent velocity reaches 12 s at a distance of ∼1 mas or ∼6 pc from the ejector. The outer part of the flow moves along a helix around a high-velocity component whose step is a factor of 4 smaller, because the longitudinal velocity is relatively low. The plasma is ejected almost toward the observer, as confirmed by its high brightness temperature T _b ≈ 8 × 10¹³ K and highly beamed emission. The polarized emission from the nozzle is axisymmetric. The orientation of the polarization of the flow along the whole length is aligned with the direction of its motion, suggesting the excitation of a ring magnetic field around it and self-focusing.     

On a klystron mechanism of generation of vibrations in pulsar magnetosphere

It has been shown that vibrations can be generated in the electron cap of the neutron star (Rylov, 1976, 1977; Jackson, 1976) under certain conditions. The mechanism of generation is like that in a klystron. The electron gas of the cap plays the role of the klystron resonant circuit. The electron beam penetrating the electron cap and returning to the star's surface plays the role of the klystron electron beam. The bunching electron stream along the magnetic axis acts like a strongly directed antenna. The conditions in which it is possible to generate these vibrations were also investigated. The energy of the accelerated primary electrons, the frequency of radiated radiowaves and the degree of the radiation directivity are evaluated.