Infrared astronomy on the midcourse space experiment

The Midcourse Space Experiment (MSX) is a multiple objective experiment scheduled to fly by the end of 1994. Infrared photometry and interferometry will be obtained by a solid hydrogen cooled, off-axis telescope of 35 cm unobscured primary aperture. The sensitivities of the line scanned arrays are comparable to IRAS bands 1 and 2 but the spatial resolution is some 30 times better. Nine broadly defined astronomy experiments are planned for the 18 month cryogen phase of the mission. Four of these experiments survey regions not adequately covered by previous infrared missions: the zodiacal cloud near the sun and the anti-solar direction, the Galactic Plane where IRAS sensitivities were limited by confusion and the gaps left by the IRAS survey. The higher sensitivity obtained from raster scans will probe Galactic structure and create intermediate spatial resolution maps of extended sources such as HII regions, the Magellanic Clouds and nearby galaxies. Measurements are also planned on a number of solar system objects such as planets, asteroids, the dust bands, comets and cometary debris trails. Moderate resolution spectra of a number of bright, discrete, extended sources will be obtained as well as low resolution spectral mapping along the Galactic Plane and Zodiacal dust cloud.     

蒙皮材料对浮空器热特性影响的研究

分析临近空间浮空器热特性的影响因素,并建立临近空间浮空器热特性的数学模型,采用Fortran语言编写程序,对蒙皮材料热辐射特性对浮空器热特性的影响进行了研究.结果表明,选用短波吸收率较低且长波辐射发射率较高的蒙皮材料时,氦气平均温度的昼夜差值较低,浮空器热性能越好.夜晚蒙皮温差随长波辐射发射率的增加而增加;而白天随短波辐射吸收率的增加而增加,在长波辐射发射率较大时,其对蒙皮温差的影响不大,然而长波辐射发射率比较小时,蒙皮温差会非常大,蒙皮温差的峰值出现于黎明和黄昏时段这两个时段.     

Olbers an interplanetary probe to study visible and infrared diffuse backgrounds

The visible extragalactic background (though as yet undetected) is insufficient to explain the abundance of heavy elements in galaxies: either there should be some diffuse extragalactic light in the near infrared (from 1 to 10 m) and/or in the far infrared (100 m) if dust has reprocessed the star light. We propose a new space mission to be dedicated to the search and mapping of primordial stellar light from the visible to the mid-infrared (20 m). In this spectrum range, detectors have reached such a sensitivity that the mission should aim at being (source) photon noise limited, and not any longer background photon noise limited. For that purpose, a small passively cooled telescope with large format CCDs and CIDs could be sent beyond the zodiacal dust cloud (which is absent beyond a solar distance of about 3 AU). In that case, the only remaining foregrounds before reaching the extragalactic background, is due to the Milky Way integrated emission from stars and the diffuse galactic light due to scattering and emission by interstellar dust, which are all unavoidable. Maps of the extragalactic light could be obtained at the arcminute resolution with high signal to noise ratio. This mission is the next logical step after IRAS, COBE and ISO for the study of extragalactic IR backgrounds. It has been proposed as a possible medium-sized mission for the post-horizon 2000 ESA program that could be a piggy back of a planetary mission.     

Clusters of Galaxies: Beyond the Thermal View

We present the work of an international team at the International Space Science Institute (ISSI) in Bern that worked together to review the current observational and theoretical status of the non-virialised X-ray emission components in clusters of galaxies. The subject is important for the study of large-scale hierarchical structure formation and to shed light on the “missing baryon” problem. The topics of the team work include thermal emission and absorption from the warm-hot intergalactic medium, non-thermal X-ray emission in clusters of galaxies, physical processes and chemical enrichment of this medium and clusters of galaxies, and the relationship between all these processes. One of the main goals of the team is to write and discuss a series of review papers on this subject. These reviews are intended as introductory text and reference for scientists wishing to work actively in this field. The team consists of sixteen experts in observations, theory and numerical simulations.     

The light of the night sky: Astronomical,interplanetary and geophysical

Summary We bring together our general results in two figures. Figure 14 portrays the resolution of the light of the night sky into its three principal components based on a series of zenith observations extending over a year at the two stationse: Fritz Peak in Colorado, U.S.A., (latitude N 39°.9, longitude W 105°.5) and Haleakala in Hawaii, U.S.A. (latitude N 20°.7, longitude W 156°.3). The observations are from a current study by Roach and Smith (1964a) using photometers centered on wavelength 5300 Å. With respect to sidereal time the airglow continuum is a constant. The two Milky Way traverses are conspicuous features of the integrated starlight curves. The variation of the zodiacal light is the result of the variable ecliptic latitude of the zenith throughout the year. A refined analysis of the data, not shown in the plot, gives a further variation of the zodiacal light as a function of - _bd, the differential ecliptic longitude between the zenith and the sun. The zodiacal light is the brighter of the three components except when the Milky Way is in the zenith. The zodiacal light tends to be systematically brighter toward the horizon so that it is definitely the most prominent of the three for the sky as a whole.The interrelationships of the constituents of the light of the night sky are shown from a different point of view in Figure 15 where the ordinate is logarithm of the surface brightness and the abscissa is logarithm of the distance or extent. Moving downward in the plot the features of the night sky appear below the line corresponding to the end of twilight. The brightness of the nightglow, the zodiacal light and gegenschein, the integrated starlight and galactic light are comparable (on the logarithm scale) but one is impressed with the vastly different linear distances in connection with the several phenomena. The nightglow is a terrestrial phenomenon having a thickness of about one atmospheric scale height (log R 7). The zodiacal light is an interplanetary phenomenon with a characteristic dimension of one astronomical unit (log R 13). The integrated starlight from our galaxy has a characteristic maximum dimension of some 30 kpc (log R 23). Finally the extra galactic nebulae which collectively contribute much less than 1% of the light of the night sky are at distances as much as log R 28. They can be photographed individually in spite of the competition of the sky background and in spite of the hazard of extinction by intervening dust.In the preparation of this report the writer has been impressed with the confluence of several circumstances that make possible the observation of the universe in the visible part of the spectrum. Any one of several contingencies might have made such observations impossible.Let us consider the matter of contrast. The prime example here is the bright (but beautiful!) day sky which prohibits serious daytime study of the astronomical sky. There follows, during a diurnal terrestrial rotation the period of twilight which under the best of circumstances lasts a little less than 1 1/2 hours but which, during the local summer, in the vicinity of polar regions persists all night. The obliquity of the ecliptic is sufficient to make a stimulating annual sequence of seasons but small enough to keep the twilight period of reasonable duration over a good portion of the earth.A hazard narrowly averted is that due to the interplanetary dust cloud leading to the zodiacal light. The concentration of dust is very small indeed (Figure 10) so that an increase by a factor often would be trivial in terms of the constitution of the solar system. But such an increase would result in a night sky so bright (average zodiacal light 2000 S₁₀ (vis) instead of 200) that the Milky Way would be difficult to see and the airglow difficult to measure. The aesthetic gain in a rather spectacular zodiacal light pattern over the sky would hardly compensate for the loss from the absence of the details of our galactic universe. The effect of such an enhanced zodiacal light would correspond to that experienced in a planetarium when the operator adjusts the rheostats to bring on dawn and the celestial objects disappear.A permanent twilight that would have the same effect would be due to the hydroxyl nightglow if (a) it were concentrated in the visible part of the spectrum rather than in the near infra red or if (b) the human eyes were sensitive in the near infrared.The narrow escape from the cosmic ignorance that would have resulted from a situation in which the observer found himself in a less favorable environment is well illustrated by the zone of avoidance of extra galactic nebulae in the vicinity of the Milky Way plane. If our galaxy were not highly flattened so that its extent perpendicular to the plane is sufficiently small to permit an observational window outward we would not have been able to photograph the extra-galactic objects and we would have been content with a rather restricted concept of a universe consisting of a single galaxy. The same dire result would have occurred if the sun to which our planet is attached were more deeply embedded in the galactic dust near the galactic center. Thus we find compensation for our non-central location.There can be little doubt that human ingenuity would in time have overcome any or all of the above circumstances as the radio astronomers have done by changing the exploring frequency so as to avoid the difficulties. But this would have taken time, especially in the absence of the stimulation of the knowledge gained by visual and photographic observations. It is likely that the time lag would have been sufficient that the present review could not have been written by the present author. It may be conjectured whether other astronomers on other planets are as fortunate or whether, after all, this is the best of all possible worlds.Contribution number 73. The report was written while the author was a Senior Specialist at the East-West Center of the University of Hawaii — on leave of absence from the Central Radio Propagation Laboratory of the U.S. National Bureau of Standards, Boulder, Colo., U.S.A.

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基于风场环境利用的平流层浮空器区域驻留关键问题研究进展

基于风场环境利用的平流层浮空器继承高空气球结构简单、技术成熟、快速响应、使用效费比高等特点，通过引入控制设计，克服轨迹控制和高度控制等方面的局限，具备一定的飞行轨迹规划和区域驻留能力，是当前临近空间飞行器发展的重要方向。本文基于对典型项目的调研分析，梳理了基于风场环境利用的平流层浮空器在区域驻留应用中的关键技术，重点讨论了风场感知与建模、风场利用方法、轨迹规划与决策等核心问题的研究现状，对现有方案进行深入分析，从实际应用的角度探讨了相关技术难题的可行解决方案。     

飞艇运动建模与仿真验证

在研究临近空间浮空器的过程中,设计了一种低空实验飞艇.为了评价该飞艇的稳定性和操纵性,建立了飞艇的六自由度运动方程数学模型,使用Matlab/Simulink软件完成了飞艇飞行仿真软件设计.另外采用Flightgear作为飞行仿真视景软件,设计飞行仿真软件驱动视景软件的网络接口程序.利用飞行仿真软件,进行了该低空飞艇运动的仿真验证.仿真结果表明,软件达到了预定的设计目标,该实验飞艇方案可行,安定面和推进动力配置基本合理.     

Comets, Asteroids and Zodiacal Light as Seen by Iso

ISO performed a large variety of observing programmes on comets, asteroids and zodiacal light – covering about 1% of the archived observations – with a surprisingly rewarding scientific return. Outstanding results were related to the exceptionally bright comet Hale–Bopp and to ISO's capability to study in detail the water spectrum in a direct way. But many other results were broadly recognised: Discovery of new molecules in comets, the studies of crystalline silicates, the work on asteroid surface mineralogy, results from thermophysical studies of asteroids, a new determination of the asteroid number density in the main-belt and last but not least, the investigations on the spatial and spectral features of the zodiacal light.     

Obscured Activity: AGN, Quasars, Starbursts and ULIGs Observed by the Infrared Space Observatory

Some of the most ‘active’ galaxies in the Universe are obscured by large quantities of dust and emit a substantial fraction of their bolometric luminosity in the infrared. Observations of these infrared luminous galaxies with the Infrared Space Observatory (ISO) have provided a relatively unabsorbed view to the sources fuelling this active emission. The improved sensitivity, spatial resolution and spectroscopic capability of ISO over its predecessor Infrared Astronomical Satellite (IRAS) of enabled significant advances in the understanding of the infrared properties of active galaxies. ISO surveyed a wide range of active galaxies which, in the context of this review, includes those powered by intense bursts of star formation as well as those containing a dominant active galactic nucleus (AGN). Mid-infrared imaging resolved for the first time the dust enshrouded nuclei in many nearby galaxies, while a new era in infrared spectroscopy was opened by probing a wealth of atomic, ionic and molecular lines as well as broad band features in the mid- and far-infrared. This was particularly useful, since it resulted in the understanding of the power production, excitation and fuelling mechanisms in the nuclei of active galaxies including the intriguing but so far elusive ultraluminous infrared galaxies. Detailed studies of various classes of AGN and quasars greatly improved our understanding of the unification scenario. Far-infrared imaging and photometry revealed the presence of a new very cold dust component in galaxies and furthered our knowledge of the far-infrared properties of faint starbursts, ULIGs and quasars. We summarise almost nine years of key results based on ISO data spanning the full range of luminosity and type of active galaxies.     

Zodiacal light — A measure of the interplanetary environment

This paper reviews research related to zodiacal light and tries to give the status for the end of 1974.     

Infrared Imaging Surveyor: IRIS

Based on the experience of the IRTS, a new infrared satellite mission, Infrared Imaging Surveyor:IRIS is now being proposed to ISAS. The IRIS will be thrown into the sun synchronous orbit at 900km altitude by the MV rocket which is now under development in ISAS. With use of new cryogenic technologies, considerably light weight with large aperture telescope is designed. Owing to the large format states-of-art array detectors, the IRIS has an enormous capability for the survey observation, and will provide new discoveries on the formation and evolution of galaxies, brown dwarfs, protoplanetary disk, interstellar matter and so on.     

Analysis and design of (LC)(LC)-type series-parallel resonantconverter

A series-parallel resonant converter employing (LC)(LC)-type tank circuit operating in lagging power factor (PF) mode is presented and analyzed using complex ac circuit analysis. Design curves are obtained and the converter is optimized under certain constraints. Detailed Space Integrated Control Experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load conditions. Results obtained from an experimental converter are also presented. The results obtained from the theory, SPICE simulation, and the experimental converter are compared. The proposed converter has high efficiency from full load to very light load (<10%). Switching frequency variation required for a wide change in the load (near load open circuit to full load) is narrow compared with the series resonant converter (SRC)     

Magnetic Fields in Galaxies

Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized emission traces turbulent fields which are strongest in spiral arms and bars (20–30?μG) and in central starburst regions (50–100?μG). Such fields are dynamically important, e.g. they can drive gas inflows in central regions. Polarized emission traces ordered fields which can be regular or anisotropic random, generated from isotropic random fields by compression or shear. The strongest ordered fields of 10–15?μG strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several spiral galaxies reveal large-scale patterns, which are signatures of regular fields generated by a mean-field dynamo. However, in most spiral galaxies observed so far the field structure is more complicated. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Ordered magnetic fields are also observed in radio halos around edge-on galaxies, out to large distances from the plane, with X-shaped patterns. Future observations of polarized emission at high frequencies, with the EVLA, the SKA and its precursors, will trace galactic magnetic fields in unprecedented detail. Low-frequency telescopes (e.g. LOFAR and MWA) are ideal to search for diffuse emission and small RMs from weak interstellar and intergalactic fields.     

Blue Jets: Upward Lightning

Blue jets are beams of blue light propagating from the tops of active thunderclouds up to altitudes of ～50 km. They resemble tall trees with quasi-vertical trunk and filamentary branches. Their apparent speeds are in the range of 10 s to 100 s km/s. Other events, having essentially lower terminal altitudes (<26 km), are named blue starters. These phenomena represent the first documented class of upward electrical discharges in the stratosphere. Some of upward discharges, termed gigantic jets, propagate into the lower ionosphere at much higher speeds in the final phase. We describe salient features of the upward discharges in the atmosphere, give an assessment of the theories of their development, and discuss the consequences for the electrodynamics and chemistry of the stratosphere. We argue that this upward lightning phenomenon can be understood in terms of the bi-directional leader, emerging from the anvil.     

轴对称近似等熵压缩流场的乘波前体优化设计

以升阻比为优化目标，在来流马赫数Ma=2—4及飞行高度H=20km-24km条件下，进行了轴对称近似等熵压缩流场的乘波前体优化设计，通过CFD验证Ma=4优化乘波体的气动特性，并研究了Ma=3优化乘波前体在非设计条件下的气动特性。结果表明：近似等熵压缩下表面的乘波前体在设计条件下具有良好的气流压缩效果，可满足机体／发动机一体化设计的需要；乘波前体升阻比在1．5—1．9之间，纵向压心位置靠后；非设计条件下，压缩波不聚焦，小于设计马赫数升阻比时降低，大于设计马赫数时升阻比略大。     

平流层浮空器保压指标对驻空性能的影响

地面保压试验是综合评估囊体材料性能的重要手段,其设计指标将影响平流层浮空器总体驻空高度与时间的变化范围。以球形超压平流层浮空器为例,建立了驻空高度运动学模型、热力学模型及基于微孔损伤的氦气渗透模型,综合考虑驻空过程中力、热耦合引起的浮空器内部氦气压力、温度和质量等的实时变化,以囊体材料微孔当量直径为桥梁建立了平流层浮空器地面保压指标与驻空高度、驻空时间的耦合关系,通过定量分析不同保压指标下浮空器驻空性能的变化情况,提取影响规律,为保压指标的合理设计提供总体参考。     

Galaxien vom Magellanschen Typ

In the first part of this paper the morphological structure of Magellanic type galaxies (Irr I) is investigated. The galaxies of Magellanic type present a basic pattern consisting of a disk, a bar, stellar arms, rudimentary or well developed, spiral filaments and condensations in the disk. With the help of this pattern a well-defined classification scheme is set up. The subgroup of Irr II-systems consists of normal galaxies which are more or less tidally disturbed. Bursts of star formation have a great influence on structure and colour of irregular galaxies. Using the ESO-B Atlas, 580 galaxies of Magellanic type (out of a sample of 3187 galaxies) were classified; 57 are new SB(s)m systems (prototype Large Magellanic Cloud). The sample shows dominant bar structures at the classification stages d-, dm-, and m. A striking feature is the asymmetric position of bar and disk. This asymmetry is a general characteristic of galaxies of types SBd-SBm IB. The asymmetry can be discribed by a relative displacement parameter \(\tilde \Lambda \) = 0.78 ±0.15, defined as the quotient of small and great distance of the bar center to the optical edge of the disk. The displacement cannot be explained by tidal interaction with neighbouring galaxies. In the second part of the paper the kinematics and dynamics of the Large Magellanic Cloud (LMC) as the nearest and best-known example of a galaxy of Magellanic type is investigated. The main structural features of the LMC are disk, bar, rudimentary and well developed stellar arms as well as spiral filaments (not necessarily connected with density waves); the γ-structure is a broken up ring structure. Embedded into these features are young, asymmetrically located spiral arm filaments. As an explanation for these structures stochastic start formation in an ordered chain reaction is proposed. The pattern of the spiral arm filaments is determined by the rotation curve. The morphological peculiarities of the LMC can also be detected in other galaxies of that type. The mean absolute displacement of the centers of bar and disk, determined from 18 galaxies, is Λ = 800 pc. The displacement between the bar center and the symmetry center of the rotation curve is of the same order. The presently known radial velocities of planetary nebulae, star clusters, Hi and Hii regions and stars belonging to the LMC have been collected in a catalogue as the basis of a discussion of the kinematics and dynamics of the LMC. Contrary to earlier work, we have used, for the first time, the radial velocities of objects of all subgroups together by a proper weighting scheme. Thus the basic kinematics and dynamics of the LMC has been deduced. The radial velocity field shows no central symmetry; it is characterized by large scale (2–3 kpc) disturbances. By comparison with the velocity field of other galaxies three main disturbances are identified: an oval distortion of the velocity field in the bar region, a radial velocity field around 30 Doradus, and disturbances connected with a warp or material above the disk in the southern quadrants. The results of a detailed numerical analysis of these three facts can be summed up as follows:

1. The rotation curve is determined over 10° diameter; it shows differential rotation, an asymmetric behavior in the south and a double structure in its Hi component. The rotation center is displaced by 0°.7 from the bar center. The orientation of the kinematic line of nodes and the systemic velocity vary as functions of the distance from the center. Therefore, it is possible to show definitely that large scale disturbances (warping, z-structure and streaming motions) are existent.
2. By variation of the kinematical parameters (systemic velocity, inclination, orientation of the line of nodes, rotation center) the dispersion of the measured radial velocities was minimized and the basic rotation curve determined. The rotation curves for the north and south side of the LMC are significantly different. The south side is either warped or there is material above the main plane. There seems to be a connection between this structure, the Panmagellanic Gas and the Magellanic Stream. The north side appears to be free of distorsion.
3. The residual velocity field (observed minus model) deduced from a basic rotation curve shows that the displacement between the rotation center and the bar center is not caused by local streaming motions. The rotation center must be the mass center. The bar shows a radial velocity field; in the 30 Doradus region inward and outward motions are found.

The mean velocity dispersion of population I objects is 10.5 km s^-1 of population II objects 16.0 km s^-1. Red and blue globular clusters show different kinematical behavior. By comparison of eight mass models, taking into consideration thickness effects and controlled by surface photometric data, the mass of the LMC is found to be (0.5 ± 0.1) × 10¹⁰ \(\mathfrak{M}_ \odot \) (assuming the inclination 33°, the systemic velocity 46.9 km s^-1, and the distance 56 kpc). Dynamically, the LMC can be described by a dominating disk potential with an additional bar potential as a disturbance. The mass of the bar is 0.6 × 10⁹ \(\mathfrak{M}_ \odot \) . The stable neutral point of such a configuration can be found in the residual velocity field. The absorption feature crossing the bar coincides with the maximum velocity gradient of the computed radial velocity field in the plane of the system.     

浮空器在武器装备信息化中的优势分析

浮空器在武器装备信息化中，是一种低成本防御性信息系统平台。首先介绍了浮空器的定义、基本组成和发展历史，然后详细分析了浮空器在工业发达国家的研究与应用现状，特别是平流层定点飞艇平台的发展趋势，最后结合我国的基本国情与武器装备信息化发展要求，分析了国内浮空器的研究发展水平、技术基础和浮空器在武器装备信息化建设中的作用和优势地位。     

Low-Mass Pre–Main-Sequence Stars in the Magellanic Clouds

The stellar Initial Mass Function (IMF) suggests that stars with sub-solar mass form in very large numbers. Most attractive places for catching low-mass star formation in the act are young stellar clusters and associations, still (half-)embedded in star-forming regions. The low-mass stars in such regions are still in their pre–main-sequence (PMS) evolutionary phase, i.e., they have not started their lives on the main-sequence yet. The peculiar nature of these objects and the contamination of their samples by the fore- and background evolved populations of the Galactic disk impose demanding observational techniques, such as X-ray surveying and optical spectroscopy of large samples for the detection of complete numbers of PMS stars in the Milky Way. The Magellanic Clouds, the metal-poor companion galaxies to our own, demonstrate an exceptional star formation activity. The low extinction and stellar field contamination in star-forming regions of these galaxies imply a more efficient detection of low-mass PMS stars than in the Milky Way, but their distance from us make the application of the above techniques unfeasible. Nonetheless, imaging with the Hubble Space Telescope within the last five years yield the discovery of solar and sub-solar PMS stars in the Magellanic Clouds from photometry alone. Unprecedented numbers of such objects are identified as the low-mass stellar content of star-forming regions in these galaxies, changing completely our picture of young stellar systems outside the Milky Way, and extending the extragalactic stellar IMF below the persisting threshold of a few solar masses. This review presents the recent developments in the investigation of the PMS stellar content of the Magellanic Clouds, with special focus on the limitations by single-epoch photometry that can only be circumvented by the detailed study of the observable behavior of these stars in the color-magnitude diagram. The achieved characterization of the low-mass PMS stars in the Magellanic Clouds allowed thus a more comprehensive understanding of the star formation process in our neighboring galaxies.     

Hubble's new view of the cosmos

Since the December 1993 repair of NASA's Hubble Space Telescope's (HST) optics by the crew of the Space Shuttle Endeavour, the rapid-fire scientific achievements have brought a new era of discovery to the field of astronomy. Hubble has confirmed some astronomical theories, challenged others, and often come up with complete surprises. Some images are so unexpected that astronomers have to develop new theories to explain what they are seeing. The HST has detected galaxies out to the visible horizon of the cosmos, and has made an attempt at pinning down the universe's expansion rate. Both of these key research areas should ultimately yield answers to age-old questions: What has happened since the beginning of time, and will the universe go on forever?