斜轴式太赫兹天线的卡焦近场全息测量研究

天线反射面的面形精度直接影响天线效率, 是望远镜的关键指标之一. 近场射电全息具有测量精度高, 便捷高效的优点, 是毫米波和亚毫米波射电望远镜面形检测最为常用的方法之一, 卡焦近场全息可以完整测量望远镜光路中整体的面形误差. 斜轴式机架结构能够更好地适应太赫兹望远镜在极端台址环境下的整体保温和热控需求, 但斜轴天线特殊的转动特性会在近场全息测量过程中引入额外的系统误差. 针对斜轴式天线的卡焦近场全息测量, 分析了数据处理中需要额外考虑的参考路接收机位置和副面衍射的影响, 并在1.2m口径斜轴式太赫兹天线上开展了测量实验. 实验结果表明, 卡焦近场全息测量的重复测量精度优于2.0μm RMS (Root Mean Square), 面形误差分布与摄影测量所得结果一致, 验证了误差分析与修正的正确性.     

抛物面天线微波全息测量及结果分析

就上海佘山25 m抛物面天线上进行的相位相关法微波全息测量及其测量结果做了一定阐述。文章首先简要提到了微波全息测量技术在国内外的发展情况以及理论依据,其次介绍了我们所建立的测量系统的组成,重点讨论了基于窄带信号测量工作的有效性和准确性,采用自校准的数据处理手段,对测量误差做了估计和实际测试。当前我们已经取得了0.14 mm的测量精度(极限误差为0.2 mm),并分析了影响测量精度的各项因素。     

新疆天文台南山26米天线全息法测量系统

南山25 m射电望远镜经过一年多的升级改造现已全面完成,主反射面直径增加至26 m,为保证Q波段(30~50 GHz)接收机的工作效率,望远镜的表面精度需达到较高的水平,微波全息法可对天线面形进行精确测量和调整,是望远镜面形首次和定期精调的首选,基于新南山26 m天线建立了一套全息法测量系统。整个系统包括参考天线、接收机、相关机、传输链路、时频参考、扫描控制和全息法处理软件等几部分,采用带通采样技术直接采集中频信号,减少了基带信号转换环节;采用高性能外部本振并利用氢钟输出的参考信号进行锁相,达到了极高的相位稳定度。目前整个系统已通过测试并取得了初步的测量结果,经处理分析,该系统工作正常,已达到应用要求。     

采用光学指向系统建立天马13m望远镜指向模型

描述了采用光学望远镜辅助天马13m射电望远镜进行指向测量以及建立指向误差修正模型的方法. 对于小口径望远镜, 指向校准目标源比较少, 用射电法建立指向模型难以覆盖全天区. 利用上海天文台天马13m射 电望远镜进行光学望远镜辅助射电望远镜指向测量研究, 在13m天线背架上安装一套光学指向系统, 获得了优 于3''的重复测量误差. 此外, 通过对影响天线指向因素的分析, 建立了包含8个误差项的指向误差修正模型以及 光轴和电轴偏差模型. 将指向模型代入天线伺服控制系统, 对校准目标射电源进行十字扫描, 得到指向样本残差约 为5''. 该研究可以为实现高精度指向建模提供一种参考方法.     

环焦天线口径面相位分析

环焦天线具有特殊的电磁特性和应用领域.对环焦天线的口径面相位误差进行了理论和仿真分析,推导了馈源和副面位置偏差引起的相位误差、主副面之间的补偿关系以及全息测量中天线转动引起的光程差.研究结果将对环焦天线的精确面形测量和补偿提供理论依据和参考.     

全息法测量天线面表面精度

该文讨论了全息法测量天线面表面精度的基本原理和实现方法，这种测量方法对于测量各种大型抛物面天线具有普遍意义。阐述了全息法的基本原理和实现全息法时必须的天线控制方法及原理，简单介绍了全息法中对测量数据的处理方法，并对全息法所得结果作了一定的总结。     

模糊控制器在25米天线副面调节中的应用

以新疆天文台南山25 m天线改造计划为背景,为达到通过副反射面补偿方法提高天线整体电性能以及自动换馈的目的,详细研究了基于模糊控制器的天线副反射面调节系统。以六自由度并联平台伺服系统为被控对象,运用Simulink仿真软件对模糊控制器进行了在无噪声阶跃输入、有噪声阶跃输入、无噪声弦波输入和有噪声弦波输入条件下的系统仿真,并进行了详细的误差分析,得到了性能最优的系统模型参数,同时得到了在模糊控制器作用下的副反射面调节系统的基本运行性能参数:在弦波信号作用下系统响应误差小于等于0.09 mm,在阶跃信号作用下系统稳态误差为0.001 1 mm,且调节时间约为0.3 s。实验结果表明基于模糊控制器的控制系统整体性能良好,能快速、稳定、准确地完成副反射面调节任务,进而提高天线的整体电性能,满足天文观测和深空探测对数据准确性和系统可靠性的要求,具有一定的应用价值。     

基于全息测量的佘山25 m射电望远镜远场分析

首先分析了佘山25 m卡塞格伦天线结构,形变与噪声这2个因素影响下的远场进行仿真分析,理想情况比较,分析这2个因素对全息测量的影响。然后利用天线结构参数分别对天线面板表面获得了二维远场的幅度和相位分布图,并与     

上海、乌鲁木齐两台Φ25m射电望远镜轨道枕板设计的分析和比较

本通过对上海、乌鲁木齐两台Φ25m天线轨道基础结构的分析测量和比较，说明了只有改造上海Φ25m天线轨道枕板结构，才能有效地控制天线的指向精度。     

关于单天线跟踪指向校准和双天线基线校准的探讨

阐述了CSRH的跟踪指向校准和天线对基线校准的方法.通过利用观测射电星Cassiopeia A或Cygnus A找出流量最大点以校准天线指向,跟踪观测GPS卫星或射电星,并借鉴Korean Solar Radio Burst Locator(KSRBL)系统的8参数校准法校正由天线安装引入的误差,校准后误差RMS值可小于22".在完成上述单天线指向跟踪校准后,应用阐述的算法可校准天线对基线误差.     

A thermodynamic model of high temperature lava vaporization on Io

We modified the MAGMA chemical equilibrium code developed by Fegley and Cameron (1987, Earth Planet. Sci. Lett. 82, 207-222) and used it to model vaporization of high temperature silicate lavas on Io. The MAGMA code computes chemical equilibria in a melt, between melt and its equilibrium vapor, and in the gas phase. The good agreement of MAGMA code results with experimental data and with other computer codes is demonstrated. The temperature-dependent pressure and composition of vapor in equilibrium with lava is calculated from 1700 to 2400 K for 109 different silicate lavas in the ONaKFeSiMgCaAlTi system. Results for five lavas (tholeiitic basalt, alkali basalt, Barberton komatiite, dunite, and a molten type B1 Ca, Al-rich inclusion) are discussed in detail. The effects of continuous fractional vaporization on chemistry of these lavas and their equilibrium vapor are presented. The predicted abundances (relative to Na) of K, Fe, Si, Al, Ca, and Ti in the vapor equilibrated with lavas at 1900 K are lower than published upper limits for Io's atmosphere (which do not include Mg). We predict evaporative loss of alkalis, Fe, and Si during volcanic eruptions. Sodium is more volatile than K, and the Na/K ratio in the gas is decreased by fractional vaporization. This process can match Io's atmospheric Na/K ratio of 10±3 reported by Brown (2001, Icarus 151, 190-195). Silicon monoxide is an abundant species in the vapor above lavas. Spectroscopic searches are recommended for SiO at IR and mm wavelengths. Reactions of metallic vapors with S- and Cl-bearing volcanic gases may form other unusual gases including MgCl₂, MgS, MgCl, FeCl₂, FeS, FeCl, and SiS.     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work,     

Research in Astronomy and Astrophysics CONTENTS

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Alkali and halogen chemistry in volcanic gases on Io

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10⁻⁶ to 10⁺¹ bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I₂ (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.     

Study on the Stressed Mirror Polishing with a Continuous Polishing Machine for Large Aperture Off-axis Aspheric Mirrors

A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope.     

The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts

Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr^− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant.     

Active hot star shells

Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells. Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fitting X-ray Afterglow Light curves of Gamma-ray Bursts by Using the Magnetar Energy Injection Model

The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 10²∼10⁴ s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.