一个甚高频频率合成器的设计

介绍一个专用甚高频频率合成器的设计方案和实施中的一些关键技术．该合成器输出频率范围为９９．３ＭＨｚ～１００．７ＭＨｚ；步距分粗（２０ｋＨｚ）细（１００Ｈｚ）两档；输出短期频率的稳定度为３×１０（－９）／２５ｍｓ和１×１０（－１０）／ｓ．     

位于日冕微波区的微波Ⅲ型爆发界面频率的发现

在北京天台１．０－２．０ＧＨｚ射电频谱仪记录到的１９９４年１月５日爆发图上，首次发现一界面频率位于１２４０ＭＨｚ与１３４０ＭＨｚ之间的微波Ⅲ型爆发对，其频率漂率为－０．２２ＧＨｚ／ｓ和＋０．２３ＧＨｚ／ｓ由此推出电子加速区位于光球之上，３．７×１０＾４ｋｍ的高度，电子加速区及Ⅲ型爆发形成区的高度范围约为１０００公里，而电子束的速度相应为０．１０２ｃ及０．１０６ｃ。     

BPM载频产生器的研制

介绍ＢＰＭ短波授时台新的载频产生器的设计与实现，该ＢＰＭ载频产生器以原子频标的５ＭＨｚ标频信号为参考，利用频率合成技术，产生出供发射机使用的２．５ＭＨｚ、５ＭＨｚ，１０ＭＨｚ、１５ＭＨｚ和２０ＭＨｚ五种高准确度的载频信号。这些信号既能单独输出，也可利用面板控制或遥控选择输出。为了保证系统的可靠性，采用了两冗余结构，并设置了必要的报警与指示。     

高性能隔离分配放大器的研制与测量

论述了现代精密时频系统对隔离分配放大器的技术要求及其重要作用,介绍了为改进我台守时系统标准频率分配子系统而研制的一个高性能隔离分配放大器。对于５ＭＨｚ信号,该分配放大器的反向隔离度和路间隔离度均优于１１５ｄＢ;相位噪声在１Ｈｚ达到－１３５ｄＢｃ／Ｈｚ;噪声本底为１５０ｄＢｃ／Ｈｚ;插入秒稳损失达到１０＾－１３量级。在１３ｄＢｍ输出情况下,谐波小于－４０ｄＢｃ。对该分配放大器的主要性能测试涉及的测量     

用于分子谱线观测的512路数字式自相关频谱仪

本文简要介绍了采用一比特自相关技术实现的５１２路数字式自相关频谱仪的工作原理及系统的硬件和软件构成。该频谱仪主要用于分米及ｃｍ波段分子谱线观测。频谱仪系统时钟可在６２５ＫＨｚ和２０ＭＨｚ之间按２的倍率选择，最大分析带宽为１０ＭＨｚ。最高频率分辨率为０．６１ＫＨｚ，相应于１８ｃｍ波段的速度分辨率为０．１ｋｍ／ｓ。文章最后给出了利用上海天文台２５ｍ射电望远镜观测ＯＨ脉泽源的结果。     

位于日冕微波区的微波III型爆发界面频率的发现

在北京天文台１．０－２．０ＧＨｚ射电频谱仪记录到的１９９４年１月５日爆发图上，首次发现一界面频率位于１２４０ＭＨｚ与１３４０ＭＨｚ之间的微波ＩＩ型爆发对，其频漂率为－０．２２ＧＨｚ／ｓ和＋０．２３ＧＨｚ／ｓ．由此推出电子加速区位于光球之上３．７×１０４ｋｍ的高度，电子加速区及ＩＩ型爆发形成区的高度范围约为１０００公里，而电子束的速度相应为０．１０２ｃ及０．１０６ｃ．     

在Orion－KL中的OH脉泽的外流模型：多重分离的旋转膨胀环

我们从对Ｏｒｉｏｎ－ＫＬ星云中ＯＨ１６６５ＭＨｚ脉泽的单基线干涉观测的分析中,提出一种新的外流模型,即多重分离的旋转膨胀环．这种模型与观测结果是一致的．通过对２４ｋｍ单基线观测得到的１９个ＯＨ１６６５ＭＨｚ脉泽斑点的相对位置图进行分析、统计、拟合和计算,得到这１９个ＯＨ１６６５ＭＨｚ脉泽斑点分别分布在三个旋转膨胀环上．这三个旋转膨胀环的视距分别为３＂．８１,５＂．８７,６＂．０;对应的环半径分别为１７４２,２７２０,２７６６ＡＵ;径向膨胀速度分别为７．０７,１６．４,２６．４ｋｍｓ－１;旋转运动的切向线速度分别为１．５５,１．２３,１．２１ｋｍｓ－１．     

脉冲星PSR1951＋32的X射线脉冲辐射

脉冲星ＰＳＲ１９５１＋３２的Ｘ射线脉冲辐射程凌翔，李惕碚，孙学军，马宇蒨，吴枚（中国科学院高能物理研究所，北京１０００３９）主题词：脉冲星－Ｘ射线源１９８７年６月，用频率３８７ＭＨｚ的射电观测发现了脉冲星ＰＳＲ１９５１＋３２［１］，同年７月，在１８０...     

短分米波段上的长周期脉动现象

在１９９０年７月３０日观测到的太阳射电大爆发中，在１４２０ＭＨｚ和２０００ＭＨｚ两个波段上发现了长周期（数＋秒）的脉冲现象。经数据处理分析，发现了几个特点：（１）脉冲的宽带大于６００ＭＨｚ。（２）１４２０ＭＨｚ上的脉动的周期较２０００ＭＨｚ上脉动的周期大，相对强度也是前者较大。（３）脉冲的相对强度随脉冲周期的增大而增大，呈较好的线性关系     

太阳射电米波频谱22周峰年观测资料转存系统

介绍了通过计算机标准ＲＳ２３２Ｃ串行通信口，把太阳射电米波声光频谱仪２２周峰年期间用ＹＥＥ８１００微机观测到的太阳２３０ＭＨｚ－３００ＭＨｚ频谱资料传到ＡＳＴ３８６ｓｘ／２０微机转存和处理，以及两台微机间数据传递过程中对数据是否随机丢失进行验证的一种方法     

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.     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length     

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.     

我国新一代VLBI数字基带转换器研制进展

数字化是目前设备研制发展的趋势,介绍了中国科学院上海天文台利用超大规模集成电路结合软件无线电技术,自主研发的我国新一代VLBI数字基带转换器(Chinese Data Acquisition System,简称CDAS).文中描述了设备的工作原理及其组成,并以VLBI观测实验数据证明其可行性.与原有的模拟设备(Anal...