大型光学望远镜扇形子镜支撑方法的探讨

基于对大型光学望远镜子镜的要求,比较六边形和扇形两种子镜的优缺点.用有限元法分析扇形子镜在自重下的变形,确定扇形子镜的支撑点数和排列方式.并具体分析了通过18点、24点、27点三种支撑点的排列方式,分别计算不同支撑点下的子镜变形.通过计算表明,27点的支撑方式可以满足子镜的镜面RMS小于10nm的技术要求,并讨论子镜的轴向和侧向支撑方案.计算了在轴向和侧向支撑的条件下,各子镜在水平,垂直以及45°三个极限位置的镜面RMS值.     

第9届亚太天文奥赛理论竞赛试题

不一定所有题目都是正确的试题,一些题目（可能是它的主问题,或是它的子问题）可能是不现实或不可能出现的。在这种情况下,你需要在答题时用英文“impossiblesituation”注明。解题过程中可使用所提供的数据表。分别是日、月、行星数据表,以及天文常数表和全天32颗最亮恒星数据表。解答中的“是”与“否”需用英文的“yes”与“no”标出。     

“复仇女神”——镜像死星?

《天文爱好者》1986年3月号曾登载了李泽清编译的文章《“复仇女神”——死星》。十几年过去了,现在又有两位科学家认为,这个“复仇女神”可能是由看不见的镜像物质(Mirror matter)组成的死星(Dead star)。 1983年,美国著名古生物学家劳普(David Raup)发现,在过去的2.5亿年里,每隔2.6千万年就有规则地、周期性地发生大量生物灭绝。1968年诺贝尔物理学奖获得者阿尔瓦雷茨(L.W.Alvarez)曾发现,大约在恐龙灭绝的同一时期,来自空间的一颗小行星或彗星撞击了地球。把两人的发现结合在一起,劳普等人提出了有名     

艺术天体摄影的意境

如果把天体摄影当作摄影的一个门类来考虑,必然要提到其质量标准和艺术标准。有一点笔者认为,作品除非达到大卫·麦林的水准或拍到了尚未发现的新天体、新现象,一般的天体摄影作品是没有什么科学价值的,这样更应该考虑上述两个标准。用跟踪法拍摄一个深空天体,其质量标准有两个,一是该深空天体拍摄的效果如何,二是照片中的天空应该是既深黑又通透,背景的恒星的点像应该是密、小、圆。后者更是检验拍摄是否成功的重要标准,达不到这个标准,便是废片。达到这样的质量标准又谈何容易,既使能达到上述质量标准,又不可能把某一深空天体…     

天体演化与元素演化之谜（一）——天文学中的佯谬之四

自从前三篇聊“天”话“佯谬”在本刊发表之后,激发了不少读者的兴致,有的爱好者还来信来电提出了一些十分有趣的题目,鼓励我继续写下去。其中一个趣题中的主角竟是“中子”!乍一想,中子似乎与天文学毫无关系。天文学的直接表象是星空,人类在没有使用火的时代,就已经对天穹上“星火”的分布十分熟悉了,     

公元前1000年至公元3000年月食推算表

奥泊尔子(Oppolzer)的“日月食典”包含有-1207年至2161年间的8000次日食和-1206年至2163年间的5200次月食,出版至今虽然已有七十余年,仍然是现在计算日月食时所不可缺少的参考书.但“日月食典”也有一些缺点,日食部分的缺点在本文中暂不讨论,单就月食部分而言主要有下面几点:(i)没有载半影月食.近年来半影月食也受到注意,苏联天文年历从1958年起开始登载半影月食,英美天文年历也从1962年起开始     

诗词歌赋中的星座世界（三）——神灵化的北斗

回生主死北斗神《全宋诗》中流传下来一首不知何人作的《璇玑殿》诗：众圣环拱位中天,统济乾坤妙转旋。高覆昆仑朝帝阙,注生回死福增延。“璇玑殿”,顾名思义,是和北斗有关系的宫殿。北斗日夜绕北极转动,故诗中有“拱位”、“转旋”之描述。古人还认为昆仑山是天北极的枢轴,故云北斗“高覆昆仑”,那么“注生回死”指的是什么呢？     

用中子星限制暗物质粒子散射截面

中子星可以通过重子物质和暗物质的相互作用吸积暗物质,且在一定条件下, 中子星吸积的暗物质粒子可以引发自引力塌缩形成小型黑洞, 生成的黑洞可能会进一步吞噬中子星.依据文献已有模型, 基于以上物理过程给出了在暗物质粒子不同质量下对暗物质粒子--中子的散射截面的限制.使用弱相互作用大质量粒子(Weakly Interacting Massive Particle, WIMP)模型, 并考虑暗物质粒子是玻色子的情形, 讨论了暗物质粒子有无自相互作用以及有无湮灭等条件下对限制暗物质参数的影响.既考虑了已发现的两个中子星系统来给出对暗物质参数空间的限制,也考虑了两个可能存在的年老中子星来预测未来观测可能对暗物质参数空间的限制.对于考虑玻色--爱因斯坦凝聚(Bose-Einstein Condensate, BEC)的玻色子暗物质, 在无自相互作用或有弱自相互作用, 无湮灭或有很小湮灭截面的条件下,中子星给出的间接观测对暗物质粒子-中子散射截面的限制的强度比XENON1T直接探测实验来得更强.未来, 如果在银心附近能观测到年老中子星, 其观测结果可以提升模型给出的对暗物质粒子--中子散射截面的限制, 从而帮助人们进一步理解暗物质.     

厄尔尼诺的起因

厄尔尼诺已成为当今妇孺皆知的“气象怪物”,不少人对它颇有神秘之感。而厄尔尼诺一词的原意也确实给人以神秘的想像,它是西班牙语“上帝之子”或“圣婴”之意。但现在的气象上的含意已完全没有这些意思了。它表示一系列的海—气反常现象,主要有以下几方面,（１）东太...     

天文奥赛有感

今年“五一”,我参加了2005年全国天文奥林匹克竞赛决赛。从5月2日至6日,我们这些来自全国各地的中学生天文爱好者齐聚北京韩村河,度过了既紧张刺激而又令人难忘的五日五夜。5月2日是报到时间,在简短的开幕式之后,我们饶有兴趣地参观了北京天文馆新馆,既感受了坐地日行八万里之神速,又领略了巡天遥看一天河之奥妙。在无限的回味中,我们乘车赶往韩村河——2005年全国天文奥林匹克竞赛决赛场地。5月3日至5月4日进行理论、实测和观测比赛。比赛前我有些激动,可能是因为第一次参加这样的比赛。铃声响了,理论考试开始了,我认真地浏览了一遍试卷,发现理论考题并没有我想象得那么难,因此紧张的心情也舒缓了许多,计划两个小时的考试我只用了一半的时间。交卷后,我     

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     

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,     

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.     

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.     

Natural superrotation of a rarefied planetary atmosphere

We consider the kinetics of a rarefied rotating planetary atmosphere. The spatial distributions of the atmospheric-gas density and mean angular velocity were determined by analyzing the exact solution of the two-dimensional kinetic equation. We show that the angular velocity of the gas at some distance from the planet could be higher than that in the initial layer starting from which the atmosphere is rarefied. Our model calculations elucidate the superrotation mechanism under consideration.