富勒烯与星际消光

近年来,富勒烯这一重要碳尘埃在天文观测上得到了证认,多种天体环境中均探测到了C₆₀和C₇₀的红外振动光谱.本文重点研究了三种主要的富勒烯C₆₀,C₇₀和C₈₄的星际丰度.利用实验获得的C₆₀,C₇₀和C₈₄的介电函数,计算了它们在可见光和紫外波段的吸收特性.通过与星际消光曲线的比较,得出C₆₀,C₇₀和C₈₄在星际空间所占碳的含量上限(相对氢来说)分别为5,7,5 ppm (其中ppm是百万分比).     

星际弥散吸收带

星际弥散带（diffuse interstellar bands;DIBs）是源自星际空间的数百条吸收谱线的总称．自20世纪20年代首次发现两条DIBs以来,对DIBs的观测和证认已有80多年的历史．迄今为止,共观测到了300多条DIBs,但没有一条DIB的载体（carrier）被完全证认．DIBs的证认被认为是困扰着天文学家80多年的天体物理学的经典难题之一．我们简要回顾了星际弥散带的观测历史,介绍了银河系和河外星系星际弥散带的一些观测特征、星际紫外消光2175A驼峰强度和星际弥散带的相关性、星际弥散带之间的相关性和星际弥散带的分类方法;对星周环境中是否存在弥散吸收带的观测结果也给予了简要的评述;讨论了星际弥散带的载体和起源．     

用红外线观察宇宙

斯皮策太空望远镜是一架天文观测航天器，它以红外线波段对太空进行天文观测，而且具有非常高的灵敏度和分辨率。红外线能够穿透星际尘埃等物质的遮蔽，因此，这架望远镜可以观测到用可见光无法看见的某些天文现象，尤其适合观测恒星的诞生。斯皮策太空望远镜在被发射上天以来的一年半的时间里，陆续拍摄到了大量清晰的红外线照片，其中许多照片揭示出以前从未见到过的宇宙景象。     

行星际闪烁（IPS）观测中的几个问题

行星际闪烁和电离层闪烁的强度功率谱覆盖的主要频段是不同的,因此可以区分．本文给出了行星际闪烁观测中电磁波频率与对应的弱散射最小日心距之间的定量关系式,以及闪烁指数随射电源日张角变化的曲线方程,并与观测事实进行了比较．     

行星际闪烁单站单频和单站双频模拟

太阳风是日地空间的主要物质来源, 太阳风的观测对日地空间环境及地球物理的研究具有重要意义. 地基行星际闪烁（IPS）观测是监测太阳风风速, 测量太阳风等离子不规则结构, 研究遥远射电源角结构的重要且有效的方法. 本文介绍行星际闪烁的基本理论以及地基观测行星际闪烁的两种单站模式： 单频模式与双频模式, 且对这两种观测模式进行了模拟和比较. 单频模式易于操作, 数据处理过程简单, 应用较广; 双频模式对观测系统和数据处理系统具有较高要求, 但能更精确测量太阳风风速. 国家天文台密云观测站50米天线正在研制行星际闪烁单站双频系统, 此系统将服务于国家“十一五”重大科技基础设施——子午工程. 该文工作是为行星际闪烁单站双频系统数据分析作前期准备.     

与HⅡ区成协的星际脉泽激发机制

从紫外光子与星际分子的相互作用出发,对与HⅡ区成协的星际脉泽提出了一种重要的激发机制.它能统一解释星际OH和水2种脉泽,并能满足各种天文条件,克服了以往某些模型的困难.     

星际H2O脉泽的观测与研究

从１９９２年９月起，对近８２个外流源或电离氢区，用紫金山天文台青海站的１３．７ｍ望远镜进行了水脉泽观测。有三个源首次测得了弱Ｈ２Ｏ脉泽辐射；对已知源的观测结果表明星际水脉泽的时变化比较普遍。流量变化２０％以上的源达７５％，在高质量外流源中水脉泽深测率比低质量外流源中的高。本文还讨论了脉泽产生率与ＣＯ谱线宽度及成协源红外辐射的相关性。     

可以看见黑洞吗？

浩瀚宇宙，奇妙无穷。我们观测宇宙，能够发现许许多多在地球上无法实现的极端状态，宇宙中物质的密度就是如此。在宇宙中．有非常小的密度，也有近乎无限大的密度。那普通的星际空间，几乎就是真空．每立方厘米空间内大约只有1个氢原子。宇宙中还有星际云、分子云等等．它们的密度依次增大。像地球一类的行星，它们的平均密度大约是每立方厘米5克；     

110m口径全可动射电望远镜专辑·编者按

<正>射电天文学诞生并发展于20世纪30年代初,为人类认识宇宙打开了一个全新的探测窗口.二次世界大战后,军用雷达被广泛用于民用天文观测,同时,一大批专用于天文研究的射电望远镜也相继建成和运行,使射电天文进入蓬勃发展的黄金期,直接促成了60年代的现代天文学"四大发现"——类星体、脉冲星、星际分子、宇宙微波背景辐射,使得射电天文成为现代天文学最活跃、最前沿的分支.     

河外星际尘埃的亚毫米波发射

本文借助于观测到的大、小麦哲伦云的星际尘埃辐射，估计总星系的冷尘埃辐射对微波背景辐射的影响。结果表明：河外星际冷尘埃辐射强度强烈地依赖于宇宙减速因子，在宇宙背景探测者（ＣＯＢＤ）的观测结果的限制下，在合理的光深范围内，宇宙减速因子趋于１。     

The synthesis of organic and inorganic compounds in evolved stars

Recent isotopic analysis of meteorites and interplanetary dust has identified solid-state materials of pre-solar origin. We can now trace the origin of these inorganic grains to the circumstellar envelopes of evolved stars. Moreover, organic (aromatic and aliphatic) compounds have been detected in proto-planetary nebulae and planetary nebulae, which are the descendants of carbon stars. This implies that molecular synthesis is actively happening in the circumstellar environment on timescales as short as several hundred years. The detection of stellar grains in the Solar System suggests that they can survive their journey through the interstellar medium and that they are a major contributor of interstellar grains.     

Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris

The interstellar medium is enriched primarily by matter ejected from old, evolved stars. The outflows from these stars create spherical envelopes, which foster gas-phase chemistry. The chemical complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of molecules than their oxygen-rich analogues. Here we report observations of molecules in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chemical compounds have been identified, including NaCl, PN, HNC and HCO+. From the spectral line profiles, the molecules can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulphur-bearing molecules (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO+ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chemically diverse as their carbon counterparts.     

The formation of a massive protostar through the disk accretion of gas

The formation of low-mass stars like our Sun can be explained by the gravitational collapse of a molecular cloud fragment into a protostellar core and the subsequent accretion of gas and dust from the surrounding interstellar medium. Theoretical considerations suggest that the radiation pressure from the protostar on the in-falling material may prevent the formation of stars above ten solar masses through this mechanism, although some calculations have claimed that stars up to 40 solar masses can in principle be formed via accretion through a disk. Given this uncertainty and the fact that most massive stars are born in dense clusters, it was suggested that high-mass stars are the result of the runaway merging of intermediate-mass stars. Here we report observations that clearly show a massive star being born from a large rotating accretion disk. The protostar has already assembled about 20 solar masses, and the accretion process is still going on. The gas reservoir of the circumstellar disk contains at least 100 solar masses of additional gas, providing sufficient fuel for substantial further growth of the forming star.     

金牛座、蛇夫座中分子云的热性质和年轻星体的演化状态

运用CO分子谱线及红外天文卫星资料,求出了金牛座、蛇夫座核心2个恒星形成区的气体运动温度T_k和尘埃温度T_d,验证了尘埃加热分子云的基本条件;着重探讨了用T_d参量比较年轻星体演化状态的方法,得出蛇夫座核心区恒星比金牛座恒星年轻的初步结论。     

A disk of dust and molecular gas around a high-mass protostar

The processes leading to the birth of low-mass stars such as our Sun have been well studied, but the formation of high-mass (over eight times the Sun's mass, M(o)) stars remains poorly understood. Recent studies suggest that high-mass stars may form through accretion of material from a circumstellar disk, in essentially the same way as low-mass stars form, rather than through the merging of several low-mass stars. There is as yet, however, no conclusive evidence. Here we report the presence of a flattened disk-like structure around a massive 15M(o) protostar in the Cepheus A region, based on observations of continuum emission from the dust and line emission from the molecular gas. The disk has a radius of about 330 astronomical units (Au) and a mass of 1 to 8 M(o). It is oriented perpendicular to, and spatially coincident with, the central embedded powerful bipolar radio jet, just as is the case with low-mass stars, from which we conclude that high-mass stars can form through accretion.     

Low-temperature crystallization of silicate dust in circumstellar disks.

Silicate dust in the interstellar medium is observed to be amorphous, yet silicate dust in comets and interplanetary dust particles is sometimes partially crystalline. The dust in disks that are thought to be forming planets around some young stars also appears to be partially crystalline. These observations suggest that as the dust goes from the precursor clouds to a planetary system, it must undergo some processing, but the nature and extent of this processing remain unknown. Here we report observations of highly crystalline silicate dust in the disks surrounding binary red-giant stars. The dust was created in amorphous form in the outer atmospheres of the red giants, and therefore must be processed in the disks to become crystalline. The temperatures in these disks are too low for the grains to anneal; therefore, some low-temperature process must be responsible. As the physical properties of the disks around young stars and red giants are similar, our results suggest that low-temperature crystallization of silicate grains also can occur in protoplanetary systems.     

关于星际分子的客观性的证明

以星际分子的发现为案例,探讨了星际分子的证认与星际分子客观性的关系;并对证认的客观性作了一定的辩护,在此基础上提出了对自然科学中“客观性”概念的新理解,认为客观性不应只是传统的“可观察性”和“可感知性”,而是“信息的可接收性和可理解性”。     

Identification of molecular-cloud material in interplanetary dust particles

Interplanetary dust particles (IDPs) collected in the Earth's stratosphere and meteorites are fragments of comets and asteroids. These are 'primitive' meteorites in part because they have preserved materials which predate the formation of the Solar System. The most primitive (least altered) meteorites contain a few parts per million of micrometre-sized dust which formed in the atmospheres of giant stars. Some meteorites have elevated D/H and 15N/14N ratios that are attributed to surviving interstellar organic molecules which have probably been strongly diluted and altered by parent-body processes. Most IDPs are chemically, mineralogically, and texturally primitive in comparison to meteorites. Here I show that H and N isotopic anomalies among fragile 'cluster' IDPs are far larger, more common, and less equilibrated than those previously observed in other IDPs or meteorites. In some cases, the D/H ratios that we measure reach the values of interstellar molecules, suggesting that molecular-cloud material has survived intact. These observations indicate that cluster IDPs are the most primitive class of Solar System materials currently available for laboratory analysis.     

No high-mass protostars in the silhouette young stellar object M17-SO1

The birth of very massive stars is not well understood, in contrast to the formation process of low-mass stars like our Sun. It is not even clear that massive stars can form as single entities; rather, they might form through the mergers of smaller ones born in tight groups. The recent claim of the discovery of a massive protostar in M17 (a nearby giant ionized region) forming through the same mechanism as low-mass stars has therefore generated considerable interest. Here we show that this protostar has an intermediate mass of only 2.5 to 8 solar masses (M(o), contrary to the earlier claim of 20M(o) (ref. 8). The surrounding circumstellar envelope contains only 0.09M(o) and a much more extended local molecular cloud has 4-9M(o).