四频率太阳射电高时间分辨率观测特征：微耀斑能量释放的证据

作为微耀斑能量释放的证据，本文扼要介绍了云南天文台“四频率太阳射电高时间分辨率同步观测系统”（１．４２，２．１３，２．８４和４．２６ＧＨｚ）１９８９年１２月－１９９３年４月的观测事例，包含低强度的毫秒尖峰辐射（ｍｓｓｐｉｋｅ），类尖峰辐射（ｓｐｉｋｅ－ｌｉｋｅ），快速脉动现象，两种新的快速精细结构──微波Ⅲ型爆和微波类斑点结构．统计了快速精细结构的寿命，在统计基础上分别以实例描述了各类现象的观测特征．     

太阳射电三频率高时间分辨率三年同步观测的结果

本文总结了1987年2月到1989年12月三波段(1.42GHz、2.84GHz和4.0GHz)高时间分辨率同步观测的资料,介绍了各波段尖峰辐射出现的频次、持续时间以及与射电爆发、光学耀斑和X射线爆的统计关系.     

太阳微波尖峰辐射的高时间、高频率分辨率偏振观测

利用北京天文台 ２．６—３．８ ＧＨｚ频谱仪的观测资料,找到 １１个微波尖峰辐射事件．尖峰一般具有数十毫秒的寿命,数百个ｓｆｕ的流量密度和数十至数百ＭＨｚ的带宽,这与以前的报道类似．尖峰的偏振度各式各样,有的尖峰还有数千ＭＨｚ／ｓ的频率漂移．某些尖峰在二个偏振态之间有８毫秒的时间延迟（最大延迟可达１６毫秒）．另外,还发现了尖峰的偏振度随频率剧烈变化的偏振反转现象．     

太阳分米波尖峰辐射最小带宽的探讨

云南天文台0.6～1.5GHz太阳射电快速动态频谱仪,在2001年6月24日的射电爆发中观测到大量尖峰。由于观测仪器有相当高的频率分辨率,使我们可以对尖峰的绝对带宽进行更精细的统计分析。由于尖峰数量很大,特别编制了识别尖峰并测量其带宽的软件来进行统计工作。结果发现76%的尖峰的绝对带宽达到仪器频率分辨率1.4MHz,其相对带宽达到0.1%。这比以前关于尖峰辐射带宽的统计结果要小很多。统计结果支持用ECM机制解释尖峰辐射。     

XRB、SGR和GRB简介

ＸＲＢ、ＳＧＲ和ＧＲＢ简介Ｘ射线爆发（Ｘ－ｒａｙＢｕｒｓｔｅｒｓ，以下简称ＸＲＢ）、软γ射线复现（Ｓｏｆｔ－ｇａｍｍａＲｅｐｅａｔｅｒｓ，以下简称ＳＧＲ）和γ射线爆发（γ－ｒａａＢｕｒｓｔｅｒｓ，以下简称ＧＲＢ）都是天空中暂现、转瞬即逝的高能现象，三...     

太阳微波尖峰辐射的高时间,高频率分辨率偏振观测

利用北京天台２．６－３．８ＧＨz频谱仪的观测资料,找到１１个微波尖峰辐射事件。 尖峰一般具有数十毫秒的寿命,数百个ｓｆｕ的流量密度和数十至数百ＭＨz的带宽,这与 以前的报道类似。尖峰的偏振度各式各样,有的尖峰还有数千ＭＨz／s的频率漂移。某些尖峰在二个偏振态之间有８毫秒的时间延迟（最大延迟可达１６毫秒）。另外,还发现了尖峰在二个偏振态之间有８毫秒的时间延迟（最大延迟可达１６毫秒）。另外,还发现了尖峰的     

一个含有丰富快速精细结构的射电大爆发

本文对１９９０年７月３０日云南天文台四波段太阳射电高时间分辨率同步观测系统＾「１，２」所观测到的太阳射电大爆发进行了分析，对在１．４２ＧＨｚ，２．００ＧＨｚ，２．８４ＧＨｚ三个波段上观测到的大量尖峰辐射作了关于寿命和强度的统计，最后，针对本次爆发中的ｍｓ－ｓｐｉｋｅｓ的特点做了一些讨论。     

太阳分米波尖峰辐射最小带宽的探讨

云南天文台0．6～1．5GHz太阳射电快速动态频谱仪，在2001年6月24日的射电爆发中观测到大量尖峰。由于观测仪器有相当高的频率分辨率，使我们可以对尖峰的绝对带宽进行更精细的统计分析。由于尖峰数量很大，特别编制了识别尖峰并测量其带宽的软件来进行统计工作。结果发现76％的尖峰的绝对带宽达到仪器频率分辨率1．4MHz，其相对带宽达到0．1％。这比以前关于尖峰辐射带宽的统计结果要小很多。统计结果支持用ECM机制解释尖峰辐射。     

一个含有丰富快速精细结构的射电大爆发

本文对１９９０年７月３０日云南天文台四波段（１．４２ＧＨｚ、２．００ＧＨｚ、２．８４ＧＨｚ和４．００ＧＨｚ）太阳射电高时间分辨率同步观测系统［１，２］所观测到的太阳射电大爆发进行了分析，对在１．４２ＧＨｚ、２．００ＧＨｚ、２．８４ＧＨｚ三个波段上观测到的大量尖峰辐射（ｍｓ—ｓｐｉｋｅｓ）作了关于寿命和强度的统计，最后，针对本次爆发中的ｍｓ—ｓｐｉｋｅｓ的特点做了一些讨论。     

南天区5GHz VLBI成图谱查的一些统计研究

本文发表已完成的两轮南天区５ＧＨｚ ＶＬＢＩ成图谱查观测的统计研究。在简要总结两轮观测结果的基础上,将它们分别与Ｐｅａｒｓｏｎ－Ｒｅａｄｈｅａｄ（ＰＲ）普查样本源和Ｗｅｈｒｌｅ等人普查的变源,以及ＥＧＲＥＴ检测到的γ射线源的统计比较．     

2.6--3.8 GHz太阳微波爆发中的精细结构

根据1994年lslike＆Benz给出的1－3GHz频带上的微波III型爆发和微波尖峰辐射的分类定义,分析北京天文台26－3．8GHz频带上观测到的微波爆发的精细结构．通过分析发现该定义有局限性．本文重新定义了该波段上的微波III型爆发和微波尖峰辐射,并讨论了这种分类定义与设备时间分辨率的关系     

1997年11月2日微波尖峰源背景参数的诊断

利用北京天文台高时间和高频率分辨率的射电频谱仪对射电尖峰的测量,可以对背景等离子体参数进行的自洽诊断（ 磁场,密度,温度,波矢,及非热电子的性质） 。该诊断基于电子回旋脉塞不稳定性和回旋共振吸收。最后从诊断结果和太阳日冕典型参数的比较以确定尖峰辐射的谐波数。     

一个新型分米波太阳微耀斑现象的观测分析

本文介绍一组短分米波（1．42GHz）太阳微耀斑的射电和光学辐射特征，它们包含53个叠加在连续辐射背景上的射电快速精细结构（FFS），即准周期快速脉冲链（称微耀斑），它们的形态相似，强度大约在150－200sfu范围内，其寿命（半功率宽）大多为15－50ms，有18个分离的双峰结构，该事件产生的7646活动区中出现两处新浮现的几个小黑子，呈现复杂极性，可能存在多重交叉小磁流环多次重联的复杂状况．本文定性地讨论了其产生机制，支持电流环爆炸性聚合模型的理论。     

The electron–cyclotron maser for astrophysical application

The electron–cyclotron maser is a process that generates coherent radiation from plasma. In the last two decades, it has gained increasing attention as a dominant mechanism of producing high-power radiation in natural high-temperature magnetized plasmas. Originally proposed as a somewhat exotic idea and subsequently applied to include non-relativistic plasmas, the electron–cyclotron maser was considered as an alternative to turbulent though coherent wave–wave interaction which results in radio emission. However, when it was recognized that weak relativistic corrections had to be taken into account in the radiation process, the importance of the electron–cyclotron maser rose to the recognition it deserves. Here we review the theory and application of the electron–cyclotron maser to the directly accessible plasmas in our immediate terrestrial and planetary environments. In situ access to the radiating plasmas has turned out to be crucial in identifying the conditions under which the electron–cyclotron maser mechanism is working. Under extreme astrophysical conditions, radiation from plasmas may provide a major energy loss; however, for generating the powerful radiation in which the electron–cyclotron maser mechanism is capable, the plasma must be in a state where release of susceptible amounts of energy in the form of radiation is favorable. Such conditions are realized when the plasma is unable to digest the available free energy that is imposed from outside and stored in its particle distribution. The lack of dissipative processes is a common property of collisionless plasmas. When, in addition, the plasma density becomes so low that the amount of free energy per particle is large, direct emission becomes favorable. This can be expressed as negative absorption of the plasma which, like in conventional masers, leads to coherent emission even though no quantum correlations are involved. The physical basis of this formal analogy between a quantum maser and the electron–cyclotron maser is that in the electron–cyclotron maser the free-space radiation modes can be amplified directly. Several models have been proposed for such a process. The most famous one is the so-called loss-cone maser. However, as argued in this review, the loss-cone maser is rather inefficient. Available in situ measurements indicate that the loss-cone maser plays only a minor role. Instead, the main source for any strong electron–cyclotron maser is found in the presence of a magnetic-field-aligned electric potential drop which has several effects: (1) it dilutes the local plasma to such an extent that the plasma enters the regime in which the electron–cyclotron maser becomes effective; (2) it generates energetic relativistic electron beams and field-aligned currents; (3) it deforms, together with the magnetic mirror force, the electron distribution function, thereby mimicking a high energy level sufficiently far above the Maxwellian ground state of an equilibrium plasma; (4) it favors emission in the free-space RX mode in a direction roughly perpendicular to the ambient magnetic field; (5) this emission is the most intense, since it implies the coherent resonant contribution of a maximum number of electrons in the distribution function to the radiation (i.e., to the generation of negative absorption); (6) it generates a large number of electron holes via the two-stream instability, and ion holes via the current-driven ion-acoustic instability which manifest themselves as subtle fine structures moving across the radiation spectrum and being typical for the electron–cyclotron maser emission process. These fine structures can thus be taken as the ultimate identifier of the electron–cyclotron maser. The auroral kilometric radiation of Earth is taken here as the paradigm for other manifestations of intense radio emissions such as the radiation from other planets in the solar system, from exoplanets, the Sun and other astrophysical objects.     

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.