太阳微波爆发中精细结构的统计研究

本文总结了北京天文台1991年的2840MHz波段微波爆发中精细结构（FS）事件的观测．从FS的时间标度、强度、共生的微波爆发的峰值流量、FS发生在微波爆发的相位和FS与Hα耀斑的关系等方面作了统计分析．发现约67％以上的FS其持续时间为几十毫秒到几百毫秒，85％以上的FS幅度小于200sfu．讨论了FS的时标、强度及22周太阳峰年期与21周FS出现率的差别．     

Rfi Mitigation And The Ska

Radio frequency interference (RFI) has plagued radio astronomy from its inception. The Workshop on the Mitigation of Radio Frequency Interference in Radio Astronomy (RFI2004) was held in Penticton, BC, Canada in July 2004 in order to consider the prognosis for the RFI problem, in particular as it impacts the planned Square Kilometre Array (SKA). This paper concludes that RFI is unlikely to be a “showstopper” in achieving SKA science goals, but that improved RFI mitigation technology may nevertheless be essential in order to take advantage of the vastly improved sensitivity, bandwidth, and field of view. Reported results provide some optimism that the desired improvements in RFI mitigation technology are possible, but indicate that much more work is required.     

Ska and Evla Computing Costs for Wide Field Imaging

I investigate the problem of high dynamic range continuum synthesis imaging in the presence of confusing sources, using scaling arguments and simulations. I derive a quantified cost equation for the computer hardware needed to support such observations for the EVLA and the SKA. This cost has two main components – from the data volume, scaling as D⁻⁶ (where D is the antenna diameter), and from the non-coplanar baselines effect, scaling as D⁻², for a total scaling of D⁻⁸. A factor of two in antenna diameter thus corresponds to 12 years of Moore’s law (18 month doubling time) cost reduction in computing hardware. For a SKA built with 12.5 m antennas observing with 1 arcsecond at 1.4 GHz, I find the computing load to be about 150 Petaflops (costing about $500 million in 2015). For 25 m antennas, the load is about 256 times lower, costing $2 million in 2015. This new cost equation differs from that of Perley and Clark (2003), which has scaling as D⁻⁶. This is because I find that the excellent Fourier plane coverage of the small antenna design does not significantly change the convergence rate of the Clean algorithm, which is already satisfactory in this regime.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.     

日冕分米波射电甚短周期脉动的观测证据

利用国家天文台云南天文台“分米波(700—1500MHz)射电频谱仪”和“四波段太阳射电高时间分辨率同步观测系统”分别于2001年6月24日和1990年7月30日观测到了两个稀少事件，前者是一个小射电爆发，其上升相伴随有短周期(约29、40和100毫秒)的脉动，后者是一个射电大爆发，在2840MHz上产生了周期约30毫秒的射电脉动，还着重讨论其甚短周期(如29—40毫秒)的脉动现象，甚短周期脉动可能是归因于起源在日冕深处不稳定区域的哨声波束周期链对射电辐射的调制，或沉降电子束驱动的静电高混杂波，经由波-波非线性相互作用导致甚短周期的射电脉动。     

BLO 0716＋714射电和光学快速变化的相关性及其含义

本文讨论ＢＬＯ０７１６＋７１４中观测到的光学和射电快速变化（ＩＤＶ）的相关性及可能的解释。详细的分析表明，这种相关性有三个特点：（１）光学变化和５ＧＨｚ射电变化呈反相关，即光学极大和５ＧＨｚ射电极小相对应，反之亦然；（２）光学变化和射电频谱指数α＿５￣（８．３）的变化相关，具体他说，光学的增强和极大都与射电频谱反转频率向高频的位移有关；（３）光学和射电都有～１天的准周期变化，特别是射电频谱指数α８５·３的变化维持了大约７个准周期。上述相关的光学和射电快速变化可以在相对论喷流的框架下作出解释。作者提出，这类现象可能与激波在磁约束的准周期振荡的相对论喷流中的传播有关。     

Thirty-Element Active Antenna Array as a Prototype of a Huge Low-Frequency Radio Telescope

An effective wide-band (10 to 60 MHz) active antenna element has been developed. The cost of one short (3 m), thin dipole with built-in amplifier and metal construction is less than 45 euro. It was shown both theoretically and experimentally that the upper limiting frequency is at least 60 MHz, the dynamic range is 90 dB/V and the share of the amplifier noise to the background antenna temperature is about 10%. The developed active dipole was tested by building a 30-element antenna array and comparing its parameters with one of the subpart of the UTR-2 radio telescope having passive dipoles of 8.6 m in length and 1.8 m in diameter. The 3C461 ionospheric scintillation spectra observed in the experiments show that the sensitivities and noise-immunities of both antennas are close. This proves the availability using of a short cheap active dipole in new generation giant radio telescopes.     

Optical brightness variability of LSI+61°303: Improving the photometric period

The U BV observations of the variable radio source LSI+61°303 carried out at the Crimean Station of the Sternberg Astronomical Institute in 1989–1990 and 1999–2002 are presented. We constructed a combined light curve of the star spanning ～6400 days from our and published data. Slow brightness variability with an amplitude of \( \sim 0^m .1\) was detected. Using the entire combined series, we searched for a periodicity in a frequency range close to the radio period \(P = 26^d .5\). The optical period was found to be exactly equal to the radio period. The shape and amplitude of the mean curves constructed with the radio period change from V to U: the detected double wave shows up most clearly in the U band.     

Diagnosing the effective parameters of the ionospheric fine structure from statistical characteristics of radio waves in the vicinity of a regular caustic

This paper is concerned with the oblique propagation of decametric radio waves in the ionosphere with random electron density irregularities. Effective parameters are introduced for calculating the influence of irregularities on the wave field structure. A technique is proposed for determining these parameters from measurements of statistical characteristics of the signal in the vicinity of a regular caustic. The technique uses asymptotic expressions obtained using the interference integral method and perturbation theory, as well as matching them to the numerical solution on the basis of the method of characteristics. A global semi-empirical model that is updated for current ionospheric conditions is used to specify the background medium. The proposed technique has been tested using data from a number of mid-latitude paths. Results obtained in this study testify that the technique deserves a practical implementation.     

全球定位系统(GPS)的最新进展(下)

3　动态 GPS定位自从利用 GPS载波相位观测的机载动态定位于 1 985年第一次得到证实之后 ,可靠的 GPS解支持航空摄影测量、遥感活动和地球物理测量的能力显著改进了。这些改进来源于若干因素的综合 :第一 ,运动 GPS接收机可以跟踪 8颗或更多颗卫星 ;第二 ,可以得到精密星历供后处理之用 ;第三 ,提出了一些算法 ,它们能以少量的相位和伪距观测量在运动中初置相位偏差。这些因素综合起来 ,产生了精确到厘米级的动态定位能力。这就是动态 GPS定位技术。它可以把距离延伸到约 1 0 0 km。采用 KARS( Kine-matic And Rapid Static)程序…