2130MHz太阳射电望远镜中频放大器的调试

本文介绍云南天文台２１３０ＭＨｚ太阳射电望远镜中频放大器的结构原理，技术指标及测试结果。     

新疆天文台南山26米天线全息法测量系统

南山25 m射电望远镜经过一年多的升级改造现已全面完成,主反射面直径增加至26 m,为保证Q波段(30~50 GHz)接收机的工作效率,望远镜的表面精度需达到较高的水平,微波全息法可对天线面形进行精确测量和调整,是望远镜面形首次和定期精调的首选,基于新南山26 m天线建立了一套全息法测量系统。整个系统包括参考天线、接收机、相关机、传输链路、时频参考、扫描控制和全息法处理软件等几部分,采用带通采样技术直接采集中频信号,减少了基带信号转换环节;采用高性能外部本振并利用氢钟输出的参考信号进行锁相,达到了极高的相位稳定度。目前整个系统已通过测试并取得了初步的测量结果,经处理分析,该系统工作正常,已达到应用要求。     

德令哈毫米波望远镜本振谐波干扰问题

射电天文中,射频干扰问题多样而复杂,面对不同的射频干扰问题,针对不同的干扰机制,采取针对性的方法。从器件阶段消减射频干扰,可以预防射频干扰进入望远镜内部。介绍了德令哈毫米波望远镜9波束边带分离型超导接收机, 1个本振链路系统分配18路本振信号方案,针对本振链路中信号发生器的谐波信号引起的中频窄带干扰,设计了注入模拟谐波信号的测试方案,确认了干扰产生机制并得出谐波信号频率与干扰信号频率和功率的对应关系,分析并验证了谐波干扰的传输路径。为了消减谐波干扰,利用YIG滤波器可变频段的带通特性,在本振链路上滤除谐波信号,防止谐波信号耦合到接收机系统,完成了谐波干扰的消减。     

德令哈13.7m望远镜接收机抗射频干扰研究

在天文观测中,射频干扰会造成假谱,降低数据的可靠性和有效性.射频干扰消减旨在减少干扰信号对射电天文观测的影响,包含器件方面的技术革新和数据处理领域的方法研究.针对德令哈13.7 m望远镜接收机中频部分引入的射频干扰,通过优化中频器件的抗射频干扰能力,提高了接收机的整体抗射频干扰能力,以主动消除方法来减少射频干扰耦合到接收机内部.分析了接收机干扰的传输路径,提出了器件射频干扰的直接耦合系数和器件射频干扰的系统耦合系数的概念,为定位干扰敏感器件并量化干扰引入比重提供了基础.经过抗射频干扰优化后,接收机抗干扰能力改善30 dB左右,望远镜的天文观测效率提高10%以上.     

天马望远镜谱线OTF观测系统

OTF(On-The-Fly)观测模式是目前单天线最有效的谱线成图观测技术,广泛应用于单天线的谱线成图观测。主要介绍OTF观测模式在天马望远镜的实现情况。首先介绍天马望远镜OTF观测模式的观测过程和基本观测参数;接着分别对天马望远镜OTF观测系统的结构、观测控制软件、DIBAS(Digital Backend System)谱线终端、中频传输系统以及数据预处理软件进行介绍;最后给出对W3区域中的6条氢复合线的试观测结果。目前,天马望远镜的OTF观测系统已完成多次对外开放的谱线成图观测,均取得较好的观测结果,验证了该系统的有效性。     

800~975MHz太阳射电数字观测终端的设计与实现

位于云南天文台凤凰山本部的10 m太阳射电望远镜是中国太阳射电物理界重要的观测设备之一,其设计之初,800~975 MHz频段受到移动电话的严重干扰,不能正常工作,因此缺失这一频段的观测资料。近年来,随着微波和数字器件性能的提升以及移动电话工作频段的改变,使得这一重要频段的观测变得可行。针对800~975 MHz频段的太阳射电天文信号,提出了一种基于现场可编程门阵列(Field Programmable Gate Array,FPGA)和千兆以太网的实时采集与处理方法。在数据采集和处理过程中,系统采用流水线方式,得到了太阳射电信号的实时频谱图;采用硬件描述语言Verilog实现了千兆以太网的数据传输,提高了传输效率;另外本系统采用分时传输机制,完成千兆以太网的UDP数据包的传输。最后还对所得数据进行了误差分析和结果分析,证明了本文提出的实时信号采集、分析和传输方法的正确性和可靠性。     

VLBI数字基带转换器通道时延一致性的调整

VLBI数字基带转换器(Digital Baseband Convertor,简称DBBC)又称为CDAS(Chinese VLBI Data Acquisition System),是上海天文台自主研发的新一代数字化终端设备。该设备可以将宽带信号分成若干个基带信号。由于其结构上采用了多芯片和多板卡结构,使得通道之间的时延存在差异。从设备结构入手,分析了各通道之间时延差异产生的主要原因,提出以复位信号为参考,基于m序列的数据同步方法以解决该问题。通过实验,证明该方法能有效地改善同一中频上各通道间时延的差异。     

3521MHz太阳射电望远镜在云台安装调试报告(Ⅵ)(续前) Ⅵ 接收机系统及其主要技术指标的测试

本文报告了3521MHz太阳射电望远镜全晶体管化的接收机系统。文中给出了中频放大系统、低频放大系统、调制源及其电源的结构原理、技术指标、测试方法及主要技术指标的测试结果。最后报告了主要调试经验。     

太阳射电800~975MHz波段高动态范围模拟接收机的研制

介绍了云南天文台10 m太阳射电望远镜800~975 MHz模拟接收机的研制。接收系统采用射频-中频两级放大+远程控制步进衰减器模式,能方便地通过远程界面控制射频或中频链路的增益倍数,使得整个接收机动态范围在-35 dB-+25 dB。这样的设计防止在该频段强RFI信号造成的接收机饱和,并且获得了大动态范围,能够满足强射电爆发的要求,弥补了10 m射电望远镜的缺省频段。     

射电望远镜控制系统中的数据传输序列化分析

控制系统能衔接、集成和管理射电望远镜的软硬件系统。控制系统的序列化工具可以将射电望远镜的不同设备、操作系统、编程语言和网络之间传输的信息进行编码和解码,增强系统之间数据的传输效率。分析和比较了3款二进制序列化工具Msgpack,Protobuf和Flatbuffers的编码原理及特性,并通过一个实例测试了它们的序列化数据大小、序列化时间和中央处理器利用率。结果表明,Msgpack的综合性能优于Protobuf和Flatbuffers,适用于周期长、需求易变的射电望远镜系统之间传输信息的编码和解码。     

Impact of the Quadrupole Moment of the Sun on the Dynamics of the Earth-Moon System

Range of values of the Sun's mass quadrupole moment of coefficient J₂ arising both from experimental and theoretical determinations enlarge across literature on two orders of magnitude, from around 10^-7 until to 10^-5. The accurate knowledge of the Moon's physical librations, for which the Lunar Laser Ranging data reach an outstanding precision level, prove to be appropriate to reduce the interval of J₂ values by giving an upper bound of J₂. A solar quadrupole moment as high as 1.1 10^-5 given either from the upper bounds of the error bars of the observations, or from the Roche's theory, is not compatible with the knowledge of the lunar librations accurately modeled and observed with the LLR experiment. The suitable values of J₂ have to be smaller than 3.0 10^-6. As a consequence, this upper bound of 3.0 10^-6 is accepted to study the impact of the Sun's quadrupole moment of mass on the dynamics of the Earth-Moon system. Such as effect (with J₂ = 5.5±1.3 × 10^-6) has been already tested in 1983 by Campbell & Moffat using analytical approximate equations, and thus for the orbits of Mercury, Venus, the Earth and Icarus. The approximate equations are no longer sufficient compared with present observational data and exact equations are required. As if to compute the effect on the lunar librations, we have used our BJV relativistic model of solar system integration including the spin-orbit coupled motion of the Moon. The model is solved by numerical integration. The BJV model stems from general relativity by using the DSX formalism for purposes of celestial mechanics when it is about to deal with a system of n extended, weakly self-gravitating, rotating and deformable bodies in mutual interactions. The resulting effects on the orbital elements of the Earth have been computed and plotted over 160 and 1600 years. The impact of the quadrupole moment of the Sun on the Earth's orbital motion is mainly characterized by variations of , , and . As a consequence, the Sun's quadrupole moment of mass could play a sensible role over long time periods of integration of solar system models. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the role of the motion of the photospheric footpoints of the magnetic field lines

By means of a simple relation between the velocity v of the fluid particle and the velocity v_f of the photospheric footpoint of the magnetic field line v_z and B_z being respectively the components of v and the magnetic field B normal to the photospheric surface, it is shown formally that through the phtospheric surface the transport of all the quantities attributed to the magnetic field, such as the magnetic flux, the magnetic energy and the helicity, is independent of v_z, and v_f is the only kinematical quantity on which the transport depends. In addition, in the neighborhood of the neutral line the velocity v_l of the moving curve of constant B_z is found to be equal approximately to the component of v or v_f in the direction of v_l. Since v_l can be measured or extimated, so can the components of v and v_f near the neutral line.     

在后牛顿引力理论(PPN形式)中引力常数变化对地球自转产生的效应

介绍和论述了在后牛顿引力理论(PPN形式)中在优越参考系和非优越参考系中经过参数化后引力常数变化对地球自转产生的效应,其中特别重点介绍了年周期变化的效应。此外也将理论结果同观测结果相对比。     

On the theory of the oblateness of the Sun

In this paper we first emphasize why it is important to know the successive zonal harmonics of the Sun's figure with high accuracy: mainly fundamental astrometry, helioseismology, planetary motions and relativistic effects. Then we briefly comment why the Sun appears oblate, going back to primitive definitions in order to underline some discrepancies in theories and to emphasize again the relevant hypotheses. We propose a new theoretical approach entirely based on an expansion in terms of Legendre's functions, including the differential rotation of the Sun at the surface. This permits linking the two first spherical harmonic coefficients (J ₂ and J ₄) with the geometric parameters that can be measured on the Sun (equatorial and polar radii). We emphasize the difficulties in inferring gravitational oblateness from visual measurements of the geometric oblateness, and more generally a dynamical flattening. Results are given for different observed rotational laws. It is shown that the surface oblateness is surely upper bounded by 11 milliarcsecond. As a consequence of the observed surface and sub-surface differential rotation laws, we deduce a measure of the two first gravitational harmonics, the quadrupole and the octopole moment of the Sun: J ₂=−(6.13±2.52)×10⁻⁷ if all observed data are taken into account, and respectively, J ₂=−(6.84±3.75)×10⁻⁷ if only sunspot data are considered, and J ₂=−(3.49±1.86)×10⁻⁷ in the case of helioseismic data alone. The value deduced from all available data for the octopole is: J ₄=(2.8±2.1)×10⁻¹². These values are compared to some others found in the literature. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005238718479     

射电日像仪灵敏度测量

灵敏度是射电望远镜的一个重要性能指标,它反映了望远镜监测弱信号的能力。基于明安图射电频谱日像仪(Mingantu Ultrawide Spectral Radioheliograph,MUSER)的调试观测,给出了日像仪灵敏度的测量方法,对天线系统以及整个阵列的灵敏度进行测量分析,得到了日像仪系统整体的灵敏度性能参数。测量同时给出了天线系统的效率以及接收机系统的增益,这将为下一步日像仪展开常规的科学观测提供参考。     

Third Integral and the Dynamics of the Galaxy in the Neighborhood of the Sun

Observational data on the dynamics of stars in the neighborhood of the sun indicate the existence of a third integral besides the integrals of the angular momentum and energy. The Poincaré integral is proposed as a third integral. The consequences of this assumption are derived and compared with available astrophysical data.     

Accounting for the viscosity of the fluid core in the problem of the physical libration of the moon

A two-component theoretical model of the physical libration of the Moon in longitude is constructed with account taken of the viscosity of the core. In the new version, a hydrodynamic problem of motion of a fluid filling a solid rotating shell is solved. It is found that surfaces of equal angular velocity are spherical, and a velocity field of the fluid core of the Moon is described by elementary functions. A distribution of the internal pressure in the core is found. An angular momentum exchange between the fluid core and solid mantle is described by a third-order differential equation with a right-hand side. The roots of a characteristic equation are studied and the stability of rotation is proved. A libration angle as a function of time is found using the derived solution of the differential equation. Limiting cases of infinitely large and infinitely small viscosity are considered and an effect of lag of a libration phase from a phase of action of an external moment of forces is ascertained. This makes it possible to estimate the viscosity and sizes of the lunar fluid core from data of observations.     

太阳质量损失对地球轨道改变的长期影响的估计

研究了太阳质量损失对地球轨道改变的长期影响。太阳质量损失包括太阳因光于辐射和太阳风流失两方面产生的质量损失。利用二体问题的中心体变质量的Jeans理论估计了太阳目前在主序阶段和将来后主序 (红巨星 )阶段由于上述两种机制造成的质量损失对地球轨道改变的长期效应。计算结果表明 :太阳质量损失在主序阶段对地球轨道改变的影响较小 ,但在后主序阶段对地球轨道改变的影响甚大 ,且此估计只是一种理论预测。