Extragalactic Astronomy with the VLTI: a new window on the Universe

Interferometry in the optical and near infrared has so far played a marginal role in Extragalactic Astronomy. Active Galactic Nuclei are the brightest and most compact extragalactic sources, nonetheless only a very limited number could be studied with speckle interferometry and none with long baseline interferometry. The VLTI will allow the study of moderately faint extragalactic objects with very high spatial resolution thus opening a new window on the universe. With this paper we focus on three scientific cases to show how AMBER and MIDI can be used to tackle open issues in extragalactic astronomy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Jets in the Fanaroff–Riley class I radio galaxies PKS B1234−723, MRC 1452−517 and PKS B2148−555

We present radio observations made with the Australia Telescope Compact Array to study the jets and lobes of three Fanaroff–Riley class I (FR I) radio galaxies: PKS B1234−723, 1452−517 and B2148−555. The total intensity and polarization radio images of the FR I jets are used to determine jet brightness and width variations, magnetic field structure and fractional polarization. The equipartition pressure is determined as a function of distance from the galaxies to probe the intergalactic medium.     

VLA observations of extreme hydrogen deficient stars

VLA observations at 2 and 6 cm have been obtained for six hydrogen-deficient stars R CrB, HD 160641, BD — 9°4395, V348 Sgr, MV Sgr and Sgrv Upper limits to the massloss rates have been estimated for some of these using the upper limits to the radio flux density. National Radio Astronomy Observatory’s Very Large Array is operated by Associated Universities Inc. under contract with National Science Foundation, USA     

Harmonic Structures of Gyrosynchrotron Radiation and Cyclotron Maser Instability

1 INTRODUCTIONSolar microwave bursts are usually produced by dtherellt radiation mechanisxns: gyroresonance absorption, Coulomb brernsstrahlung of the thermal baCkground plasma, as well asgyrosynchrotron radiation of the nonihermal electrons (Hildebrandt et al. 1998). Meanwhile,cyclotron or synchrotron maser instabilities may be responsible for microwave spaaes, blips, andtype ill bursts (Wu 1985; Huang 1987; Huang et al. 1996; Huang 1998), which are usuajly superposed on the ambient mi…     

Advances in Numerical Modeling of Astrophysical and Space Plasmas

Advances in the simulation of astrophysical and cosmic plasmas are the direct result of advances in computational capabilities, today consisting of new techniques such as multilevel concurrent simulation, multi-teraflop computational platforms and experimental facilities for producing and diagnosing plasmas under extreme conditions for the benchmarking of simulations. Examples of these are the treatment of mesoscalic plasma and the scaling to astrophysical and cosmic dimensions and the Accelerated Strategic Computing Initiative whose goal is to construct petaflop (10¹⁵ floating operations per second) computers, and pulsed power and laser inertial confinement plasmas where megajoules of energy are delivered to highly-diagnosed plasmas. This paper concentrates on the achievements to date in simulating and experimentally producing plasmas scaled to both astrophysical and cosmic plasma dimensions. A previous paper (Part I, Peratt, 1997) outlines the algorithms and computational growth.     

Solar Type III Bursts and the Generation of Backward Langmuir Wave

It is generally believed that the conversion of Langmuir wave (LW) to electromagnetic wave is the generating mechanism of solar type III bursts. The Langmuir wave can be easily excited by the instability of the electron-beam current, and the interaction of the forward and backward Langmuir waves is considered to be the cause for the second harmonic of a type III burst, but, so far, the dispersion equation and generating mechanism of the backward Langmuir wave have not yet been thoroughly studied. For the equation of two-stream instability with temperature included, an analytical solution is derived. It is found that the dispersion relation of the forward LW strongly depends on the beam-current speed, while that of the backward LW depends only on the thermal velocity, when the other parameters are fixed. These analytical results are partially confirmed by particle-in-cell (PIC) simulations. With the PIC simulation, the generating mechanism of the backward LW is studied, and it is revealed that the backward LW can not be excited directly by the electron-beam current, and that its energy is obtained basically from the scattering of the forward LW. However, the electron-beam current does cause a direct amplification of the second harmonic of the forward LW.     

对称模式下的CHAMP弯曲角掩星数据同化

简单介绍了无线电掩星技术探测行星大气的发展史,列举了该技术中存在的若干问题。从 Eyre提出的统计学的最优估计反演方法,比较了用相位、弯曲角和折射率作为同化因子时出现的问题和各自的优缺点。对弯曲角同化因子,以欧洲中期天气预报中心(ECMWF)资料为背景场,运用一维变分技术,进行CHAMP掩星观测资料变分同化反演,从而获得水汽和温度剖面。将反演获得的气象剖面与非同化的剖面作比较,并且采用相应的探空气球资料作为验证,可以看出变分同化技术比传统的标准反演技术反演误差小。证实掩星数据资料的一维变分同化技术可以改进目前的数值天气预报模式。