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.     

康普顿化的计算-推广的Kompaneets方程与Monte Carlo方法比较

在X射线天文学以及辐射物理学中,当硬X射线穿过" 冷"的等离子体时所发生的Compton软化是一种重要的辐射转移过程.简要介绍推广的Kompaneets方程,该方程在hv〈mec2及kTe〈mec2较宽松的条件下广泛成立,因此不仅能处理Compton硬化过程,而且也适用于Compton软化过程,后者在目前快速发展的X射线和γ射线天文学中十分重要.基于此方程,我们对天体物理中4种常见辐射谱(Gauss型发射谱线、黑体辐射谱、幂律辐射谱和热轫致辐射谱)在Compton软化情况下的谱演化进行了数值求解,并同Monte Carlo模拟结果做比较,证实了推广的Kompaneets方程的正确性和有效性.最后指出此方程在X射线天文学和γ射线天文学中的重要意义和潜在应用.     

利用雷达资料反演方法对北京地区一次强对流天气过程的分析

利用多普勒雷达变分分析系统(VDRAS),对2006年8月1日傍晚北京城区出现的一次强对流天气过程(伴有冰雹、大风及强降水)的三维风场、温度场进行了初步分析.结果表明:(1)初始对流生成于北京西北部山区的河北省境内,系统过山移进北京城区时,受局地的动力及热力条件作用,迅速组织并强烈发展,形成带状的MCS即飑线;(2)在飑线生成之前,北京城区及东南部边界层低层存在较强的东风气流,并迅速扩展向西北方向延伸,与过山的西北偏北气流形成强的边界层辐合线.该近地面辐合线是飑线生成的主要触发机制,而边界层低层东风的加强和减弱以及北进和南退对辐合线的维持、飑线的生成、发展和减弱都起着重要的作用;(3)在边界层辐合线的作用下,不断有新生对流系统发展;(4)对流系统在整个发展过程中呈明显的带状分布特征,是一次典型的飑线过程,并伴有明显的阵风锋.     

哈雷彗星的羟基射电谱线观测

本文主要论述用25米射电望远镜和自相关频谱仪于1986年4月13—17日(UT)期间在我国陕西眉县首次对哈雷彗星羟基分子1667 MHz射电话线的观测及归算结果。由谱线轮廓的幅度、宽度、形状和面积相继导出的谱线强度为-2.4Jy,膨胀速度为0.92kms~(-1),速度的一级矩为0.20kms~(-1),以及羟基的母分子产生率为1.7×10~(29)mols~(-1)。文中所给出的宇宙羟基源W3和W12的观测结果,分别用来检验设备系统探测射电谱线的功能及对哈雷彗星的羟基谱线进行强度定标。这些结果均同理论预期或以往的有关观测相符合。     

Radiative acceleration of coronal gas in Seyfert nuclei

The line ratios from coronal gas in Seyferts can be successfully fitted with photoionized clouds of high densities and low volume filling factor. The ionization parameter implied is sufficiently high that models must consider the effect of radiation pressure from the active nucleus. In spite of the gravitational force of the nucleus, radiation pressure is sufficiently strong to compress and radially accelerate the internally stratified gas clouds provided that these contain small amounts of dust (≃ 10 per cent of the solar neighbourhood value). This radial acceleration could explain the blueshift of the coronal lines relative to the systemic velocity without the need to invoke an ambient 'pushing' wind. Embedded dust has the interesting effect of making the photoionized clouds marginally ionization-bounded instead of matter-bounded.     

Solar EUV line identifications from delayed beam-foil spectra

A number of electric dipole transitions from low-lying long-lived levels in Si-, P- and S-like ions of Fe and neighbouring elements have been identified by their longevity in delayed EUV spectra after foil excitation of fast ion beams. Some of these new identifications pertain to previously unidentified lines in solar flare spectra.     

Combining optical spectroscopy and interferometry

Modern optical spectrographs and optical interferometers push the limits in the spectral and spatial regime, providing important new tools for the exploration of the Universe. In this contribution I outline the complementary nature of spectroscopic and interferometric observations and discuss different strategies for combining such data. Most remarkable, the latest generation of “spectro‐interferometric” instruments combine the milliarcsecond angular resolution achievable with interferometry with spectral capabilities, enabling direct constraints on the distribution, density, kinematics, and ionization structure of the gas component in protoplanetary disks. I will present some selected studies from the field of star‐ and planet formation and hot star research in order to illustrate these fundamentally new observational opportunities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Monte Carlo Simulation of Lyα Line Profiles

In this paper, a code for simulating the Lyα line profiles by the Monte Carlo method is introduced. This code is developed on the basis of an idea given by Anne Verhamme et al. and by combining with another simulation method. For different models, the Lyα line profiles under different conditions are simulated. The simulation method of this code is given in detail, and the simulated results are discussed as well.