Emission-line CCD imaging of three southern symbiotic stars

Symbiotic stars that are strong radio sources and have cool dust emitting in the infrared are expected to have extended emission nebulae around them. In order to search for such emission nebulae, we have carried out CCD imaging of three symbiotic stars (R Aqr, RR Tel and H1-36) with narrow-band filters centred at the emission lines of [O III] λ5007, Hα λ6563, [N II] λ6584, [S II] λ6717 + 6731. RR Tel and H1-36 images do not show any extended nebulosities around them. The CCD image of the R Aqr nebulosity in the high excitation [O m] line is different from its image in Hα and the low excitation lines of [N II] and [S II] indicating ionization-stratification in the nebula. In H1-36 the optical nebulosity (if it exists) is smaller than ∽2 arcsec while the radio image size is known to be large (∽5 arcsec). This behaviour is opposite to that seen in R Aqr in which the radio emission comes from the core region of a much larger optical nebulosity. Interstellar and/or circumstellar extinctions are suggested to be responsible for this difference     

光学系统参数确定带宽约束的天文图像盲反卷积

大气湍流极大限制了地基大口径望远镜观测天文目标图像的空间分辨率.根据最大似然估计原理,提出了用实际光学带宽约束的可有效减小天文观测图像中大气湍流影响的盲反卷积方法,通过共轭梯度优化算法使卷积误差函数趋向最小.建立了望远镜光学系统参数和图像频域带宽的关系,采用变量正性约束、点扩散函数带宽有限约束,提高算法的收敛性.为避免图像处理中有效傅立叶变换频率超出截止频率,要求采集望远镜焦面图像时单个成像单元(如CCD像素单元)应小于四分之一衍射斑直径.算法中未用目标支持域约束,所提出的方法适用于全视场天文图像恢复.用计算机模拟和对实际天文目标双鱼座图像数据的恢复结果验证了所提出方法的有效性.     

Improved astrometry of space debris with image restoration

In order to implement an observing strategy,image degradation that occurs during optical observation of space debris is ineluctable and has distinct characteristics. Image restoration is presented as a way to remove the influence of degradation in CCD images of space debris,based on assumed PSF models with the same FWHM as images of the object. In the process of image restoration,the maximum entropy method is adopted. The results of reduction using observed raw CCD images indicate that the precision in estimating positions of objects is improved and the effects of degradation are reduced. Improving the astrometry of space debris using image restoration is effective and feasible.     

Multi-resolution imaging and spectra of extended sources

I introduce a straightforward technique for the filtering of extended astronomical images into components of different spatial scales. For a positive original image, each component is positive definite, and the sum of all components equals the original image. In this way, the components are each individually suitable for flux measurements and broadband spectra calculations. I present an illustration of this technique on the radio galaxy Cygnus A.     

Evidence for parsec-scale absorption from VSOP observations of the BL Lacertae object 0735+178

VLBI total intensity and linear polarization images of the BL Lacertae object 0735+178 have been obtained at     using the     VLA as a ground array together with the HALCA orbiting antenna, and at     about a month later using the VLBA. The most surprising result to come from a comparison of these two images, which have nearly equivalent resolution, is that the path of the jet appears to be appreciably different at the two wavelengths. We have interpreted this as evidence for free–free absorption to the east of the core, near a bend of about 90° in the 2-cm image where the emission is very weak in the 6-cm image. Overall, the polarization structures seen in corresponding regions at the two wavelengths are in good agreement. We find tentative evidence for enhanced rotation measures near two sharp bends in the VLBI jet.     

Magnetic Stereoscopy

The space mission Solar TErrestrial RElations Observatory (STEREO) will provide images from two viewpoints. An important aim of the STEREO mission is to get a 3D view of the solar corona. We develop a program for the stereoscopic reconstruction of 3D coronal loops from images taken with the two STEREO spacecraft. A pure geometric triangulation of coronal features leads to ambiguities because the dilute plasma emissions complicates the association of features in image 1 with features in image 2. As a consequence of these problems, the stereoscopic reconstruction is not unique and multiple solutions occur. We demonstrate how these ambiguities can be resolved with the help of different coronal magnetic field models (potential, linear, and non-linear force-free fields). The idea is that, due to the high conductivity in the coronal plasma, the emitting plasma outlines the magnetic field lines. Consequently, the 3D coronal magnetic field provides a proxy for the stereoscopy, which allows to eliminate inconsistent configurations. The combination of stereoscopy and magnetic modelling is more powerful than one of these tools alone. We test our method with the help of a model active region and plan to apply it to the solar case as soon as STEREO data become available.     

Monte Carlo simulations of the broad-band X-ray continuum of SS433

We develop a Monte Carlo technique based on L.B. Lucy's indivisible photon packets method to calculate X-ray continuum spectra of Comptonized thermal plasma in arbitrary geometry and apply it to describe the broad-band X-ray continuum of the galactic superaccreting microquasar SS433 observed by INTEGRAL . A physical model of the X-ray emitting region is proposed that includes thermal emission from the accretion disc, jets and hot corona where the photons of different origin are Comptonized. From comparison with INTEGRAL observations, we estimate physical parameters of the complex X-ray emitting region in SS433 and present model spectra for different viewing angles of the object.     

太阳宁静区的高分辨率像复原

本文介绍在怀柔６０ｃｍ多通道太阳望远镜上运用斑点干涉像复原方法所取得的一些初步结果,对用短暴光方法（暴光时间不大于１０毫秒）获得的一系列“冻结”大气后的目标像用斑点干涉像复原方法进行处理,即可获得消除了地球大气影响的目标复原像,斑点掩模法即为斑点干涉像复原方法的一种,我们用它对日面中心的宁静区米粒进行处理,复原出了分率不劣于０．〃５的白光米粒象。     

The robust detection of stars on CCD images

Two parameters are developed to analyze the CCD images from ground-based and/or space telescopes. The first parameter, deduced from the intensity profile of the object sharp, is useful to resolve stars and hot pixels. The second parameter shape distinguishes the stars from the background cosmic-ray events using geometric characteristics defined by its shapes. The parameters are applied to a simulated OMC/INTEGRAL image and a HST image.     

Software for producing trichromatic images in astronomy

We present a software package for combining three monochromatic images of an astronomical object into a trichromatic color image. We first discuss the meaning of true colors in astronomical images. We then describe the different steps of our method, choosing the relevant dynamic intensity range in each filter, inventorying the different colors, optimizing the color map, modifying the balance of colors, and enhancing contrasts at low intensity levels. While the first steps are automatic, the last two are interactive.     

Research on Improving SNR of Large Angle Synchronous Satellite Based on Sub-pixel Translation and Superposition

Geosynchronous satellite with big inclination is not completely stationary relative to the ground. Its sub-satellite point moves periodically in the north-south direction with ground track of shape like “8”. The larger the inclination angle is, the larger the range of motion is. Such effect makes the effective exposure time of Geosynchronous satellite limited when observe it by optical telescope with stare mode, and the SNR (Signal Noise Ratio) of Geosynchronous satellite image could not be increased with long exposure time. In the monitoring of Geosynchronous orbit without changing hardware, a method called sub-pixel translating superposition of successive frames of images is proposed. By translating and aligning images in the sub-pixel scale according to the moving speed of the object and the time interval of the adjacent frame images, the positions of the Geosynchronous satellite in the image sequences are coincident, and then by superposition of these translational images, the SNR of moving Geosynchronous objects and the detection capability of the whole system can be improved. Results of superposition of real observed images show that the method can remarkably improve the SNR of moving. When five images are superimposed, compared with the SNR of the original image, the SNR of the superimposed image by integer pixels is increased by around 1.7 times, and the SNR of the superimposed image by sub-pixel is increased by about 2 times.     

基于大视场反卷积的天文图像叠加方法

地基望远镜在成像过程中,由于受大气湍流、望远镜静态像差、跟踪误差、指向误差及视场变化的影响,不同视场区域的PSF (Point Spread Function)具有差异;同时,不同望远镜获取的图像PSF也存在差异.将多个望远镜获取的星象直接叠加至相同的区域后,图像质量受像质最差的望远镜限制,最终观测分辨率和灵敏度均会受到影响.通过图像复原,可以提高图像质量,进而提高叠加效果.根据该思路提出了1种基于PSF分区的迭代图像复原方法:该方法首先通过SOM (Self-organizing Maps)对PSF进行聚类分析,利用同类别PSF的平均PSF进行反卷积,再将反卷积结果按PSF聚类结果分割为不同大小的子图,最后将子图进行拼接.图像复原在提高图像质量的同时,降低了PSF不一致性对图像叠加带来的影响.将几个望远镜在同一时刻获取的图像经反卷积处理之后利用图像配准算法进行矫正并叠加,可获得高信噪比图像.对实际望远镜获取的数据处理后的结果表明:图像在进行复原和叠加过程中,星象目标信噪比不断提升,提高了成像系统对暗星的探测能力.     

Quasi-stereoscopic imaging of the solar X-ray corona

The first published three-dimensional images of the solar X-ray corona, obtained by means of solar rotational parallax, are presented in stereographic form. Image pairs approximately 12 hours apart during times of stable coronal conditions were selected from the digitized images obtained with theSkylab X-ray Spectrographic Telescope. The image resolution limit is approximately 10 arc sec. Many coronal structures not visible in the separate images are clearly observed when the image pairs are viewed stereoscopically. This method gives a preview of the potential resources for solar research and forecasting of solar-geomagnetic interactions that could be provided by stereoscopic observations of the Sun using a small group of spacecraft. The method is also applicable to other X-ray, ultraviolet, or other wavebands in which the corona has extended, transparent structure.     

由斑点图重建天文图像的方法

首先介绍了斑点图形成机制以及获取方法,并借助计算机模拟了斑点图的生成。然后重点描述斑点图的图像重建方法,包括频率域和空间域重建方法。在频率域重建方法部分依次详细叙述了用于复原模信息的斑点干涉法和用于复原相位信息的由模复原相位法、Knox-Thompson法、斑点掩模法;空间域重建方法部分介绍了典型的LWH法和迭代位移叠加法;另外,盲消卷积法也为斑点图重建提供了新的思路,文章对此方法也做了介绍;特别地,还对国内在该领域的相关工作做了介绍;关于斑点图重建方法在天文学、天体物理学等领域的应用,文章做了有针对性的介绍;最后一章是斑点图图像重建方法的总结。     

低对比度扩展目标跟踪算法

针对如太阳表面米粒结构和太阳黑子这类低对比度扩展目标，研究了互相关因子和绝对差分两种跟踪算法的有效性，并给出了根据所采集的图像进行后处理所得到的小整体倾斜信号，此外还比较了去除整体倾斜前后的太阳表面米粒结构长曝光像的对比度。     

CLASS B 1359 + 154: Modelling lensing by a group of galaxies

The recently discovered gravitationally lensed system CLASS B1359 +154 appears to have six detectable images of a single background source at a redshift of 3.235. A group of galaxies acts as the lens, at a redshift of ∼ 1. The present work identifies two distinct, physically plausible image configurations, a 7-image one and a 9-image one. Mass models are constructed corresponding to realizations of these two configurations. Both models call for, in addition to non-singular galaxy-type lenses, a larger scale mass component that resembles the extended dark matter distributions seen in relatively low-redshift galaxy groups. It is presently observationally impossible to study the extended X-ray emission from a group at such a high redshift, hence lensing studies are of some interest. A lensed system with a high image multiplicity does not necessarily admit of a unique lensing interpretation; discrimination is possible with additional observable details (e.g., the image parities, which are uncommon among even the simpler systems).     

Infrared polarimetry and imaging of ultracompact partially ionized optical sources in the orion nebula

Hubble Space Telescope images of the Orion nebula taken with the Wide-Field Camera have revealed subarcsecond structure in several dozen objects which are apparently ionized externally from nearby stars. We have obtained near-IR images and IR polarimetry of the Orion region to search for correlations with the WFC objects. We find that all of the ultracompact WFC objects are associated with IR features of some sort, and that some are associated with strongly polarized IR emission. The object with strongest polarization also shows small IR lobes. In addition, we find some previously unreported sources, showing polarized IR emission, outside the field of the HST images, which we believe may be the same sorts of object. We note that the object with strongest polarization has a double-lobed appearance in the K band image.     

基于亚像素图像平移叠加提高大倾角同步卫星信噪比的方法研究

大倾角地球同步轨道(GEO)卫星相对地面并非完全静止,其星下点做南北方向的"8"字周期运动,倾角越大运动范围越大.这会降低地面望远镜对其进行凝视观测时的有效曝光时间,无法获得较高的信噪比.对地球同步轨道的监测中,在硬件条件不变的前提下,提出亚像素图像平移叠加方法.根据目标的运动速度和相邻帧图像的时间间隔,在亚像素尺度平移并对齐多幅图像,使GEO目标星象在图像序列中的位置重合,通过叠加多幅序列图像来提高目标信噪比,从而达到提升整个系统探测能力的目的.实测图像叠加结果表明,该方法可以显著提高该类目标的信噪比.叠加5幅图像时,整数像素叠加图像的信噪比约为原图像的1.7倍,而亚像素叠加图像的信噪比是原图像的2倍左右.