低纬子午环配备CCD探测器(Ⅰ)——观测原理

这一组文章,从观测原理、各种仪器常数和误差测定方法的叙述到测定精度的估计,系统地论述了在低纬子午环上配备CCD探测器后将能达到的绝对定位精度及其对建立高精度天球参考架的作用。文章(Ⅰ)中简述了充分发挥地面观测优势的途径,低纬子午环配备CCD探测器后的观测方式、星过时刻和天顶距的计算公式,还估算了在小角天体测量中相对位置的测定精度,并且得出,采用了CCD探测器后,降低了对测微器的跟踪精度要求。     

低纬子午环配备CCD相对定位精度的估计

本文给出了利用计算机模拟方法对低纬子午环配备CCD探测器进行高精度测量中CCD相对定位精度的估计,并对所得到的结果进行了初步分析。     

土星卫星运动的现代理论和CCD观测定标归算

在目前土卫CCD观测中，采用亮卫星的理论值定标的方法已被广泛采用，然面如何尽可能减小理论引入的误差对定标的影响仍是一个有待研究的问题，在最新研究中，采用3000多个最新的CCD观测对4个土卫现代理论作实算分析和比较，并由对归算结果的初步分析得出一些有价值的结论。     

CCD联合平差方法及其初步实例检验

在常规照相天体测量工作中 ,对暗天体的定位是采用逐级定标星过渡的方法实现的。由于星表系统差和局部差的存在 ,最终定位结果可能包含难以把握的误差积累。在CCD小视场观测情况下时常难以找到足够数量的定标星。鉴于此 ,推导了CCD观测联合平差方法的严格矢量表达式 ,以期通过共同星的过渡 ,实现大天区统一平差。原理上此方法可实现相对于河外天体的定位 ,以削弱星表系统差和局部差对定位结果的影响。讨论了CCD联合平差方法实现中的问题 ,包括底片常数模型选择、切点位置改正、共同星的较差改正和法方程解算方法等 ,并分析了具体的处理措施。用实例初步检验了CCD联合平差方法的效果 ,表明通过对多张CCD观测的联合平差 ,可以削弱单张CCD观测参考星数目过少、单张CCD观测参考星分布不均、个别参考星存在位置偏差和局部区域参考星存在系统性位置偏差等不利因素对归算结果的影响 ,进而达到扩大视场和提高归算精度的目的     

CCD联合平差方法及其初步实例检验

在常规照相天体测量工作中，对暗天体的定位是采用逐级定标星过渡的方法实现的。由于星表系统差和局部差的存在，最终定位结果可能包含难以把握的误差积累。在CCD小视场观测情况下时常难以找到足够数量的定标星。鉴于此，推导了CCD观测联合平差方法的严格矢量表达式，以期通过共同星的过渡，实现大天区统一平差。原理上此方法可实现相对于河外天体的定位，以削弱星表系统差和局部差对定位结果的影响。讨论了CCD联合平差方法实现中的问题，包括底片常数模型选择、切点位置改正、共同星的较差改正和法方程解算方法等，并分析了具体的处理措施。用实例初步检验了CCD联合平差方法的效果，表明通过对多张CCD观测的联合平差，可以削弱单张CCD观测参考星数目过少、单张CCD观测参考星分布不均、个别参考星存在位置偏差和局部区域参考星存在系统性位置偏差等不利因素对归算结果的影响，进而达到扩大视场和提高归算精度的目的。     

人卫观测中拖长星像的中心定位

提出应用于人造卫星观测中确定拖长星像中心的平均几何中心法 ,介绍了该方法的基本原理与实现步骤。将中值滤波应用于CCD数据的预处理并收到较好的效果。利用实际观测资料初步验证了平均几何中心法 ,结果表明 ,与通常采用的重心法相比 ,此方法对人卫观测中的拖长星像进行中心定位的精度较高。     

人卫观测中拖长星像的中心定位

提出应用于人造卫星观测中确定拖长星像中心的平均几何中心法，介绍了该方法的基本原理与实现步骤。将中值滤波应用于CCD数据的预处理并收到较好的效果。利用实际观测资料初步验证了平均几何中心法，结果表明，与通常采用的重心法相比，此方法对人卫观测中的拖长星像进行中心定位的精度较高。     

CCD用于建立惯性坐标系(Ⅰ) 测定河外星系与定标星的相对位置

本文叙述了用CCD测量河外星系与定标星之间相对位置的方法。由于CCD测量的每次露光时间短,可以采用连续重迭露光测量的方法,扩大可观测的天区,克服CCD测量视场太小的缺点;再利用它因视场小,象场误差可以忽略,能采用四常数模型的特点,使得在整个重迭露光测量的范围内,只要两颗定标星就能测定出河外星系的相对位置。文中推导了用两颗定标星测定河外星系相对位置的公式,并给出了各底片常数测定误差的估计。     

基于科学CCD的低纬子午环的数据采集系统

本文主要介绍基于科学CCD的低纬子午环数据采集系统的硬件构成及软件设计。为了能绝对而又精确地确定天体的位置 ,低纬子午环需要配备多种精密的测量装置 ,如 :GPS与时钟、 9路Reticon线阵、视频CCD、科学CCD、圆感应同步器、光栅线性位移传感器等。为了能有序地控制并采集这些装置的数据 ,我们设计了一个包含 3个PC机的数据采集与控制系统。文中将描述测量装置的功能 ,然后介绍数据采集方法及软件设计     

研制低纬子午环初衷的沿革

介绍了在低纬子午环研制过程中，如何跟踪国内外测量方法和科学技术的发展，调整该仪器的主要课题目标：开始时仅计划在低纬度地区进行天体位置的绝对测定，改善基本星表系统；在１ｍ望远镜试验ＣＣＤ底片重迭法成功后，打算把该仪器绝对测定的恒星位置与河外天体联系起来，间接地建立准惯性天球参考架；当国外传统子午环配备ＣＣＤ测微器作相对测量后，提出了在该仪器上配备ＣＣＤ测微器作绝对测定的方法，用其观测数据直接建立实用的准惯性天球参考架，并为太阳系和银河系研究提供有用数据的总体目标。     

A substructure analysis of the A3558 cluster complex

The 'algorithm driven by the density estimate for the identification of clusters' ( DEDICA ) is applied to the A3558 cluster complex in order to find substructures. This complex, located at the centre of the Shapley Concentration supercluster, is a chain formed by the ACO clusters A3556, A3558 and A3562 and the two poor clusters SC 1327-312 and SC 1329-313. We find a large number of clumps, indicating that strong dynamical processes are active. In particular, it is necessary to use a fully three-dimensional sample (i.e. using the galaxy velocity as third coordinate) in order also to recover the clumps superimposed along the line of sight. Even though a large number of detected substructures was already found in a previous analysis, this method is more efficient and faster when compared with a wide battery of tests, and permits the direct estimate of the detection significance. Almost all subclusters previously detected by the wavelet analyses found in the literature are recognized by DEDICA . On the basis of the substructure analysis, we also briefly discuss the origin of the A3558 complex by comparing two hypotheses: (i) the structure is a cluster–cluster collision seen just after the first core–core encounter; or (ii) this complex is the result of a series of incoherent group–group and cluster–group mergings, focused in that region by the presence of the surrounding supercluster. We studied the fraction of blue galaxies in the detected substructures and found that the bluest groups reside between A3562 and A3558, i.e. in the expected position for the scenario of cluster–cluster collision.     

A multiwavelength view of the ISM in the merger remnant galaxy Fornax A

We present multi-wavelength imagery of the merger remnant galaxy NGC 1316 with an objective to study the dust content and its association with the other phases of the interstellar medium. Color-index maps as well as extinction maps derived for this galaxy reveal an intricate and complex dust morphology in NGC 1316, i.e. there is a prominent lane in the inner part, while at about 6-7 kpc it apparently takes the form of an arc-like pattern extending along the northeast direction. In addition to this, several other dust clumps and knots are also evident in this galaxy. The dust emission mapped using Spitzer data at 8 μm indicates even more complex morphological structures of the dust in NGC 1316. The extinction curve derived over the optical to near-IR bands closely follows the standard Galactic curve, suggesting similar properties of the dust grains. The dust content of NGC 1316, estimated from optical extinction, is ～ 2.13 105M⊙ . This is a lower limit compared to that estimated using the IRAS flux densities of ～5.17×106M⊙ and the flux densities at 24, 70 and 160 μm from MIPS ～3.2×107M⊙ . High resolution Chandra observations of this merger remnant system have provided an unprecedented view of the complex nature exhibited by the distribution of hot gas in NGC 1316, which closely matches the morphology of ionized gas and to some extent also the dust. X-ray color-color plots for the resolved sources within the optical D 25 extent of NGC 1316 have enabled us to separate them into different classes.     

A re-determination of the boundaries of the cusp

Ariel 4 data (Goodallet al., 1973) of February 4 to May 5 1972 have been used to investigate the cusp boundaries. Data with the same local time (LT) and magnetic local time (MLT) around noontime and at high invariant latitudes (INL) have been used to represent the cusp area. (1) For noontime hours (MLT=1200 and LT=1200) high electron density values are observed. (2) the boundary towards the equator of the high density region starts at 76°–77° INL and the poleward boundary is at about 82° INL. Therefore, high electron densities are observed along an INL interval of 5°–6° at the Ariel 4 heights of 500–600 km, agreeing with other investigations.     

A possible shock wave in the intergalactic medium of the cluster of galaxies A754

The cluster of galaxies A754 is undergoing a merger of several large structural units. X-ray observations show the nonequilibrium state of the central part of the cluster, in which a cloud of cold plasma ～500 kpc in size was identified amid the hotter cluster gas. The X-ray image of A754 exhibits a brightness discontinuity, which can be interpreted as a shock wave in front of a moving cloud of dense gas. The shock parameters are determined from the jump in intergalactic gas density using the ROSAT image. The estimated Mach number is M₁ = 1.71 _?0.24 ^+0.45 at a 68% confidence level.     

A binary merger model for the formation of the Supernova 1987A triple-ring nebula

We examine a binary merger model for the formation of the mysterious triple-ring nebula surrounding Supernova 1987A, which still has not been convincingly explained in detailed hydrodynamical calculations. During the merger of 15 and  5 M_⊙  binary systems, mass is ejected primarily at mid-latitudes for a sufficiently evolved primary, as demonstrated by Morris & Podsiadlowski. This material is swept up by the fast wind of the central star during its post-merger blue supergiant phase, leading to a density contrast of ∼150 in the outer rings at the time of the supernova. The equatorial ring probably formed later when the star contracted to become a blue supergiant. The asymmetry between the northern and southern outer rings can be explained by a 10 per cent asymmetry during the merger, perhaps due to a pulsational instability in the common envelope.
We present a parameter study from which we determine a mass-loss rate in the blue supergiant wind in the range  1.5–3 × 10⁻⁷ M_⊙ yr⁻¹  in agreement with previous estimates. The morphology of the best model is consistent with the well-known Hubble Space Telescope image at better than 5 per cent and is also in broad agreement with light-echo observations. The circumstellar environment on larger scales (up to 3 pc) is also investigated. We conclude with a brief discussion of the bipolar nebulae surrounding the Galactic stars, Sheridan 25, HD 168625 and η Carinae.     

A study of the variability of the Delta Scuti-stars

A total of 321 observations of the Delta Scuti star BD –6°4932, obtained in 1968 by Hall and Mallama (1970), are analyzed. We find four frequencies which represent the light curves satisfactorily.The three periods:P ₁=0 _. ^d 240,P ₃=0 _. ^d 182 andP ₄=0 _. ^d 114 seem to correspond to the radial modes of pulsation withK=0, 1, and 3, respectively. The last periodP ₂=0 _. ^d 220 can be related to a non-radial mode.     

A static theory of the stability of the equilibrium

A static relativistic theory of the stability of the equilibrium of an isentropic spherically-symmetric star is deduced from the properties of a functionu which is solution of a second-order differential equation, and which is related to the model by means of the formulau = m(v, c)/c, wherem is the mass-energy inside the coordinate volumev and c is the central mass-energy density.Work done in the Laboratorio Astrofisico di Frascati, Roma.     

A couple of LBV stars in the SerOB1 A association

From the concentration of stars, cold gas, and dust in the direction l = 14.?7; b = ?0.?9, we have proved the existence of the SerOB1A association at a distance of about 2.1 kpc from the Sun and described its structure. For 29 stars belonging to the association and its vicinity, we present data on radial velocities and profiles of stellar and interstellar lines derived from original high-resolution spectra and obtained from the literature. New spectroscopic data on the unique couple HD168607 and HD168625 are given including the evidence on belonging of both stars to luminous blue variables (LBVs), proving their mutual proximity and membership in SerOB1 A, and also indicating their participation in evolution of the association.