一种质点系统平衡态的非线性稳定性

在具各向异性速度分布的质点系统的总能量小于零时，由大量静态维里定理构造了该系统的一个旋转椭球形平衡态。讨论该平衡态的非线性稳定性。发现在上述平衡态附近旋转随球作拟周期或近拟周期运动，尽管存在混沌运动和轨道扩散行为，但是对实际的时间尺度而言，可以认为该平衡态具有非线性稳定性。有关结果在用N-体数值模拟研究恒星系统振动行为时有一定的应用价值。     

宇宙学常数与高红移星系观测

最近对哈勃常数的观测趋于一个大的值，引进宇宙学常数为主的宇宙学成了保持平坦宇宙并解决年龄矛盾的主要方法．本文讨论了（ｈ，Ω∧，ΩＭ）＝（０．８，０．８，０．２）的宇宙模型的一些后果，并和高红移椭球星系的观测，以及星系计数的观测作了比较．尽管观测事实表明Ω∧＝０．８模型比Ω∧＝０模型更具有优势，但这个结论仍是模糊的．除了年龄问题外，还不能排除（０．８，０，１）标准宇宙学的存在．     

极亮红外星系的HST面源测光研究

星系间的相互作用和合并是一个非常普遍的现象,在星系的形成和演化过程中扮演了一个重要角色。理论和实测都有表明星系并合是椭圆星系形成的重要途径。极亮红外星系（ＵＬＩＲＧｓ）与星系间的相互作用和并合密切相关,是研究星系并合现象的理想实验室,对它们的测光研究将有助于理解星系的并合过程。哈勃望远镜（ＨＳＴ）的高分辨率观测为这方面的研究提供了条件。我们利用哈勃望远镜（ＨＳＴ）的宽场行星照相机（ＷＦＰＣ２）对极亮红外星短曝光巡天的Ｉ波段数据,选出了一个子样本。该子样本由２１个以单核为主的极亮红外星系组成,这些星系一般处于星系并合的晚期。我们对这些星系进行了面源测光研究,并根据面亮度轮廓与Ｒ１／４律的差别利用χ＾２判据律将它们分成了两大类：第一类八个星系的面亮度轮廓可以用Ｒ１／４律很好地拟合;而第二类星系在面亮度轮廓与Ｒ１／４     

星系的基本面

基本面最早是在早型星系中发现的一种经验标度律,它是一个关于星系的有效半径、中心速度弥散度和有效半径内的平均面亮度之间的紧密相关关系.基本面对早型星系的形成机制、动力学演化理论等提出了很强的观测约束;不仅如此,它还可作为独立的星系距离测定方法,用于哈勃常数的定标和星系本动速度场的测量.对早型星系基本面的研究进展做了简要评...     

星系结构和动力学

从星系形成和演化的角度出发，对星系结构和动力学进行的粗略的评述，内容包括：（1）初步描述了星系中各主要成分的物理特征（空间分布，运行学和化学）及其形成和演化，（2）Damped Lyman-alpha systems(DLAs)是本地星系的化石，对其进行观测研究是HST的主要任务之一，对DLAs宽的谱线轮廓的物理机制和其恒星形成，化学演化进行了讨论，（3）目前已证明Lyman Break方法是发现高红移高恒星形成星系的有效手段，讨论了Lyman Break Galaxies的动力学过程和恒星形象，（4）旋涡星系和椭圆星系的Scaling Law是星系形成和演化所必须解释的问题，对近期该方面的研究结果作了介绍，（5）整体超星的反馈作用在星系形成和演化中起了重要作用，评述了该物理过程对星系演化的影响；（6）随着观测资料的不断积累，各种物体对河外背景辐射的贡献已成了一个重要的研究方向，讨论了宇宙整体的星形成历史和化学演化，（7）银河系是进行星系形成和演化研究的归算零点，介绍了银河系的结构，动力学及演化。     

棒旋星系原是“老资格”

“哈勃”空间望远镜的最新观测表明,在70亿年前棒旋星系的数量要比现在少得多,表明棒旋星系是趋于成熟的年龄较老的星系,并且确证了“衡量旋涡星系‘成熟度’的一个重要指标就是看它的核心有没有‘恒星棒’”这一看法。     

超新星在旋涡星系中的径向分布

本文研究了在1993年3月28日之前发现的899颗超新星（SNe）的样本．其中277颗SNe被用来研究超新星在其母星系中的径向分布．我们研究了四个星系样本中超新星在产生单个超新星（称为一般超新星）的星系及在产生多个超新星（称为多重超新星）的星系中的径向分布．这四个星系样本为：总旋涡星系样本，Sb～SbC星系样本，SC星系样本，Sc～Sd星系样本．研究的结果表明：一多重超新星比一般超新星在其母星系中具有更集中于星系核心（大多数恒星形成发生的地方）的倾向，说明星系中心的恒星形成活动会影响多重超新星事件的发生从而影响超新星的频率分布     

遥远的宇宙天体：活动星系核

我们所处的宇宙非常巨大,大得超出人们的想象能力。宇宙的基本构成单元是星系,星系的大小不同,形态各异,亮暗不一,颜色迥然。它们共同组成这个多姿多彩的宇宙。天文学家经过长期的观测和归纳,按形状将星系分为以下几类。其中一类星系看起来是一个椭圆形的弥漫天体,被称为椭圆星系（图1左上）;而有些星系是盘状结构,它们有一个明亮的核心,并从核心向外伸展出两条或多条弯曲的旋臂,看起来象一个旋涡一样,所以叫旋涡星系（图1右上）;有些旋涡星系的中心是一个明亮的棒状物,旋臂从棒的两端向外弯曲伸展出动,这类星系中棒旋星系（图1左下）。     

神秘的活动星系核

随着观测仪器的发展和观测技术的提高,人类发现的星系已经多达上百亿个。为了研究它们,几十年来已经建立了多种分类系统,其中影响最大、应用最广的当属哈勃分类。在这种分类中,星系按形状可分为椭圆星系、旋涡星系和不规则星系。这些星系中的绝大多数都相当宁静,物质活动的规模都较小,我们称之为正常星系。     

宇宙信息

哈勃空间望远镜观测到了四个星系的碰撞过程,发现这些看似年轻的矮旋涡星系,其实是100亿年来演化处于停滞状态的年老星系。这四个星系——两个已经并合,一个处于正向,另一个处于侧向——构成了距离地球1．66亿光年的希克森致密星系团31。其中每个星系的直径大约2万光年,彼此之间的距离都在7．5万光年之内,做为比较,银河系的直径大约为10万光年。     

Long-term evolution of spheroidal galaxies with locally isotropic velocity distribution

The short-term evolution of spheroidal galaxies has been explored by S. Chandrasekhar et al. and G. S. Sunder et al. In this paper, we study their long-term evolution with Laskar's method of frequency analysis. The main new results are as follows: (1) There exists a unique equilibrium, which is spherically symmetric. This equilibrium has a critical linear stability. (2) Generally speaking, the semi-axes exhibit quasiperiodic or nearly quasi-periodic (in a time scale longer than a Hubble time) oscillations around the radius of the above-mentioned equilibrium, so the equilibrium is practically stable. (3) There are cases in which one of the semi-axes tends fast to zero while the other to some finite value. The limit state is generally planar rather than linear, i.e. it is the symmetric semi-axis that tends to zero. This implies that some disk galaxies may have originated from spheroidal pregalaxy material.     

Observational Tests of the Galaxy Formation Process

The mutual feedback between star formation and nuclear activity in large spheroidal galaxies may be a key ingredient to overcome several difficulties plaguing current semi-analytic models for galaxy formation. We discuss some observational implications of the model by Granato et al. for the co-evolution of galaxies and active nuclei at their centers and stress the potential of the forthcoming surveys of the Sunyaev-Zeldovich effect on arcminute scales, down to μK levels, to investigate the early galaxy-formation phases, difficult to access by other means.     

星系振动的动力学研究进展

概括地介绍了盘星系的运动学边缘弯曲现象、盘星系中心的HI发射线空洞和棒旋星系中核球的长轴和棒的长轴不互相平行也不互相垂直等星系振动的问接观测证据;综述了星系振动动力学的理论研究情况,主要介绍了利用非静态维里方程和N体数值模拟得到的有关结果;展望了该领域今后的发展趋势,指出了建立引力自治的星系振动模型的必要性。     

UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I &; Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for the Sculptor and Fornax dwarf spheroidal galaxies which have been previously had single element (low resolution) calcium abundance studies (Tolstoy et al., 2001). See Figures 1 and 2.     

Essential properties of the cD galaxy in Abell 1795 — I. General optical and X-ray structure,dynamics and formation

We investigate current problems connected with the formation of cD galaxies. The subject of the present paper is to compare internal properties of the cD galaxy Zw162010 with cluster properties of Abell 1795. This consideration is a first attempt to find commonly valid essential correlations between peculiarities of brightest cluster members as structures and active phenomena and global cluster properties as for instance galaxy populations and concentration degrees. The colours, the X-ray emission, and the velocity of the cD galaxy are used to discuss the obvious influence of the environment on the evolution of the active nucleus. In a second paper (Kirchner et al. 1992) the radio structure is used to investigate the influence of the surrounding cluster medium onto the development of the active nucleus. Furtheron, various jet ejection scenarios will be quantitatively examined.     

Evolution of Polytropic Reimann Disks in Halos

The equilibrium of elliptical Riemann disks with a polytropic equation of state and their evolution under the influence of viscosity and gravitational radiation inside spheroidal halos with a relative surface mass density k. The evolutionary trajectory of a disk inside a halo with k<0.5, which is analogous to the evolution of an isolated disk, differs from that of a disk inside a denser halo.     

Discovery of Five Narrow-Line Seyfert 1 Galaxies and Im- plications on the NLS1 Model

We report the discovery of five Narrow-Line Seyfert 1 galaxies (NLSls) identified from the ROSAT All-Sky Survey bright sources. One of them has a quasar-like luminosity and two, including the quasar-like one, have close companions and/or show interacting features. We calculate the central black hole masses and Eddington ratios for the five NLSls. In combination with the objects of Kaspi et al., we find that NLSls have smaller central black hole masses and higher accretion rate than normal Seyfert 1s.     

Discovery of Five Narrow－Line Seyfert 1 Galaxies and Implications on the NLS1 Model

We report the discovery of five Narrow-Line Seyfert 1 galaxies (NLSls) identified from the ROSAT All-Sky Survey bright sources. One of them has a quasarlike luminosity and two, including the quasar-like one, have close companions and/or show interacting features. We calculate the central black hole masses and Eddington ratios for the five NLSls. In combination with the objects of Kaspi et al., we find that NLSls have smaller central black hole masses and higher accretion rate than normal Seyfert ls.     

星系际弥散恒星成分研究进展

对于星系际弥散恒星的研究是分别从观测、数值模拟和半解析模型这三个方面进行的.现在已经在邻近星系团及中低红移处观测到弥散恒星,甚至在Virgo及Coma星系团中观测到了单个的弥散恒星.观测数据的积累使得人们能够从统计上了解星系际弥散恒星的性质.研究表明星系际弥散恒星围绕着星系团势阱中心呈椭球状对称分布,其在星系团恒星总质...