Seyfert 2 星系光谱偏振的汤姆逊散射机制     

朱青峰  林宣滨  程福臻 《中国天文和天体物理学报》1999,(4)

利用简单的ｔｏｒｎｓ束流模型定量计算Ｓｅｙｆｅｒｔ２型星系的偏振度和散射流量的角分布,在“一次电子散射”的假定下,得到偏振度约为１０％～８０％．而偏振流量的角分布与ｔｏｒｎｓ半张角θｃ和观测角φｏ都有关．特别是当φｏ　５５°时,观测方向的流量和总的散射流量的比值为一定值（０．１６）．用这种纯电子散射模型来解释ＮＧＣ１０６８的光谱偏振更为合适．对于其它一些具有低的偏振度的Ｓｅｙｆｅｒｔ２星系,尘埃的作用则不能忽略．  相似文献   

BL Lac天体处于高态与低态时的短时标光变的差异及机制研究     

白金明  谢光中 《中国天文和天体物理学报》1999,(3)

分析了１９９３－１９９５年ＢＬＬａｃ、ＯＪ２８７和ＰＫＳ０７３５＋１７８三颗ＢＬＬａｃ天体光变的监测结果,并结合文献上他人发表的资料,发现一些ＢＬＬａｃ天体处于高态时活动性较强,短时标光变频繁发生,而处于低态时活动性较弱,短时标光变很少发生．文中提出活动星系核的相对论性喷流方向会改变,从而导致长期光变;高态是喷流方向与观测者视线夹角较小的表现,而低态则是夹角较大的表现。利用该模型能够解释ＢＬＬａｃ天体短时标光变行为在高态和低态下的差别,并能很好地解释Ｔａｋａｌｏ等人监测ＯＪ２８７时发现的新现象．  相似文献   

近距中等光度IRAS星系的射电观测     

李永生  苏步美 《天文学报》1999,40(2):206-212

使用澳大利亚ＡＴ对６个近距中等红外光度的ＩＲＡＳ星系在双频上同时进行了观测．其中ＩＲＡＳ２０２７２－４７３８、ＩＲＡＳ２３１５６－４２３８探测到射电发射．获得了它们的射电流量、峰值位置、源的大小、频谱指数等射电参数,用红外、射电、光学资料对射电源进行了证认．并结合以前的观测资料讨论了这类星系射电发射的特点．  相似文献   

Three-dimensional distribution of high-velocity stars     

J. Greiner 《Astronomische Nachrichten》1990,311(1):35-39

Numerical calculations support the conjecture that high velocity stars born in or near the rotating disk are not distributed spherically throughout the galaxy. Instead an empty funnel region forms around the rotation axis of the galaxy, where no stars reside. The funnel appears only for high velocity stars, such as old pulsars. Within about 50 kpc distance from the galactic center the funnel shape is almost not dependent on the existence of a massive corona.  相似文献   

星系形态分类的研究进展     

汪敏  孔旭 《天文学进展》2007,25(3):215-225

传统的哈勃星系形态分类法可以很好地对近邻的亮星系进行分类,但对低面亮度星系、矮椭球星系、矮旋涡星系以及高红移星系等都已无能为力。德沃古勒分类系统、叶凯士分类系统和范登伯分类系统是在哈勃分类法的基础上进行了发展和细化,利用光的中心聚集度或光度级等作为星系形态分类的参数。模型化分类系统试图定量地测量星系形态参数,但需要假定星系面亮度分布满足一定的形式,如r~(1/4)律、指数律等。最近几年,又有一些学者提出了非模型化分类系统,给出了若干个可以直接测量星系形态的结构参数,如:聚集度指数C、非对称指数A、簇聚指数S、基尼系数G及矩指数M_(20)。这些参数可以反映星系的形成历史、恒星形成、与其他星系的相互作用、已经发生或正在进行的并合活动等。它们不仅可以有效地给出近邻星系的分类特性,还能用于测量高红移星系的形态。该文介绍了不同的星系形态分类方法,比较了各类方法的优点和不足。在此基础上,最后介绍了基于非模型化分类系统的星系形态分类的研究进展。  相似文献   

卫星双向时间比对及其误差分析   总被引：26，自引：0，他引：26  

刘利  韩春好 《天文学进展》2004,22(3):219-226

介绍了卫星双向时间比对(TwsTT)方法的发展过程及其基本原理，讨论了TwsTT的误差源，分析了各误差源对比对精度的影响。得出影响TwSTT精度的主要误差源为设备时延误差和路径传播时延误差，而由于卫星和地面站运动引起的误差相对较小，从而给出了实际应用时不同比对精度下需要考虑的误差源及对误差源的精度要求。  相似文献   

Dwarf galaxies captured by giants in clusters     

Lilia P. Bassino  Juan C. Muzzio  Josefa Pérez 《Celestial Mechanics and Dynamical Astronomy》1998,72(3):157-168

We performed simple numerical simulations to investigate the capture of dwarf galaxies by larger ones in the environment of a cluster of galaxies. The number of captures is small compared to the total number of dwarfs, but it is significant because these galaxies are the most abundant members of galaxy clusters. Our models show that, having a more massive central galaxy or a less massive background halo in the cluster, increases the number of captures. A high proportion of the orbits of the captured dwarfs are very eccentric. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Dynamical friction on a satellite of a disk galaxy: The circular orbit     

M. J. Valtonen  L. Valtaoja  B. Sundelius  K. J. Donner  G. G. Byrd 《Celestial Mechanics and Dynamical Astronomy》1990,48(2):95-113

In a previous paper, we have studied dynamical friction during a parabolic passage of a companion galaxy past a disk galaxy. This paper continues with the study of satellites in circular orbits around the disk galaxy. Simulations of orbit decay in a self gravitating disk are compared with estimates based on two-body scattering theories; the theories are found to give a satisfactory explanation of the orbital changes. The disk friction is strongly dependent on the sense of rotation of the companion relative to the rotation of the disk galaxy as well as on the amount of mass in a spherical halo. The greatest amount of dynamical friction occurs in direct motion if no spherical halo is present. Then the infall time from the edge of the disk is about one half of the orbital period of the disk edge. A halo twice as massive as the disk increases the infall time four fold. The results of Quinn and Goodman, obtained with a non-self-gravitating method, agree well with our experiments with massive halos (Q ₀ 1.5), but are not usable in a more general case. We give analytic expressions for calculating the disk friction in galaxies of different disk/halo mass ratios.  相似文献   

Global properties of nearby galaxies in various environments     

I. D. Karachentsev  A. V. Kasparova 《Astronomy Letters》2005,31(3):152-159

We analyze a sample of the Local Volume that contains 451 galaxies within 10 Mpc. We compare the various global parameters of these galaxies with their tidal index that characterizes the local density of the environment. The closest correlation is observed between the density of the galaxy’s environment and its morphological type. The abundance of neutral hydrogen in the members of close groups was found to be, on average, a factor of 3 lower than that in isolated galaxies. However, much of this difference is attributable to different morphological composition for the group members and field galaxies. The total mass-to-luminosity ratio is virtually independent of the tidal index of the galaxy, which indirectly indicates a low percentage of tidal systems among dwarf galaxies. All of the galaxies with three or more companions in the Local Volume are shown to have masses above the threshold value of 10¹⁰M_⊙.  相似文献   

Gravitational lensing by stars in a galaxy halo: Theory of combined weak and strong scattering     

Nityananda  Rajaram  Ostriker  J. P. 《Journal of Astrophysics and Astronomy》1984,5(3):235-250

The theory of gravitational lensing of background quasars by stars in the halo of a galaxy is considered. In the limiting case of small ‘optical depth’, only one star is close enough to the beam to cause strong scattering, and the effect of all the other stars is treated as a perturbation with both systematic and random components. The perturbation coming from weak scattering can increase the number of images and the amplification in those cases where the amplification is already high; such events are preferentially selected in flux limited observations. The theory is applicable to the apparent association of background quasars with foreground galaxies. A comparison with earlier work on the same problem is given. The relevance of these results to gravitational lensing by galaxies as perturbed by random inhomogeneities surrounding the ray path is also briefly discussed.  相似文献