银河系旋臂结构和运动学的VLBI高精度探测     

徐烨 《天文学进展》2011,29(2):123-131

直接测量恒星形成区的距离;从而确定银河系的旋臂结构以及银河系运动学的工作正在逐步展开.通过对恒星形成区脉泽的多历元VLBI观测,利用类星体和脉泽相位参考技术,精确地测定脉泽的位置、自行和视差.精确的距离能够确定旋臂的位置,从而建立银河系旋臂结构的新模型;运用绝对自行确定该处天体的三维运动,由此精确测定银河系的旋转曲线,...  相似文献   

银河系卫星星系研究进展     

康熙 《天文学进展》2011,29(1):1-18

对银河系内卫星星系进行全面的"人口普查"具有重要的意义。目前已经发现了二十几个卫星星系,其光度范围分布很广,最暗的矮星系比球状星体还暗。叙述了卫星星系的光度分布、空间分布和动力学性质。总结了观测和理论研究进展,并讨论了星流和伽玛射线在研究银河系结构和暗物质性质方面的贡献。表明了卫星星系的统计分布能用来很好地限制冷暗物质理论和星系形成的相关物理过程,同时指出当前研究的局限性和可能的发展方向。  相似文献   

M 87核区X射线辐射起源的研究     

于照茏 《天文学进展》2011,29(1)

利用耦合的吸积-喷流模型,对巨椭圆星系M 87(NGC 4486)核区的高分辨率观测到的多波段能谱分布进行了研究,重点是核区的X射线辐射起源问题.研究结果表明,M 87核区的X射线辐射是由喷流主导的,而不是此前认为的由径移主导的吸积流(ADAFs)主导的.  相似文献   

H<Emphasis Type="Italic">α</Emphasis> survey of the local volume: Isolated southern galaxies     

S. S. Kaisin  A. V. Kasparova  A. Yu. Knyazev  I. D. Karachentsev 《Astronomy Letters》2007,33(5):283-291

We present our Hα observations of 11 isolated southern galaxies: SDIG, PGC 51659, E 222-010, E 272-025, E 137-018, IC 4662, Sag DIG, IC 5052, IC 5152, UGCA 438, and E 149-003, with distances from 1 to 7 Mpc. We have determined the total Hα fluxes from these galaxies. The star formation rates in these galaxies range from 10^?1 (IC 4662) to 10^?4 M _⊙ yr^?1 (SDIG) and the gas depletion time at the observed star formation rates lies within the range from 1/6 to 24 Hubble times H ₀ ^?1 .  相似文献   

Analyzing empowerment: An ongoing process of building state-civil society relations - The case of Walnut Way in Milwaukee     

Parama Roy 《Geoforum》2010,41(2):337-348

Arguments regarding citizen involvement and empowerment within neoliberal urban politics are ample in geographic literature. Existing discussions often define and evaluate empowerment as either some social, political, or economic end-product of a specific event. Such singular conceptualization is problematic. First, different kinds of social, political, and economic changes can simultaneously empower/disempower communities in contradictory ways. In addition, the view of empowerment as an end-product of a present event obscures a more nuanced understanding of empowerment as an ongoing process of state-civil society relation-building. An in-depth assessment of such a process is only possible with reference to the past and the potential future occurrences. Elwood’s (2002) multi-dimensional conceptualization of empowerment recognizes the limitations of a singular definition of empowerment. However, it falls short of operationalizing empowerment as a temporal process with a historically and geographically contingent past, dynamic present, and future in the making. Therefore, in this paper I expand on Elwood’s framework to show how a process-based view as opposed to a narrow end-product-based or event-based one can provide a deeper understanding of state-civil society interaction and community empowerment. This paper analyzes the interaction between the City of Milwaukee, the residents of a predominantly black inner-city neighborhood, the Walnut Way, and their community organization, the Walnut Way Conservation Corp. within a land-use dispute related to the development of a park space into a housing project. Using data collected through semi-structured in-depth interviews, archival research, and participant observation, this paper emphasizes that despite methodological limitations of collecting long-term data, community empowerment can and should be studied as a process with reference to the past, present, and potential future state-civil society interactions.  相似文献   

星系团二维分布的分形特征     

邓新发  邓祖淦  刘永镇 《中国天文和天体物理学报》1995,(4)

本文采用分形分析法分别研究了全天区富星系团表中北银纬和南银纬不同深度和不同富性的子样本的二维分布规律，结果发现星系团的二维分布是一个多级分形结构，在Ｄ≤４和Ｄ＝５＋６类子样本中，不同分形级之间的转变尺度所对应的投影尺度均为～４２ｈ~（－１）Ｍｐｃ。在整个尺度范围内，北银纬、南银纬样本星系团的分布规律很相似。  相似文献   

Anisotropic Inhomogeneous Riemann S-Ellipsoids in Spheroidal Halos. I.     

M. G. Abrahamyan 《Astrophysics》2005,48(4):514-531

The classical Riemann S-ellipsoids are generalized to account for a Ferrers inhomogeneity in the mass distribution, a three-dimensional anisotropy of the velocity dispersions, and the gravitation of a spheroidal halo. The Ferrers inhomogeneity does not affect the equilibrium and stability conditions for the ellipsoids, but only changes the numerical coefficients in the equilibrium parameters. The anisotropy of the velocity dispersions changes both the equilibrium conditions and the criterion for stability of the ellipsoids, either extending or limiting the region in which the ellipsoids exist. A halo extends this region in all cases and stabilizes the ellipsoids. The observed of the velocity dispersions of stars in the neighborhood of the sun are obtained using the inhomgeneous model. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 613–632 (November 2005).  相似文献   

The method of a two-point conditional column density for estimating the fractal dimension of the distribution of galaxies     

Yu. V. Baryshev  Yu. L. Bukhmastova 《Astronomy Letters》2004,30(7):444-450

We suggest a new method for estimating the fractal dimension of the spatial distribution of galaxies: the method of selected cylinders. We show the capabilities of this method by constructing a two-point conditional column density for galaxies with known redshifts from the LEDA database. The fractal dimension of a sample of LEDA and EDR SDSS galaxies has been estimated to be 2.1±0.1 for cylinder lengths of 200 Mpc. A major advantage of the suggested method is that it allows scales comparable to the catalog depth to be analyzed for galaxy surveys in the form of conical sectors and small fields in the sky.  相似文献   

Probing the Formation and Evolution of early-type galaxies: the SAURON project     

E. Emsellem  The Sauron Team 《Astrophysics and Space Science》2002,281(1-2):363-366

We are conducting a systematic study of a carefully selected sampleof nearby E/S0 galaxies and Sa bulges using the unique panoramic integral-fieldspectrograph SAURON, mounted at the WHT. The goal of the SAURON projectis to fully map the gaseous/stellar kinematics and the stellar populations of a representative sample of 80 early-type galaxies up to 1 Re,probing different environments (clusters, field). These data, used in combination with existing ground-based and HST observations, and fed to the theoretical machinery we have developed, will allow to determine theintrinsic dynamical structure of the galaxies. We will also measure the masses of central black holes, relate the internal dynamics to the ageand metallicity of the stellar populations, and establish the historyof metal enrichment as a function of Hubble type and environment. Some brief results on two targets observed during the SAURON campaign will serve as an illustration of the unique and high quality data we are currently gathering. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

M31的观测与研究进展     

孙振娜  侯金良  常瑞香  陈力 《天文学进展》2004,22(2):163-178

介绍了本星系群中最大的旋涡星系M31(仙女星系)的基本观测性质。与银河系结构类似，M31的基本成分包括：核、核球、盘和晕。对以上各个成分的观测和研究进展分别作了综述，重点是盘的星族成分和恒星形成历史，以及球状星团的分布和晕的形成历史。同时与银河系的各种观测特征和形成机制作了详细的比较。  相似文献