活动星系核与类星体中致密天体的形成与并合：伽玛爆发与引力辐射     

王建民 《紫金山天文台台刊》1999,18(3):271-273

频繁的超新星爆发可用以解释活动星系核与类星体的超高金属丰度。星团中的恒星与吸积盘相互作用导致致密天体中子星和黑洞的形成率很高,这些致密天体与红巨星很容易形成双星系统,而后形成（ＮＳ／ＢＨ,ＮＳ／ＢＨ） 双星由于引力辐射最终导致并合而形成伽玛射线爆发。我们估计了伽玛射线爆的爆发频率,发现与观测相符。  相似文献   

“地球空间双星探测计划”及其与全球环境变化的关系          下载免费PDF全文

刘振兴 《第四纪研究》2002,22(6):500-509

本文论述了“地球空间双星探测计划”(简称双星计划)及其与全球环境变化的关系。地球空间双星探测计划包括两颗小卫星,分别运行于目前国际上地球空间探测卫星尚未覆盖的近地赤道区和近地极区。双星计划的主要科学目标是用高分辨率的仪器在近地空间的主要活动区探测场和粒子的时空变化;研究磁层空间暴(磁层亚暴、磁暴和磁层粒子暴)的触发机制及其对太阳活动和行星际扰动的响应过程;建立地球空间环境的动态模式。为了实现科学目标,赤道区卫星和极区卫星上各载有8台探测仪器。近地赤道区卫星的轨道是:近地点550km左右,远地点60000km左右,倾角约28.5°;近地极区卫星的轨道是:近地点700km,远地点40000km,倾角约90°。为了使双星计划与欧洲空间局ClusterII卫星相配合,赤道区卫星计划于2003年6月发射,极区卫星计划于2003年12月发射。双星计划与ClusterII卫星相配合,可形成地球空间6点探测计划,这将成为21世纪初国际上重要的地球空间探测计划。本文概要讨论了双星计划与地球系统各圈层的关系,包括与大气圈、生物圈、地球内部各圈层及全球环境变化的关系。  相似文献   

History of Star Formation and Chemical Enrichment in the Milky Way Disk   总被引：2，自引：0，他引：2  

Rui-Xiang Chang  Cheng-Gang Shu  Jin-Liang Hou Shanghai Astronomical Observatory  Chinese Academy of Sciences  Shanghai CAS-Peking University Joint Beijing Astronomical Center  Beijing 《中国天文和天体物理学报》2002,2(3)

Based on a physical treatment of the star formation law similar to that given by Efstathiou, we have improved our two-component chemical evolution model for the Milky Way disk. Two gas infall rates are compared, one exponential, one Gaussian. It is shown that the star formation law adopted in this paper depends more strongly on the gas surface density than that in Chang et al. It has large effects on the history of star formation and gas evolution of the whole disk. In the solar neighborhood, the history of chemical evolution and star formation is not sensitive to whether the infall rate is Gaussian or exponential. For the same infall time scale, both forms predict the same behavior for the current properties of the Galactic disk. The model predictions do depend on whether or not the infall time scale varies with the radius, but current available observations cannot decide which case is the more realistic. Our results also show that it would be inadequate to describe the gradient evolution along the Gala  相似文献   

HST colour–magnitude diagrams of six old globular clusters in the LMC     

K. A. G. Olsen  P. W. Hodge  M. Mateo  E. W. Olszewski  R. A. Schommer  N. B. Suntzeff  & A. R. Walker 《Monthly notices of the Royal Astronomical Society》1998,300(3):665-685

We report on HST observations of six candidate old globular clusters in the Large Magellanic Cloud (LMC): NGC 1754, 1835, 1898, 1916, 2005 and 2019. Deep exposures with the F555W and F814W filters provide us with colour–magnitude diagrams that reach to an apparent magnitude in V of ∼25, well below the main-sequence turn-off. These particular clusters are associated with significantly high LMC field star densities and care was taken to subtract the field stars from the cluster colour–magnitude diagrams accurately. In two cases there is significant variable reddening across at least part of the image, but only for NGC 1916 does the differential reddening preclude accurate measurements of the CMD characteristics. The morphologies of the colour–magnitude diagrams match well those of Galactic globular clusters of similar metallicity. All six have well-developed horizontal branches, while four clearly have stars on both sides of the RR Lyrae gap. The abundances obtained from measurements of the height of the red giant branch above the level of the horizontal branch are 0.3 dex higher, on average, than previously measured spectroscopic abundances. Detailed comparisons with Galactic globular cluster fiducials show that all six clusters are old objects, very similar in age to classical Galactic globulars such as M5, with little age spread among the clusters. This result is consistent with ages derived by measuring the magnitude difference between the horizontal branch and main-sequence turn-off. We also find a similar chronology by comparing the horizontal branch morphologies and abundances with the horizontal branch evolutionary tracks of Lee, Demarque &38; Zinn. Our results imply that the LMC formed at the same time as the Milky Way Galaxy.  相似文献   

A search for high-velocity gas in massive star formation regions     

Yue-fang Wu  Yue-xing Li  Li-feng Zheng 《Chinese Astronomy and Astrophysics》1998,22(4):863-462

From the IRAS-PSC, 97 sources with steep FIR spectrum and another 8 were chosen for a search for high-velocity gas. Observations of the CO (J =1−0) line were made with the 13.3-m telescope at the Qinghai Station. The results show that 102 sources are associated with molecular gas. 9 of the sources have reference position problem and 21 have multiple spectrum. Of the remaining 72, 29 contain high-velocity gas, and of these 18 are new molecular outflow candidates. Their properties are discussed briefly in connection with massive young stellar objects.  相似文献   

北京天文台的WET三通道高速光度计     

姜晓军  胡景耀 《天文学报》1998,39(4):438-443

对北京天文台新近改造成的三通道高速光度计的结构和性能进行介绍,并给出了在兴隆站85公分望远镜的一些实测结果.  相似文献   

The globular cluster system of the Sagittarius dwarf spheroidal galaxy: the age of Terzan 8     

Montegriffo  Bellazzini  Ferraro  Martins  Sarajedini  & Fusi Pecci 《Monthly notices of the Royal Astronomical Society》1998,294(2):315-326

We present deep V - and I -band CCD photometry of the globular cluster Terzan 8, recently found to be a member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. We accurately estimate the metallicity of Terzan 8, and provide the first direct determination of the colour excess toward this cluster. Our robust age estimate confirms that this cluster is indeed coeval with typical Galactic globulars of comparable metal content, and thus it is probably significantly older than at least two other Sagittarius clusters, Terzan 7 and Arp 2. The implications of this result on the star formation history of the Sagittarius galaxy are briefly discussed.  相似文献   

Dynamical studies of cluster pairs in the Magellanic Clouds     

M. R. de Oliveira  H. Dottori  & E. Bica 《Monthly notices of the Royal Astronomical Society》1998,295(4):921-932

We performed N -body simulations of star cluster encounters with Hernquist's TREECODE in a CRAY YMP-2E computer under different initial conditions (relative positions and velocities, cluster sizes, masses and concentration degrees). The total number of particles per simulation ranged from 1024 to 20480. These models are compared with a series of isodensity maps of cluster pairs in the Magellanic Clouds. Evidence is found that during the interactions, transient morphological effects such as an expanded halo, isophotal deformation and isophotal twisting can occur as a result of tidal effects and dynamical friction. The simulations also show that different outcomes are possible depending on the initial parameters: (i) long-standing changes of concentration degree can occur after the collision; (ii) one member can disaggregate; or (iii) the pair can coalesce into a single cluster with a distinct structure compared with the original ones. These simulations can reproduce a wide range of morphological structures in observed cluster pairs.  相似文献   

A comprehensive nbody study of mass segregation in star clusters: energy equipartition and escape     

E. Khalisi &#;  P. Amaro-Seoane &#;  R. Spurzem &#; 《Monthly notices of the Royal Astronomical Society》2007,374(2):703-720

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Five young star clusters in the outer region of the Small Magellanic Cloud     

Andrés E. Piatti  Ata Sarajedini  Doug Geisler  Carme Gallart  Marina Wischnjewsky† 《Monthly notices of the Royal Astronomical Society》2007,382(3):1203-1212

Colour–magnitude diagrams in the Washington system are presented for the first time for five star clusters projected on to the outer region of the Small Magellanic Cloud (SMC). The clusters are found to have ages in the range 0.1–1.0 Gyr, as derived from the fit of isochrones with   Z = 0.004  . This sample increases substantially the number of young clusters in the outer SMC – particularly in the south-east quadrant – with well-derived parameters. We combine our results with those for other clusters in the literature to derive as large and homogeneous a data base as possible (totalling 49 clusters) in order to study global effects. We find no conclusive evidence for a dispersion in the cluster ages and metallicities as a function of their distance from the galaxy centre, in the SMC outer region. L 114 and 115, although very distant, are very young clusters, lying in the bridge of the SMC and therefore most likely formed during the interaction which formed this feature. We also find very good agreement between the cluster age–metallicity relation (AMR) and the prediction from a bursting model from Pagel & Tautvaišienė with a burst that occurred 3 Gyr ago. Comparing the present cluster AMR with that derived by Harris & Zaritsky for field stars in the main body of the SMC, we find that field stars and clusters underwent similar chemical enrichment histories during approximately the last couple of Gyr, but their chemical evolution was clearly different between 4 and 10 Gyr ago.  相似文献