检索结果-南通市图书馆

Ionization state of cosmic hydrogen by early stars and quasars

Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： xiao-chun mao1,2.1 {2. astronomical Observatories, chinese academy of sciences. beijing 100012, china 2.Graduate University of chinese academy of sciences. beijing 100049, china national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Graduate University of chinese academy of {2. Beijing 100049 China

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2.≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 2. per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2.- 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2.and 2. at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A Date Recovery System launched for chronological studies in ancient china

引用

Science china(Physics,Mechanics & Astronomy) 2008年第1期51卷 105-110页

作者： LI Yong national astronomical Observatories,{2. academy of sciences.beijing 100012,china 1. national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

Benefited from the performance of the Xia-Shang-Zhou Chronology Project(XSZP) in china and our new astronomical chronology method designed and processed for {2. particular 60-day-cycle Ganzhi(the heavenly stems and earthly branches)date records,we launch a Date Recovery System(DRS)for ancient china. Of high analysis function,this software can recover and convert the complete or incomplete date information originally from Ganzhi style in the historical period of china to the Gregorian Calendar System,which may have wide applications in the area of literary history,archaeology and cultural relic,etc.,and solve the Goldbach Puzzles of {2. *** an example,we give the detailed process for the sculptures on four bronze wares with the Ganzhi data and afterwards employ this software and provide their possible dates corresponding to Gregorian system.

关键词： chronology date ephemeris software

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Modeling earthquake indexes derived from the earthquake warning system upon the planet earth

引用

Science china(Physics,Mechanics & Astronomy) 2010年第12期53卷 2293-2299页

作者： LI Yong national astronomical Observatories,{2., china 1. national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

By studying the correlation between historical earthquake data and the distributional characteristics of parameters of solid earth tides in the earthquake epicenter, we are able to design a forecasting function of earthquake probability. We put forward a design method for the Earthquake Warning System. The model could theoretically simulate and be used to predict the probability of strong earthquakes that could occur anywhere at any time. In addition, the system could also conveniently obtain global or partial Modeling Earthquake Indexes to finally combine the precise pointing prediction and forecast of partial indexes. The literature quotes global data values, provided by NEIC, of 1544 M ≥ 6.5 earthquakes. It also gives examples of instantaneous earthquake indexes of the whole world and Taiwan Region on 1st January 2.10, UT=0:00 and the average earthquake index near the Taiwan Region. According to the 10-year pointing prediction of strong earthquakes in San Francisco, the literature provides the average earthquake index on 2.th June 2.15 (± 15 days), in its neighborhood.

关键词： earthquake earthquake warning system astrogeodynamics index

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

2.ASS photometry and age estimation of the globular clusters in the outer halo of M31

引用

Research in Astronomy and Astrophysics 2012年第2期12卷 115-126页

作者： Jun Ma 1,2. national astronomical Observatories,{2. academy of sciences.beijing 100012,china 2.Key Laboratory of Optical Astronomy,national astronomical Observatories,{2. academy of sciences.beijing 100012,china national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

We present the first photometric results in J, H and Ks from 2.ASS （Two Micron All Sky Survey） imaging of 10 classical globular clusters （GCs） in the far outer regions of M31. Combined with the V and I photometric data from previous literature, we constructed a color-color diagram between J - Ks and V - Ⅰ. By comparing the integrated photometric measurements with evolutionary models, we estimate the ages of these clusters. The results showed that all of these clusters are older than 3 × 109 yr, and among them four are older than 10 Gyr and the other six have intermediate ages between 3 - 8 Gyr. The masses for these outer-halo GCs are from 7.0 × 104 M to 1.02.× 10^6 M. We argued that GC2.and GC3, whose ages, metallicities and distance moduli are almost the same, were accreted from the same satellite galaxy, if they did not form in situ. The statistical results show that the ages and metallicities of these 10 M31 outer-halo GCs do not vary with projected radial position, and a relationship between age and metallicity does not exist.

关键词： galaxies: halos - galaxies: individual (M31) - star clusters: general

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Infrared Galaxies in the Nearby Universe

引用

chinese Journal of Astronomy and Astrophysics 2008年第6期8卷 643-652页

作者： Jian-Ling Wang 1 national astronomical Observatories,{2. academy of sciences.beijing 100012,china 2.Graduate School of {2. academy of sciences.beijing 100049,china national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China Graduate School of chinese academy of {2. Beijing 100049 China

We used the Sloan Digital Sky Survey （SDSS） Data Release 5 （DR5） to study the morphological properties of 1137 nearby infrared （IR） galaxies, most of which are brighter than 15.9 mag in r-band. This sample was drawn from a cross-correlation of the Infra-Red astronomical Satellite （IRAS） point source catalog redshift survey with DR5 at z ≤ 0.08. Based on this IR galaxy sample, we constructed five volume-limited sub-samples with IR luminosity ranging from 10^9.5 L⊙ to 10^12.⊙. By deriving the IR luminosity functions （LF） for different morphological types, we found that normal spiral galaxies are the dominant population below LIR ~ 8 ~ 10^10 L⊙; while the fraction of barred spiral galaxies increases with increasing IR luminosity and becomes dominant in spiral galaxies beyond LIR ≈ 5 × 10^10L⊙. As the IR luminosity decreases, the IR galaxies become more compact and have lower stellar masses. The analysis also shows that normal spiral galaxies give the dominant contribution to the total comoving IR energy density in the nearby universe, while, in contrast, the contribution from peculiar galaxies is only 39%.

关键词： galaxies evolution galaxies interactions galaxies starburst infrared galaxies galaxies luminosity function

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Expected Number Counts of Radio Galaxy Clusters

引用

chinese Journal of Astronomy and Astrophysics 2002年第2期2卷 106-111页

作者： Wei Zhou national astronomical Observatories,{2. national astronomical Observatories Chinese Academy of Sciences Beijing 100012

Clusters of galaxies may contain radio sources if they still experience successive mergers at present. This has been confirmed by radio observations that about 30% of nearby clusters possess radio halos. We present a theoretical pre- diction of radio cluster counts using a semi-analytic approach which incorporates the empirical correlation between radio power and dynamical mass of clusters, and the cluster mass function described by the Press-Schechter formalism. The total population of radio clusters over the whole sky and their redshift distribution are given.

关键词： cosmology: theory-galaxies: cluster: general-radio sources:extended

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Simulation of interplanetary scintillation with SSSF and SSDF mode

引用

Science china(Physics,Mechanics & Astronomy) 2010年第1期53卷 187-192页

作者： LIU LiJia & PENG Bo national astronomical Observatories,{2., china 1. national astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

The sun has the biggest effect on the Earth in many ways. Observing the solar wind is an important method to study the solar-earth environment. Ground-based interplanetary scintillation observations are an effective method of monitoring solar wind speed, studying the random fluctuations of the interplanetary plasma and the structures of radio sources. Two modes of single-station observations, namely, single station-single frequency (SSSF) and single station dual-frequency (SSDF), are briefly introduced and numerically simulated in this paper. The SSSF mode are easier to carry out and has been widely used. Although the observing system and data processing system of the SSDF mode are more complicated, it can measure the solar wind speed more accurately. A new SSDF system is under construction in Miyun, NAOC (the national astronomical Observatories, {2. academy of sciences., with a 50 m telescope, which will serve the Meridian Project, and this paper is devoted to preparing for this new system.

关键词： interplanetary scintillation single station-single frequency single station dual-frequency simulation

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

“Double dawn”eclipse and the rotational variation of the earth

引用

chinese Science Bulletin 2000年第11期45卷 988-991页

作者： ZHANG Peiyu & HAN Yanben1. Purple Mountain Observatory, chinese academy of {2. Nanjing 2.0008, china 2. beijing astronomical Observatory, chinese academy of sciences. beijing 100012, national astronomical Observatory, chinese academy of sciences. beijing 100012, china Purple Mountain Observatory Chinese Academy of Sciences Nanjing China beijing astronomical Observatory Chinese Academy of Sciences Beijing national astronomical Observatory Chinese Academy of Sciences Beijing China

A record of 'double dawn' at State Zheng in the first year of the reign of King Yi in Western Zhou Dynasty in the chronicle 'Bamboo Annals' (Zhushu Jinian) is discussed. We think that it may be a record of an annular solar eclipse happening in 899 BC. The record and the AT, which describes the secular variation of the earth’s rotation, are analyzed and discussed.

关键词： solar eclipse earth’s rotation.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Vilnius Photometry and Reddening of the Young Open Cluster NGC 6913

引用

chinese Journal of Astronomy and Astrophysics 2001年第4期1卷 333-343页

作者： Jun-Jie Wang and Jing-Yao Hu (national astronomical Observatories,{2. beijing astronomical Observatory,{2. chinese academy of sciences.Peking University Joint beijing As chinese academy of {2.Peking University Joint beijing Astrophysical Center Beijing 100871

stars in the NGC 6913 field with both UBV and Vilnius photometry are selected to be the sample. The membership probability of the stars is greater than 50%. The correlation among Vilnius photometry, UBV photometry and reddening in the cluster is reviewed. It is found that the photometry in the Vilnius X, Y and Z bands can be used to make rough spectral classification. The values of E(B - V) are well correlated with the Vilnius colors of X - Y, Y - Z, Z - V and V - S in NGC 6913. The ratio of (V - S)/(Y - Z) of the MPCM (Most Possible Cluster Members) is a constant (1.30 -±0.06), and has no effect on the values of E(B - V), (B - V)0 and V0. Comparing with the observational data of all the stars of NGC 6913 region, we propose that the value of (V - S)/(Y - Z) can probably be used to select the preliminary candidates of one open cluster. In addition, 12.variable stars are discovered in the NGC 6913 region, in which star #155 has a variation with an amplitude of 4.2. mag.

关键词： Galaxy: open clusters and associations - ISM: dust extinction

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

The Kiloparsec-scale Structure of 3C 2.6

引用

chinese Journal of Astronomy and Astrophysics 2004年第1期4卷 28-36页

作者： Tao An, xiao-Yu Hong and Wei-Hua WangShanghai astronomical Observatory, {2. academy of sciences. Shanghai 2.0030 national astronomical Observatories, chinese academy of sciences. beijing 100012 Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 []National Astronomical Observatories Chinese Academy of Sciences Beijing 100012

We present radio images of the compact steep spectrum (CSS) quasar 3C 2.6 acquired with the Very Large Array (VLA) at 8.4 and 2..5 GHz. The source exhibits a two-sided core-jet structure with a bright central component and two extended components one to the east (P.A. 100°) and another to the southwest (P.A. - 116°). From the compact core, an extension runs towards the southwest component up to - 0.7 arcsecond. The emission between the primary central component and the southwest component exhibits a knotty structure. A gradual change of the jet position angles from -135° to -12.° in the inner southwest jet suggests a local bend. The position angle changes of the major eastern components E2.and El suggest that the eastern jet likely follows a curved trace. The bends in the jet trace may be associated with a relativistic precession or some interaction between the jet and the ambient matter. A mean spectral index of a2..58.4- 0.76 (Xv Va) is estimated for the core component. Steep spectra are also obtained for the extended southwest component (2.6', P.A. -116°) and eastern component (0.8', P.A. 100°), with a2..58.4-0.88 and a2..58.4-1.79, respectively. The radio morphologies and spectral index distributions suggest that the core seen in our images is likely to be the beamed inner jet while the real nucleus is dimmed by it beaming away from us.

关键词： galaxy: quasar: individual - radio continuum: VLA

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：