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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 national astronomical observatories, {2. {3. of Sciences, Beijing 100012. china 2.Graduate University of {2. {3. of Sciences, Beijing 100049, china national astronomical {2. Chinese Academy of Sciences Beijing 100012 China Graduate University of chinese academy of Sciences 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 43.% 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

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A Date Recovery System launched for chronological studies in ancient china

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

作者： LI Yong national astronomical {2.,{3. academy of Sciences,Beijing 100012.china national astronomical {2. Chinese Academy of Sciences Beijing 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

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Thermal analysis of the baffle structure of the Solar Space Telescope

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Science china(Physics,Mechanics & Astronomy) 2010年第9期53卷 1755-1764页

作者： LI Rong1,2.3.& WANG Sen1,3.1 national astronomical {2.,chinese academy of Sciences,Beijing 100012.china 2.Graduate University of chinese academy of Sciences,Beijing 100049,china 3.Key Laboratory of Solar Activity,national astronomical {2. of chinese academy of Sciences,Beijing 100012.china national astronomical {2. Chinese Academy of Sciences Beijing China Graduate University of chinese academy of Sciences Beijing China Key Laboratory of Solar Activity National Astronomical Observatories of Chinese Academy of Sciences Beijing China

The SST(Space Solar Telescope) is an astronomical telescope with a primary mirror of 1 m in *** observes the sun with a small view field to ensure that its high spatial resolution imaging has 0.1″-0.15″ and high SNR(signal to noise ratio).Surrounding the small view field is still the sun,which is an intense source of both heat and stray *** baffles(the main baffle,the aperture,and the outer baffle),which are used to eliminate the stray light,will change the thermal flux in the SST and will weaken the effect of the thermal control *** this study,the compatibility analysis of the thermal effect of baffle structures in SST is *** GCF(Geometry Composing Function) and BRDF(Bidirectional Reflectance Distribution Function),which are two inherent related parameters in the compatibility analysis,are *** objective and method of the compatibility analysis are *** the thermal analysis software,the temperature fields are calculated for different lengths of the main baffle,different radii of apertures,different lengths of the outer baffle with a 3. tilt angle and 16' tilt angle,and different tilt angles of the outer baffle with a 2.0 mm length.A series of configurations and sizes of the baffles are studied with the goals of both thermal control and elimination of stray *** design of the baffle structure of SST is achieved:the main baffle of length 4100 mm,the internal shield of radius 494 mm,the outer baffle of length 2.0 mm,and the outer baffle of tilt angle 3. are successfully *** paper presents the relationship between the thermal control design and stray light elimination plan in the *** aims of the optimal design of the baffle structure of SST are *** thoughts and methods of the optimal analysis are also useful for similar optical telescopes designed for solar observation.

关键词： baffle the main baffle the outer baffle GCF BRDF

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

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

作者： LI Yong national astronomical {2., {3. academy of Sciences, Beijing 100012. china national astronomical {2. Chinese Academy of Sciences Beijing 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

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2.ASS photometry and age estimation of the globular clusters in the outer halo of M3.

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

作者： Jun Ma 1,2. national astronomical {2.,chinese academy of Sciences,Beijing 100012.china 2.Key Laboratory of Optical Astronomy,national astronomical {2.,chinese academy of Sciences,Beijing 100012.china national astronomical {2. 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 M3.. 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 M3. 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 (M3.) - star clusters: general

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Simulation of interplanetary scintillation with SSSF and SSDF mode

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

作者： LIU LiJia & PENG Bo national astronomical {2., {3. academy of Sciences, Beijing 100012. china national astronomical {2. Chinese Academy of Sciences Beijing 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 {2., {3. 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

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What does the Sun tell and hint now?

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Research in Astronomy and Astrophysics 2009年第9期9卷 959-965页

作者： Ke-Jun Li1,2.1 national astronomical observatories /Yunnan Observatory,chinese {2. of Sciences,Kunming 650011,{3. 2.Key Laboratory of Solar Activity,national astronomical observatories,chinese {2. of Sciences,Beijing 100012.{3. national astronomical {2./Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Key Laboratory of Solar Activity National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China

Some historical records, which have held since the beginning of modern solar activity cycles, are being broken by the present Sun： cycle 2. records the longest cycle length and fall time; latitudes of high-latitude sunspots belonging to a new cycle around the minimum time of the cycle are statistically the lowest at present, compared with those of other cycles; there are only one or no sunspots in a month appearing at high latitudes for 58 months, which is the first time that such a long duration has been observed. The solar dynamo is believed to be slowing down due to：（1） the minimum smoothed monthly mean sunspot number is the smallest since cycle 16 onwards, and even probably among all modern solar cycles; and （2. once the time interval between the first observations of two neighboring sunspot groups is larger than 14 d, it should be approximately regarded as an observation of no sunspots on the visible solar disk, called a spotless event. Spotless events occur with the highest frequency around the minimum time of cycle 2., and the longest spotless event also appears around the minimum time for observations of the Sun since cycle 16. Cycle 2. is expected to have the lowest level of sunspot activity from cycle 16 onwards and even probably for all of the modern solar cycles.

关键词： Sun: activity -- Sun: general -- sunspots

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A network flow algorithm to position tiles for LAMOST

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Research in Astronomy and Astrophysics 2009年第11期9卷 1277-1284页

作者： Guang-Wei Li and Gang Zhao national astronomical {2., {3. academy of Sciences, Beijing 100012. china national astronomical {2. Chinese Academy of Sciences Beijing 100012 China

We introduce the network flow algorithm used by the Sloan Digital Sky Survey （SDSS） into the sky survey of the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST） to position tiles. Because fibers in LAMOST＇s focal plane are distributed uniformly, we cannot use SDSS＇ method directly. To solve this problem, firstly we divide the sky into many small blocks, and we also assume that all the targets that are in the same block have the same position, which is the center of the block. Secondly, we give a value to limit the number of the targets that the LAMOST focal plane can collect in one square degree so that it cannot collect too many targets in one small block. Thirdly, because the network flow algorithm used in this paper is a bipartite network, we do not use the general solution algorithm that was used by SDSS. Instead, we give our new faster solution method for this special network. Compared with the Convergent Mean Shift Algorithm, the network flow algorithm can decrease observation times with improved mean imaging quality. This algorithm also has a very fast running speed. It can distribute millions of targets in a few minutes using a common personal computer.

关键词： methods data analysis -- methods statistical

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The Kiloparsec-scale Structure of 3. 2.6

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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. {3. of Sciences, Shanghai 2.003. national astronomical observatories, {2. {3. of Sciences, Beijing 100012 Shanghai astronomical Observatory Chinese Academy of Sciences Shanghai 200030 national astronomical {2. Chinese Academy of Sciences Beijing 100012

We present radio images of the compact steep spectrum (CSS) quasar 3. 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 -13.° 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

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Infrared Galaxies in the Nearby Universe

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

作者： Jian-Ling Wang 1 national astronomical {2.,{3. academy of Sciences,Beijing 100012.china 2.Graduate School of {3. academy of Sciences,Beijing 100049,china national astronomical {2. Chinese Academy of Sciences Beijing 100012 China Graduate School of chinese academy of Sciences Beijing 100049 China

We used the Sloan Digital Sky Survey （SDSS） Data Release 5 （DR5） to study the morphological properties of 113. 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 3.%.

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

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