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Gravitational lensing properties of an isothermal universal halo profile

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Research in Astronomy and Astrophysics 2013年第5期13卷 517-525页

作者： Xin-Zhong Er national astronomical observatories Chinese Academy of Sciences

N-body simulations predict that dark matter halos with different mass scales are described by a universal model, the Navarro-Frenk-White （NFW） den- sity profiles. As a consequence of baryonic cooling effects, these halos will become more concentrated, and similar to an isothermal sphere over a large range in radii （～ 300 h-1 kpc）. The singular isothermal sphere （SIS） model however has to be trun- cated artificially at large radii since it extends to infinity. We model a massive galaxy halo as a combination of an isothermal sphere and an NFW density profile. We give an approximation for the mass concentration at different baryon fractions and present exact expressions for the weak lensing shear and flexion for such a halo. We compare the lensing properties with the SIS and NFW profiles. We find that the combined pro- file can generate higher order lensing signals at small radii and is more efficient in generating strong lensing events. In order to distinguish such a halo profile from the SIS or NFW profiles, one needs to combine strong and weak lensing constraints for small and large radii.

关键词： gravitational lensing -- galaxies: halos -- cosmology: dark matter

Distribution of magnetic shear angle at the ascending phase of CYCLE 23

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Science China Mathematics 2002年第z1期45卷 12-18页

作者：敦金平张洪起张柏荣李如风 national astronomical observatories Chinese Academy of Sciences Beijing 100012 China National Astronomical Observatories Chinese Academy of Sciences Kunming 650011 China national astronomical observatories Chinese Academy of Sciences Beijing 100012 China national astronomical observatories Chinese Academy of Sciences Kunming 650011 China

Using the vector magnetograms observed at Huairou Solar Observing Station of Na- tional astronomical observatories, the magnetic shear angles of solar active regions at the as- cending phase of cycle 23 (1996-2000) were calculated. It is found that the statistical distribution of the magnetic shear angles can be fitted well by Gaussian curves. And the dominant sign of the magnetic shear angles is negative (positive) in the northern (southern) hemisphere. It is consistent with the N-S sign asymmetry of force-free field constant a and current helicity.

关键词： solar activity, magnetic shear angles.

FAST VLBI: current status and future plans

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Research in Astronomy and Astrophysics 2020年第5期20卷 165-170页

作者： Ru-Rong Chen Hai-Yan Zhang Cheng-Jin Jin Zhi-Shen Gao Yan Zhu Kai Zhu Peng Jiang You-Ling Yue Ji-Guang Lu Bo Zhang Wu Jiang Ren-Jie Zhu Shao-Guang Guo Bo Xia Rong-Bing Zhao FAST Collaboration national astronomical observatories Chinese Academy of SciencesBeijing 100101China CAS Key Laboratory of FAST National Astronomical ObservatoriesChinese Academy of SciencesBeijing 100101China Shanghai astronomical observatory Chinese Academy of SciencesShanghai 200030China

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)is the largest single-dish radio telescope in the world,and is now being commissioned after the first light in September *** long baseline interferometry(VLBI)is among the key science topics according to the original *** FAST VLBI system has been established,and the first VLBI fringe has been successfully *** will significantly improve the sensitivity of the existing VLBI networks in the future,and some science projects in need of high sensitivity will benefit from its participation.

关键词： instrumentation:interferometers telescopes site testing

Terrain reconstruction from Chang'e-3 PCAM images

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Research in Astronomy and Astrophysics 2015年第7期15卷 1057-1067页

作者： Wen-Rui Wang Xin Ren Fen-Fei Wang Jian-Jun Liu Chun-Lai Li national astronomical observatories Chinese Academy of Sciences

The existing terrain models that describe the local lunar surface have limited resolution and accuracy, which can hardly meet the needs of rover navigation,positioning and geological analysis. China launched the lunar probe Chang＇e-3 in December, 2013. Chang＇e-3 encompassed a lander and a lunar rover called ＂Yutu＂（Jade Rabbit）. A set of panoramic cameras were installed on the rover mast. After acquiring panoramic images of four sites that were explored, the terrain models of the local lunar surface with resolution of 0.02 m were reconstructed. Compared with other data sources, the models derived from Chang＇e-3 data were clear and accurate enough that they could be used to plan the route of Yutu.

关键词： space vehicles: rover -- space vehicles: instruments: panoramic camera-- methods: terrain reconstruction -- techniques: image processing: orthoimage

The spatial distribution of old neutron stars in the Galaxy

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Science China(Physics,Mechanics & Astronomy) 2010年第10期53卷 1939-1946页

作者： WEI YingChun ZHANG ChengMin WU XinJi ZHAO YongHeng CHOU ChiKang LUO ALi national astronomical observatories Chinese Academy of SciencesBeijing 100012China Department of Astronomy Peking UniversityBeijing 100871China national astronomical observatories/Urumqi observatory Chinese Academy of SciencesUrumqi 830011China

The spatial distributions of old neutron stars (NSs) with ages 109 to 1010 yr in our Galaxy are investigated by Monte Carlo simulation under two different initial random velocity *** is found that the scale heights of the distribution increase with the Galactic radial *** location of the peak of the NS distribution is closer to the Galactic center than that of their *** results from our detailed numerical analysis reveal that there is resemblance between the simulated old NS distribution and the structure of the observed HI disk.

关键词： neutron stars Galaxy structure Galaxy disk star evolution

Different Features of Jets and Isotropic Fireballs in Gamma-ray Burst Phase

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Chinese Journal of Astronomy and Astrophysics 2006年第1期6卷 69-76页

作者： Yun-Ming Dong Lan-Wei Jia Xiao-Hong Zhao Yunnan astronomical observatory/national astronomical observatories Chinese Academy ofSciences Kunming 650011 Graduate University of Chinese Academy of Sciences Beijing 100049

We investigated physical quantities including the spectrum, emission lines and pulse profiles expected from a uniform jet, a spherical fireball and the 1/Г region （the portion of the spherical fireball with opening angle 1/Г） in the prompt emission phase, after taking into consideration of the Doppler effect under the fireball framework. Our study shows that： a） for these physical quantities the spherical fireball and the uniform jets do not present obvious differences, so we cannot use these to distinguish a spherical fireball from a uniform jet; b） for the spherical fireball and a uniform jet, the observed quantities mainly come from the 1/Г region, so we can simply use the 1/Г region in approximate calculations; c） broadening of emission lines is a general phenomena, which mainly comes from the curvature effect; d） the 1/Г region plays different roles in different frequency ranges, and the radiation from the 1/Г region is greater in the higher than in the lower frequencies.

关键词： gamma-rays: bursts--gamma-rays: theory--radiation mechanisms: non-thermal --relativity

A method to predict amplitude and date of maximum sunspot number

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Chinese Science Bulletin 2000年第14期45卷 1287-1290页

作者： HAN YanbenBeijing astronomical observatory, Chinese Academy of Sciences, national astronomical observatories, Chinese Academy of Sciences, Beijing 100012, China Beijing astronomical observatory Chinese Academy of Sciences National Astronomical Observatories Chinese Academy of Sciences Beijing China

A method to predict the amplitude and date of the maximum sunspot number is introduced. The regression analysis of the relationship between the variation rate of monthly sunspot numbers in the initial stage of solar cycles and both of the maximum and the time-length of ascending period of the cycle showed that they are closely correlative. In general, the maximum will be larger and the ascending period will be shorter when the rate is larger. The rate of sunspot numbers in the initial 2 years of the 23rd cycle is thus analyzed based on these grounds and the maximum of the cycle is predicted. For the smoothed monthly sunspot numbers, the maximum will be about 139.2 ±18.8 and the time-length of ascending period will be about 3.31 ±0.42 years, that is to say, the maximum will appear around the spring of the year 2000. For the mean monthly ones, the maximum will be near 170.1±22.9 and the time-length of ascending period will be about 3.42 ±0.46 years, that is to say, the appearing date of the maximum

关键词： solar activity prediction sunspot number 23rd solar cycle.

Data processing and error analysis for the CE-1 Lunar microwave radiometer

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Research in Astronomy and Astrophysics 2013年第3期13卷 359-372页

作者： Jian-Qing Feng Yan Su Jian-Jun Liu Yong-Liao Zou Chun-Lai Li national astronomical observatories Chinese Academy of Sciences

The microwave radiometer （MRM） onboard the Chang＇ E-1 （CE-I） lu- nar orbiter is a 4-frequency microwave radiometer, and it is mainly used to obtain the brightness temperature （TB） of the lunar surface, from which the thickness, temperature, dielectric constant and other related properties of the lunar regolith can be derived. The working mode of the CE-1 MRM, the ground calibration （including the official calibration coefficients）, as well as the acquisition and processing of the raw data are introduced. Our data analysis shows that TB increases with increasing frequency, decreases towards the lunar poles and is significantly affected by solar illumination. Our analysis also reveals that the main uncertainty in TB comes from ground calibration.

关键词： space vehicles -- instruments: microwave radiometer -- Moon: bright-ness temperature -- method: data processing -- error analysis

Radio spectral index from NVSS and TGSS

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Research in Astronomy and Astrophysics 2019年第7期19卷 59-66页

作者： Prabhakar Tiwari national astronomical observatories Chinese Academy of Sciences

I extract the radio spectral index,α,from 541 195 common sources observed in the 150 MHz TIFR GMRT Sky Survey(TGSS) and the 1.4 GHz NRAO VLA Sky Survey(NVSS).This large common source catalog covers about 80% of the *** flux density limits in these surveys are such that the observed galaxies are presumably hosts of active galactic nuclei(AGNs).I confirm the steepening of αwith increasing flux density for this large sample and provide a parametric fit between α and flux ***,I divide the data into low flux(LF) and high flux(HF) density samples with roughly equal numbers of *** LF sample contains all galaxies below 100 m Jy TGSS and 20 m Jy NVSS flux density and the HF sample is all galaxies above 100 m Jy TGSS and 20 m Jy NVSS.I observe an increase in α with source size(TGSS measured),saturating for large sizes to 0.89 ± 0.22 and 0.76 ± 0.21 for the LF and HF sources,respectively.I discuss the observed results and possible physical mechanisms to explain observedα dependence with source size for LF and HF samples.

关键词： galaxies:high-redshift galaxies:active galactic nuclei