$\textstyle \parbox{150mm}{
{\LARGE\bf Chinese Journal of Astronomy and Astrophysics}\\
}$

2006, Vol.6, No.1 (February 20, 2006)



Contents


RESEARCH PAPERS


Extragalactic Astronomy


Stars

The Sun


Astrometry




Abstract

Refractive Focusing by Interstellar Clouds and the Rapid Polarization Angle Swing in QSO1150+812

Shan-Jie Qian1, T. P. Krichbaum2, Xi-Zhen Zhang1, L. Fuhrmann2, G. Cimò2, A. Kraus2, T. Beckert2, S. Britzen3, A. Witzel2, J.A. Zensus2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; rqsj@bao.ac.cn
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany

Abstract
A very rapid polarization position angle swing of $\sim
180^{\circ}$ (with a time scale of $\sim$6 hours) observed at 2cm in QSO1150+812 (z=1.25) was reported by Kochenov & Gabuzda. This very rare event is difficult to explain. We found a possible interpretation in the framework of a source model consisting of three polarized components, in which two compact polarized components are nearly simultaneously occulted by an interstellar cloud, with consequent focusing-defocusing effects. A specific plasma-lens model is proposed which can reasonably fit the polarized flux density curve with results derived for the two lensed components. Some physical parameters of the plasma-lens and the source components are estimated. The two compact polarized components are estimated to have brightness temperatures of $\sim
6 \times 10^{12}$K. Thus a bulk relativistic motion with a Lorentz factor less than 10 is required to meet the inverse-Compton limit.

Key Words:   radio continuum: galaxies - galaxies: compact - polarization - scattering - quasars: individual: 1150+812

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Elliptical Galaxies with Emission Lines from the Sloan Digital Sky Survey

Ying-He Zhao, Qiu-Sheng Gu, Zhi-Xin Peng, Lei Shi, Xin-Lian Luo and Qiu-He Peng

Department of Astronomy, Nanjing University, Nanjing 210093; qsgu@nju.edu.cn

Abstract
As part of a study of star formation history along the Hubble sequence, we present here the results for 11 elliptical galaxies with strong nebular emission lines. After removing the dilution from the underlying old stellar populations by use of stellar population synthesis model, we derive the accurate fluxes of all the emission lines in these objects, which are then classified, using emission line ratios, into one Seyfert 2, six LINERs and four HII galaxies. We also identify one HII galaxy (A1216+04) as a hitherto unknown Wolf-Rayet galaxy from the presence of the Wolf-Rayet broad bump at 4650Å. We propose that the star-forming activities in elliptical galaxies are triggered by either galaxy-galaxy interaction or the merging of a small satellite/a massive star cluster, as has been suggested by recent numerical simulations.

Key Words:   Galaxies: elliptical and lenticular, cD - Galaxies: starburst - Galaxies: individual: A1212+06, A1216+04, CGCG13-83, IC 225

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A Multiwavelength Study of the Jets in FR-I Radio Galaxies: I. Data and Analysis

Da-Min Meng and Hong-Yan Zhou

Center for Astrophysics, and Department of Astronomy and Applied Physics, University of Science and Technology of China, Hefei 230026; mdm@mail.ustc.edu.cn

Abstract
We compile a sample of 11 Fanaroff-Riley type I Radio Galaxies (FR-I RGs) with multi-wavelength observations to address the dynamic behavior of jets in these objects. Optical images acquired by the Hubble Space Telescope (HST) are carefully analyzed. The method and reduction procedure are described in detail. Unresolved optical cores emerge after having properly removed starlight from the host galaxies in eight of the FR-I RGs, of which five are new identifications. Broad band spectral properties of these newly identified compact cores are compared with that previously found in FR-I RGs, as well as the low-energy-peaked BL Lac objects. The similarity between them argues for the same non-thermal synchrotron origin. Well-resolved optical jets with knotty morphologies are found in three FR-I RGs in our sample, namely 3C15, 3C66B and B20755+37. The optical counterparts to the inner radio/X-ray jets are identified and a clear one-to-one correspondence between the optical, radio and X-ray knots is found. The structure and information on the optical jets are discussed. Physical parameters such as the knots position, flux and size are also presented. Detailed comparison between the multi-wavelength data and radiative and dynamic models of jet will be made in a forthcoming paper.

Key Words:   galaxies: active -- galaxies: jets

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Super-Large-Scale Structures in the Sloan Digital Sky Survey

Xin-Fa Deng1, Yi-Qing Chen2, Qun Zhang1, Ji-Zhou He1

1 Mathematics and Physics College, Nanchang University, Jiangxi 330047; xinfadeng@163.com
2 Management College, Nanchang University, Nanchang 330047

Abstract
We study the super-large-scale structures in the Sloan Digital Sky Survey by cluster analysis, and examine the geometry and the properties of the member galaxies. Two subsamples are selected from the SDSS, Subsample 1 at the celestial equator and Subsample 2 further north. In Subsample 1 we discover two compact super-large-scale structures: the Sloan Great Wall and the CfA Great Wall. The Sloan Great Wall, located at a median redshift of z=0.07804, has a total length of about 433Mpc and a mean galaxy density of about six times that of the whole sample. Most of its member galaxies are of medium size and brightness. The CfA Great Wall, located at a median redshift of z=0.03058, has a total length of about 251Mpc and includes large percentages of faint and small galaxies and relatively fewer early-type galaxies.

Key Words:   galaxy: distances and redshifts -- large-scale structure of universe

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Scale Heights of Non-Edge-on Spiral Galaxies

Tao Hu1, Qiu-He Peng1,2,3, Ying-He Zhao1

1 Department of Astronomy, Nanjing University, Nanjing 210093; taohu@nju.edu.cn
2 Joint Astrophysics Center of Chinese Academy of Science-Peking University, Beijing 100871
3 The Open Laboratory of Cosmic Ray and High Energy Astrophysics, Chinese Academy of Sciences, Beijing 100039

Abstract
We present a method of calculating the scale height of non-edge-on spiral galaxies, together with a formula for errors. The method is based on solving Poisson's equation for a logarithmic disturbance of matter density in spiral galaxies. We show that the spiral arms can not extend to inside the ``forbidden radius'' r0, due to the effect of the finite thickness of the disk. The method is tested by re-calculating the scale heights of 71 northern spiral galaxies previously calculated by Ma, Peng & Gu. Our results differ from theirs by less than 9%. We also present the scale heights of a further 23 non-edge-on spiral galaxies.

Key Words:   galaxy: disk -- galaxies: fundamental parameters -- galaxies: spiral -- galaxies: structure

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The Relationship between the Rise Width and the Full Width of $\gamma$-ray Burst Pulses and Its Implications

Rui-Jing Lu1,2,3, Yi-Ping Qin1,2 and Ting-Feng Yi2

1 National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; luruijing@126.com; ypqin@ynao.ac.cn
2 Department of Physics, Guangxi University, Nanning, Guangxi 530004
3 Graduate University of Chinese Academy of Sciences, Beijing 100049

Abstract
We investigate the relationship between the rise width and the full width of gamma-ray burst pulses. Theoretical analysis shows that either width is proportional to $\Gamma^{-2}\Delta\tau_{\theta,\rm FWHM}\frac{R_c}{c}$ ($\Gamma$ the Lorentz factor of the bulk motion, $\Delta \tau _{\theta,\rm
\rm FWHM}$ a local pulse's width, Rc the radius of fireballs and c the velocity of light). We study the relationship for four samples of observed pulses. We find: (1) merely the curvature effect could reproduce the relationship between the rise and full widths with the same slope as derived from the model of Qin et al.; (2) gamma-ray burst pulses, selected from both the short and long GRBs, follow the same sequence in the rise width vs. full width diagram, with the shorter pulses at one end; (3) all GRBs may intrinsically result from local Gaussian pulses. These features place constraints on the physical mechanism(s) for producing long and short GRBs.

Key words:  gamma rays: bursts - gamma rays: theory - methods: data analysis

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A Study of the Molecular Cloud S64 with Multiple Lines of CO Isotopes

Lei Zhu, Yue-Fang Wu and Yue Wei

Department of Astronomy, Peking University, Beijing 100871; yfwu@vega.pku.edu.cn

Abstract
We report on a study of the molecular cloud S64 with observations at millimeter wavelengths of multiple molecular lines of CO isotopes. A weak outflow is found, and its physical parameters are estimated. The departure of the core of S64 from the S64 HII region indicates that there are still other star formation activities in that region.

Key Words:   stars: formation -- ISM: clouds -- ISM: individual: S64 -- ISM: jets and outflows -- ISM: evolution -- ISM: kinematics and dynamics

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

Yun-Ming Dong, Lan-Wei Jia and Xiao-Hong Zhao

Yunnan Astronomical Observatory/National Astronomical Observatories, Chinese Academy of Sciences, Kunming 650011; dongym@ynao.ac.cn
Graduate University of Chinese Academy of Sciences, Beijing 100049

Abstract
physical quantities including the spectrum, emission lines and pulse profiles expected from a uniform jet, a spherical fireball and the $1/\Gamma$ region (the portion of the spherical fireball with opening angle $1/\Gamma$) 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 $1/\Gamma$ region, so we can simply use the $1/\Gamma$ region in approximate calculations; c) broadening of emission lines is a general phenomena, which mainly comes from the curvature effect; d) the $1/\Gamma$ region plays different roles in different frequency ranges, and the radiation from the $1/\Gamma$ region is greater in the higher than in the lower frequencies.

Key Words:   gamma-rays: bursts--gamma-rays: theory--radiation mechanisms: non-thermal --relativity

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Energy Buildup, Flux Confinement and Helicity Accumulation in the Solar Corona

You-Qiu Hu and Wen Li

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026; huyq@ustc.edu.cn

Abstract
Starting from a dipole field and a given distribution of footpoint displacement of field lines on the photosphere, we find axisymmetric, force-free field solutions in spherical coordinates that have the same distribution of normal field on the photosphere and magnetic topology as the dipole field. A photospheric shear is introduced in the azimuthal direction in a region that strides across the equator and ends at latitude $\lambda_s$. The footpoint displacement has a sine distribution in latitude and a peak amplitude of $\varphi_m$. The magnetic energy E, azimuthal flux $F_\varphi$, and magnetic helicity HT in the solar corona are then calculated for each force-free field solution. It is found that for a given shear region range $\lambda_s$, all of the three quantities increase monotonically with increasing $\varphi_m$. In particular, both $F_\varphi$ and HT have a linear dependence on $\varphi_m$. When $\varphi_m$ reaches a certain critical value $\varphi_{mc}$, the force-free field loses equilibrium, leading to a partial opening of the field and the appearance of a current sheet in the equatorial plane. At this point, E, $F_\varphi$ and HT reach their maximum values, Ec, $F_{\varphi c}$ and HTc. Ec increases, and $F_{\varphi c}$ and HTc decrease with decreasing $\lambda_s$. It is found that Ec is always smaller than the open field energy, in agreement with the Aly conjecture. Of the three critical parameters, Ec has the weakest dependence on $\lambda_s$. Therefore, if one is interested in the transition of a magnetic configuration from a stable state to a dynamic one, the magnetic energy is probably the most appropriate marker of the transition.

Key Words:   Sun: magnetic fields -- Sun: force-free fields -- methods: numerical

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Three-dimensional Distribution of the Escape Photons of H$\alpha$ Flares

Ming-Guo Sun1, 3, Zhong-Quan Qu1, Zhi Xu2, Xiao-Yu Zhang1, Cheng-Lin Xu1, 3, Shuai Wang1, 3 and Chun-Lan Jin1, 3

1 Yunnan Astronomical Observatory/National Astronomical Observatories, Chinese Academy of Sciences, Kunming 650011; sunmg@ynao.ac.cn
2 Department of Astronomy, Nanjing University, Nanjing 210093
3 Graduate University of the Chinese Academy of Sciences, Beijing 100049

Abstract
A technique for obtaining a three-dimensional distribution of received photons in H$\alpha$ flares in the solar atmosphere is presented. It is well known that during flares hydrogen atoms in the chromosphere and photosphere are excited (even ionized) by the downward heating of non-thermal particles and then emit H$\alpha$ photons. We trace back these H$\alpha$ photons to their original layers by use of the contribution function in the theory of spectral line formation, and so acquire their three-dimensional (3D) distribution. This technique is applied to the two-ribbon flare of 2002 January 20. The atmospheric models are obtained by fitting the ``quasi-profiles" with the help of the generally used model atmospheres. Since the variety of the 3D images reflects the response of the atmospheric layers to the impact of energy transport, an analysis of the development of the flare is given through a comparison of the 3D images with the 2D temperature distribution.

Key Words:   line: formation - radiative transfer - sun: flares

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Magnetic Helicity Injection in Solar Active Regions

Hong-Qi Zhang

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; hzhang@bao.ac.cn

Abstract
We present the evolution of magnetic field and its relationship with magnetic (current) helicity in solar active regions from a series of photospheric vector magnetograms obtained by Huairou Solar Observing Station, longitudinal magnetograms by MDI of SOHO and white light images of TRACE. The photospheric current helicity density is a quantity reflecting the local twisted magnetic field and is related to the remaining magnetic helicity in the photosphere, even if the mean current helicity density brings the general chiral property in a layer of solar active regions. As new magnetic flux emerges in active regions, changes of photospheric current helicity density with the injection of magnetic helicity into the corona from the subatmosphere can be detected, including changes in sign caused by the injection of magnetic helicity of opposite sign. Because the injection rate of magnetic helicity and photospheric current helicity density have different means in the solar atmosphere, the injected magnetic helicity is probably not proportional to the current helicity density remaining in the photosphere. The evidence is that rotation of sunspots does not synchronize exactly with the twist of photospheric transverse magnetic field in some active regions (such as, delta active regions). They represent different aspects of magnetic chirality. A combined analysis of the observational magnetic helicity parameters actually provides a relative complete picture of magnetic helicity and its transfer in the solar atmosphere.

Key Words:   Sun: activity - Sun: magnetic fields

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Time Evolution of the Turnover Frequency for Diagnosis of the Coronal Magnetic Field

Guang-Li Huang

Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008; glhuang@pmo.ac.cn

Abstract
Two impulsive microwave bursts observed by Owens-Valley Solar Arrays (OVSA) are studied. The fast time variation of the turnover frequency in these bursts is quite different from the constant value in the earlier conclusion. The observational turnover frequencies are consistent with the calculations using the non-thermal gyro-synchrotron radiation model. We find the turnover frequency may play an important role for calculating the coronal magnetic field on the basis of Dulk and Marsh's approximations.

Key Words:   Sun: radio radiation -- Sun: corona -- Sun: magnetic fields

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Atmospheric Excitation of Time Variable Length-of-Day on Seasonal Scales

Li-Hua Ma, and Yan-Ben Han

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; mlh@bao.ac.cn

Abstract
We use the method of wavelet transform to analyze the time series of the Earth's rotation rate of the EOP (IERS) C04. The result shows that the seasonal (annual and semiannual) variation of the length-of-day (LOD) has temporal variability in its period length and amplitude. During 1965.0-2001.0, the periods of the semiannual and annual components varied mainly from 175-day to 190-day and from 360-day to 370-day, respectively; while their amplitudes varied by more than 0.2ms and 0.1ms, respectively. Analyzing the axial component of atmospheric angular momentum (AAM) during this period, we have found that time-variations of period lengths and amplitudes also exist in the seasonal oscillations of the axial AAM and are in good consistency with those of the seasonal LOD change. The time variation of the axial AAM can explain largely the change of the LOD on seasonal scales.

Key Words:   Earth rotation -- seasonal variation -- wavelet transform

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ChJAA, 2006, Vol.6, No.1

Chinese Journal of Astronomy and Astrophysics: Online Edition

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