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{\LARGE\bf Chinese Journal of Astronomy and Astrophysics}\\

2007, Vol.7, No.2 (April 20, 2007)




Extragalactic Astronomy


The Sun

Instruments, Observational Techniques and Data Processing

Astrophysical Processing

Astrometry and Celestial Mechanics

History of Astronomy



The Long-term Survival Chances of Young Massive Star Clusters

Richard de Grijs1,2 and Geneviève Parmentier3

1 Department of Physics & Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, U. K.; R.deGrijs@sheffield.ac.uk
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
3 Institute of Astrophysics & Geophysics, Université de Liège, Allée du 6 Août, 17, Sart-Tilman (B5c), B-4000 Liège, Belgium

We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto-globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.

Key Words:   stellar dynamics -- globular clusters: general -- galaxies: interactions - Magellanic Clouds -- galaxies: starburst -- galaxies: star clusters
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Mid-to-Far Infrared Spectral Energy Distribution of Galaxies in the Spitzer First Look Survey Field

Xiao-Qing Wen1,2, Hong Wu2, Chen Cao2 and Xiao-Yang Xia1,2

1 Department of Physics, Tianjin Normal University, Tianjin 300074
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; hwu@bao.ac.cn

We made model fitting to the mid-to-far infrared spectral energy distributions (SEDs) for different categories of galaxies in the main extragalactic field of the Spitzer First Look Survey with the aid of spectroscopic information from the Sloan Digital Sky Survey. We find that the mid-to-far infrared SEDs of HII galaxies, mixture type galaxies and LINERs can be well fitted by the one-parameter ($\alpha$) dust model of Dale et al. plus the 13 Gyr dust-free elliptical galaxy model. The statistics of $\alpha$ values indicates that all these galaxies tend to be quiescent, although the HII galaxies are relatively more active than the LINERs. The mid-infrared SEDs of absorption galaxies are well fitted simply by the 13 Gyr dust-free elliptical galaxy template, and the near-to-mid infrared SEDs of QSOs can be represented by AGN NGC 5506.

Key Words:   galaxies: general - infrared: galaxies - galaxies: active - galaxies: statistics
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Cross-Correlation Detection of Point Sources in the WMAP First Year Data

Jian-Yin Nie1 and Shuang-Nan Zhang1,2

1 Department of Physics and Center for Astrophysics, Tsinghua University, Beijing 100084; science@sina.com
2 Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049

We apply a Cross-Correlation (CC) method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a powerful tool to examine the WMAP foreground residuals which can be further cleaned accordingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the flux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.

Key Words:   cosmic microwave background: WMAP -- cross-correlation -- radio point source
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Relation between the ``Double-Hump" Behavior in the Radio Band and the Broad-Line Luminosity for Blazars

Zhao-Hua Xie1, Hong Dai2,3, Jian-Ming Hao1, Lei-Ming Du1, and Xiong Zhang1

1 Physics Department, Yunnan Normal University, Kunming 650092; xiez@graduate.hku.hk
2 Yunnan Astrophysics Center, Yunnan University, Kunming 650091
3 Graduate School of Chinese Academy of Sciences, Beijing 100049

The physics behind the spectral energy distribution (SED) of blazars remains open. We assembled 36 blazars to tackle the factors that control their SED. Now, many blazar spectra have the ``double hump" feature in the radio and far-IR frequencies. For these a parameter, $\triangle$, is created to characterize the behavior of the SED. We found a significant correlation between the broad-line luminosity ($L_{\rm BLR}$) and $\triangle$. Because $L_{\rm BLR}$ is an indicator of the accreting power of the source in blazars, we derived a linear correlation, $\triangle \propto
\dot{M}^{1/3.18}$, which suggests that the SED of blazars may depend on the accretion rate, like that of BL Lac objects. We also found a significant correlation between $\dot{m}$ and $\triangle$ for a sample of 11 blazars (out of one of 36) with available black hole masses. This implies the Eddington accretion ratio may influence the shape of the SED of blazars.

Key Words:   accretion: accretion disks -- black hole physics -- galaxies: active -- galaxies: emission lines -- galaxies: nuclei
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Refractive Focusing of Interstellar Clouds and Intraday Polarization Angle Swings

Shan-Jie Qian1, T. P. Krichbaum2, Long Gao1, Xi-Zhen Zhang1, A. Witzel2 and 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

Intraday variations of compact extragalactic radio sources in flux density and polarization are generally interpreted in terms of refractive scintillation from the continuous interstellar medium of our Galaxy. However, continuous polarization angle swings of $\sim$180$\dg$ (for example, the one observed in the QSO0917+624) could not be interpreted in this way. Qian et al. have shown that the polarization angle swing observed in the QSO1150+812 can be explained in terms of focusing-defocusing effect by an interstellar cloud, which occults two closely-placed polarized components. Here we further show that the polarization angle swing event observed in the QSO0917+624 can also be explained in this way. We also found evidence for the cloud eclipsing a non-polarized (core) component during a short period outside the swing. A particular (and specific) plasma-lens model is proposed to model-fit the polarization swing event of 0917+624. Some physical parameters related to the plasma-lens and the source components are estimated. The brightness temperatures of the two lensed components are estimated to be $\sim$1.6 x 1013K. Thus bulk relativistic motion with a Lorentz factor less than $\sim$20 may be sufficient to avoid the inverse - Compton catastrophe.

Key Words:   radio continuum: galaxies -- polarization: intraday variability -- scattering: refractive focusing -- quasars: Individual: QSO 0917+624
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Distributions of Neutron Exposures in AGB Stars and the Galaxy

Wen-Yuan Cui1,2,4, Feng-Hua Zhang2,Wei-Juan Zhang2, Lu Zhang3, Bo Zhang1,2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
2 Department of Physics, Hebei Normal University, Shijiazhuang 050016; zhangbo@hebtu.edu.cn
3 Department of Modern Physics, University of Science and Technology of China, Hefei 230026
4 Graduate School of Chinese Academy of Sciences, Bejing 100049

Based on the s-process nucleosynthesis model with the 13C $(\alpha, n)^{16}$O reaction occurring under radiative conditions in the interpulse phases, we investigate the characteristics of the distribution of neutron exposure in low-mass Asymptotic Giant Branch (AGB) stars. We introduce a new concept, the distribution of neutron exposures of the Galaxy (NEG), to study the chemical evolution characteristics of the Galaxy for s-process elements. Using a chemical evolution model of the Galaxy, we develop a model for the NEG and obtain the evolution results of the NEG in different epochs. The present results appear to reasonably reproduce the distribution of neutron exposures of the solar system (hereafter NES). The main component and the strong component in the NES are built up in different epochs. The strong component of the s-process is mainly synthesised in the low-mass and metal-poor AGB stars, and the main component is produced by the s-process in the low-mass AGB stars with higher metallicities.

Key Words:   Galaxy: evolution -- stars: AGB and post-AGB-- stars: abundances
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On the Physical Processes in Contact Binary Systems

Run-Qian Huang1, Han-Feng Song1,2 and Shao-Lan Bi1

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

Three important physical processes occurring in contact binary systems are studied. The first one is the effect of spin, orbital rotation and tide on the structure of the components, which includes also the effect of meridian circulation on the mixing of the chemical elements in the components. The second one is the mass and energy exchange between the components. To describe the energy exchange, a new approach is introduced based on the understanding that the exchange is due to the release of the potential, kinetic and thermal energy of the exchanged mass. The third is the loss of mass and angular momentum through the outer Lagrangian point. The rate of mass loss and the angular momentum carried away by the lost mass are discussed. To show the effects of these processes, we follow the evolution of a binary system consisting of a $12M_{\odot}$ and a $5M_{\odot}$ star with mass exchange between the components and mass loss via the outer Lagrangian point, both with and without considering the effects of rotation and tide. The result shows that the effect of rotation and tide advances the start of the semi-detached and the contact phases, and delays the end of the hydrogen-burning phase of the primary. Furthermore, it can change not only the occurrence of mass and angular momentum loss via the outer Lagrangian point, but also the contact or semi-contact status of the system. Thus, this effect can result in the special phenomenon of short-term variations occurring over a slow increase of the orbital period. The occurrence of mass and angular momentum loss via the outer Lagrangian point can affect the orbital period of the system significantly, but this process can be influenced, even suppressed out by the effect of rotation and tide. The mass and energy exchange occurs in the common envelope. The net result of the mass exchange process is a mass transfer from the primary to the secondary during the whole contact phase.

Key Words:   stars: binaries: general -- stars: mass-loss -- stars: evolution
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Implementation of New OPAL Tables in Eggleton's Stellar Evolution Code

Xue-Fei Chen1 and Christopher A. Tout2,3

1 National Astronomical Observatories / Yunnan Observatory, CAS, Kunming 650011 xuefeichen717@hotmail.com
2 Institute of Astronomy, The Observatories, Madingley Road, Cambridge CB3 0HA, England
3 Centre for Stellar and Planetary Astrophysics, School of Mathematics, Monash University, Clayton, Victoria 3800, Australia

Based on previous works of OPAL, we construct a series of opacity tables for various metallicities Z=0, $0.000\,01$, $0.000\,03$, $0.000\,1$, $0.000\,3$, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for ${\log}_{10}(T/{\rm K})>
3.95$ and Alexander's for ${\log}_{10}(T/{\rm K})< 3.95$. At ${\rm
log}_{10}(T/{\rm K})=3.95$, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and $5\,M\odot$ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.

Key Words:   radiative transfer -- stars: evolution -- stars: general
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A Photometric Study of the Near Contact Binary UU Lyncis

Li-Ying Zhu1,2,3, Sheng-Bang Qian1,2, Soonthornthum Boonrucksar4, Jia-Jia He1,2,3, and Jin-Zhao Yuan1,2,3

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; lyzhu16@vip.sohu.com
2 United Laboratory of Optical Astronomy, Chinese Academy of Sciences (ULOAC), 100012 Beijing
3 Graduate School of Chinese Academy of Sciences, Beijing 100049
4 Department of Physics, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand

The near-contact binary UU Lyn with an F3V-type primary was observed in 2005 and 2006. With the latest version of the Wilson-Devinney code, the photometric elements were computed. The results reveal that UU Lyn is a marginal contact system with a large temperature difference of about 1900K between the primary and secondary components. All available eclipse times, including new ones, were used in the analysis. The results show that the orbital period of this system undergoes a continuous decrease at a rate of dP/dt=-1.84 x 10-8dyr-1. With the period decrease, UU Lyn may evolve from the present short-period marginal contact system into a contact system with true thermal contact. This target might just be undergoing the cycles predicted by the theory of thermal relaxation oscillations (TRO). It is an interesting example resembling BL And, GW Tau, ZZ Aur, KQ Gem, CN And and AD Cnc, that lie in the key evolutionary stage.

Key Words:   techniques: photometric -- binaries: eclipsing -- stars: individual: UU Lyncis
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TZ Lyrae: an Algol-type Eclipsing Binary with Mass Transfer

Yuan-Gui Yang and Xin-Guo Yin

Physics Department of Huaibei Coal Industry Teachers College, Huaibei 235000; yygcn@163.com

We present a detailed investigation of the Algol-type binary TZ Lyrae, based on 55 light minimum timings spanning 90 years. It is found that the orbital period shows a long-term increase with a cyclic variation superimposed. The rate of the secular increase is dP/dt=+7.18 x 10-8 d yr-1, indicating that a mass transfer from the less massive component to the more massive one at a rate of $dm=+2.21\times10^{-8}\mathrm{M_\odot~yr^{-1}}$. The cyclic component, with a period of $P_{3}=45.5\,{\rm yr}$ and an amplitude of $A=0\fd0040$, may be interpreted as either the light-time effect in the presence of a third body or magnetic activity cycles in the components. Using the latest version Wilson-Devinney code, a revised photometric solution was deduced from B and V observations. The results show that TZ Lyr is an Algol-type eclipsing binary with a mass ratio of $q=0.297(\pm0.003)$. The semidetached configuration with a lobe-filling secondary suggests a mass transfer from the secondary to the primary, which is in agreement with the long-term period increase of the binary system.

Key Words:   stars: binaries: close -- stars: binaries: eclipsing -- stars: individual: TZ Lyrae
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Magnetic Properties of Metric Noise Storms Associated with Coronal Mass Ejections

Ya-Yuan Wen, Jing-Xiu Wang and Yu-Zong Zhang

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

Using Nançay Radioheliograph (NRH) imaging observations, combined with SOHO/Michelson Doppler Imager (MDI) magnetogram observations and coronal magnetic field extrapolation, we studied the magnetic nature of metric noise storms that are associated with coronal mass ejections (CMEs). Four events are selected: the events of 2000 July 14, 2001 April 26, 2002 August 16 and 2001 March 28. The identified noise storm sources cover or partially cover the active regions (ARs), but the centers of storm sources are offset from the ARs. Using extrapolated magnetic field lines, we find that the noise storm sources trace the boundary between the open and closed field lines. We demonstrate that the disappearance of noise storm source is followed by the appearance of the burst source. The burst sources spread on the solar disk and their distributions correspond to the extent of the CME in LASCO C2 field of view. All the SOHO/Extreme Ultraviolet Imaging Telescope (EIT) dimmings associated with noise storm sources are located at the periphery of noise storms where the magnetic lines of force were previously closed and low-lying. When the closed field becomes partially or fully open, the basic configurations of noise storm sources are changed, then the noise storm sources are no longer observed. These observations provide the information that the variations of noise storms manifest the restructuring or reconfiguring of the coronal magnetic field.

Key Words:   Sun: corona -- Sun: coronal mass ejection (CME) -- Sun: radio radiation
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Solar Magnetism and the Activity Telescope at HSOS

Hong-Qi Zhang1,Dong-Guang Wang1, Yuan-Yong Deng1, Ke-Liang Hu1, Jiang-Tao Su1, Jia-Ben Lin1, Gang-Hua Lin1, Shi-Mo Yang2, Wei-Jun Mao3, Ya-Nan Wang3, Qi-Qian Hu3, Jun-Sun Xue3, Hai-Tian Lu3, Hou-Kun Ni3, Han-Liang Chen3, Xiao-Jun Zhou3, Qing-Sheng Zhu3, Lü-Jun Yuan3 and Yong Zhu3

1 Huairou Solar Observing Station, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; hzhang@bao.ac.cn
2 Space Technical Laboratory, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
3 Nanjing Institute of Astronomical Optics and Technology, National Astronomical Observatories, Chinese Academy of Sciences, Nanjing 210042

A new solar telescope system is described, which has been operating at Huairou Solar Observing Station (HSOS), National Astronomical Observatories, Chinese Academy of Sciences (CAS), since the end of 2005. This instrument, the Solar Magnetism and Activity Telescope (SMAT), comprises two telescopes which respectively make measurements of full solar disk vector magnetic field and H$\alpha$ observation. The core of the full solar disk video vector magnetograph is a birefringent filter with 0.1Å bandpass, installed in the tele-centric optical system of the telescope. We present some preliminary observational results of the full solar disk vector magnetograms and H$\alpha$ filtergrams obtained with this telescope system.

Key Words:   Sun: activity -- Sun: telescope -- Sun: magnetic fields
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A Comparison of BBN, ADTree and MLP in separating Quasars from Large Survey Catalogues

Yan-Xia Zhang and Yong-Heng Zhao

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

We compare the performance of Bayesian Belief Networks (BBN), Multilayer Perception (MLP) networks and Alternating Decision Trees (ADtree) on separating quasars from stars with the database from the 2MASS and FIRST survey catalogs. Having a training sample of sources of known object types, the classifiers are trained to separate quasars from stars. By the statistical properties of the sample, the features important for classification are selected. We compare the classification results with and without feature selection. Experiments show that the results with feature selection are better than those without feature selection. From the high accuracy found, it is concluded that these automated methods are robust and effective for classifying point sources. They may all be applied to large survey projects (e.g. selecting input catalogs) and for other astronomical issues, such as the parameter measurement of stars and the redshift estimation of galaxies and quasars.

Key Words:   astronomical databases: miscellaneous -- catalogs -- methods: data analysis -- methods: statistical
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Measurements for the Performance of the Digital Autocorrelation Spectrometer

Fa-Chun Lu1,2, Jarken Esimbek1, Jian-Jun Zhou1,2 and Xing-Wu Zheng3

1 National Astronomical Observatories/Urumqi Observatory, Chinese Academy of Sciences, Urumqi 830011; lufc@ms.xjb.ac.cn
2 Graduate University of Chinese Academy of Sciences, Beijing 100049
3 Department of Astronomy, Nanjing University, Nanjing 210093

Injecting phase calibration (PCAL) signals to the feed horn of the observation system and analyzing the output response signals of the spectrometer, we measured the working performance of a 4096-channel digital autocalibration spectrometer. The results demonstrate that the spectrometer has a fine working performance: (1) the channels are distributed uniformly in the spectrometer; (2) line drift produces little effect on the observation results; (3) spectral resolution shows little changes with observation time. The distribution of the frequency resolution in an 80 MHz bandwidth was measured. A trial observation on the two molecular spectral lines of H2CO and H110$_{\alpha}$ taken with this spectrometer is described.

Key Words:   instrumentation: spectrometer -- ISM: molecules -- radio lines: ISM
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Maser Emission of Relativistic Electrons Spiralling and Drifting in Curved Magnetic Fields

Jiong Liu, Ye-Fei Yuan and Xiao-Long Deng

Center for Astrophysics, University of Science and Technology of China, Hefei 230026; liujiong@mail.ustc.edu.cn

Synchro-curvature radiation describes the emission from a relativistic charged particle which is moving and spiralling in a curved magnetic field. We investigate the maser emission for synchro-curvature radiation including drift of the guiding center of the radiating electron. It is shown that under some conditions the absorption coefficient can be negative, so maser can happen. These conditions are different from those needed for maser emission of curvature radiation including drift of the charged particles. We point out that our results, including the emissivity, can reduce to these of curvature radiation. Previously it was found that synchro-curvature radiation can not generate maser in vacuum, but we argue that synchro-curvature radiation including drift can generate maser even in vacuum. We discuss the possibilities of the potential applications of the synchro-curvature maser in modeling gamma ray bursts and pulsars.

Key Words:   masers -- plasmas -- radiation mechanisms: non-thermal
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Eclipses and Occultations of Galilean Satellites Observed at Yunnan Observatory in 2003

Qing-Yu Peng1,3 and Benoît Noyelles1,2,

1 Department of Computer Science, Jinan University, Guangzhou 510632; pengqy@pub.guangzhou.gd.cn
2 Institut de mécanique céleste et de calcul des éphémérides - Observatoire de Paris, UMR 8028 du CNRS, 77 avenue Denfert-Rochereau, F-75014 Paris, France
3 Joint Laboratory for Optical Astronomy, Chinese Academy of Sciences, Kunming 650011

We describe and analyze observations of mutual events of Galilean satellites made at the Yunnan Observatory in February 2003 from CCD imaging for the first time in China. Astrometric positions were deduced from these photometric observations by modelling the relative motion and the photometry of the involved satellites during each event.

Key Words:   planets and satellites: individual: Jupiter -- astrometry -- eclipse -- occultation
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The Historical Re-Brightening and Distance Recheck of SN 1006

Shi-Yang Jiang and Fu-Yuan Zhao

National Astronomical Observatory, Chinese Academy of Sciences, Beijing 100012; jiangsy@bao.ac.cn

We presume the re-brightening of SN 1006 in AD 1016 as recorded in the ancient Chinese literature to be true and the re-brightening was caused by the encounter either of photons or the shock wave from the SN outburst with the circumstellar thin envelope materials. Based on these considerations, and combining the observational results on the optical proper motion of the N-W limb and the radio observations of the other parts of the supernova remnant G327.6+14.5, we re-determine the distance to SN 1006. For the photon-encounter model, the average radius of the envelope material would be 10ly; and for the shock wave-encounter model, the radius would be about 1ly. We then set up four equations to solve for the distance of the SN, the initial shock speed, the expansion index for two different parts of the supernova remnant, and the real original radius of the thin envelope nebula. It is indicated that only the case of photon-encounter will lead to a reasonable result. We derived a distance of 5074ly (1.56kpc), an original shock expansion velocity of 0.071c, an expansion index of 0.72 for the N-W limb of the SNR, and 0.76 for the other parts . We deem that the SNR evolution is still in the stage of reverse shock.

Key Words:   supernova: supernova remnant -- SN 1006 distance -- Zhou-Bo Star -- planetary nebula
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Gamma-Ray Bursts in the Swift Era   
(ChJAA, 7, 1, 2007) There are some misprinted characters in Figure 2 on page 7 in the paper version (the on-line version is right). The Printers deeply regret this error and offer their sincere apologies to the author. The editors thank Professor Tan Lu for kindly alerting us this error. Please note also the following erratum on page 1 of this paper, `accepted 2006 January 20' should read `accepted 2007 January 20'.
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ChJAA, 2007, Vol.7, No.2

Chinese Journal of Astronomy and Astrophysics: Online Edition


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