| 2003,
Vol.3, No.6 (December 20, 2003)
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Letter
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Extragalactic
Astronomy
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Stars
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The Sun
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Astrometry and celestial mechanics
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Instruments, observational techniques and data processing
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Three Super Active Regions in the Descending Phase of Solar Cycle 23 Hong-Qi Zhang, Xing-Ming Bao, Yin Zhang, Ji-Hong Liu, Shu-Dong Bao, Yuan-Yong Deng, Wei Li, Jie Chen, Jin-Ping Dun, Jiang-Tao Su, Juan Guo, Xiao-Fan Wang, Ke-Liang Hu, Gang-Hua Lin and Dong-Guang Wang Affiliation: National Astronomical Observatories, CAS (NAOC), Beijing 100012, China E-mail: hzhang@bao.ac.cn
Abstract |
Discovery of an Optical Jet in the Rosette Nebula: Rosette HH2 Jin-Zeng Li Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 E-mail: ljz@bao.ac.cn Abstract |
Vertical Scale Parameter Estimates for 48 Non-edge-on Spiral Galaxies Jun Ma (1,2) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China (2) CAS-Peking Univ. Joint Astrophy. Center, Peking Univ., Beijing, China E-mail: majun@vega.bac.pku.edu.cn
Abstract |
The Two Mini-lobes of the CSO OQ208 --- VLBI Observations at 5 GHz and 8.4 GHz Wei-Hua Wang, Xiao-Yu Hong and Tao An (1,2) Affiliation: (1) Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (2) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 E-mail: whwang@center.shao.ac.cn Abstract We present the results of VLBI observations at 5 GHz and 8.4 GHz of the compact symmetric object (CSO) OQ208. Images taken on four epochs at 5 GHz and one at 8.4 GHz show that the parsec radio structure of the source consists of two mini-lobes, both of them are resolved into two hot-spots. We note that the component D is stronger than the component C in the south-west region at 5 GHz, indicating that component D is less free-free absorbed than C at low frequency. On the basis of the separation of components A and D, a proper motion of 0.032±0.02 mas yr-1 between the two mini-lobes is estimated. This value is about half the previous estimates based on the separation of components A and C with 8.4 GHz VLBI data. The reason for the decrease in the expansion velocity is discussed. Key words: galaxies: individual (Mkn 668, OQ208) --- galaxies: active PDF file (183 KB) | gzipped PS file (193 KB) | Back to Contents |
The Binary Black Hole Scenario for the BL Lacertae Object AO 0235+16 G. E. Romero (1), Jun-Hui Fan (2,*) and S. E. Nuza (3) Affiliation: (1) Instituto Argentino de Radioastronomía, C.C.5, (1894) Villa Elisa, Bs. As., Argentina; romero@irma.iar.unlp.edu.ar (2) Center for Astrophysics, Guangzhou University, Guangzhou 510400; fjh@gzhu.edu.cn (3) Departamento de Física J. J. Giambiagi, FCEN, UBA, Pabellón 1, Ciudad Universitaria, 1428 Buenos Aires, Argentina E-mail: fjh@gzhu.edu.cn (coressponding author) Abstract Recent analysis of the long term radio light curve of the extremely variable BL Lacertae object AO 0235+16 by Raiteri et al. have revealed the presence of recurrent outbursts with a period of 
5.7±0.5 yr. Periodicity analysis of the optical light curve also shows evidence for a shorter period. Here we discuss whether such a
behavior can be explained by a binary black hole model where the accretion disk of one of the supermassive black holes is precessing
due to the tidal effects of the companion. We estimate the mass of the accreting hole and analyze constraints on the secondary mass and
the orbital parameters of the system. It is possible to provide a viable interpretation of the available multiwavelength data.Key words: galaxies: active -- BL Lacertae objects: individual: AO 0235+16 -- gamma rays: theory -- black hole physics PDF file (240 KB) | gzipped PS file (209 KB) | Back to Contents |
Extinction of Beamed Gamma-ray Burst Afterglows in a Dense Circumstellar Cloud Shun-Lin Liang, Zi-Gao Dai, Yong-Feng Huang and Tan Lu Affiliation: (1) Department of Astronomy, Nanjing University, Nanjing 210093 E-mail: liangshunlin@sina.com ; daizigao@public1.ptt.js.cn (corresponding author) Abstract Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30 pc within the initial solid angle of the jet. As the jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results show that a break appears in the light curve of optical afterglow but it extends over a factor of 80 in time rather than a factor of
10 in time for the case of strong dust
extinction and a factor of 60 in time for the case without dust extinction. These results may provide a way to judge how large
the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can
provide a good fit to the multi-color observations of this event.Key words: gamma-rays: bursts --- dust: extinction --- stars: formation PDF file (323 KB) | gzipped PS file (251 KB)| Back to Contents |
Strange Stars: Can Their Crust Reach the Neutron Drip Density? Hai Fu and Yong-Feng Huang Affiliation: Department of Astronomy, Nanjing University, Nanjing 210093, China E-mail: hyf@nju.edu.cn Abstract The electrostatic potential of electrons near the surface of static strange stars at zero temperature is studied within the frame of the MIT bag model. We find that for QCD parameters within rather wide ranges, if the nuclear crust on the strange star is at a density leading to neutron drip, then the electrostatic potential will be insufficient to establish an outwardly directed electric field, which is crucial for the survival of such a crust. If a minimum gap width of 200 fm is brought in as a more stringent constraint, then our calculations will completely rule out the possibility of such crusts. Therefore, our results argue against the existence of neutron-drip crusts in nature. Key words: dense matter --- elementary particles --- stars: neutron PDF file (402 KB) | gzipped PS file (212 KB) | Back to Contents |
Spectral Properties of Anomalous X-ray Pulsars Ye Lu, Wei Wang and Yong-Heng Zhao Affiliation: National Astronomical Observatories, CAS (NAOC), Beijing 100012, China E-mail: ly@bao.ac.cn (corresponding author) Abstract We examine the spectra of the persistent emission from anomalous X-ray pulsars (AXPs) and their variation with the spin-down rate  . Based on an accretion-powered model, the influences of both the magnetic field and the mass accretion rate on the
spectral properties of AXPs are addressed. We then investigate the relation between the spectral property of AXPs and mass accretion
rate  . The result shows that there exists a linear correlation between the photon index and the mass accretion rate: the
spectral hardness increases with increasing
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A possible emission mechanism for the explanation of the spectral properties of
AXPs is also discussed.Key words: pulsars: general --- stars: neutron --- X-rays: stars --- accretion: accretion disks PDF file (176 KB) | gzipped PS file (128 KB) | Back to Contents |
The Chemical Classification of the AGB Star IRAS 17515--2407 Pei-Sheng Chen (1) and Pin Zhang (1,2) Affiliation: (1) National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011 (2) Cosmic Ray Institute, Yunnan University, Kunming 650091; iraspsc@yahoo.com.cn E-mail: ym990715@public.km.yn.cn (corresponding author) Abstract The chemical classification of IRAS 17515--2407 has been debated for a long time. Up to now there are two contenders, oxygen-rich or carbon-rich. We believe that IRAS 17515--2407 is an oxygen-rich source: because (i) it shows the silicate self-absorbed emission; (ii) in the near infrared-IRAS diagram it is located in the oxygen-rich object region and (iii) particularly, it has detected SiO maser emission. Key words: stars: AGB -- stars: chemical classification -- stars: maser -- infrared: stars PDF file ( 109KB) | gzipped PS file (82 KB) | Back to Contents |
Magnetic Energy of Force-Free Fields with Detached Field Lines Guo-Qiang Li and You-Qiu Hu Affiliation: (1) School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026 E-mail: ligq@mail.ustc.edu.cn (corresponding author) Abstract Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma  (the ratio between gas pressure and magnetic pressure) is taken to be so small
( = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve
quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic
energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in
equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the
threshold is exceeded. The energy threshold is found to be larger than that of the
corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed
or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example
showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines
is allowed to be detached from the solar surface. The implication of
such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic
fields.Key words: Sun: magnetic fields --- Sun: coronal mass ejections (CMEs) --- methods: numerical PDF file (168 KB) | gzipped PS file (124 KB) | Back to Contents |
Verification of Short-Term Predictions of Solar Soft X-ray Bursts for the Maximum Phase (2000--2001) of Solar Cycle 23 Cui-Lian Zhu and Jia-Long Wang Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 E-mail: zcl@bao.ac.cn (corresponding author) Abstract We present a verification of the short-term predictions of solar X-ray bursts for the maximum phase (2000--2001) of Solar Cycle 23, issued by two prediction centers. The results are that the rate of correct predictions is about equal for RWC-China and WWA; the rate of too high predictions is greater for RWC-China than for WWA, while the rate of too low predictions is smaller for RWC-China than for WWA. Key words: Sun: X-ray bursts --- Sun: Short-term prediction PDF file (109 KB) | gzipped PS file (44 KB) | Back to Contents |
A Check on the Variations of Earth's Rotation with an Ancient Solar Eclipse Yan-Ben Han and Qi-Yuan Qiao Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 E-mail: hyb@bao.ac.cn (corresponding author) Abstract We address the relation between an ancient total eclipse, which occurred on A.D.1542 August 11 and the variation of Earth's rotation. The total eclipse was recorded in some ancient Chinese books, especially in local chronicles. Some of the documents include useful information for determining the location of the totality zone. The parameters of the eclipse are calculated by using the DE406 Ephemeris. A high-precision value of  T which expresses the variation of the Earth's rotation, of about
300 380 s, is obtained.Key words: solar eclipse --- Earth rotation PDF file (186 KB) | gzipped PS file (210 KB) | Back to Contents |
A Tilt-correction Adaptive Optical System for the Solar Telescope of Nanjing University Chang-Hui Rao (1), Wen-Han Jiang (1), Cheng Fang (2), Ning Ling (1), Wei-Chao Zhou (1), Ming-De Ding (2), Xue-Jun Zhang (1), Dong-Hong Chen (1), Mei Li (1), Xiu-Fa Gao (2) and Tian Mi (2) Affiliation: (1) Adaptive Optics Lab., Institute of Optics and Electronics, Chinese Academy of Sciences, P. O. Box 350, Chengdu 610209 (2) Astronomy Department, Nanjing University, Nanjing 210093, China E-mail: chrao@sc.homeway.com.cn (corresponding author) Abstract A tilt-correction adaptive optical system installed on the 430 mm Solar Telescope of Nanjing University has been put in operation. It consists of a tip-tilt mirror, a correlation tracker and an imaging CCD camera. An absolute difference algorithm is used for detecting image motion in the correlation tracker. The sampling frequency of the system is 419 Hz. We give a description of the system's configuration, an analysis of its performance and a report of our observational results. A residual jitter of 0.14 arcsec has been achieved. The error rejection bandwidth of the system can be adjusted in the range 5--28 Hz according to the beacon size and the strength of atmospheric turbulence. Key words: telescopes --- atmospheric effects --- instrumentation --- adaptive optics --- Sun: atmospheric motions PDF file (1253 KB) | gzipped PS file (2338 KB) | Back to Contents |
Wavelet Analysis of Space Solar Telescope Images Xi-An Zhu (1,2) , Sheng-Zhen Jin (1), Jing-Yu Wang (1) and Shu-Nian Ning (2) Affiliation: (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing, 100012 (2) Department of Mechanical and Electric Engineering, China College of Mining and Technology, Beijing 100083 E-mail: zhuan@sst.bao.ac.cn (corresponding author) Abstract The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job. Key words: stars: images --- techniques: image processing --- methods: wavelet analysis PDF file (509 KB) | gzipped PS file (590 KB) | Back to Contents |
