| 2002,
Vol.2, No.6 (December 20, 2002)
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Letters
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Extragalactic astronomy
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Stars
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The Sun
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Instruments, observational techniques and data processing
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| Searching for Variable Stars in and around Open Clusters
Yu Xin, Xiao-Bin Zhang and Li-Cai Deng Affiliation: National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China E-mail: xinyu@ns3.bao.ac.cn (corresponding author)
Abstract |
Inclination of Broad Line Region in Narrow Line and Broad Line Seyfert 1 Galaxies Tian-Zhi Zhang and Xue-Bing Wu (*) Affiliation: Department of Astronomy, School of Physics, Peking University, Beijing 100871 E-mail: wuxb@bac.pku.edu.cn (corresponding author) Abstract |
Properties of Broad Band Continuum of Narrow Line Seyfert 1 Galaxies Hong-Yan Zhou and Ting-Gui Wang (1,2) Affiliation: (1) Center for Astrophysics, University of Science and Technology of China, Hefei 230026 (2) National Astronomical Observatories, Chinese Academic of Science, Beijing 100012 E-mail: mtzhou@mail.ustc.edu.cn (corresponding author)
Abstract |
| Dynamical Evolution of Gamma-Ray Burst Remnants with Evolving
Radiative Efficiency Jin-Bo Feng (1), Yong-Feng Huang (1,2,*), Zi-Gao Dai (1) and Tan Lu (1,2) Affiliation: (1) Department of Astronomy, Nanjing University, Nanjing 210093 (2) LCRHEA, Institute for High-Energy Physics, Chinese Academy of Sciences, Beijing 100039 E-mail: hyf@nju.edu.cn (corresponding author) Abstract In previous works, a generic dynamical model has been suggested by Huang et al., which is shown to be correct for both adiabatic and radiative blastwaves, in both ultra-relativistic and non-relativistic phases. In deriving their equations, Huang et al. have assumed that the radiative efficiency of the fireball is constant. They then applied their model directly to realistic cases where the radiative efficiency evolves with time. In this paper, we abandon the above assumption and re-derive a more accurate dynamical equation for gamma-ray burst remnants. Numerical results show that the model presented by Huang et al. is accurate enough in general cases. Key words: gamma rays: bursts --- hydrodynamics --- radiation mechanisms: nonthermal PDF file (178 KB) | gzipped PS file (270 KB) | Back to Contents |
How Fast Could a Proto-pulsar Rotate? Ren-Xin Xu, Hong-Guang Wang and Guo-Jun Qiao Affiliation: Department of Astronomy, School of Physics, Peking University, Beijing 100871 E-mail: rxxu@bac.pku.edu.cn (corresponding author) Abstract According to two estimated relations between the initial period and the dynamo-generated magnetic dipole field of pulsars, we calculate the statistical distributions of pulsar initial periods. It is found that proto-pulsars are very likely to have rotation periods between 20 and 30 ms, and that most of the pulsars rotate initially at a period < 60 ms. Our result supports the asymmetric neutrino emission model for pulsar kick. Key words: pulsars --- neutron stars --- magnetic fields PDF file (168 KB) | gzipped PS file (582 KB) | Back to Contents |
Energetics and Propagation of Coronal Mass Ejections in Different Plasma Environments Jun Lin Affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA E-mail: jlin@cfa.harvard.edu Abstract Based on previous work, we investigate the propagation of CMEs in a more realistic plasma environment than the isothermal atmosphere, and find that it is a slightly faster reconnection for flux ropes to break free. The average Alfvén Mach number MA for the inflow into the reconnection site has to be at least 0.013 in order to give a plausible eruption (compared to MA=0.005 for the isothermal atmosphere). Taking MA=0.1, we find that the energy output and the electric field induced inside the current sheet match the temporal behavior inferred from the energetic, long duration, CME-associated X-ray events. The results indicate that catastrophic loss of equilibrium in the coronal magnetic field provides the most promising mechanism for major solar eruptions, and that the more energetic the eruption is, the earlier the associated flare peaks. The variation of the output power with the background field strength revealed by our calculations implies the poor correlation between slow CMEs and solar flares. This work also further confirms the explanation we proposed for the peculiar motion of giant X-ray arches and anomalous post-flare loops. Their kinematic pattern and observed heights are determined by the local Alfvén speed and its variation with height. Key words: Sun: CMEs --- Sun: atmosphere --- Sun: magnetic fields PDF file (301 KB) | gzipped PS file (417 KB)| Back to Contents |
The Prediction of Maximum Amplitudes of Solar Cycles and the Maximum Amplitude of Solar Cycle 24 Jia-Long Wang (1), Jian-Cun Gong (2), Si-Qing Liu (2), Gui-Ming Le (2) and Jing-Lan Sun (1) Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China (2) Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100080 E-mail: Jialongw@btamail.net.cn (corresponding author) Abstract We present a brief review of predictions of solar cycle maximum amplitude with a lead time of 2 years or more. It is pointed out that a precise prediction of the maximum amplitude with such a lead-time is still an open question despite progress made since the 1960s. A method of prediction using statistical characteristics of solar cycles is developed: the solar cycles are divided into two groups, a high rising velocity (HRV) group and a low rising velocity (LRV) group, depending on the rising velocity in the ascending phase for a given duration of the ascending phase. The amplitude of Solar Cycle 24 can be predicted after the start of the cycle using the formula derived in this paper. Now, about 5 years before the start of the cycle, we can make a preliminary prediction of 83.2  119.4 for its maximum amplitude.Key words: Sun: sunspots -- Sun: activity PDF file (146 KB) | gzipped PS file (363 KB) | Back to Contents |
| Inhomogeneity in Spectral Transmission of the Coated
UBVRI Filters of BFOSC and its Influence on Photometry Bao-An Yao (1) and Lin Huang (2) Affiliation: (1) Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (2) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 E-mail: yba@center.shao.ac.cn (corresponding author) Abstract In order to realize the Johnson UBV and Kron-Cousins RI photometric systems in BFOSC, glass filters were purchased according to the Bessell prescription. All the filters are anti-reflection coated on both sides to increase the transmission. By comparing two dome flat-field exposures taken through any one of these filters set in two orientations 90° apart, inhomogeneities in the filter transmission is clearly demonstrated. Using a PDS microphotometer, we have confirmed that the form of their spectral transmission curve varied from point to point on the filters. This kind of inhomogeneity cannot be eliminated by dividing by flat-fielding exposure and must be ascribed to inhomogeneities in the coating. This is not some accidental defect in coating, it is in the existing coating technique because all the filters (including the narrow-band interference ones) for the BFOSC and a H 
filter made by another manufacturer
showed a similar pattern. We found that for the studies of variable stars with amplitudes less than
0.05 mag. or studies aiming at establishing accurate C-M diagrams of star clusters, the usual
uncoated Schott glass filters of Bessell's prescription are to be preferred.Key words: methods: data analysis --- techniques: photometric PDF file (329 KB) | gzipped PS file (59 KB) | Back to Contents |
5007 forbidden line and the stellar velocity dispersion, we also estimated the BLR inclinations for 50 narrow line
Seyfert 1 galaxies (NLS1s). We found that the inclinations of broad Line
Seyfert 1 galaxies (BLS1s) are systematically greater than those of NLS1s, which seldom exceed
30°. This may be an important factor that leads to the differences between NLS1s and BLS1s if the
BLR of NLS1s is really disk-like.
6%) of Radio Loud (RL) NLS1s is significantly less than that
of BLS1s (