2003, Vol.3, No.1 (February 20, 2003)


Contents

Invited Review
Letter
Stars
  • Statistical Properties of the Highest Pulses in Gamma-Ray Bursts  p.38
    Yi-Ping Qin, En-Wei Liang, Guang-Zhong Xie and Cheng-Yue Su
     Abstract | | PDF file (199 KB) | PS file *.gz  (313 KB)  
  • Statistical Properties of 6.7 GHz Methanol Maser Sources   p.49
    Ye Xu, Xing-Wu Zheng and Dong-Rong Jiang 
    Abstract | | PDF file (285 KB) | PS file *.gz  (396 KB) 
Extragalactic Astronomy
  • Polarization Position Angle Swings caused by Relativistic Effects   p.75
    Shan-Jie Qian and Xi-Zhen Zhang
    Abstract | | PDF file (228 KB) | PS file *.gz  (371 KB) 
The Sun
  • The H$\beta$ Chromospheric Magnetic Field in a Quiescent Filament   p.87
    Xing-Ming Bao and Hong-Qi Zhang
    Abstract | | PDF file (305 KB) | PS file *.gz  (4939 KB) 


Abstract

``Small Equipment Strategy'' in the Development of Astronomy 

Shou-Guan Wang

Affiliation:  National Astronomical Observatories, CAS (NAOC), Beijing 100012, China

E-mail:   shouguanwang@yahoo.com.cn 

Abstract

Astronomy is an observational science. This paper points out that in the development of astronomy, the means of observation at every stage has as its main body the  large equipment of the time, but equally important is the simultaneous development of small equipment as strategic complement. A number of historical examples are cited. The recently suggested ``Special Radio Telescope Dedicated to Pulsar Research'' originates in the small equipment strategy, and a brief introduction to this instrument is included here.

Key words: instrumentation --- telescopes

PDF file (165 KB) | gzipped PS file (167 KB) | Back to Contents

The Kinematic Theory of Solar Dynamo   

Ke-Ke Zhang (1) and Xin-Hao Liao (2)

Affiliation: (1) School of Mathematical Sciences, University of Exeter, EX4 4QE, UK
             (2) Shanghai Astronomical Observatory, Shanghai 200030, China

E-mail:   kzhang@ex.ac.uk   (corresponding author), xhliao@center.shao.ac.cn 

Abstract

Generation of the Sun's magnetic fields by self-inductive processes in the solar electrically conducting interior, the solar dynamo theory, is a fundamentally important subject in astrophysics. The kinematic dynamo theory concerns how the magnetic fields are produced by kinematically possible flows without being constrained by the dynamic equation. We review a number of basic aspects of the kinematic dynamo theory, including the magnetohydrodynamic approximation for the dynamo equation, the impossibility of dynamo action with the solar differential rotation, the Cowling's anti-dynamo theorem in the solar context, the turbulent alpha effect and recently constructed three-dimensional interface dynamos controlled by the solar tachocline at the base of the convection zone.

Key words: Solar magnetic fields --- kinematic dynamos --- magnetohydrodynamics

PDF file (742KB) | gzipped PS file (328 KB) | Back to Contents

What Can the Redshift Observed in EXO 0748--676 Tell Us?

Ren-Xin Xu 

 Affiliation:  Department of Astronomy, School of Physics, Peking University,
Beijing 100871, China

E-mail:   rxxu@bac.pku.edu.cn 

Abstract

The mass-radius relations for bare and crusted strange stars are calculated with the bag model. Comparing these relations with the observed one derived from the redshift of EXO 0748--676, we come to the conclusion that it is incorrect to say that EXO 0748--676 cannot be a strange star. Various strange star models can show that EXO 0748--676 could have a mass of (1.3~ 1.7) $M_{\odot}$ and a radius of (8.4~ 11.4) km. It is proposed that a proportion of nascent strange stars could be bare and have masses ~0.1 $M_{\odot}$, and their masses increased over a long period of accretion.

Key words: stars: fundamental parameters --- dense matter --- stars: neutron

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Statistical Properties of the Highest Pulses in Gamma-Ray Bursts

Yi-Ping Qin (1), En-Wei Liang (1,2), Guang-Zhong Xie (1)
and Cheng-Yue Su (1,3)

 Affiliation: (1) National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011
       (2) Department of Physics, Guangxi University, Nanning 530004, China
       (3) Department of Physics, Guangdong Industry University, Guangzhou 510643, China
                          
E-mail:  qinyp@public.km.yn.cn   (corresponding author)

Abstract

We study the statistical properties of the highest pulses within individual gamma-ray bursts (GRBs). A wavelet package analysis technique and a developed pulse-finding algorithm have been applied to identify the highest pulses from burst profiles observed by BATSE on board CGRO from 1991 April 21 to 1999 January 26. The statistical light curves of the highest pulses in four energy channels have been derived by an aligning method, which illustrate the temporal evolution of the pulse emission. Our result that narrower pulses go with higher energies is consistent with previous findings. By normalizing both the pulse durations and counts to unity, ``characteristic'' profiles of the highest pulses in the four channels are also derived. The four characteristic profiles are turned out to be almost the same, thus strongly support the previous conclusion that the temporal profiles in different energy channels are self-similar and the previous conjecture on GRB pulses, implying that the emission process is similar at different energies. The cosmological time dilation effect is examined by investigating the relationship between the pulse flux and pulse duration. An anti-correlation between the two was found, which agrees with the expectation of the cosmological time dilation effect. Also, the evolution of the pulse duration with the observational epoch is studied. The result shows that the pulse duration tends to be shorter in later epochs. This trend cannot be explained by the present theoretical models, and may represent a great challenge to current theories.

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

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Statistical Properties of 6.7 GHz Methanol Maser Sources
Ye Xu (1,2), Xing-Wu Zheng (3) and Dong-Rong Jiang (2)

Affiliation:   (1) National Astronomical Observatories, Chinese Academy of Sciences, Urumqi 830011, China
          (2) Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
          (3) Department of Astronomy, Nanjing University, Nanjing 210093, China

E-mail:   xuye@nju.edu.cn  (corresponding author)
  
Abstract

We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 $\leq$ [25-12] $\leq$ 1.30 and 1.30 $\leq$ [60-12] $\leq$ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s-1, and one from about 11 to 20 km s-1. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.

Key words: masers --- ISM: molecules --- stars: circumstellar matter --- stars: formation --- ISM: HII regions

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A Study of Star Formation in BRC18

Sheng-Li Qin and Yue-Fang Wu

Affiliation: Department of Astronomy, Peking University, Beijing 100871, China
                         
E-mail:   ywu@bac.pku.edu.cn   (corresponding author)

Abstract

Using the 13.7 m radio telescope at Delingha, the millimeter-wave radio observatory of Purple Mountain Observatory, we made mapping observations in 12CO J=10 line towards IRAS 05417+0907, located in the bright-rimmed cloud (BRC) BRC18. We used a 7×7 grid with 1' spacing, a finer and larger grid than the one used by Myers et al. Our results show that there is a bipolar outflow near IRAS 05417+0907. Combining with the observations at other wave bands, we find that the star formation process in this region is triggered by radiation-driven implosion. The significant difference between the masses of BRC18 and the cores and the relatively large ratio of associated source bolometric luminosity to the mass show that the star formation in BRC18 may be taking place in a sequence.

Key words: ISM: clouds --- star: formation --- individual: IRAS 05417+0907

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Polarization Position Angle Swings caused by Relativistic Effects

Shan-Jie Qian and Xi-Zhen Zhang 
Affiliation:  National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
                    
E-mail:  rqsj@bao.ac.cn   (corresponding author)

Abstract

Polarization position angle swings of ~180° observed in extragalactic radio sources are a regular behavior of variability in polarization. They should be due to some kind of physically regular process. We consider relativistic shocks which propagate through and `illuminate' regular configurations of magnetic field, producing polarization angle swing events. Two magnetic field configurations (force-free field and homogeneous helical field) are considered to demonstrate the results. It is shown that the properties of polarization angle swings and the relationship between the swings and variations in total and polarized flux density are critically dependent on the configuration of magnetic field and the dynamical behavior of the shock. In particular, we find that in some cases polarization angle swings can occur when the total and polarized flux densities only vary by a very small amount. These results may be useful for understanding the polarization variability with both long and short timescales observed in extragalactic radio sources.

Key words: radio continuum: galaxies --- polarization --- galaxies: magnetic fields

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The Hβ Chromospheric Magnetic Field in a Quiescent Filament

Xing-Ming Bao and Hong-Qi Zhang 

 Affiliation:  National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
                    
E-mail:   baoxm@sun10.bao.ac.cn  (corresponding author)

Abstract

We observed the line-of-sight magnetic field in the chromosphereand photosphere of a large quiescent filament on the solar disk on September 6, 2001 using the Solar Magnetic Field Telescope in Huairou Solar Observing Station. The chromospheric and photospheric magnetograms together with Hβ filtergrams of the filament were examined. The filament was located on the neutral line of the large scale longitudinal magnetic field in the photosphere and the chromosphere. The lateral feet of the filament were found to be related to magnetic structures with opposite polarities. Two small lateral feet are linked to weak parasitic polarity. There is a negative magnetic structure in the photosphere under a break of the filament. At the location corresponding to the filament in the chromospheric magnetograms, the magnetic strength is found to be about 40--70 Gauss (measuring error about 39 Gauss). The magnetic signal indicates the amplitude and orientation of the internal magnetic field in the filament. We discuss several possible causes which may produce such a measured signal. A twisted magnetic configuration inside the filament is suggested .

Key words: Sun: chromosphere --- Sun: filaments --- Sun: magnetic fields

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ChJAA, 2003, Vol.3, No.1

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

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