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

2007, Vol.7, No.6 (December 20, 2007)



Astrophysical Processes

Extragalactic Astronomy


The Sun and Solar System

Astrometry and Celestial Mechanics

Instruments, Observational Techniques and Data Processing


A New Formulation for General Relativistic Force-Free Electrodynamics and Its Applications

Cong Yu

National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; yccit@yahoo.com.cn

We formulate the general relativistic force-free electrodynamics in a new 3+1 language. In this formulation, when we have properly defined electric and magnetic fields, the covariant Maxwell equations could be cast in the traditional form with new vacuum constitutive constraint equations. The fundamental equation governing a stationary, axisymmetric force-free black hole magnetosphere is derived using this formulation which recasts the Grad-Shafranov equation in a simpler way. Compared to the classic 3+1 system of Thorne and MacDonald, the new system of 3+1 equations is more suitable for numerical use for it keeps the hyperbolic structure of the electrodynamics and avoids the singularity at the event horizon. This formulation could be readily extended to non-relativistic limit and find applications in flat spacetime. We investigate its application to disk wind, black hole magnetosphere and solar physics in both flat and curved spacetime.

Key Words:   method: analytical -- magnetic fields -- accretion -- jet -- relativity

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Space-Time Geometry of Quark and Strange Quark Matter

Ihsan Yilmaz 1,2 and Can Aktas 3

1 Çanakkale Onsekiz Mart University, Arts and Sciences Faculty, Department of Physics, Terzioglu Campus, 17020 Çanakkale, Turkey; iyilmaz@comu.edu.tr

2 Çanakkale Onsekiz Mart University, Astrophysics Research Center, 17020 Çanakkale, Turkey

3 Çanakkale Onsekiz Mart University, Arts and Sciences Faculty, Department of Mathematics, Terzioglu Campus, 17020 Çanakkale, Turkey

We study quark and strange quark matter in the context of general relativity. For this purpose, we solve Einstein's field equations for quark and strange quark matter in spherical symmetric space-times. We analyze strange quark matter for the different equations of state (EOS) in the spherical symmetric space-times, thus we are able to obtain the space-time geometries of quark and strange quark matter. Also, we discuss the features of the obtained solutions. The obtained solutions are consistent with the results of Brookhaven Laboratory, i.e. the quark-gluon plasma has a vanishing shear (i.e. quark-gluon plasma is perfect).

Key Words:   cosmology -- theory, early universe

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A Study of the Star-forming Dwarf Galaxy NGC 855 with Spitzer

Sheng-Peng Li 1, Qiu-Sheng Gu 1, Ying-He Zhao 1, Jia-Sheng Huang 2 and Xin-Lian Luo 1

1 Department of Astronomy, Nanjing University, Nanjing 210093; sandaoren@163.com

2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138

We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band H$\alpha$ and Spitzer data. Both the H$\alpha$ and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate (SFR) of 0.022 and 0.025$M_\odot$yr-1, respectively, from the Spitzer IRAC 8.0$\mu $m and MIPS 24$\mu $m emission data. The HI observation suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0$\mu $m bands, located at about 10'' away from the nucleus of NGC 855. Given the strong 8.0$\mu $m but faint H$\alpha$ emission, we expect that it is a heavily obscured star-forming region, which needs to be confirmed by further optical spectroscopic observations.

Key Words:   galaxies: elliptical -- galaxies: individual: NGC 855
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Variable Star Status of Two Stars: V204 and I-I-39 in M3

Bao-An Yao

Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030; yba@shao.ac.cn

The star I-I-42 (=vZ1390), a cluster member in M3, located near the red edge of the instability strip of the horizontal branch, was discovered by Roberts and Sandage as a low amplitude variable, it was designated as V204 in the ``second catalogue of variable stars in globular clusters", but its coordinates given in all versions of this catalogue are wrong since 1955. We argue that V204 is indeed a low amplitude HB variable star, located near to the red edge of the instability strip, with a period of 0.74785$^{\rm {d}}$ and an amplitude of about 0.04mag in V. We also find that the red cluster member star I-I-39 is a low amplitude variable with a period of 1.16$^{\rm {d}}$ and amplitude of about 0.03mag in V which might be pulsating at the second overtone.

Key Words:   globular cluster -- stars: variables -- stars: individual (V204 and I-I-39)

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Very Early Optical Afterglows for Geometric Models of X-ray Flashes and X-ray Rich GRBs

Ting Yan 1,2,3, Da-Ming Wei 1,2,4 and Yi-Zhong Fan 1,2,5

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

2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

3 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA

4 Joint Center for Particle Nuclear Physics and Cosmology of Purple Mountain Observatory - Nanjing University, Nanjing 210008

5 The Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel

If X-ray flashes (XRFs) and X-ray rich Gamma-ray Bursts (XRRGs) have the same origin as the Gamma-ray bursts (GRBs) but are viewed off-center from structured jets, their early afterglows may differ from those of GRBs, and when the ultra-relativistic outflow interacts with the surrounding medium, there are two shocks formed, a forward shock (FS), and a reverse shock (RS). We calculate numerically the early afterglow powered by uniform jets, Gaussian jets and power-law jets in the forward-reverse shock scenario. A set of differential equations govern the dynamical evolution. The synchrotron self-Compton effect has been taken into account in the calculation. In the uniform jets, the very early afterglows of XRRGs and XRFs are significantly lower than the GRBs and the observed peak times of RS emission are later in the interstellar medium environment. The RS components in XRRGs and XRFs are difficult to detect, but in the stellar wind environment, the reduction of the very early flux and the delay of the RS peak time are not so remarkable. In nonuniform jets (Gaussian and power-law jets), where there are emission materials on the line of sight, the very early light curve resembles equivalent isotropic ejecta in general although the RS flux decay index shows notable deviations if the RS is relativistic (in stellar wind).

Key Words:   X-rays: general -- Gamma rays: bursts -- radiation mechanisms: non-thermal

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Radio Phase-Resolved Spectra of the Conal-Double Pulsar B1133+16 

Jian-Ling Chen 1, Hong-Guang Wang 1, Wan-Hai Chen 1, Hui Zhang 2 and Yi Liu 1

1 Center for Astrophysics, Guangzhou University, Guangzhou 510006; chenjianling62@163.com

2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Based on dividing the profile into a number of absolute phase intervals, the phase-resolved spectra (PHRS) are derived from published time-aligned average profiles at radio frequencies over two decades for the classic conal-double pulsar B1133+16. The relative spectral index, defined as the difference between the spectral indices of a reference and the given arbitrary phase interval, is obtained by power-law fit at each phase interval. The derived phase-resolved spectra show an ``M-like'' shape, of which the leading part and trailing part are approximately symmetrical. The basic feature of the PHRS is that the spectrum first flattens then steepens as the pulse phase sweeps from the profile center to the profile edges. The PHRS provide a coherent explanation of the major features of profile evolution of B1133+16, namely, the pulse width shrinkage with increasing frequency and the frequency evolution of the relative intensity between the leading and trailing conal components, and the bridge emission. The PHRS may be an indicator for emission spectral variation across the pulsar magnetosphere. Possible mapping from PHRS to emission-location-dependent spectral variation is presented, and some intrinsic mechanisms are discussed.

Key Words:   pulsars: individual (B1133+16) -- method: data analysis

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Generation of Interstellar Class II 72-81A+ and 72-81A- Methanol Masers

Han-Ping Liu 1 and Jin Sun 2

1 Department of Physics, Beijing Normal University, Beijing 100875; gaozm@bnu.edu.cn

2 Department of Astronomy, Beijing Normal University, Beijing 100875

New methanol maser lines at 7$_{2}\to6_{3}$A-(86.6GHz) and 7$_{2}\to6_{3}$A+(86.9GHz) together with two candidate methanol maser lines at 7$_{2}\to8_{1}$A-(80.99GHz) and 7$_{2}\to8_{1}$A+(111.29GHz) have been detected in W3(OH). We use a pumping mechanism, i.e., methanol masers without population inversion, to explain the formation of weak methanol masers of 7$_{2}\to8_{1}$A+ and 7$_{2}\to8_{1}$A-. We explain well why the line-shape of the transition 7$_{2}\to8_{1}$A+ is not typical. A similar argument can be applied to the $\Lambda $-type level system 72A-, 63A- and 81A-, as well as to the 7$_{2}\to8_{1}$A- 80.99GHz masers.

Key Words:   pumping mechanism -- Class II methanol sources -- maser without inversion -- coherent microwave field

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Improbability of DUrca Process Constraints EOS

Hao Tong and Qiu-He Peng

Department of Astronomy, Nanjing University, Nanjing 210093; htong_2005@163.com

According to recent observational and theoretical progresses, the DUrca process (direct Urca process) may be excluded from the category of neutron star cooling mechanisms. This result, combined with the latest nuclear symmetry energy experiments, will provide us an independent way of testing the EOS (equation of state) for supernuclear density. For example, soft EOSs, such as FPS, will probably be excluded.

Key Words:   equation of state -- neutrinos -- stars: neutron

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An Alternative Explanation for a Screw-like Meteoric Train Photographed by Double-Station Observations

Guang-Jie Wu 1,2

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; yawugj@163.com

2 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008

Two-station observation of meteors, especially a meteor trains, provides an effective approach to the measurement of the physical parameters. We have collected four special groups of photographs of meteoric trains taken at two stations during Leonids 2001. One representative group has been measured and analyzed in detail. An analysis has been reported in our first paper. In this paper, an alternative explanation for the screw-like meteoric train is suggested based on some physical calculations. The results reveal that this train has a screw-like structure and, apparently, spoke beams. The mother meteor of this train may be negatively charged and moves forward along a left-hand screw trajectory under the effect of the geomagnetic field. The spoke beams might be the visual effect of the long time exposure of many particles released from the disintegrated meteoroid.

Key Words:   meteors, meteoroids -- magnetic fields

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Short-Term Period Variation of Relative Sunspot Numbers

Zhi-Qiang Yin 1,3, Yan-Ben Han 1, Li-Hua Ma 1, Gui-Ming Le 1,2 and Yong-Gang Han 1

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

2 Key Laboratory of Radiometric Calibration and Validation for Environmental Satellites, China Meteorological Administration, Beijing 100081

3 Graduate School of Chinese Academy of Sciences, Beijing 100049

We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10-23. The characteristics of some of the periods shorter than $\sim 600$-day are discussed. The results exhibit not only the variation of some short periods in the 14 solar cycles but also the characteristics and differences around solar peaks and valley years. The short periodic components with larger amplitude such as $\sim$27, $\sim$150 and $\sim$360-day are obvious in some solar cycles, all of them are time-variable, also their lengths and amplitudes are variable and intermittent in time. The variable characteristics of the periods are rather different in different solar cycles.

Key Words:   Sun: sunspots -- short-term period -- methods: data analysis -- wavelet

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Excitation of Annual Polar Motion by the Pacific, Atlantic and Indian Oceans

Jin Ma 1,2, Yong-Hong Zhou 1, De-Chun Liao 1 and Jian-Li Chen 3

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 majin@shao.ac.cn

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

3 Center for Space Research, University of Texas at Austin, Austin TX 78712, USA

The global oceans play important roles in exciting the annual polar motion besides the atmosphere. However, it is still unclear about how large the regional oceans contribute to the annual polar motion. We investigate systemically the contributions of the Pacific, Atlantic and Indian Oceans to the excitation of the annual polar motion, based on the output data of ocean current velocity field and ocean bottom pressure field from ``Estimating the Circulation and Climate of the Ocean (ECCO)'' ocean circulation model over the period 1993-2005. The result shows that due to its particular location and shape, the Atlantic Ocean makes a less significant contribution to the x-component of the annual polar motion excitation than the Pacific and Indian Oceans, while all these three oceans contribute to the y-component of the annual polar motion excitation to some extent.

Key Words:   annual polar motion -- excitation -- oceanic angular momentum function (OAMF) -- atmospheric angular momentum function (AAMF)

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Simulation Study on High Energy Cosmic Electron Detection by Shower Image

Rong Xu 1,2,3, Jin Chang 1,3, S. Torii 4, K. Kasahara 5, T. Tamura4 and K. Yoshida 4

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

2 Graduate School of Chinese Academy of Sciences, Beijing 100049

3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

4 Institute of Physics, Kanagawa University, Yokohama, Kanagawa, Japan

5 Shibaura Institute of Technology, Omiya, Saitama, Japan

Many projects have recently been carried out and proposed for observing high energy electrons since it is realized that cosmic ray electrons are very important when studying the dark matter particles and the acceleration mechanism of cosmic rays. An imaging calorimeter, BETS (Balloon-borne Electron Telescope with Scintillator fiber), has been developed for this purpose. Using pattern analysis of the shower development, the electrons can be selected from those primary cosmic ray proton events with flux heights one-tenth that of the electrons. The Monte-Carlo simulation is indispensable for the instrument design, the signal trigger and the data analysis. We present different shower simulation codes and compare the simulation results with the beam test and the flight data of BETS. We conclude that the code FLUKA2002 gives the most consistent results with the experimental data.

Key Words:   methods: analytical -- Monte-Carlo simulation -- cosmic rays

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ChJAA, 2007, Vol.7, No.5

Chinese Journal of Astronomy and Astrophysics: Online Edition


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