$\textstyle \parbox{150mm}{ {\LARGE\bf Chinese Journal of Astronomy and Astrophysics}\\ }$

2006, Vol.6, No.6 (December 20, 2006)



Contents
RESEARCH PAPERS

Extragalactic Astronomy
Astrophysical Processes
Stars
The Solar System
The Sun
Astrometry




Abstract

Chemical Evolution of Blue Compact Galaxies

Fei Shi1,2, Xu Kong1 and Fu-Zhen Cheng1

1 Center for Astrophysics, University of Science and Technology of China, Hefei 230026 sfemail@mail.ustc.edu.cn;
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Abstract
Based on a sample of 72 Blue Compact Galaxies (BCGs) observed with the 2.16m telescope of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC) and about 4000 strong emission line galaxies from the Sloan Digital Sky Survey, we analyzed their chemical evolution history using the revised chemical evolution model of Larsen et al. Our sample covers a much larger metallicity range (7.2< 12+log(O/H)<9.0). We found that, in order to reproduce the observed abundance pattern and gas fraction over the whole metallicity range, a relatively continuous star formation history is needed for high metallicity galaxies, while assuming a series of instantaneous bursts with long quiescent periods (some Gyrs) for low metallicity galaxies. Model calculations also show that only the closed-box model is capable of reproducing the observational data over the whole metallicity range. Models that consider the ordinary winds and/or inflow can only fit the observations in the low metallicity range, and a model with enriched wind cannot fit the data in the whole metallicity range. This implies that the current adopted simple wind and inflow models are not applicable to massive galaxies, where the underlying physics of galactic winds or inflow could be more complicated.

Key Words:   galaxies: abundance -- galaxies: evolution -- galaxies: starburst -- stars: formation
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On the Geometry of Broad-Line Regions in BL Lac Objects

Yun Xu1,2 and Xin-Wu Cao1

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 xuyun@shao.ac.cn
2 Graduate School of Chinese Academy of Sciences, Beijing 100049

Abstract
The geometry of broad-line regions (BLRs) in active galactic nuclei (AGNs) is still controversial. We use a sample of BL Lac objects, of which the black hole masses $M_{\rm bh}$ are estimated from their host galaxy absolute magnitude at R-band, M R, by using the empirical relation between MR and black hole mass $M_{\rm bh}$. The sizes of the broad-line regions for Mg are derived from the widths of Mg lines and the black hole masses. Compared with the empirical relation between BLR size $R_{\rm BLR}$ and MgII line luminosity $L_{\rm Mg}$, it is found the BLR sizes in the BL Lac objects derived in this paper are 2-3 orders of magnitude higher. If the BLR geometry of these sources is disklike, then the viewing angle between the axis and the line of sight is in the range of $\sim 2^\circ-15^\circ$, which is consistent with the unification scheme.

Key Words:   galaxies: active--BL Lacertae objects: general--accretion, accretion disks--black hole physics
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Do Radio-loud Active Galactic Nuclei really follow the same $M_{\rm BH}$- $\sigma_{\rm *}$ Relation as Normal Galaxies?

Yi Liu1,2 and Dong-Rong Jiang1

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030; yliu@shao.ac.cn
2 Graduate School of Chinese Academy of Sciences, Beijing 100049

Abstract
In an examination of the relationship between the black hole mass $M_{\rm BH}$ and stellar velocity dispersion $\sigma_{\rm *}$ in radio-loud active galactic nuclei (AGNs), we studied two effects which may cause uncertainties in the black hole mass estimates of radio-loud AGNs: the relativistic beaming effect on the observed optical continuum radiation and the orientation effect on the broad emission line width. After correcting these two effects, we re-examined the $M_{\rm BH}$- $\sigma_{\rm [OIII]}$ relation for a sample of radio-loud and radio-quiet AGNs, and found the relation for radio-loud AGNs still deviated from that for nearby normal galaxies and radio-quiet AGNs. We also found there is no significant correlation between radio jet power and narrow [OIII] line width, indicating absence of strong interaction between radio jet and narrow line region. It may be that the deviation of the $M_{\rm BH}$- $\sigma_{\rm *}$ relation of radio-loud AGNs is intrinsic, or that the [OIII] line width is not a good indicator of $\sigma_{\rm *}$ for radio-loud AGNs.

Key Words:   black hole physics -- galaxies: active -- galaxies: nuclei -- quasars: general
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Chaotic Feature in the Light Curve of 3C 273

Lei Liu

Institute of Particle Physics, Huazhong Normal University, Wuhan 430079; liuphy@mail.ccnu.edu.cn

Abstract
Some nonlinear dynamical techniques, including state-space reconstruction and correlation integral, are used to analyze the light curve of 3C 273. The result is compared with a chaotic model. The similarities between them suggest there is a low-dimension chaotic attractor in the light curve of 3C 273.

Key Words:   galaxies: active -- galaxies: individual: 3C 273
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A Study of Binary Stellar Population Synthesis of Elliptical Galaxies

Zhong-Mu Li1,2, Feng-Hui Zhang1 and Zhan-Wen Han1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; zhongmu.li@gmail.com
2 Graduate School of Chinese Academy of Sciences, Beijing 100049

Abstract
We determined the relative stellar ages and metallicities of about 80 elliptical galaxies in both low and high density environments using the latest binary stellar population (BSP) synthesis model and tested the predictions of a recent hierarchical formation model that adopted the new $\Lambda$CDM cosmology. The stellar ages and metallicities were estimated from two high-quality published spectra line indices, the H$\beta$ and [MgFe] indices. The results show that the stellar populations of elliptical galaxies are older than 3.9Gyr and more metal rich than 0.02. Most of our results are in agreement with the model predictions: (1) elliptical galaxies in denser environment are redder and have older populations than field galaxies; (2) elliptical galaxies with more massive stellar components are redder and have older and more metal rich populations than less massive ones; (3) the most massive galaxies have the oldest and most metal rich stars. However, some of our results differ from the model predictions on the metallicity distributions of low- and high-density elliptical galaxies and the dependence on the distance to the cluster center.

Key Words:   galaxies: stellar content -- galaxies: formation -- galaxies: elliptical and lenticular, cD
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An Efficient High-Resolution Shock-Capturing Scheme for Multi-Dimensional Flows
I. Hydrodynamics

Cong Yu

National Astronomical Observatories / Yunnan Astronomical Observatory, Chinese Academy of Sciences, Kunming 650011; yccit@yahoo.com.cn
Graduate School of Chinese Academy of Sciences, Beijing 100049

Abstract
Many problems at the forefront of theoretical astrophysics require a treatment of dynamical fluid behavior. We present an efficient high-resolution shock-capturing hydrodynamic scheme designed to study such phenomena. We have implemented a weighted, essentially non-oscillatory (WENO) scheme to fifth order accuracy in space. HLLE approximate Riemann solver is used for the flux computation at cell interface, which does not require spectral decomposition into characteristic waves and so is computationally friendly. For time integration we apply a third order total variation diminishing (TVD) Runge-Kutta scheme. Extensive testing and comparison with schemes that require characteristic decomposition are carried out demonstrating the ability of our scheme to address challenging open questions in astrophysics.

Key Words:   accretion -- hydrodynamics -- method: numerical -- shock waves
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Automatic Normalization and Equivalent-Width Measurement of High-Resolution Stellar Spectra

Jing-Kun Zhao, Gang Zhao, Yu-Qin Chen, Jian-Rong Shi, Yu-Juan Liu and Ju-Yong Zhang

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

Abstract
It is well known that normalization, radial velocity correction and equivalent-width measurement of high-resolution stellar spectra are time-consuming work. In order to improve the efficiency we present an automatic method for these routines. The continuum is determined by fitting the `high points' in the spectrum. After continuum normalization, the program automatically searches for the position of the H$\alpha$ line and obtains a rough radial velocity, then computes an accurate radial velocity by cross-correlation between the given spectrum and the solar spectrum. In this method, the equivalent-width is automatically measured using Gaussian fitting. A comparison between our results and those from traditional analysis shows that the typical error for equivalent width is around 3.8% in our method. Developing such automatic routines does not mean to replace the interactive reduction method: it is just for a quick extraction of information from the spectra, especially those obtained in large sky surveys.

Key Words:   techniques: radial velocities - stars: abundances
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Newly Identified Silicate Carbon Stars from IRAS Low-Resolution Spectra

Pei-Sheng Chen1 and Pin Zhang1,2

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; iraspsc@yahoo.com.cn
2 Cosmic Ray Institute, Yunnan University, Kunming 650091

Abstract
The discovery of silicate carbon star poses a challenge to the theory of stellar evolution in the late stage, hence it is important to look for more silicate carbon stars. To this end we have carried out cross-identifications between the new IRAS Low-Resolution Spectrum (LRS) database and the new carbon star catalog, CGCS3. We have found nine new silicate carbon stars with silicate features around 10$\mu $m and/or 18$\mu $m. These newly identified stars are located in the Regions IIIa and VII in the IRAS two-color diagram, which means they indeed have typical far infrared colors of silicate carbon stars. The infrared properties of each of these sources are discussed.

Key Words:   stars: AGB and post-AGB -- star: carbon -- infrared: stars
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Chaos in Compact Binaries with Frequency Map Analysis

Yi Xie and Tian-Yi Huang

Department of Astronomy, Nanjing University, Nanjing 210093; yi.s.xie@gmail.com

Abstract
The dynamics of compact binaries is very complicated because of spin-orbit coupling and spin-spin coupling. With Laskar's frequency map analysis (FMA) and frequency diffusion as an indicator, we found that misalignment of the spins and orbital angular momentum has a great effect on the dynamics, and for systems with different mass ratios $\beta\equiv m_2/m_1$ chaos occurs at different spin-orbit configurations. For equal-mass binaries ($\beta=1$), chaos occurs when the spins nearly cancel each other out. For some other systems (for example $\beta\sim1/2$), the binaries are irregular, even chaotic, when the spins are perpendicular to the orbital angular momentum. For the case where gravitational radiation is taken into account, we give an analytic estimation for the frequency diffusion based on the decay of the orbit, which is roughly consistent with our simulations. This means the FMA is not suitable as a chaos indicator for weak chaotic cases with dissipative terms.

Key Words:   celestial mechanics -- (stars:) binaries (including multiple): close
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Photometric Monitoring of ROSAT-Selected Weak Line T Tauri Stars

Li-Feng Xing1,2,3, Xiao-Bin Zhang1 and Jian-Yan Wei1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; lfxing@bao.ac.cn
2 Department of Technology and Physics, Zhengzhou University of Light Industry, Zhengzhou 450002
3 Graduate School of Chinese Academy of Sciences, Beijing 100049

Abstract
We monitored the light curves of 22 weak-line T Tauri stars (WTTSs) discovered among the X-ray sources in the field of the Taurus-Auriga cloud. For 12 of the 22 WTTSs photometric periodic variability is confirmed and their rotational periods are determined using Phase Dispersion Minimization (PDM) and Fourier analysis. Most of them are found to have periods shorter than one day. This gives further evidence for the spin up of solar-type stars predicted by the models of angular momentum evolution of pre-main sequence stars.

Key Words:   stars: late-type -- stars: pre-main sequence -- stars: rotation
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The Magnetic Field Effect on Planetary Nebulae

A. R. Khesali and K. Kokabi

Department of Physics, University of Mazandaran, Babolsar, Iran; khesali@umz.ac.ir
Research Institute for Astronomy and Astrophysics of Maragha, Maragha, Iran

Abstract
In our previous work on the 3-dimensional dynamical structure of planetary nebulae the effect of magnetic field was not considered. Recently Jordan et al. have directly detected magnetic fields in the central stars of some planetary nebulae. This discovery supports the hypothesis that the non-spherical shape of most planetary nebulae is caused by magnetic fields in AGB stars. In this study we focus on the role of initially weak toroidal magnetic fields embedded in a stellar wind in altering the shape of the PN. We found that magnetic pressure is probably influential on the observed shape of most PNe.

Key Words:   ISM: Planetary nebulae - magnetic field: PNe - magnetic field
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CCD Photometry of Asteroid (147) Protogeneia

Xi-Liang Zhang1,2, Xiao-Bin Wang1 and Li-Yun Zhang1,2

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

Abstract
We measured the light-curve of the asteroid (147) Protogeneia in November 2004, with a CCD detector attached to the 1-meter telescope at the Yunnan Observatory, China. The synodic period and maximum amplitude of (147) at this apparition are 7.852 hours and 0.25mag, respectively. The value of a/b for (147), from a preliminary estimation, is not less than 1.26:1.

Key Words:   asteroid - photometric observation - synodic period
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Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

Tian-Xi Zhang1,2, Arjun Tan1 and Shi Tsan Wu2

1 Physics Department, Alabama A & M University, Normal, AL 35762, USA tianxi.zhang@email.aamu.edu
2 Center for Space Plasma and Aeronomic Research, The University of Alabama in Huntsville, AL 35899, USA

Abstract
Heating and acceleration of electrons in solar impulsive hard X-ray (HXR) flares are studied according to the two-stage acceleration model developed by Zhang for solar 3He-rich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons (up to 40 MK) through Landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flare-produced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.

Key Words:   acceleration of particles - instabilities - plasmas - Sun: flares - Sun: particle emission - Sun: X-ray
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Formation of the CME Leading Edge Observed in the 2003 February 18 Event

Xing-Ming Bao1, Hong-Qi Zhang1 and Jun Lin2,3

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; xbao@bao.ac.cn
2 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

Abstract
This work investigates a typical coronal mass ejection (CME) observed on 2003 February 18, by various space and ground instruments, in white light, H$\alpha$, EUV and X-ray. The H$\alpha$ and EUV images indicate that the CME started with the eruption of a long filament located near the solar northwest limb. The white light coronal images show that the CME initiated with the rarefaction of a region above the solar limb and followed by the formation of a bright arcade at the boundary of the rarefying region at height 0.46$R_{\odot}$ above the solar surface. The rarefying process synchronized with the slow rising phase of the eruptive filament, and the CME leading edge was observed to form as the latter started to accelerate. The lower part of the filament brightened in H$\alpha$ as the filament rose to a certain height and parts of the filament was visible in the GOES X-ray images during the rise. These brightenings imply that the filament may be heated by the magnetic reconnection below the filament in the early stage of the eruption. We suggest that a possible mechanism which leads to the formation of the CME leading edge and cavity is the magnetic reconnection which takes place below the filament after the filament has reached a certain height.

Key Words:   Sun: coronal mass ejections (CMEs) - Sun: filaments - Sun: flares
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Solar Energetic Particle Event of 2005 January 20: Release Times and Possible Sources

Gui-Ming Le1, 2, 3,4, Yu-Hua Tang3 and Yan-Ben Han1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; legm@nsmc.cma.gov.cn
2 Key Laboratory of Radiometric Calibration and Validation for Environmental Satellites, China Meteorological Administration, Beijing 100081
3 Department of Astronomy, Nanjing University, Nanjing 210093
4 National Center for Space Weather, China Meteorological Administration, Beijing 100081

Abstract
Based on cosmic ray data obtained by neutron monitors at the Earth's surface, and data on near-relativistic electrons measured by the WIND satellite, as well as on solar X-ray and radio burst data, the solar energetic particle (SEP) event of 2005 January 20 is studied. The results show that this event is a mixed event where the flare is dominant in the acceleration of the SEPs, the interplanetary shock accelerates mainly solar protons with energies below 130 MeV, while the relativistic protons are only accelerated by the solar flare. The interplanetary shock had an obvious acceleration effect on relativistic electrons with energies greater than 2 MeV. It was found that the solar release time for the relativistic protons was about 06:41 UT, while that for the near-relativistic electrons was about 06:39 UT. The latter turned out to be about 2 min later than the onset time of the interplanetary type III burst.

Key Words:   Sun: flare - Sun: particle acceleration - shock acceleration - interplanetary >ropagation
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Atmospheric and Oceanic Excitations to LOD Change on Quasi-biennial Time Scales

Li-Hua Ma1, De-Chun Liao1,2 and Yan-Ben Han1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 mlh@bao.ac.cn
2 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030

Abstract
We use wavelet transform to study the time series of the Earth's rotation rate (length-of-day, LOD), the axial components of atmospheric angular momentum (AAM) and oceanic angular momentum (OAM) in the period 1962-2005, and discuss the quasi-biennial oscillations (QBO) of LOD change. The results show that the QBO of LOD change varies remarkably in amplitude and phase. It was weak before 1978, then became much stronger and reached maximum values during the strong El Nino events in around 1983 and 1997. Results from analyzing the axial AAM indicate that the QBO signals in axial AAM are extremely consistent with the QBOs of LOD change. During 1963-2003, the QBO variance in the axial AAM can explain about 99.0% of that of the LOD, in other words, all QBO signals of LOD change are almost excited by the axial AAM, while the weak QBO signals of the axial OAM are quite different from those of the LOD and the axial AAM in both time-dependent characteristics and magnitudes. The combined effects of the axial AAM and OAM can explain about 99.1% of the variance of QBO in LOD change during this period.

Key Words:   Earth's variable rotation - atmospheric angular momentum - oceanic angular momentum
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ChJAA, 2006, Vol.6, No.6

Chinese Journal of Astronomy and Astrophysics: Online Edition

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