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

2005, Vol.5, No.1 (February 20, 2005)

Contents

LETTER


RESEARCH PAPERS

Extragalactic Astronomy Stars The Sun


Abstract

A New Interpretation of the Bipolar HII Region S106 from HCN J=3-2 Mapping Observations

Sheng-Li Qin1, Jun-Jie Wang1, Gang Zhao1 and Martin Miller2

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

2 Institute of Physics, Köln University, Köln 50937, Germany

Abstract
The first mapping observations of the bipolar HII region S106 in HCN J=3-2 line were made by KOSMA submillimeter telescope in April, 2004. The results show that there is a bipolar outflow centered on the high-mass star S106 IRS4 and that the flat structure of molecular cloud core is perpendicular to the axis of the outflow. This image roughly corresponds to the optical image where a dark lane bisects the bipolar HII region. Together with the optical, infrared and radio data, we conclude that the central UC HII region and molecular outflow formed before the two lobes of the bipolar HII region, and that a neutral disk is responsible for the bipolar HII region and the outflow.

Key words:   ISM: clouds - nebulae: HII region - star: formation - individual: S106

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Two-fluid Dynamics in Clusters of Galaxies Pairwise Velocity Statistics of Dark Halos

Yu-Qing Lou 1, 2, 3

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012;

2 Department of Physics & Tsinghua Center for Astrophysics (THCA), Tsinghua University, Beijing 100084; lou@oddjob.uchicago.edu; louyq@tsinghua.edu.cn

3 Department of Astronomy and Astrophysics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 USA

Abstract
We develop a theoretical formulation for the large-scale dynamics of galaxy clusters involving two spherical `isothermal fluids' coupled by their mutual gravity and derive asymptotic similarity solutions analytically. One of the fluids roughly approximates the massive dark matter halo, while the other describes the hot gas, the relatively small mass contribution from the galaxies being subsumed in the gas. By properly choosing the self-similar variables, it is possible to consistently transform the set of time-dependent two-fluid equations of spherical symmetry with self-gravity into a set of coupled nonlinear ordinary differential equations (ODEs). We focus on the analytical analysis and discuss applications of the solutions to galaxy clusters.

Key words:   dark matter -- hydrodynamics -- ISM: general -- galaxies: clusters -- outflows, winds -- shocks

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The Relation between the Inclinations of Broad Line Regions and the Accretion Disk

Wei-Hao Bian1, 2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012;

2 Department of Physics, Nanjing Normal University, Nanjing 210097; whbian@njnu.edu.cn

Abstract
According to the standard model, an active galactic nucleus (AGN) consists of an inner accretion disk with a jet around a central massive black hole, and a number of outer broad line regions (BLRs) and narrow line regions (NLRs). The geometrical relationship between the BLRs and the accretion disk is not well understood. Assuming the motion of the BLRs is virialized and its configuration is disk-like, we derived its inclination to the line of sight for a sample of AGNs from their bulge stellar velocity dispersion, their size of the BLRs and their H$\beta$ linewidth. Compared with the inclination of the accretion disk obtained from the X-ray Fe K$\alpha$ emission lines, we found that there is no positive correlation between the two. Our results showed that BLRs are not coplanar with the accretion disk and that we should be cautious of using the BLRs inclination as the disk inclination. The non-coplanar geometry of the outer BLRs and the inner accretion disk provides clues to the origin of BLRs and the properties of the accretion disk. Our preferable interpretation is that BLRs arise out of the outer part of a warped accretion disk.

Key words:   galaxies: active -- galaxies: nuclei -- galaxies: Seyfert

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Interstellar Refractive Scintillation and Intraday Polarization Angle Swings

Shan-Jie Qian1, Xi-Zhen Zhang1 and A. Kraus2

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

2 Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany

Abstract
Intraday polarization angle swings of $\sim 180^{\circ}$ observed in two sources (QSO 0917+624 and QSO 1150+812) are discussed in the framework of refractive interstellar scintillation by a continuous interstellar medium. Model-fits to the I-, Q- and U- light curves were made for both sources. It is shown that for the case of 0917+624 both the intraday intensity variations and the polarization angle swing of $\sim 180^{\circ}$ could be explained consistently in terms of a four-component model, which comprises one steady and two scintillating polarized components and one further non-polarized scintillating component. The polarization angle swing of $\sim 180^{\circ}$ observed in 1150+812, which occurred when the polarized flux density was almost constant, could not be explained in terms of refractive scintillation by a continuous medium and might be due to other mechanisms (e.g., scintillation by interstellar clouds).

Key words:   radio continuum: galaxies -- polarization: intraday variability -- scattering: refractive scintillation -- quasars: individual: QSO 0917+624 and 1150+812

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The Hybrid Nature of 0846+51W1: a BL Lac Object with a Narrow Line Seyfert 1 Nucleus

Hong-Yan Zhou, Ting-Gui Wang, Xiao-Bo Dong, Cheng Li and Xue-Guang Zhang

Center for Astrophysics, University of Science and Technology of China, Hefei 230026; mtzhou@ustc.edu.cn

Abstract
We found a NLS1 nucleus in the extensively studied eruptive BL Lac object, 0846+51W1, out of a large sample of NLS1s compiled from the spectroscopic dataset of SDSS DR1. Its optical spectrum can be well decomposed into three components: a power law component from the relativistic jet, a stellar component from the host galaxy, and a component from a typical NLS1 nucleus. The emission line properties of 0846+51W1, FWHM (H$\beta$) $\simeq 1710$ km s-1 and $\frac{ \rm [OIII]\lambda 5007}{\rm H\beta} \simeq 0.32$ from its SDSS spectrum observed when it was in the faint state, fulfil the conventional definition of NLS1. Strong FeII emission is detected in the SDSS spectrum, which is also typical of NLS1s. We tried to estimate its central black hole mass using various techniques and found that 0846+51W1 is very likely emitting at a few $\times 10\%$ of the Eddington luminosity. We speculate that Seyfert-like nuclei, including NLS1s, might be concealed in a significant fraction of BL Lacs but have remained largely unobserved because, often, their optical-UV continuum is overwhelmed by the synchrotron emission.

Key words:   galaxies: active -- galaxies: Seyfert -- galaxies: BL Lacertae -- quasars: individual (0846+51W1) -- radiation: lines, continuum

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Images at 20cm and the Spectrum Index of NGC2997

Hui Men and Jin-Lin Han

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

Abstract
We present total intensity maps of the galaxy NGC2997 at frequencies 1435.1MHz ($\lambda$21cm) and 1652.4MHz ($\lambda$18cm) observed with the Very Large Array (VLA). The high spatial resolution allows us to distinguish two dominant arms. Using multi-frequency data, we separate the thermal and non-thermal contributions to the radio emission. The thermal emission is about 35% of the total emission at $\lambda$3 cm. We use it to estimate a space-averaged thermal electron density, ${\langle}n_{\rm e} {\rangle}\sim 0.049\mbox{ cm}^{-3}$. The spectral index map shows that the optical arms and the central part of the galaxy have flatter spectra. We also determine the flux densities of 22 radio sources in the field-of-view of $25^{\prime}$.

Key words:   galaxies: individual (NGC2997) -- galaxies: ISM -- galaxies: spiral -- radio continuum: galaxies

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Polarization in Gamma-Ray Bursts Produced by Pinch Discharge

Mei Wu1, Li Chen2 and Ti-Pei Li1,3, 1

1Key Lab. of Particle Astrophys., Inst. of High Energy Phys., Chinese Academy of Sciences, Beijing 100039; litp@mail.ihep.ac.cn
2 Department of Astronomy, Beijing Normal University, Beijing 100875; chenli@bnu.edu.cn
3 Center for Astrophysics, Tsinghua University, Beijing 100084

Abstract  
Large-voltage, high-temperature plasma columns produced by pinch discharge can generate $\gamma$-ray flashes with energy spectra and spectral evolution consistent with what are observed in $\gamma$-ray bursts (GRBs), and the inverse Compton scattering (ICS) during the discharge process can produce high linear polarization. Our calculation indicates that the observed polarization depends on the angle between the line-of-sight to the GRB and the direction of the pinch discharge, but only weakly depends on observed $\gamma$-ray energy.

Key words:   gamma-ray: bursts -- radiation mechanism: non-thermal -- polarization

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Influence of the Choice of Core-Envelope Transition Point on the Binary Merger of Two Main-sequence Components

Xue-Fei Chen1, 2 and Zhan-Wen Han1

1 National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; xuefeichen717@hotmail.com
2 Graduate School of the Chinese Academy of Sciences, Beijing 100039

Abstract  
We have studied the influence of different choices of core-envelope transition point on the final merger of contact binaries with two main-sequence components. A binary of $1.00+0.90 M_\odot$ with an initial orbital period of 0.35d is examined. The mass fraction of the primary mixed with the matter of the secondary, $q_{\rm mix}$, determined by the chosen core-envelope transition point, ranges from 0.04 to 1.00 in our analysis. If as $q_{\rm mix}<0.8$, none of the helium-rich matter in the center of the primary is mixed into the envelope, and there is little distinction in the evolutionary tracks of the mergers. The timescales of the mergers remaining on the main sequence, $t_{\rm BS}$, are very similar ( $\sim 6.2\times 10 ^8$yr) if $q_{\rm mix}<0.71$, since no hydrogen-rich matter of the secondary is mixed into the core of the mergers; for $q_{\rm mix}>0.71$, the larger $q_{\rm mix}$ is, the greater the mixing, hence the longer the blue straggler lifetime, $t_{\rm BS}$, and also the greater the luminosity. For $q_{\rm mix}=1.00$, $t_{\rm BS}\sim 8.5\times 10 ^8$yr. Estimation by $\nabla_{\rm r} -\nabla _{\rm a}=0.0$ shows that the point at which $t_{\rm BS}$ begins to increase is about $q_{\rm mix}=0.68$. In comparison with the homogeneously mixed models, the merger with a helium profile similar to that of the primary is less luminous and has a shorter $t_{\rm BS}$.

Key words:   stars: binaries -- stars: evolution -- stars: blue stragglers

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Evolution of a Long-lived Sunspot Group and Its Associated Solar-terrestrial Events

Gui-Qing Zhang and Li-Rong Tian

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

Abstract  
A long-lived sunspot group (AR9604) on the south hemisphere that lasted five solar rotations and produced some strong bursts is analyzed. The focus is on its evolving features. Its whole life was successfully maintained by four Emerging Flux Regions (EFRs). Apart from the one that lasted only a short time and did not produce any bursts, the other three EFRs have the following common features: (1) A positive writhe of magnetic flux tubes and a twist of the field lines of the same sign, indicating kink instability. (2) A clockwise rotation and a high tilt because the writhe was right-handed. (3) A compact ``island $\delta $'' structure of the sunspot group indicating concentrated kink instability. Since magnetic reconnection easily occurs at the kinked point of a very kink-unstable flux tube, these features should be the inducement of the strong bursts.

Key words:   Sun -- active region evolution

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A Probable Short Decimetric Type I-like Noise Storm:  Associated with Type III Bursts?

Rui-Xiang Xie1, Min Wang1 and Yi-Hua Yan2

1 National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; wmynao@163.net
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Abstract  
A rare Type I-like noise storm was observed with the solar radio spectrometers (1.0-2.0GHz and 2.60-3.8GHz) at National Astronomical Observatories of China (NAOC) on September 23, 1998. We concentrate on checking the Type I-like noise storm occurred in the decay phase of a Type IV radio burst. This noise storm consists of many Type I bursts and isolated Type III or Type III pair bursts. It has a bandwidth of $\leq 0.5$GHz. The duration of each Type I burst is of the order of 100-300ms. The total duration is greater than 11 minutes. The circular polarization degree of the components of Type I and associated Type III bursts are about 40%-100% and almost 100%, respectively, which is greater than that of the background continuum (nearly the precision of our instrument). This short decimetric Type I-like storm may be another kind or the extension of the kind of metric Type I storm, and may possess the duality of metric and decimetric radio emission. It may be in favor of an earlier emission mechanism of the fundamental plasma radiation due to the coalescence of Langmuir waves with low-frequency waves.

Key words:   Sun -- radio radiation -- Type I noise storm

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The Influence of Ion-Acoustic Turbulence on the Electron Acceleration in the Reconnecting Current Sheet

Gui-Ping Wu1, Guang-Li Huang2 and Yu-Hua Tang3

1 Department of Physics, Southeast University, Nanjing 210096; wuguiping@seu.edu.cn
2 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008
3 Department of Astronomy, Nanjing University, Nanjing 210093

Abstract  
Through solving the single electron equation of motion and the Fokker-Planck equation including the terms of electric field strength and ion-acoustic turbulence, we study the influence of the ion-acoustic wave on the electron acceleration in turbulent reconnecting current sheets. It is shown that the ion-acoustic turbulence which causes plasma heating rather than particle acceleration should be considered. With typical parameter values, the acceleration time scale is around the order of 10-6s, the accelerated electrons may have approximately a power-law distribution in the energy range $20\sim 100$ keV and the spectral index is about 3$\sim$10, which is basically consistent with the observed hard X-ray spectra in solar flares.

Key words:   turbulence -- acceleration of particles -- Sun: X-rays, gamma rays

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Evidence for a Strong Correlation of Solar Proton Events with Solar Radio Bursts

Xiao-Cong Li and Lian-Sheng Kang

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; li_xiaocong@163.com

Abstract  
A statistical analysis is made on the correlation between solar proton events with energies >10Mev and solar radio bursts during the four-year period from 1997 November to 2000 November. We examine 28 solar proton events and their corresponding solar radio bursts at 15400, 8800, 4995, 2695, 1415, 606, 410 and 245MHz. The statistical result shows that there is a close association between solar proton events and $\geq 3$ solar radio bursts occurring at several frequencies, one or two days before. In particular, it is noteworthy that proton events occurring in pairs within the same month are preceded 1-2 days by individual radio bursts and most of the radio bursts of solar flares occur at all eight frequencies. Those 245MHz radio bursts associated with proton events have intense peak fluxes (up to 67000 sfu). Solar proton events are preceded 1 or 2 days by $\geq 3$ radio bursts at several frequencies and proton events occurring in pairs within the same month are preceded 1 or 2 days by some individual radio bursts. These correlations may be used for providing short-term or medium-term prediction of solar proton events.

Key words:   solar proton event -- solar radio burst

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ChJAA, 2005, Vol.5, No.1

Chinese Journal of Astronomy and Astrophysics: Online Edition

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Created by Aiying Zhou 2005-02-01