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

2006, Vol.6, No.4 (August 20, 2006)



Contents


 RESEARCH PAPERS

Cosmology
Extragalactic Astronomy
Stellar Clusters
Stars
The Sun
Instruments, Observational Techniques and Data Processing




Abstract

On the Large-Scale Structure of the Universe as given by the Voronoi Diagrams

L. Zaninetti

Dipartimento di Fisica Generale, Via Pietro Giuria 1 10125 Torino, Italy; zaninetti@ph.unito.it

Abstract
The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2,3),--2D cut of 3D Voronoi diagram--are explored, with the single-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2,3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size.

Key Words:   surveys -- galaxies: clusters: general -- (cosmology:) large-scale structure of Universe
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Estimating Black Hole Masses of AGNs using Ultraviolet Emission Line Properties

Min-Zhi Kong1, 2, Xue-Bing Wu2, Ran Wang2 and Jin-Lin Han1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; kmz@bao.ac.cn
2 Department of Astronomy, Peking University, Beijing 100871

Abstract
Based on measured broad line region sizes in the reverberation-mapping AGN sample, two new empirical relations are introduced to estimate the central black hole masses of radio-loud high-redshift (z>0.5) AGNs. First, using the archival $\it IUE/HST$ spectroscopy data at UV band for the reverberation-mapping objects, we obtained two new empirical relations between the BLR size and / emission line luminosity. Secondly, using the newly determined black hole masses of the reverberation-mapping sample as calibration, we found two new relationships for determining the black hole mass with the full width at half maximum and the luminosity of / line. We then apply the relations to estimate the black hole masses of the AGNs in the Large Bright Quasar Survey and a sample of radio-loud quasars. For the objects with small radio-loudness, the black hole mass estimated using the $R_{\rm BLR}$ -$L_{\eMg/\eC}$ relation is consistent with that from the $R_{\rm BLR}$ - $L_{\rm 3000\,\AA/1350\,\AA}$ relation. For radio-loud AGNs, however, the mass estimated from the $R_{\rm BLR}$ -$L_{\eMg/\eC}$ relation is systematically lower than that from the continuum luminosity $L_{\rm 3000\,\AA/1350\,\AA}$ . Because jets could have significant contributions to the UV/optical continuum luminosity of radio-loud AGNs, we emphasize once again that for radio-loud AGNs, the emission line luminosity may be a better tracer of the ionizing luminosity than the continuum luminosity, so that the relations between the BLR size and UV emission line luminosities should be used to estimate the black hole masses of high redshift radio-loud AGNs.

Key Words:   galaxies: nucleus -- galaxies: high-redshift -- quasars: emission lines -- ultraviolet: galaxies
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Isolated Main Galaxy Pairs from the SDSS Data Release 4

Xin-Fa Deng1, Yi-Qing Chen2, Ping Wu1, Cheng-Hong Luo1 and Ji-Zhou He1

1 Mathematics and Physics College, Nanchang University, Nanchang 330047; xinfadeng@163.com
2 Management College, Nanchang University, Nanchang 330047

Abstract
From the Main galaxy data of the SDSS Data Release 4 (SDSS4), we have identified close galaxy pairs at neighbourhood radius R = 100kpc by three-dimensional cluster analysis. Using the criterion that an ``isolated galaxy pair" must be separated from its ``nearest neighbor'' by more than 500kpc, we constructed an isolated galaxy pair sample of 1158 pairs. We also constructed a random pair sample by randomly selecting 1158 galaxy pairs from the Main galaxy sample, which has the same redshift distribution as the isolated galaxy pair sample, and in which the two components of any pair have the same redshifts. Comparative studies of luminosity and size between the members of the galaxy pairs are performed. We find and further confirm there is no tendency for paired galaxies to have similar luminosities or sizes. From the isolated pair sample we also selected a subsample with the magnitude limit of the primary raised by 2 magnitudes, so as to include pairs in which the secondary is 2 magnitudes fainter than the primary. This subsample contains 82 pairs. A random pair sample is similarly constructed.

Key Words:   galaxy: fundamental parameters- galaxies: interactions
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A Periodicity Analysis of the Light Curve of 3C 454.3

Huai-Zhen Li1, 2, Guang-Zhong Xie1, 3, Shu-Bai Zhou1,4, Hong-Tao Liu1, Guang-Wei Cha1, Li Ma4 and Li-Sheng Mao5

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; hzhli2003@163.com
2 Graduate School of Chinese Academy of Sciences, Beijing 100049
3 Yunnan Astronomical Center, Yunnan University, Kunming 650091
4 Physics Department, Yunnan University, Kunming 650091
5 Physics Department, Yunnan Normal College, Kunming 650091

Abstract
We analyzed the radio light curves of 3C 454.3 at frequencies 22 and 37 GHz taken from the database of Metsähovi Radio Observatory, and found evidence of quasi-periodic activity. The light curves show great activity with very complicated non-sinusoidal variations. Two possible periods, a very weak one of $1.57\pm0.12$  yr and a very strong one of $6.15\pm0.50$  yr were consistently identified by two methods, the Jurkevich method and power spectrum estimation. The period of $6.15\pm0.50$  yr is consistent with results previously reported by Ciaramella et al. and Webb et al. Applying the binary black hole model to the central structure we found black hole masses of $1.53\times10^{9} M_{\odot}$ and $1.86 \times 10^{8} M_{\odot}$ , and predicted that the next radio outburst is to take place in 2006 March and April.

Key Words:   galaxies: individual (3C 454.3)-- galaxies: fundamental parameters -- methods: data analysis
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Re-Identification of the `Enigmatic' X-ray Source 1RXS J114003.0+124112

Jiang-Hua Wu1, Tigran Movsessian2, Yang Chen3, Xiang-Tao He3, Xu Zhou1 and Jun Ma1

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; jhwu@bao.ac.cn
2 Byurakan Astrophysical Observatory, Aragatsotn Prov. 378433, Armenia
3 Department of Astronomy, Beijing Normal University, Beijing 100875

Abstract
The ROSAT X-ray source 1RXS J114003.0+124112 was identified as a starburst galaxy at redshift 0.177 by He et al. The authors also noted that the source is almost two orders of magnitude brighter in X-ray than the X-ray-brightest starburst galaxy and it seems to be in a merging system, making this source an enigmatic system demanding further observations. Here we report a re-identification of 1RXS J114003.0+124112 using observations on the 2.6m telescope at Byurakan Astrophysical Observatory, Armenia and the SDSS data. The results indicate that the starburst activity is associated with the brighter object of the system, while the fainter object is a typical Seyfert1 galaxy at a different redshift (0.282). Therefore, the two objects are not in a merging system, and the Seyfert1 galaxy naturally accounts for the high X-ray flux. Three more objects reside in the vicinity, but they are all too faint to be responsible for the high X-ray flux.

Key Words:   galaxies: active -- galaxies: Seyfert -- galaxies: starburst -- X-rays: individual (1RXS J114003.0+124112)
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Membership and Segregation Effects in the Young Open Cluster NGC 6530

Jun-Liang Zhao1, Li Chen1 and Wen Wen1,2

1 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030; chenli@shao.ac.cn
2 Shanghai University, Shanghai 200444

Abstract
From photographic plate data of Shanghai Astronomical Observatory with a time baseline of 87 years, proper motions and membership probabilities of 364 stars in the open cluster NGC 6530 region are reduced. On the basis of membership determination, luminosity function and segregation effect of the cluster are discussed with details. Spatial mass segregation is obviously present in NGC 6530 while there is no clear evidence for a velocity-mass (or velocity-luminosity) dependence. The observed spatial mass segregation for NGC 6530 might be due to a combination of initial conditions and relaxation process.

Key words:   open clusters and associations: individual (NGC 6530)
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Population Synthesis for the Symbiotic Stars with Main-sequence Accretors

Guo-Liang Lü1,2, Chun-Hua Zhu3, Bin Wu1,2 and Zhan-Wen Han1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; ytlgl@yahoo.com.cn
2 Graduate School of Chinese Academy of Sciences, Beijing 100049
3 Department of Physics, Xinjiang University, Urumqi 830046

Abstract
Using a population synthesis code, we have investigated the formation of symbiotic systems in which the hot component is a main-sequence star that is accreting matter from the cool component via Roche lobe overflow (RLOF). The RLOF can be divided into two cases: dynamically unstable and stable. In the first case, the birthrate of symbiotic stars is 0.056yr-1 or  0.045yr-1 depending on different assumptions; in the stable RLOF case, it is 0.002yr-1 or 0.005yr-1. The number of symbiotic stars with main-sequence accretors and unstable RLOF in our galaxy is about 5, that with stable RLOF is about 60 to 280. Comparison between our results with those of Yungelson et al. shows that symbiotic stars with MS accretors make only a small contribution $(\ls 8\%)$ to the whole population of symbiotic stars in the Galaxy.

Key Words:   binaries: symbiotic -- accretion: accretion disks -- stars: evolution -- main-sequence star
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Collapse Velocity and Prompt Explosion for the Presupernova Model Ws15$M_{ \odot}$

Zhi-Quan Luo1, 2, Men-Quan Liu1 and Qiu-He Peng3 and Zuo-Heng Xie4

1 Institute of Theoretical Physics, China West Normal University, Nanchong 637002; zqluo@tom.com
2 Department of Physics, Sichuan University, Chengdu 610065
3 Department of Astronomy, Nanjing University, Nanjing 210093
4 Institute of Applied Mathematics, Chinese Academy of Sciences, Beijing 100080

Abstract
For the presupernova model Ws15$M_{ \odot}$ , we re-calculate the electron capture (EC) timescale and hydrodynamical (HD) timescale. We found that the EC timescale can be smaller than the HD timescale in the inner region of the collapse iron core at the moment immediately before the shock wave bounce. The change in these two timescales at the late stage of core collapse is expected to affect the collapse velocity. If the late-time collapse velocity is artificially increased by a small quantity, then prompt explosion of the supernova may happen. Further calculations are still needed to check the plausibility of the acceleration mechanism caused by the faster EC process.

Key Words:   star: supernova -- nuclear reaction -- nucleosynthesis
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The Relation between the Critical Accretion Rate of Progenitors of SNe Ia and Metallicity

Xiang-Cun Meng1,2, Xue-Fei Chen1, 2, Christopher A. Tout3, 4 and Zhan-Wen Han1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; conson859@msn.com
2 Graduate School of Chinese Academy of Sciences, Beijing 100049
3 Institute of Astronomy, The Observatories, Madingley Road, Cambridge CB3 0HA, England
4 Centre for Stellar and Planetary Astrophysics, School of Mathematics, Monash University, Clayton, Victoria 3800, Australia

Abstract
A carbon-oxygen white dwarf may explode in a Type Ia supernova by accreting matter from its companion via either Roche lobe overflow or from winds, but there exists a critical accretion rate of the progenitor system for the explosion. We study the relation between the critical accretion rate and the metallicity via an AGB star approach. The result indicates that the critical accretion rate depends not only on the hydrogen mass fraction and the white dwarf mass, but also on the metallicity. The effect of the metallicity is smaller than that of the white dwarf mass. We show that it is reasonable to use the model with stellar mass 1.6 $M_{ \odot}$ for real white dwarfs.

Key Words:   stars: evolution -- star: AGB -- star: supernova: general
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Vector Magnetic Field Measurement of NOAA AR 10197

Hong-Fei Liang1,2,3, Hai-Juan Zhao4 and Fu-Yuan Xiang5

1 National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; njuf2003@yahoo.com.cn
2 Graduate School of Chinese Academy of Sciences, Beijing 100049
3 Yunnan Normal University, Kunming 650092
4 National Satellite Meteorological Center, China Meteorological Administration, Beijing 100081
5 Xiangtan University, Xiangtan 411105

Abstract
A set of two-dimensional Stokes spectral data of NOAA AR 10197 obtained by the Solar Stokes Spectral Telescope (S3T) at the Yunnan Observatory are qualitatively analyzed. The three components of the vector magnetic field, the strength H, inclination $\gamma$ and azimuth $\chi$ , are derived. Based on the three components, we contour the distributions of the longitudinal magnetic field and transverse magnetic field. The active region (AR) has two different magnetic polarities apparent in the longitudinal magnetic map due to projection effect. There is a basic agreement on the longitudinal magnetic fields between the S3T and SOHO/MDI magnetograms, with a correlation coefficient $\rho_{Bl}=0.911$ . The transverse magnetic field of the AR has a radial distribution from a center located in the southwest of the AR. It is also found that the transverse magnetic fields obtained by Huairou Solar Observing Station (HRSOS) have a similar radial distribution. The distributions of transverse magnetic field obtained by S3T and HRSOS have correlation coefficients, $\rho_{\rm Azimu}=0.86$ and $\rho_{Bt}=0.883$ , in regard to the azimuthal angle and intensity.

Key Words:   line: profiles -- sun: sunspots -- sun: vector magnetic field -- polarization
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The Relationship between Magnetic Gradient and Magnetic Shear in Five Super Active Regions Producing Great Flares

Hai-Min Wang 1,2 , Hui Song2, Ju Jing2, Vasyl Yurchyshyn2, Yuan-Yong Deng1, Hong-Qi Zhang1, David Falconer3, and Jing Li4

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; haimin@flare.njit.edu
2 Big Bear Solar Observatory, New Jersey Institute of Technology, Big Bear City, CA 92314, USA
3 Marshall Space Flight Center, SD50, Huntsville, AL 35812, USA
4 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA

Abstract
We study the magnetic structure of five well-known active regions that produced great flares (X5 or larger). The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July 14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the X10 flare on 2003 October 29, both in AR 10486. The last five events had corresponding LASCO observations and were all associated with Halo CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory, Huairou Solar Observing Station, Marshall Space Flight Center and Mees Solar Observatory. In particular, we studied the magnetic gradient derived from line-of-sight magnetograms and magnetic shear derived from vector magnetograms, and found an apparent correlation between these two parameters at a level of about 90%. We found that the magnetic gradient could be a better proxy than the shear for predicting where a major flare might occur: all six flares occurred in neutral lines with maximum gradient. The mean gradient of the flaring neutral lines ranges from 0.14 to 0.50 G km-1, 2.3 to 8 times the average value for all the neutral lines in the active regions. If we use magnetic shear as the proxy, the flaring neutral line in at least one, possibly two, of the six events would be mis-identified.

Key Words:   Sun: activity -- Sun: flares -- Sun: magnetic fields -- Sun: coronal mass ejections (CMEs)
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The Relation between the Amplitude and the Period of Solar Cycles

Zhan-Le Du1,2, Hua-Ning Wang1, and Xiang-Tao He2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; zldu@bao.ac.cn
2 Department of Astronomy, Beijing Normal University, Beijing 100875

Abstract
The maximum amplitudes of solar activity cycles are found to be well anti-correlated (r = -0.72) with the newly defined solar cycle lengths three cycles before (at lag -3) in 13-month running mean sunspot numbers during the past 190 years. This result could be used for predicting the maximum sunspot numbers. The amplitudes of Cycles 24 and 25 are estimated to be 149.5$\pm$ 27.6 and 144.3$\pm$ 27.6, respectively.

Key Words:   Sun: activity -- Sun: sunspots -- Sun: general
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Image Field Deformation of LAMOST due to Differential Atmospheric Refraction

Jin-Ling Li, Bo Zhang, Yong Yu, Zhao-Xiang Qi and Ming Zhao

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

Abstract
A vectorial expression of the image field deformation of LAMOST due to the differential atmospheric refraction is presented. The calculated results are compared with those from previous analyses based on the traditional spherical trigonometric formulas. It is demonstrated that different tangential displacements of star images during the observation tracking given by various authors are simply due to different reference points adopted. It is pointed out that the observational celestial pole is the center of the apparent diurnal motion, that, by referring to the observational celestial pole, the effect of the differential refraction on the image field of LAMOST during the 1.5-hour tracking period is approximately equivalent to a constant rotation of -13.65'' for all declination belts. It is therefore unnecessary to design a particular tracking velocity for each observation, and this will be obviously advantageous to the observation implementation. If the maximum tracking error of the fibers is 0.2'', then the fibers are required to be able to re-position during observational tracking for sky regions south of declination $+20^{\circ}$ and north of declination $+60^{\circ}$ .

Key Words:   telescopes -- atmospheric effects -- methods: analytical -- methods: statistical -- astrometry
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Comparison between Windowed FFT and Hilbert-Huang Transform for Analyzing Time Series with Poissonian Fluctuations: A Case Study

Dong Han1 and Shuang-Nan Zhang2,3

1 Department of Engineering Physics & Center for Astrophysics, Tsinghua University, Beijing 100084; handong@mail.tsinghua.edu.cn
2 Department of Physics & Center for Astrophysics, Tsinghua University, Beijing 100084
3 Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049

Abstract
Hilbert-Huang Transform (HHT) is a novel data analysis technique for nonlinear and non-stationary data. We present a time-frequency analysis of both simulated light curves and an X-ray burst from the X-ray burster 4U 1702-429 with both the HHT and the Windowed Fast Fourier Transform (WFFT) methods. Our results show that the HHT method has failed in all cases for light curves with Poissonian fluctuations which are typical for all photon counting instruments used in astronomy, whereas the WFFT method can sensitively detect the periodic signals in the presence of Poissonian fluctuations; the only drawback of the WFFT method is that it cannot detect sharp frequency variations accurately.

Key Words:   methods: data analysis -- stars: oscillations (including pulsations) -- X-rays: bursts  
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ChJAA, 2006, Vol.6, No.4

Chinese Journal of Astronomy and Astrophysics: Online Edition

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