2003, Vol.3, No.2 (April 20, 2003)


Contents

Cosmology
  • Rhombic Cell Analysis -- A New Way of Probing the Large-Scale
    Structure of the Universe. I. General Considerations  
    p.95
    T. Kiang 
    Abstract | | PDF file (768 KB) | PS file *.gz  (163 KB) 
  • Early Tracking Behavior in Small-field Quintessence Models   p.105
    Wei Wang and Bo Feng
    Abstract | | PDF file (1078 KB) | PS file *.gz  (204 KB) 
Extragalactic Astronomy
  • On the Black Hole -- Bulge Mass Ratios in Narrow-Line Seyfert I Galaxies   p.119
    Wei-Hao Bian and Yong-Heng Zhao
    Abstract | | PDF file (139 KB) | PS file *.gz  ( 48 KB) 
Stars
  • Statistics of the Instability Strip of $\beta$ Cephei Stars  p.125
    Bin Tian, Hui Men, Li-Cai Deng, Da-Run Xiong and Hui-Lai Cao
    Abstract | | PDF file (741 KB) | PS file *.gz  (142 KB)  
  • A Kinematical Study of the NGC~7538 IRS~1 Region   p.133
    Ye Xu, Xing-Wu Zheng and Dong-Rong Jiang 
    Abstract | | PDF file (2960 KB) | PS file *.gz  (551 KB) 
  • A Possible Explanation of the O'Connell Effect in Close Binary Stars   p.142
    Qing-Yao Liu and Yu-Lan Yang   
    Abstract | | PDF file (484 KB) | PS file *.gz  (116 KB) 
  • Searching for Variable Stars in the Field of NGC 7789   p.151
    Xiao-Bin Zhang, Li-Cai Deng, Yu Xin and Xu Zhou   
    Abstract | | PDF file (8187 KB) | PS file *.gz  (1442 KB) 
  • An Estimation of the Initial Period of Pulsars   p.166
    Zhan-Kui Huang and Xin-Ji Wu   
    Abstract | | PDF file (395 KB) | PS file *.gz  ( 90 KB) 
The Sun
Instruments, Observational Techniques and Data Processing
  • Learning Vector Quantization for Classifying Astronomical Objects   p.183
    Yan-Xia Zhang and Yong-Heng Zhao
    Abstract | | PDF file (149 KB) | PS file *.gz  ( 55 KB) 


Abstract


Rhombic Cell Analysis -- A New Way of Probing the Large-Scale Structure of the Universe. I. General Considerations
 

T. Kiang


Affiliation:  Dunsink Observatory, Dublin 15, Ireland

E-mail:   tkiang@eircom.net 

Abstract

A new way of probing the large-scale structure of the universe is proposed. Space is partitioned into cells the shape of rhombic dodecahedron. The cells are labelled ``filled'' or ``empty'' according as they contain galaxies or not. The cell size is so chosen as to have nearly equal numbers of filled and empty cells for the given galaxy sample. Two observables on each cell are definable: the number of its like neighbors, n1, and a two-suffixed topological type $\tau$, the suffixes being the numbers of its like and unlike neighbor-groups. The frequency distributions of n1 and $\tau$ in the observed set of filled (empty) cells are then considered as indicators of the morphology of the set. The method is applied to the CfA catalogue of galaxies as an illustration. Despite its limited size, the data offers evidence 1) that the empty cells are more strongly clustered than the filled cells, and 2) that the filled cells, but not the empty cells, have a tendency to occur in sheets. Further directions of development both in theory and application are indicated.

Key words: cosmology: large-scale structure of Universe --- cosmology: observations --- CfA Catalogue

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Early Tracking Behavior in Small-field Quintessence Models   

Wei Wang (1) and Bo Feng (2)

Affiliation: (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
             (2) Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039

E-mail:  wwang@lamost.bao.ac.cn    (corresponding author), fengbo@mail.ihep.ac.cn 

Abstract

We study several quintessence models which are exotic at Q = 0, and use a simple constraint $Q\ge H/2\pi$, to check when they enter the tracking regime, disregarding the details of inflation. We find that it can also give strong constraints for $V=V_0Q^{-\alpha}$, which has to enter the tracking regime after $\ln z \sim 10$, while for the
supergravity model $V=V_0 Q^{-\alpha}{\rm exp} (kQ^2/2)$, the constraint is much weaker. For the exponential form of inverse power-law potential $V=V_0{\rm exp} (\lambda/Q)$, it exhibits no constraints.

Key words: cosmology: theory

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The Universe With Bulk Viscosity

Arbab I. Arbab 

Affiliation:  Department of Physics, Teacher's College, Riyadh 11491, P. O. Box 4341, Saudi Arabia
Comboni College for Computer Science, P. O. Box 114, Khartoum, Sudan

E-mail:   arbab@ictp.trieste.it  

Abstract

Exact solutions for a model with variable G, $\Lambda$ and bulk viscosity are obtained. Inflationary solutions with constant (de Sitter-type) and variable energy density are found. An expanding anisotropic universe is found to isotropize during its expansion but a static universe cannot isotropize. The gravitational constant is
found to increase with time and the cosmological constant decreases with time as $\Lambda \propto t^{-2}$.

Key words: cosmology: theory --- cosmological parameters

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On the Black Hole -- Bulge Mass Ratios in Narrow-Line Seyfert I Galaxies

Wei-Hao Bian
(1,2) and Yong-Heng Zhao (1)

Affiliation: (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
             (2) Department of Physics, Nanjing Normal University, Nanjing 210097
                          
E-mail:   whbian@lamost.bao.ac.cn   (corresponding author)

Abstract

We present estimated ratios of the central black hole mass to the bulge mass (Mbh/Mbulge) for 15 Narrow Line Seyfert I galaxies (NLS1s). It is found that NLS1s apparently have lower mass ratios: the average mass ratio is about 1×10-4 with a spread of 2, which is one order of magnitude lower than for Broad Line AGNs and quiescent galaxies. This lower value, as compared to that established essentially for all other types of galaxies, can be accounted for by an underestimation of the black hole masses and an overestimation of the bulge masses in the NLS1s.

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

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Statistics of the Instability Strip of $\beta$ Cephei Stars

Bin Tian
(1,2), Hui Men (1,3), Li-Cai Deng (1,4), Da-Run Xiong (2) and Hui-Lai Cao (1,4)

Affiliation:   (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
          (2) Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008
          (3) Department of Astronomy, Nanjing University, Nanjing 210093, China
          (4) CAS-PKU Joint Beijing Astrophysics Center (BAC), Beijing 100871

E-mail:   tb1@263.net   (corresponding author)
  
Abstract

We present a study of the $\beta$ Cephei instability strip based on a sample of 49 stars of this type. After deriving their effective temperatures and luminosities from their observed (BV), (UB) colors and parallaxes we find their positions in the HR diagram to be mostly confined to the main sequence, and their masses to lie between
7$M_\odot$ and 30$M_\odot$. Their distribution on the HR diagram matches well with our previous theoretical instability strip which has an upper bound in the luminosity and rather tight boundaries in the effective temperature.

Key words: stars --- $\beta$ Cephei star --- instabilities

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A Kinematical Study of the NGC 7538 IRS 1 Region

Ye Xu (1,2,3), Xing-Wu Zheng (2) and Dong-Rong Jiang (3)


Affiliation: (1) National Astronomical Observatories, Chinese Academy of Sciences, Urumqi 830011
             (2) Department of Astronomy, Nanjing University, Nanjing 210093
             (3) Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030
                         
E-mail:   xuye@nju.edu.cn   (corresponding author)

Abstract

We present high angular resolution images of both NH3 (1, 1) and (2, 2) lines toward NGC 7538 IRS 1. The density and velocity-position plots have been used to study the interaction among the outflows, winds and their environment. For the first time we have found an expanding half-shell of molecular gas around the HII region associated with IRS 1, which may be produced by the interaction of the bipolar outflows and the winds originating in IRS 13, and optical HII region NGC 7538 with ambient molecular gas.

Key words: HII regions --- ISM: clouds --- ISM: individual (NGC 7538) --- ISM: kinematics

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A Possible Explanation of the O'Connell Effect in Close Binary Stars

Qing-Yao Liu and Yu-Lan Yang  (1,2)

Affiliation: (1)  National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011
             (2) United Laboratory of Optical Astronomy, Chinese Academy of Sciences
                    
E-mail:  bily@public.km.yn.cn   (corresponding author)

Abstract

A theoretical model for explaining the O'Connell effect of close binary stars is given based on the hypothesis that the circumstellar material of a binary system is captured by its components. The results inferred from the model suggest that late-type and/or short-period binaries can easily produce obvious O'Connell effect and that the occurrence of O'Connell effect has no relation with the type of binaries. These conclusions are in agreement with the observed results. The observed O'Connell effects of six binary systems are examined by the model. For three W-subtype W UMa binaries (YY Eri, BX Per and SW Lac), the densities of the materials captured by the two components are assumed to be equal, and the calculated O'Connell effect is found to be almost equal to the observed effect. For three A-subtype W UMa systems (CN And, FG Hya and AU Ser), the two densities are assumed to be different, and are calculated separately. The calculated O'Connell effect turns out to agree better with the observed effect than that was formerly obtained.

Key words: binaries: close --- star: W UMa --- circumstellar matter

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Searching for Variable Stars in the Field of NGC 7789

Xiao-Bin Zhang, Li-Cai Deng, Yu Xin and Xu Zhou  (1,2)

Affiliation:  (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
              (2) CAS-PKU Joint Beijing Astrophysics Center, Beijing 100871
                    
E-mail:   xzhang@bao.ac.cn  (corresponding author)

Abstract

We present the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 7789. In a field of about one degree centering on the cluster, a total of 28 new variable stars are discovered (14 W UMa systems, nine EA-type eclipsing binaries, one RR Lyr star, and four unclassified). In addition, we recovered 11 old variables previously discovered by other authors. Preliminary parameters are given for some of these variables.

Key words: open clusters: individual (NGC 7789) --- stars: variables (general) --- binaries: general

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An Estimation of the Initial Period of Pulsars

Zhan-Kui Huang (1,2) and Xin-Ji Wu (1,2,3) 

Affiliation:  (1) Department of Astronomy, Peking University, Beijing 100871
              (2) Chinese Academy of Sciences-Peking University Joint Beijing Astrophysics Center, Beijing 100871
              (3) National Astronomical Observatories, Urumqi Astronomical Observatory, Chinese Academic of Science, Urumqi 830011
                    
E-mail:   wuxj@bac.pku.edu.cn  (corresponding author)

Abstract

The initial period of a pulsar is an important factor in our understanding of the formation of neutron stars and of the nature of the equation of state of neutron star matter. Up to now this quantity can only be obtained for a few pulsars for which accurate age and braking index are known. Based on the theory of the off-center dipole emission, in which pulsars obtain their high velocities depending on the initial periods, we calculate the initial period using the proper motion data. Because the orbital velocity of the progenitor and asymmetric kick in the supernova explosion may also contribute to the observed velocity of the pulsar, the derived values of initial periods are lower limits. For normal pulsars, the initial periods are in the range of 0.6 $\sim$ 2.6 ms. For the millisecond pulsars, the initial periods are comparable to their current periods, and the ratio between the initial period and the current period increases with the decrease of the current period. For PSR B1937+21 with the shortest period of 1.56 ms, the ratio is 0.77.

Key words: pulsars --- stars: neutron

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Size-Flux Relation in Solar Active Regions

O. V. Chumak (1,2) and Hong-Qi Zhang (1) 

Affiliation:  (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
              (2) Sternberg Astronomical Institute, Moscow State University, Moscow 119992, Russia
                    
E-mail:   chumak@sai.msu.ru  (corresponding author)

Abstract

We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing.

Key words: Sun: activity --- Sun: magnetic fields

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Learning Vector Quantization for Classifying Astronomical Objects

Yan-Xia Zhang and Yong-Heng Zhao 

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

Abstract

The sizes of astronomical surveys in different wavebands are increasing rapidly. Therefore, automatic classification of objects is becoming ever more important. We explore the performance of learning vector quantization (LVQ) in classifying multi-wavelength data. Our analysis concentrates on separating active sources from non-active ones. Different classes of X-ray emitters populate distinct regions of a multidimensional parameter space. In order to explore the distribution of various objects in a multidimensional parameter space, we positionally cross-correlate the data of quasars, BL Lacs, active galaxies, stars and normal galaxies in the optical, X-ray and infrared bands. We then apply LVQ to classify them with the obtained data. Our results show that LVQ is an effective method for separating AGNs from stars and normal galaxies with multi-wavelength data.

Key words: method: data analysis --- method: statistical --- catalogs

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ChJAA, 2003, Vol.3, No.2

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

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