ChJAA -- 2005, Vol.5, No.2

The Origin of Infrared Emission from the Infrared Luminous Galaxy NGC 4418

Lei Shi and Qiu-Sheng Gu

Department of Astronomy, Nanjing University, Nanjing 210093; qsgu@nju.edu.cn

Abstract
We present a study of the origin of infrared (IR) emission in the optically normal, infrared luminous galaxy NGC 4418. By decomposing the stellar absorption features and continua in the range of 3600-8000Å from the Sloan Digital Sky Survey into a set of simple stellar populations, we derive the stellar properties for the nuclear region of NGC 4418. We compare the observed infrared luminosity with the one derived from the starburst model, and find that star-forming activity contributes only 7% to the total IR emission, that as the IR emission region is spatially very compact, the most possible source for the greater part of the IR emission is a deeply embedded AGN, though an AGN component is found to be unnecessary for fitting the optical spectrum.

Key words: galaxies: general -- galaxies: active -- galaxies: stellar content -- galaxies: individual (NGC 4418)

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Merger Dynamics of the Pair of Galaxy Clusters -- A399 and A401

Qi-Rong Yuan ^{1, 2}, Peng-Fei Yan^3, Yan-Bin Yang ² and Xu Zhou^2

¹ Department of Physics, Nanjing Normal University, Nanjing 210097; yuanqirong@njnu.edu.cn
² National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
³ Department of Mathematics and Physics, Qingdao University of Science and Technology, Qingdao 266042

Abstract
Convincing evidence for a past interaction between the two rich clusters A399 and A401 was recently found in the X-ray imaging observations. We examine the structure and dynamics of this pair of galaxy clusters. A mixture-modeling algorithm was applied to obtain a robust partition into two clusters, which allowed us to discuss the virial mass and velocity distribution of each cluster. Assuming that these two clusters follow a linear orbit and they have once experienced a close encounter, we model the binary cluster as a two-body system. As a result, four gravitationally bound solutions are obtained. The recent X-ray observations seem to favor a scenario in which the two clusters with a true separation of $5.4h^{-1}$ Mpc are currently expanding at 583 along a direction with a projection angle of $67.5\dg$ , and they will reach a maximum extent of $5.65 h^{-1}$ Mpc in about $1.0 h^{-1}$ Gyr.

Key words: galaxies: clusters: individual (A399, A401) -- galaxies: kinematics and dynamics

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A Photometric Study of the W UMa-type Eclipsing Binary System GSC 0445-1993

Yuan-Gui Yang ^{1, 2, 3}, Sheng-Bang Qian ^{1, 2} and M. D. Koppelman⁴

¹ National Astronomical Observatories /Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; yygcn@163.com
² United Laboratory of Optical Astronomy, Chinese Academy of Sciences (ULOAC), Beijing
³ Graduate School of Chinese Academy of Sciences, Beijing 100039
⁴ Starhouse Observatory, 1523 Valders Ave N, Golden Valley, MN USA

Abstract
Several new light minimum times for the eclipsing binary GSC 0445-1993 have been determined from the observations by Koppelman et al. and the orbital period of this system was revised. A photometric analysis was carried out using the 2003 version of the Wilson-Devinney code. The results reveal that GSC 0445-1993 is a W-type eclipsing binary with a mass ratio of $q=0.323(\pm 0.002)$ and an over-contact degree of $f=22.8\%(\pm 4.2\%)$ . A small temperature difference between the components of $\Delta T=135 \mathrm{K}$ and an orbital inclination of $i=65.7^{\circ} (\pm 0.3\dg)$ were obtained. The asymmetry of its light curve (i.e., the O'Connell effect) for this binary star is explained by the presence of a dark spot on the more massive component.

Key words: stars: binaries: close -- stars: binaries: eclipsing -- star: individual: GSC 0445-1993

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C¹⁸O Observations of the Dark Molecular Cloud L134 and Gas Depletion onto Dust

Xin-Jie Mao and Xiao-Xia Sun

Department of Astronomy, Beijing Normal University, Beijing 100875; maoxj@bnu.edu.cn

Abstract
We map the dark molecular cloud core of L134 in the $\rm C^{18}{\rm O}$ (J=1-0) emission line using the PMO 13.7m telescope, and present a contour map of integrated intensity of C¹⁸O (J=1-0) emission. The C¹⁸O cloud is inside the distribution of extinction A_B, the visual extinction of blue light, as well as inside the ¹³CO cloud in the L134 region. The depletion factors in this C¹⁸O cloud are generally greater than unity, which means there is gas depletion onto dust. Since only a minimum A_B = 9.7 mag is available, and our observations measure both undepleted and depleted regions along the line of sight, the depletion factors could very likely be larger in the central core than the calculated value. So we conclude that depletion does occur in the bulk of the C¹⁸O cloud through a comparison between the C¹⁸O and blue extinction maps in the L134 region. There is no direct evidence as yet for star formation in L134, and so cores on the verge of collapse will not be visible in CO and other gas molecules.

Key words: ISM: clouds -- ISM: individual (L134) -- ISM: molecules -- ISM: extinction

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Sequences in the Hardness Ratio-Peak Energy Plane of Gamma-Ray Bursts

Xiao-Hong Cui^{1, 4}, En-Wei Liang^{1, 2, 3} and Rui-Jing Lu^{1, 2, 4}

¹ National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; ciwei8008@163.com
² Department of Physics, Guangxi University, Nanning 530004
³ Department of Astronomy, Nanjing University, Nanjing 210093
⁴ Graduate School of the Chinese Academy of Sciences, Beijing 100039

Abstract
The narrowness of the distribution of the peak energy of the $\nu F_{\nu}$ spectrum of gamma-ray bursts (GRBs) and the unification of GRB populations are great puzzles yet to be solved. We investigate the two puzzles based on the global spectral behaviors of different GRB populations, the long GRBs, the short GRBs, and the X-ray flashes (XRFs), in the $HR-E_{\rm {p}}$ plane (HR the spectral hardness ratio) with BATSE and HETE-2 observations. It is found that the long GRBs and the XRFs observed by HETE-2 seem to follow the same sequence in the $HR-E_{\rm {p}}$ plane, with the XRFs at the low end of this sequence. We fit the sequence by a universal Band function, and find that this sequence is mainly defined by the low energy index $\alpha$ , and is insensitive to the high energy index, $\beta$ . With fixed $\beta=-5$ , a best fit is given by $\alpha=-1.00$ with $\chi^2_{\min}/{\rm dof}=2.2$ . The long and short GRBs observed by BATSE follow significantly different sequences in the $HR-E_{\rm p}$ plane, with most of the short GRBs having a larger hardness ratio than the long GRBs at a given $E_{\rm {p}}$ . For the long GRBs a best-fit yields $\alpha=-0.30$ and $\beta=-2.05$ . For the short GRBs, a best fit gives $\alpha=-0.60$ with $\chi^2_{\min}=1.1$ (with $\beta$ fixed at -2.0 because it is numerically unstable). The $\alpha$ value for the short GRBs is significantly greater than that for the long GRBs. These results indicate that the global spectral behaviors of the long GRB sample and the XRF sample are similar, while that of the short GRBs is different. The short GRBs seem to be a unique subclass of GRBs, and they are not the higher energy extension of the long GRBs.

Key words: gamma ray: bursts -- gamma ray: observations -- methods: statistical

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First MERLIN Observations of Line Emission from the OH Megamaser toward IRAS10173+0828

Zhi-Yao Yu

Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030; zyyu@center.shao.ac.cn
National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Abstract
Many galaxies are thought to contain massive black holes, with masses in excess of ten million solar masses, at their centres and warped circumnuclear toruses. The best evidence comes from observing gas or masers rotating rapidly within a circumnuclear torus surrounding a central body. Here we report on the first MERLIN observations of line emission from the OH megamaser toward IRAS10173+0828. The position of peak flux contours of the OH megamaser is consistent with that of the continuum in IRAS10173+0828. This means that the OH megamaser is a diffuse unsaturated maser which could amplify the diffuse 18 cm continuum emission with an amplification factor of order unity.

Key words: masers -- ISM: molecules -- galaxies: nuclei -- galaxies: active -- galaxies: kinematics and dynamic -- galaxies: ISM

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Statistics of Galactic Supernova Remnants

Jian-Wen Xu, Xi-Zhen Zhang and Jin-Lin Han

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

Abstract
We collected the basic parameters of 231 supernova remnants (SNRs) in our Galaxy, namely, distances (d) from the Sun, linear diameters (D), Galactic heights (Z), estimated ages (t), luminosities (L), surface brightness ( $\Sigma$ ) and flux densities (S₁) at 1-GHz frequency and spectral indices ( $\alpha$ ). We tried to find possible correlations between these parameters. As expected, the linear diameters were found to increase with ages for the shell-type remnants, and also to have a tendency to increase with the Galactic heights. Both the surface brightness and luminosity of SNRs at 1-GHz tend to decrease with the linear diameter and with age. No other relations between the parameters were found.

Key words: methods: statistical -- (ISM:) supernova remnants

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A Survey and Statistics of Interstellar OH and H₂O Masers

Han-Ping Liu¹, J. R. Forster² and Jin Sun³

¹ Department of Physics, Beijing Normal University, Beijing 100875; gaozm@bnu.edu.cn
² University of California, Berkeley, and Hat Creek Radio Observatory, 42231 Bidwell Road, Hat Creek, CA 96040
³ Department of Astronomy, Beijing Normal University, Beijing 100875

Abstract
We present a statistical analysis of a sky survey of interstellar H₂O and OH masers. These masers can be classified into three categories: isolated H₂O masers, isolated OH masers, and simple OH/H₂O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain $\sim$ 10⁵ yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.

Key words: surveys -- masers -- radiation mechanism: non-thermal -- HII regions

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Proton and He^{2 +} Temperature Anisotropies in the Solar Wind Driven by Ion Cyclotron Waves

Quan-Ming Lu and Shui Wang

School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026; qmlu@ustc.edu.cn

Abstract
We carried out one-dimensional hybrid simulations of resonant scattering of protons and He^{2 +} ions by ion cyclotron waves in an initially homogeneous, collisionless and magnetized plasma. The initial ion cyclotron waves have a power spectrum and propagate both outward and inward. Due to the resonant interaction with the protons and He^{2 +} ions, the wave power will be depleted in the resonance region. Both the protons and He^{2 +} ions can be resonantly heated in the direction perpendicular to the ambient magnetic field and leading to anisotropic velocity distributions, with the anisotropy higher for the He^{2 +} ions than for the protons. At the same time, the anisotropies of the protons and He^{2 +} ions are inversely correlated with the plasma $\beta _{\vert \vert p} = 8\pi n_p k_B T_{\vert \vert p} / B_0^2$ , consistent with the prediction of the quasilinear theory (QLT).

Key words: solar wind -- plasmas -- waves

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Waiting Time Distribution of Coronal Mass Ejections

Chin-Teh Yeh, Ming-De Ding and Peng-Fei Chen

Department of Astronomy, Nanjing University, Nanjing 210093; jdye@nju.edu.cn

Abstract
Inspired by the finding that the large waiting time of solar flares presents a power-law distribution, we investigate the waiting time distribution (WTD) of coronal mass ejections (CMEs). SOHO/LASCO CME observations from 1996 to 2003 are used in this study. It is shown that the observed CMEs have a similar power-law behavior to the flares, with an almost identical power-law index. This strongly supports the viewpoint that solar flares and CMEs are different manifestations of the same physical process. We have also investigated separately the WTDs of fast-type and slow-type CMEs and found that their indices are identical, which imply that both types of CME may originate from the same physical mechanism.

Key words: solar flares -- coronal mass ejections

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Latitudinal Distribution of Solar Flares and Their Association with Coronal Mass Ejections

Pankaj K. Shrivastava¹ and Neelam Singh

Department of Physics, Government New Science College, Rewa (M. P.) India; pankaj_in_2001@rediffmail.com

Abstract
Major solar flare events have been utilised to study the latitudinal frequency distribution of solar flares in northern and southern hemispheres for the period of 1986 to 2003. A statistical analysis has been performed to obtain the correlation between Coronal Mass Ejections (CMEs) and Forbush decrease (Fds) of cosmic ray intensity. Almost the same flares distribution in both hemispheres is found in association with CMEs. In a further analysis, it is noted that a larger number of CME-associated solar flares located in the northern hemisphere are found to be more effective in producing Forbush decreases.

Key words: Solar flares -- coronal mass ejections -- Forbush decrease

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Automated Stellar Classification for Large Surveys with EKF and RBF Neural Networks

Ling Bai^{1, 2}, Ping Guo¹ and Zhan-Yi Hu²

¹ Department of Computer Science, Beijing Normal University, Beijing 100875 pguo@bnu.edu.cn
² National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing 100080

Abstract
An automated classification technique for large size stellar surveys is proposed. It uses the extended Kalman filter as a feature selector and pre-classifier of the data, and the radial basis function neural networks for the classification. Experiments with real data have shown that the correct classification rate can reach as high as 93%, which is quite satisfactory. When different system models are selected for the extended Kalman filter, the classification results are relatively stable. It is shown that for this particular case the result using extended Kalman filter is better than using principal component analysis.

Key words: methods: data analysis -- techniques: spectroscopic -- stars: general -- galaxies: stellar content

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DEFPOS and Its First Results

M. Sahan¹, I. Yegingil ¹, N. Aksaker ¹, Ü. Kiziloglu ² and M. Akyilmaz ¹

¹ Department of Physics, Çukurova University, 01330, Adana, Turkey msahan2000@yahoo.com
² Department of Physics, Middle East Technical University, Ankara, Turkey

Abstract
A spectrometer was built to examine the interstellar medium (ISM) using the hydrogen Balmer $\alpha$ line. It is called Dual Etalon Fabry-Perot Optical Spectrometer (DEFPOS). DEFPOS will be coupled to coudé exit of the 150 cm telescope (RTT150) installed at TÜBITAK National Observatory (TUG). DEFPOS was ready for observations about two years ago, but work was still continuing on the RTT150 coudé exit alignment. So we have started observing HII regions with DEFPOS without the RTT150. We present here some characteristics of the instrument and some of the results obtained.

Key words: ISM: general -- ISM: HII regions -- instrumentation: Interferometers -- techniques: interferometric -- atmospheric effect

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ChJAA, 2005, Vol.5, No.2

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org

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Created by Aiying Zhou 2005-04-06