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{\LARGE\bf Chinese Journal of Astronomy and Astrophysics}\\

2007, Vol.7, No.3 (June 20, 2007)




Extragalactic Astronomy


The Sun

Instruments, Observational Techniques and Data Processing


Molecular Cores in Different Evolutionary Stages near Luminous IRAS Sources and UC HII Regions

Lei Zhu and Yue-Fang Wu

Department of Astronomy, Peking University, Beijing 100871; zhul@vega.bac.pku.edu.cn

We report the results of 12CO and 13CO J=1-0 observations of eight candidates of Ultra-Compact (UC) HII regions with the Purple Mountain Observatory (PMO) Qinghai 13.7-m telescope, which resulted in revealing 11 molecular cores. Their masses range from 130 to 1.7 x 10$^4\,M_\odot$, with different spatial scales ($1 \sim$ 6pc). Also presented are the relevant HCO+ J=1-0 maps, which enabled us to investigate more detailed structures of these cores. Further comparisons show that four of the cores deviated from the centers of infrared (MIR) emission of Midcourse Space Experiment (MSX), while others correspond either to bright MIR sources or diffuse MIR background. This indicates various evolutionary phases of the cores, including quite early ones for those without MIR sources.

Key Words:   stars: formation -- ISM: clouds -- ISM: molecules -- ISM: evolution
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X-Ray Properties of the Point Source Population in the Spiral Galaxy NGC 5055 (M63) with Chandra

Bing Luo1, Ji-Yao Chen1, Zhong-Li Zhang2, Yu Wang2, Jing-Ying Wang2 and Hai-Guang Xu2

1 Department of Physics, Fudan University, Shanghai 200433; wenyu_wang@sjtu.edu.cn
2 Department of Physics, Shanghai Jiao Tong University, Shanghai 200240

Using ACIS S3 data we studied the X-ray properties of low- and high-mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within two effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the X-ray emission of the galaxy, accounting for about 80% of the total counts in 0.3-10keV. From spectral fittings we calculated the 0.3-10.0keV luminosities of all the detected X-ray point sources and found that they span a wide range from a few times 1037erg s-1 to over 1039erg s-1. After compensating for incompleteness at the low luminosity end, we found that the corrected XLF of the bulge population is well fitted with a broken power-law with a break at 1.57+0.21-0.20 x 1038erg s-1, while the profile of the disk population's XLF agrees with a single power-law distribution of slope 0.93+0.07-0.06. The disk population is significantly richer at $\ga
2\times10^{38}$erg s-1 than the bulge population, indicating that the disk may have undergone relatively recent, strong starbursts that significantly increased the HMXB population, although ongoing starbursts are also observed in the nuclear region. Similar XLF profiles of the bulge and disk populations were found in M81. However, in most other spiral galaxies different patterns of spatial variation of the XLF profiles from the bulge to the disk have been observed, indicating that the star formation and evolution history may be more complex than we have expected.

Key Words:   galaxies: individual (NGC 5055)--X-ray:binaries--stars: luminosity function--stars: formation
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Effects of Redshift on the Classifying Criteria of BL Lacertae Objects

Li Ma1,3, Luo-En Chen2,3, Guang-Zhong Xie3,4, Ji-Yang Ren2, Zhao-Hua Xie1, Shu-Bai Zhou3, 4, Hui Wu1 and Dong-Cheng Mei4

1 Department of Physics, Yunnan Normal University, Kunming 650092; astromali@126.com
2 Department of Physics, Yuxi Normal College, Yuxi 653100
3 National Astronomical Observatories/ Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011
4 Department of Physics, Yunnan University, Kunming 650091

We have collected a sample of 70 BL Lacs (33 radio-selected BL Lacs and 37 X-ray selected BL Lacs) with multi-waveband data for investigating the classifying criteria of BL Lacertae Objects. For each source, we estimate its luminosities in radio, optical and X-ray, the broad-band spectral index from radio to X-ray and the peak frequency of the synchrotron emission, and make a statistical analysis of the data obtained. Our main results are as follows: (1) The broad-band spectral index and the peak frequency have no correlation with the redshift, while they are inversely correlated with each other and they could be regarded as equivalent classifying criteria of BL Lac objects. (2) There are significant effects of the luminosity/redshift relation on the observed luminosity distribution in our sample, hence, if the radio luminosity is to be used as a classifying criterion of BL Lac objects, it should not be regarded as equivalent to the broad-band spectral index or the peak frequency. (3) Our results supply a specific piece of evidence for the suggestion that the use of luminosities always introduces a redshift bias to the data and show that the location of the peak frequency is not always linked to the luminosity of any wave band.

Key Words:   galaxies: BL Lacertae objects: general--galaxies: fundamental parameters--galaxies: high-redshift
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Disk-Corona Model in Active Galactic Nuclei: an Observational Test

Fang Yang1,2, Chen Hu3,2, Yan-Mei Chen1,2, Jian-Min Wang1

1 Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049; yangfang@mail.ihep.ac.cn
2 Graduate School of Chinese Academy of Sciences, Beijing 100049
3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

We compiled a sample of 98 radio-quiet active galactic nuclei observed by ASCA, Chandra, XMM-Newton, INTEGRAL and Swift with the aim of testing the formation of hot corona and the magnetic shear stress operating in a disk-corona system. We found a strong correlation between the hard X-ray luminosity, bolometric luminosity $L_{\rm Bol}$ and Eddington luminosity $L_{\rm Edd}$, in the sense that the fraction f of hard X-ray to the bolometric luminosity is inversely proportional to the Eddington ratio. This correlation favors the shear stress tensor being of the form of $t_{\rm r\phi}\propto
P_{\rm gas}$, with which the disk-corona structure is stable.

Key Words:   accretion, accretion disks -- galaxies: active -- magnetic fields
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A Possible Periodicity in the Radio Light Curves of 3C 454.3

Shan-Jie Qian1,2, N. A. Kudryavtseva2,4,5, S. Britzen2, T. P. Krichbaum2, Long Gao1, A. Witzel2, J. A. Zensus2, M. F. Aller3, H. D. Aller3 and Xi-Zhen Zhang1

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
3 Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
4 Astronomical Institute of St.-Petersberg State University, Petrodvoretz, St.-Petersburg, Russia
5 International Max-Planck Research School for Radio and Infrared Astronomy at the Universities of Bonn and Cologne

During the period 1966.5-2006.2 the 15GHz and 8GHz light curves of 3C 454.3 (z=0.859) show a quasi-periodicity of $\sim$12.8 yr ($\sim$6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes of a binary system and rotating with the period of the orbital motion. The periodic variations in the radio fluxes of 3C 454.3 are suggested to be mainly due to the lighthouse effects (or the variation in Doppler boosting) of the precessing jets caused by the orbital motion. In addition, variations in the rate of mass accreting onto the black holes may be also involved.

Key Words:   radio continuum: galaxies -- Quasars: individual: 3C 454.3
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The Multi-Wavelength Quasar Survey III. Quasars in Field 836

Yu Bai1, Yang Chen1, Xiang-Tao He1, Jiang-Hua Wu2, Qing-Kang Li1, Richard F. Green3, Wolfgang Voges4

1 Department of Astronomy, Beijing Normal University, Beijing 100875; cheny@bnu.edu.cn
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
3 Kitt Peak National Observatory, NOAO, Tucson, AZ85726-6732, USA
4 Max-Planck-Institute für Extraterrestrische Physik, D-85740 Garching, Germany

This is the third paper in a series connected with our Multiwavelength Quasar Survey. The survey is aimed to provide a quasar sample more complete than any previous survey by using a combined selection technique to reduce selection effects. We present the observational results for the X-ray candidates in field f836. We found 15 X-ray AGNs in this field of which eight are new discoveries. The X-ray data and optical spectra of these AGNs are given. We give the X-ray candidate selection criteria, which proved to be highly efficient in isolating X-ray AGNs.

Key Words:   galaxies: active: individual (field f836) -- X-rays: galaxies: quasars
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A Possible 456-Day Optical Period of OQ 530

Yi Liu, Juan Li and Jun-Hui Fan

Center for Astrophysics, Guangzhou University, Guangzhou 510006; jhfan_cn@yahoo.com.cn

The post-1994 observations of the blazar OQ 530 in optical BVRI bands, and radio observations at 22GHz and 37GHz were collected. The date compensated discrete Fourier transform (DCDFT) and CLEANest methods were used to search for possible periodicities. Two possible periods of $456\pm100$ days and $258\pm29$ days were found in the optical bands. The existence of possible correlations between the optical and radio emissions was investigated by means of discrete correlation function (DCF) analysis, and no significant correlation was found. Some possible mechanisms for the periodic variability are discussed.

Key Words:   galaxies: active -- BL Lacertae objects: general -- BL Lacertae objects: individual: OQ 530
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Populations of Bright X-ray Sources in the Starburst Galaxies NGC 4038/4039

Xi-Wei Liu and Xiang-Dong Li

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

Assuming a naive star formation history, we construct synthetic X-ray source populations, using a population synthesis code, for comparison with the observed X-ray luminosity function (XLF) of the interacting galaxies NGC 4038/4039. We have included high- and intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disk-fed black holes in modeling the bright X-ray sources detected. We find that the majority of the X-ray sources are likely to be intermediate-mass X-ray binaries, but for typical binary evolution parameters, the predicted XLF seems to be steeper than observed. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, and suggest super-Eddington accretion luminosities or the existence of intermediate-mass black holes to account for the high luminosity end and the slope of the XLF in NGC 4038/4039.

Key Words:   binaries: close -- galaxies: individual (NGC 4038/4039) -- stars: evolution -- X-ray: binaries
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A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows

Yong-Feng Huang1, 2, Ye Lu2, 3, Anna Yuen Lam Wong2 and Kwong Sang Cheng2

1 Department of Astronomy, Nanjing University, Nanjing 210093; hyf@nju.edu.cn
2 Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.

Key Words:   gamma rays: bursts -- relativity -- shock waves -- ISM: clouds
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The Chemical Composition of the Field Zero-Age Star HD 77407

Xue-Liang Zhu1,2, Jian-Rong Shi2, Gang Zhao2, Ji Li2,3 and Qing-Xiang Nie1

1 College of Physics and Electronics, Shandong Normal University, Jinan 250014
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; gzhao@bao.ac.cn
3 Department of Physics, Hebei Normal University, Shijiazhuang 050016

High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of the star is determined by fitting the H$_{\alpha}$ line wings. The parameters derived for this star are $T_{\rm eff}$=5900K, $\log~g$=4.47 and [Fe/H] = +0.07. It is found that the derived iron content is slightly higher than what is given in the published literature. This star shows a relative overabundances of Ca and Ba, and underabundances of Na, V and Ni with respect to the solar mix. Activity of the star is indicated by the filled in H$_{\alpha}$ and Caii triplet line cores. It has been confirmed that our spectroscopic approach yields fairly reliable and consistent results for active stars.

Key Words:   stars: abundances -- stars: ZAMS -- stars: individual: HD77407
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Orbits of Ten Visual Binary Stars

B. Novakovic

Astronomical Observatory, Volgina 7, 11160 Belgrade 74, Serbia; bnovakovic@aob.bg.ac.yu

We present the orbits of ten visual binary stars: WDS 01015+6922, WDS 01424-0645, WDS 01461+6349, WDS 04374-0951, WDS 04478+5318, WDS 05255-0033, WDS 05491+6248, WDS 06404+4058, WDS 07479-1212, and WDS 18384+0850. We have also determined their masses, dynamical parallaxes and ephemerides.

Key Words:   binaries: visual
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Pulsation and Long-Term Variability of the High-Amplitude $\delta$ Scuti Star AD Canis Minoris

Pongsak Khokhuntod1, Jian-Ning Fu2, Chayan Boonyarak1, Kanokwan Marak1, Li Chen2 and Shi-Yang Jiang 3

1 Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand
2 Department of Astronomy, Beijing Normal University, Beijing 100875; jnfu@bnu.edu.cn
3 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

Time-series photometry was made for the large-amplitude $\delta$ Scuti star AD CMi in 2005 and 2006. High-quality photometric data provided in the literature were used to analyze the pulsation of the star, with the derived multiple frequencies fitted to our new data. Besides the dominant frequency and its harmonics, one low frequency (2.27402 c d-1) is discovered, which provides a reasonable interpretation for the long-noticed luminosity variation at the maximum and minimum light. Combining the nine new times of light maxima determined from the new data with the 64 times collected from the literature, we analyzed the long-term variability of AD CMi with the O-C technique. The results provide the updated value of period of 0.122974478 days, and seem to be in favor of the model of combination of the evolutionary effect and light-time effect of a binary system, of which some parameters are hereby deduced.

Key Words:   techniques: photometric -- stars: variables: $\delta$ Scuti -- stars: individual: AD CMi
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Relationships between Relative Spectral Lags and Relative Widths of Gamma-ray Bursts

Zhao-Yang Peng1, 4, Rui-Jing Lu2, Yi-Ping Qin1, 2, 3 and Bin-Bin Zhang1, 4

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; pzy@ynao.ac.cn

2 Physics Department, Guangxi University, Nanning 530004
3 Center for Astrophysics, Guangzhou University, Guangzhou 510400
4 Graduate School of Chinese Academy of Sciences, Beijing 100049

The phenomenon of gamma-ray burst (GRB) spectral lags is very common, but a definitive explanation has not yet been given. From a sample of 82 GRB pulses we find that the spectral lags are correlated with the pulse widths, however, there is no correlation between the relative spectral lags and the relative pulse widths. We suspect that the correlations between spectral lags and pulse widths might be caused by the Lorentz factor of the GRBs concerned. Our analysis on the relative quantities suggests that the intrinsic spectral lag might reflect other aspect of pulses than the aspect associated with the dynamical time of shocks or that associated with the time delay due to the curvature effect.

Key Words:   gamma-rays: bursts -- methods: statistical -- gamma-rays: theory
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Low Dimensional Chaos from the Group Sunspot Numbers

Qi-Xiu Li1, 2 and Ke-Jun Li1

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

We examine the nonlinear dynamical properties of the monthly smoothed group sunspot number Rg and find that the solar activity underlying the time series of Rg is globally governed by a low-dimensional chaotic attractor. This finding is consistent with the nonlinear study results of the monthly Wolf sunspot numbers. We estimate the maximal Lyaponuv exponent (MLE) for the Rg series to be positive and to equal approximately $0.0187\pm0.0023$ $(\rm month^{-1})$. Thus, the Lyaponuv time or predictability time of the chaotic motion is obtained to be about $4.46\pm0.5$ years, which is slightly different with the predictability time obtained from Rz. However, they both indicate that solar activity forecast should be done only for a short to medium term due to the intrinsic complexity of the time behavior concerned.

Key Words:   Sun: activity - Sun: sunspot - chaos - Sun: Wolf sunspot numbers
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Support Vector Machine combined with K-Nearest Neighbors for Solar Flare Forecasting

Rong Li, Hua-Ning Wang, Han He, Yan-Mei Cui and Zhan-Le Du

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

A method combining the support vector machine (SVM) the K-Nearest Neighbors (KNN), labelled the SVM-KNN method, is used to construct a solar flare forecasting model. Based on a proven relationship between SVM and KNN, the SVM-KNN method improves the SVM algorithm of classification by taking advantage of the KNN algorithm according to the distribution of test samples in a feature space. In our flare forecast study, sunspots and 10cm radio flux data observed during Solar Cycle 23 are taken as predictors, and whether an M class flare will occur for each active region within two days will be predicted. The SVM-KNN method is compared with the SVM and Neural networks-based method. The test results indicate that the rate of correct predictions from the SVM-KNN method is higher than that from the other two methods. This method shows promise as a practicable future forecasting model.

Key Words:   Sun: flare -- Sun: sunspot -- Sun: activity -- Sun: magnetic fields
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Estimating Photometric Redshifts with Artificial Neural Networks and Multi-Parameters

Li-Li Li1,2, Yan-Xia Zhang1, Yong-Heng Zhao1 and Da-Wei Yang2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012; lily@lamost.org
2 College of Physics Science and Information Engineering, Hebei Normal University, Shijiazhuang 050016

We calculate photometric redshifts from the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) Galaxy Sample using artificial neural networks (ANNs). Different input sets based on various parameters (e.g. magnitude, color index, flux information) are explored. Mainly, parameters from broadband photometry are utilized and their performances in redshift prediction are compared. While any parameter may be easily incorporated in the input, our results indicate that using the dereddened magnitudes often produces more accurate photometric redshifts than using the Petrosian magnitudes or model magnitudes as input, but the model magnitudes are superior to the Petrosian magnitudes. Also, better performance results when more effective parameters are used in the training set. The method is tested on a sample of 79346 galaxies from the SDSS DR2. When using 19 parameters based on the dereddened magnitudes, the rms error in redshift estimation is $\sigma_z=0.020184$. The ANN is highly competitive tool compared to the traditional template-fitting methods when a large and representative training set is available.

Key Words:   galaxies: fundamental parameters -- techniques: photometric -- method: data analysis
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ChJAA, 2007, Vol.7, No.3

Chinese Journal of Astronomy and Astrophysics: Online Edition


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