ChJAA -- 2004, Vol.4, No.3

2004, Vol.4, No.3 (June 20, 2004)

Contents

LETTER

Solar Radio Bursts in the Period Oct. 22--Nov. 4, 2003 p.205
Cheng-Ming Tan, Qi-Jun Fu, Yi-Hua Yan and Yu-Ying Liu
Abstract | | PDF file (695 KB) | PS file *.gz (946 KB)

RESEARCH PAPERS

Cosmology

Rhombic Cell Analysis. II. Application to the IRAS/PSCz Catalogue p.209
Tao Kiang, Yong-Feng Wu and Xing-Fen Zhu
Abstract | | PDF file (241 KB) | PS file *.gz (239 KB)

Extragalactic Astronomy

Chandra Observation of Point Sources in the X-Ray Elliptical Galaxy NGC 1407 p.221
Zhong-Li Zhang and Hai-Guang Xu
Abstract | | PDF file (320 KB) | PS file *.gz (437 KB)

BL Lacertae: Hard Optical Spectrum and GeV $\gamma$ -ray Emission p.231
Shan-Jie Qian, Xi-Zhen Zhang and T. P. Krichbaum
Abstract | | PDF file (233 KB) | PS file *.gz (178 KB)

Astrometry and celestial mechanics

Chandler Wobble Period and Q Derived by Wavelet Transform p.247
De-Chun Liao and Yong-Hong Zhou
Abstract | | PDF file (332 KB) | PS file *.gz (533 KB)

Stars

The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga p.258
Jin-Zeng Li
Abstract | | PDF file (183 KB) | PS file *.gz (167 KB)

Effect of Conversion Efficiency on Gamma-Ray Burst Energy p.267
Lei Xu and Zi-Gao Dai
Abstract | | PDF file (190 KB) | PS file *.gz (154 KB)

Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma p.275
Bin Luo and Shuang-Nan Zhang
Abstract | | PDF file (159 KB) | PS file *.gz (153 KB)

A Spectral Atlas of F and G Stars p.279
V. G. Klochkova, Gang Zhao, V. E. Panchuk and S. V. Ermakov
Abstract | | PDF file (172 KB) | PS file *.gz (204 KB) | Data file *.tar.gz (1751 KB)

Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912 p.284
Xue-Peng Chen and Yong-Qiang Yao
Abstract | | PDF file (451 KB) | PS file *.gz (1891 KB)

Abstract

Solar Radio Bursts in the Period Oct. 22--Nov. 4, 2003

Cheng-Ming Tan, Qi-Jun Fu, Yi-Hua Yan and Yu-Ying Liu

Affiliation: National Astronomical Observatories, Chinese Academy of Science, Beijing 100012

E-mail: tanchm@bao.ac.cn

Abstract

A series of solar radio bursts were observed in AR NOAA 10486 with the Solar Broadband (1.1--7.6 GHz) Radio Spectrometers (SBRS of China). Here we analyze four significant events associated with CME events and strong X-ray flares that occurred on 2003 October 22, 26, 27, 29. The Oct. 26 event is a long duration event (LDE) with drift pulsation structure (DPS), narrowband dm-burst (DCIM), and more than seven types of Fine Structures (FSs); its time of the maximum flux (07:30 UT) is about half an hour later than the X-flare (06:54 UT).

Key words: Sun: flares --- Sun: radio radiation --- Sun: fine structures

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Rhombic Cell Analysis. II. Application to the IRAS/PSCz Catalogue

Tao Kiang (1), Yong-Feng Wu (2) and Xing-Fen Zhu (2)

Affiliation:   (1) Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin 15, Ireland
                    (2) Center for Astrophysics, University of Science and Technology of China, Hefei 230026

E-mail:    tkiang@eircom.net (corresponding author)

Abstract

Rhombic cell analysis as outlined in the first paper of the present series is applied to samples of varying depths and liming luminosities of the IRAS/PSCz Catalogue. Numerical indices are introduced to summarize essential information. Because of the discrete nature of the analysis and of the space distribution of galaxies, the indices for a given sample must be regarded as each having an irreducible scatter. Despite the scatter, the mean indices show remarkable variations across the samples. The underlying factor for the variations is shown to be the limiting luminosity rather than the sampling depth. As samples of more and more luminous galaxies are considered over a range of some 2.5 magnitudes (a factor of some 75 in space density), the morphology of the filled and empty regions defined by the galaxies degrades steadily towards insignificance, and the degrading is faster for the filled than the empty region.

Key words: cosmology: large-scale structure of Universe --- cosmology: observations --- IRAS/PSCz catalogue

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Chandra Observation of Point Sources in the X-Ray Elliptical Galaxy NGC 1407

Zhong-Li Zhang (1,2) and Hai-Guang Xu (2)

Affiliation:   (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
                    (2) Department of Physics, Shanghai Jiao Tong University, Shanghai 200030; hgxu@sjtu.edu.cn

E-mail:   zebrafish@sjtu.edu.cn (corresponding author)

Abstract

With the Chandra pointing observation of about 50 ks, we have detected 41 point sources in the X-ray relatively faint elliptical galaxy NGC 1407, most of which appear to be low mass X-ray binaries. In luminosity flux units, these resolved point sources contribute about 17.8 % of the total emission of the galaxy in 0.3--10 keV. Of the remaining diffuse emission, about 53.4 % (or 43.9 % of total) may arise from unresolved point sources. We find six ultraluminous X-ray sources with luminosities above 10³⁹ erg s^-1. This number is less than has been found in NGC 720, but more than in NGC 4697 and NGC 1553, so suggesting a possible correlation between the number of ULXs and the total X-ray luminosity of early-type galaxies. A central point-like source is detected whose luminosity (2.36±0.14×10³⁹ erg s^-1) is the highest among all resolved sources. However, because of its relatively low hardness ratio, we speculate that it is not likely to be a low luminosity AGN.

Key words: binaries: close --- galaxies: elliptical and lenticular --- galaxies: individual: NGC 1407 --- X-rays: binaries --- X-rays: galaxies

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BL Lacertae: Hard Optical Spectrum and GeV $\gamma$ -ray Emission

Shan-Jie Qian (1), Xi-Zhen Zhang (1) and T. P. Krichbaum (2)

Affiliation: (1) National Astronomical Observatories, CAS (NAOC), Beijing 100012, China
(2) Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

E-mail: rqsj@bao.ac.cn (corresponding author)

Abstract

The spectral energy distribution (SED) of the $\gamma$ -ray flare observed in July 1997 in BL Lacertae is re-considered. It is pointed out that the optical observations made by Webb et al. showed the associated optical flare has a hard spectrum (the average spectral index ${\alpha}_{\rm opt} \sim 0.48$ , ${F_{\nu}}{\,}{\propto}{\,}{{\nu}^{-\alpha}}$ ), and the ASCA observations made by Tanihata et al. showed very steep spectra in the soft X-ray band (0.7--1.5 keV) ( ${\alpha}_{\rm x}$ $\sim$ 3 -- 4). We find that the flux densities and spectral indices in both the optical and soft X-ray bands are closely consistent with a `canonical' synchrotron spectrum emitted by relativistic electrons of a power-law energy distribution with a high energy cutoff, and thus the peak of the SED of the synchrotron radiation (in representation of ${\nu}{F_{\nu}}$ ) is located in the EUV -- soft X-ray bands. Therefore, the GeV $\gamma$ -ray emission observed in the July 1997 outburst may be mainly due to the synchrotron self--Compton (SSC) process, contrasting with the current explanations in terms of external radiation Compton (ERC) process, in which the seed photons are mostly taken to be the UV emission from the clouds of the broad emission line region. We argue that the hard optical spectra observed during the $\gamma$ -ray outburst may be an important signature for the acceleration of high energy electrons ( ${\gamma}_e$ $\sim$ 10⁴) in the $\gamma$ -ray emitting region.

Key words: galaxies: compact --- gamma rays: observations --- quasars: individual: BL Lacertae

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Chandler Wobble Period and Q Derived by Wavelet Transform

De-Chun Liao and Yong-Hong Zhou

Affiliation:   National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
                    Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030

E-mail:   ldc@center.shao.ac.cn (corresponding author)

Abstract

We apply complex Morlet wavelet transform to three polar motion data series, and derive quasi-instantaneous periods of the Chandler and annual wobble by differencing the wavelet transform results versus the scale factor, and then find their zero points. The results show that the mean periods of the Chandler (annual) wobble are 430.71±1.07 (365.24±0.11) and 432.71±0.42 (365.23±0.18) mean solar days for the data sets of 1900--2001 and 1940--2001, respectively. The maximum relative variation of the quasi-instantaneous period to the mean of the Chandler wobble is less than 1.5 % during 1900--2001 (3%--5% during 1920--1940), and that of the annual wobble is less than 1.6 % during 1900--2001. Quasi-instantaneous and mean values of Q are also derived by using the energy density---period profile of the Chandler wobble. An asymptotic value of Q=36.7 is obtained by fitting polynomial of exponential of $\sigma ^{- 2}$ to the relationship between Q and $\sigma$ during 1940--2001.

Key words: polar motion --- Chandler wobble --- wavelet transform --- instantaneous period

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The Status of ROSAT X-ray Active Young Stars toward Taurus-Auriga

Jin-Zeng Li

Affiliation:    National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

E-mail:      ljz@bao.ac.cn

Abstract

We present an astrometric study of the candidates of T Tauri stars (TTS) and non-TTS X-ray sources around Tau-Aur, based on the Hipparcos Catalogue and the ACT Reference Catalogue. The ROSAT selected X-ray sources are found to be a mixed population. A few of them are associated with the Tau-Aur or Orion Star Forming Regions (SFR). Some, with distances similar to that of Tau-Aur but with discrepant proper motions, are probable or sure Pleiades super-cluster members or other late type young active stars with unresolved nature, more likely to originate in rapidly moving cloudlets, or else having originated from different sites other than Tau-Aur and moved to the present locations. A good many of the non-TTS X-ray sources are considered as Hyades cluster members. Some TTS candidates could be foreground pre-main sequence stars or actually young dwarfs not yet depleted of their Lithium. Under the hypothesis that the sources we studied are representative of the ROSAT selected TTS candidates discovered in the outskirts of the Tau-Aur region, we conclude that only up to one third of the weak-line TTS candidates could be expected to be physically associated with the Tau-Aur association. Along with the parallax and proper motion analysis of the non-TTS X-ray sources around the Tau-Aur SFR, our result suggests that the vast majority of the young active X-ray sources within an angular diameter of about 30° of the Tau-Aur SFR, belong to four main subgroups that are spatially separate.

Key words: stars: formation --- stars: pre-main sequence --- stars: late-type --- Astrometry

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Effect of Conversion Efficiency on Gamma-Ray Burst Energy

Lei Xu and Zi-Gao Dai

Affiliation: Department of Astronomy, Nanjing University, Nanjing 210093

E-mail: dzg@nju.edu.cn (corresponding author)

Abstract

Beaming effect makes it possible that gamma-ray bursts have a standard energy, but the gamma-ray energy release is sensitive to some parameters. Our attention is focused on the effect of the gamma ray conversion efficiency ( $\eta_{\gamma}$ ), which may range between 0.01 and 0.9, and which probably has a random value for different GRBs under certain conditions. Making use of the afterglow data from the literature, we carried out a complete correction to the conical opening angle formula. Within the framework of the conical jet model, we ran a simple Monte Carlo simulation for random values of $\eta_{\gamma}$ , and found that the gamma-ray energy release is narrowly clustered, whether we use a constant value of $\eta_{\gamma}$ or random values for different gamma-ray bursts.

Key words: gamma rays: bursts --- ISM: jets

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Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma

Bin Luo and Shuang-Nan Zhang

Affiliation:     Physics Department and Center for Astrophysics, Tsinghua University, Beijing 100084;
                      Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039

E-mail:   luobin@tsinghua.org.cn    (corresponding author)

Abstract

In normal one-temperature plasma the motion of ions is usually neglected when calculating the Bremsstrahlung radiation of the plasma. We calculate the Bremsstrahlung radiation of a two-temperature plasma by taking into account of the motion of ions. Our results show that the total radiation power is always lower if the motion of ions is considered. We also apply the two-temperature Bremsstrahlung radiation mechanism for an analytical Advection-Dominated Accretion Flow (ADAF) model; we find the two-temperature correction to the total Bremsstrahlung radiation for ADAF is negligible.

Key words: plasmas --- radiation mechanisms: thermal

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A Spectral Atlas of F and G Stars

V. G. Klochkova (1,2), Gang Zhao (1), V. E. Panchuk (1,2) and S. V. Ermakov (1,2)

Affiliation: (1) National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
                   (2) Special Astrophysical Observatory Russian Academy of Sciences, Nizhnij Arkhyz, Karachai-Cherkessia, 369167 Russia

E-mail:     gzhao@bao.ac.cn (corresponding author)

Abstract

We present an atlas of a group of bright stars in the range of spectral classes F--G and luminosity classes I--V. The spectra were obtained with spectral resolution R $\sim$ 15 000 within spectral region 4500--6620Å. Typical spectra of stars with different metallicity [Fe/H] are included. We also show the digital version of the spectral data in FITS format.

Key words: stars: atlas --- stars: spectral class --- stars: F-G type

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Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912

Xue-Peng Chen and Yong-Qiang Yao

Affiliation: Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008

E-mail: xpchen@pmo.ac.cn (corresponding author)

Abstract

Near-infrared images and K-band spectroscopy of the massive star-forming region IRAS 23151+5912 are presented. The JHK' images reveal an embedded infrared cluster associated with infrared nebula, and the H₂ (2.12 µm) narrow-band image provides for the first time evidence of outflow activity associated with the cluster. That the cluster is young can be shown by the high percentage of infrared excess sources and the outflow activity. We suggest an age of the cluster of $\sim$ 10⁶ yr. Eight young stars are found in the bright nebular core around IRAS 23151+5912. By the color-magnitude diagrams of the cluster, we found five high-mass YSOs and four intermediate-mass YSOs in the cluster. Eight H₂ emission features are discovered in the region with a scattered and non-axisymmetric distribution, indicating the existence of multiple outflows driven by the cluster. Diffuse H₂ emission detected to the north and to the west of the cluster may result from UV leakage of the cluster. Br $\gamma$ , H₂, and CIV emission lines are found in the K-band spectrum of the brightest source, NIRS 19, indicating the presence of envelope, stellar wind, and shock in the circumstellar environment. We have estimated an O7--O9 spectral type for the central massive YSO (20 $\sim$ 30 $M_{\odot}$ ), with an age of less than 1×10⁶ yr.

Key words: infrared radiation --- stars: formation: --- ISM: individual: IRAS 23151 + 5912 --- ISM: jets and outflows

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