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

2005, Vol.5, No.6 (December 20, 2005)



Extragalactic Astronomy
Stars The Sun

Astrometry and Celestial Mechanics


A Composite Model for GHz Peaked Spectra of Radio Sources

Jun Yang 1,2,3 - Xiang Liu 1 - Zhi-Qiang Shen 2

1 National Astronomical Observatories/Urumqi Observatory, Chinese Academy of Sciences, Urumqi 830011; junyang@shao.ac.cn
2 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030
3 Graduate University of the Chinese Academy of Sciences, Beijing 100049

GHz-Peaked Spectrum (GPS) radio sources are powerful and compact sources with convex spectra. With increasing observational findings, it has been realized that either Synchrotron Self-Absorption (SSA) alone or Free-Free Absorption (FFA) alone is not enough to account for all the spectral features. We present a model consisting of an SSA region partially covered by FFA plasma, and derive a composite spectral formula. By applying the model to a sample of 19 GPS sources having strong absorption, it is found that the external FFA process makes the SSA peak frequency linearly shift to a higher (observed) peak frequency. The shift indicates that the FFA does play a role at the frequency close to the observed peak frequency.

Key Words:   radio continuum: galaxies -- galaxies: active -- quasars: general

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X-ray Emission Lines in GRB Afterglows: Evidence for a Two-component Jet Model

Wei-Hong Gao1, 2 and Da-Ming Wei1,2

1 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008; whgao@pmo.ac.cn
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012

X-ray emission lines have been observed in X-ray afterglows of several $\gamma$-ray bursts (GRBs). It is a major breakthrough for understanding the nature of the progenitors. It has been proposed that the X-ray emission lines can be well explained by the Geometry-Dominated models, but in these models the illuminating angle is much larger than that of the collimated jet of the GRB. For GRB 011211, we have obtained an illuminating angle of about $\theta\sim45^{\circ}$, while the angle of the GRB jet is only $3.6^{\circ}$. So we propose that the outflow of GRBs with emission lines should have two distinct components: a wide component that illuminates the reprocessing material and produces the emission lines and a narrow one that produces the GRB. Observations show the energy for producing the emission lines is higher than that of the GRB. In this case, when the wide component dominates the afterglows, a bump should appear in the GRB afterglow. For GRB 011211, the bump should occur within 0.05 days of the GRB, which is obviously too early for the observation to catch it. Alongside the X-ray emission lines there should also be a bright emission component between the UV and the soft X-rays. These features can be tested by the Swift satellite in the near future.

Key Words:   gamma rays: bursts -- line: profiles -- ISM: jets and outflows -- supernovae: general

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S1280 and S1284: Two Oscillating Blue Stragglers in the Open Cluster M67

Xiao-Bin Zhang, Rong-Xian Zhang and Zhi-Ping Li

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

We present results of a time-series CCD photometry of two blue stragglers in the open cluster M67 that are also oscillating variables, S1280 and S1284. The observations obtained on 11 nights confirmed the $\delta$ Scuti-like variability of the two stars. Four and five main pulsating frequencies are detected for S1280 and S1284, respectively, through a power spectral analysis. A preliminary mode identification indicates that the two stars are both in radial oscillation. Based on the nature of oscillation, the physical parameters of the two stars are determined, and their evolutionary status discussed.

Key Words:   blue straggler -- open cluster: individual (M67) -- stars: oscillation -- stars: individual (S1280, S1284)

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Infrared Characteristics of Associated Sources of Water Masers

Jarken Esimbek1, 2, Yue-Fang Wu1 and Jun-Zhi Wang1

1 Department of Astronomy, Peking University, Beijing 100871; jarken@ms.xjb.ac.cn
2 National Astronomical Observatories/Urumqi Observatory, Chinese Academy of Sciences, Urumqi 830011

We present an analysis of the infrared properties of 1417 water masers collected from the literature published by December 2004. The associated infrared sources of the water masers were identified with IRAS and MSX (Midcourse Space Experiment) catalogues. There are 1252 water masers associated with IRAS sources within 1, which include 700 interstellar and 552 stellar sources. For 382 sources, the IRAS counterpart identification and the maser classification are new. We found the colors of the interstellar maser sources are much redder than those of the stellar ones at IRAS wavelength bands; 99% of the interstellar maser sources are above black body line, while 95% of the stellar masers are below. The distribution difference of the two kinds of masers shown in the color-color diagram is due to their different optical depths and temperature distributions of dust regions. There are 743 water masers with MSX counterparts, of which 552 are interstellar masers and 191 are stellar masers. MSX colors of the associated sources of water masers are here analyzed for the first time. The color differences among the MSX bands are small and the interstellar masers are redder than the stellar masers. There is a correlation between the intensity of the stellar water maser emission and that of the 12$\mu$m and 25$\mu$m emissions, while there is no correlation between the water maser emission and the 8$\mu$m emission. The infrared intensity increases with increasing wavelength for the interstellar masers, while it is the opposite for stellar masers. These results may provide clues for the pumping of water maser and for the properties of the two kinds of maser emission regions.

Key Words:   masers -- ISM: kinematics and dynamics -- stars: mass loss

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A Study on the Correlations between the Twin kHz QPO Frequencies in Sco X-1

Hong-Xing Yin1, Cheng-Min Zhang1, Yong-Heng Zhao1, Li-Ming Song2 and Fan Zhang2

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012
2 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039; zhangcm@bao.ac.cn

For the bright neutron star low-mass X-ray binary Sco X-1, we analyzed all updated frequencies of the twin kilohertz quasi-periodic oscillations (kHz QPOs), their correlations and distributions. We found that the frequency separation of the kHz QPO peaks appears not to be a constant, rather, it decreases with increasing inferred mass accretion rate. We show that the currently available data of Sco X-1 by Rossi X-ray Timing Explorer are inconsistent with the proposals of the beat model that the frequency separation is a constant. Our conclusions are consistent with those of some previous researchers and we discuss further implications for the kilohertz QPO models.

Key Words:   X-rays: accretion disks -- stars: neutron -- X-rays: stars

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A Spectroscopic Study of the SU UMa-type Dwarf Nova YZ Cnc during its 2002 Superoutburst

Ying-He Zhao, Zong-Yun Li, Xiao-An Wu and Qiu-He Peng

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

We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over 11h on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed ``W" profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of H$\beta$ has an amplitude of $49\pm10$ km s-1 and a phase offset of $-0.07\pm0.04$, which are very similar to those measured in quiescence. However, the $\gamma$ velocity deviates strongly from the systemic velocity measured in quiescence, by some $\pm$60 km s-1. Large shifts of $\sim$70 km s-1 in the orbital-averaged velocity and $\sim$0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk.

Key words:  accretion, accretion disks -binaries: close - novae, cataclysmic variables - stars: dwarf novae - stars: individual (YZ Cancri)

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A Monte Carlo Study of the Evolution of the Scale Height of Normal Pulsars in the Galaxy

Ying-Chun Wei1, Xin-Ji Wu2,1, Qiu-He Peng3, Na Wang1 and Jin Zhang1

1 National Astronomical Observatories/Urumqi Observatory, Chinese Academy of Sciences, Urumqi 830011
2 Department of Astronomy, Peking University, Beijing 100871; wuxj@bac.pku.edu.cn
3 Department of Astronomy, Nanjing University, Nanjing 210093

Based on the undisturbed, finite thickness disk gravitational potential, we carried out 3-D Monte Carlo simulations of normal pulsars. We find that their scale height evolves in a similar way for different velocity dispersions ($\sigma _{v}$): it first increases linearly with time, reaches a peak, then gradually decreases, and finally approaches a stable asymptotic value. The initial velocity dispersion has a very large influence on the scale height. The time evolution of the scale height is studied. When the magnetic decay age is used as the time variable, the observed scale height has a similar trend as the simulated results in the linear stage, from which we derive velocity dispersions in the range $70\sim 178$km s - 1, which are near the statistical result of $90 \sim 270$km s - 1 for 92 pulsars with known transverse velocities. If the characteristic age is used as the time variable, then the observed and theoretical curves roughly agree for t>108 yr only if $\sigma _{v }<25$km s - 1.

Key Words:   pulsar: general - stars: evolution - Galaxy: structure - Galaxy: disk

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An Analysis of the Condensation Temperature of Elements of Extrasolar Planetary Systems

Cong Huang1, Gang Zhao2, Hua-Wei Zhang1 and Yu-Qin Chen2

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

Using high signal-to-noise ratio spectra of extrasolar planet-hosting stars, we obtained the atmospheric parameters, accurate metallicities and the differential abundance for 15 elements (C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Ni and Ba). In a search for possible signatures of metal-rich material accreting onto the parent stars, we found that , for a given element, there is no significant trend of increasing [X/H] with increasing condensation temperature $T_{\rm c}$. In our sample of planet-harboring stars, the volatile and refractory elements behave similarly, and we can not confirm if there exists any significant dependence on the condensation temperature $T_{\rm c}$.

Key Words:   planetary systems -- stars: abundance -- stars: late-type

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Can the bump in the composite spectrum of GRB 910503 be an emission line feature of gamma-ray bursts?

Yi-Ping Qin1,2 and Fu-Wen Zhang1,2,3

1 National Astronomical Observatories, Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011; fwzhang@hotmail.com
2 Physics Department, Guangxi University, Nanning 530004
3 Graduate University of Chinese Academy of Sciences, Beijing 100049

Appearing in the composite spectral data of BATSE, EGRET and COMPTEL for GRB 910503, there is a bump at around 1600keV. We perform a statistical analysis on the spectral data, trying to find out if the bump could be accounted for by a blue-shifted and significantly broadened rest frame line due to the Doppler effect of an expanding fireball surface. We made an F-test and adopted previously proposed criteria. The study reveals that the criteria are well satisfied and the feature can be interpreted as the blue shifted 6.4keV line. From the fit with this line taken into account, we find the Lorentz factor of this source to be $\Gamma =116^{+9}_{-9}$ (at the 68% confident level, $\triangle\chi^{2}=1$) and the rest frame spectral peak energy to be E0,p=2.96+0.24-0.18keV. Although the existence of the emission line feature requires other independent tests to confirm, the analysis suggests that it is feasible to detect emission line features in the high energy range of GRB spectra when taking into account the Doppler effect of fireball expansion.

Key Words:   gamma-rays: bursts -- gamma-rays: theory -- radiation mechanisms: nonthermal -- relativity

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A Parametric Survey of the CME Triggering Process by Numerical Simulations

Xiao-Yan Xu, Peng-Fei Chen and Cheng Fang

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

Observations indicate that solar coronal mass ejections (CMEs) are closely associated with reconnection-favored flux emergence, which was explained in the emerging flux trigger mechanism for CMEs by Chen & Shibata based on numerical simulations. We present a parametric survey of the triggering agent: its polarity orientation, position, and the amount of the unsigned flux. The results suggest that whether a CME can be triggered depends on both the amount and location of the emerging flux, in addition to its polarity orientation. A diagram is presented to show the eruption and non-eruption regimes in the parameter space. The work is aimed at providing useful information for the space weather forecast.

Key Words:   Sun: coronal mass ejections (CMEs)--Sun: filaments

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A Multi-Wavelength Study of the 3B/X1.2 Flare Observed on 2003 October 26

Hui Li1, Jian-Ping Li2, Cheng Fang2, Brigitte Schmieder3,4,Arkadiusz Berlicki3,5 and Qiu-Sheng Du1

1 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008; lihui@mail.pmo.ac.cn
2 Department of Astronomy, Nanjing University, Nanjing 210093
3 Observatoire de Paris, Section de Meudon, LESIA, F-92195, Meudon Principal Cedex, France
4 Institute of Theoretical Astrophysics, University of Oslo, Blindern, N-0315 Oslo, Norway
5 Astronomical Institute of the Wroc\law University, ul.Kopernika 11, 51-622 Wroc\law, Poland

We report results from a multi-wavelength study of the 3B/X1.2 two-ribbon disk flare (S15E44), which was well observed by both ground-based and space-borne instruments. Two pairs of conjugate kernels - K1 and K4, and K2 and K3 - in the images are identified. These kernels are linked by two different systems of EUV loops. K1 and K4 correspond to the two 17GHz and 34GHz microwave sources observed by the Nobeyama Radioheliograph (NoRH), while K2 and K3 have no corresponding microwave sources. Optical spectroscopic observations suggest that all the four kernels are possible precipitating sites of non-thermal electrons. Thus the energy of electron deposited in K2 and K3 should be less than 100keV. Two-dimensional distributions of the full widths at half maximum (FWHM) of the profiles and the (LOS) velocities derived from the profiles indicate that the largest FWHM and LOS velocity tends to be located near the outer edges of kernels, which is consistent with the scenario of current two-ribbon flare models and previous results. When non-thermal electron bombardment is present, the observed and profiles are similar to previous observational and theoretical results, while the profiles are different from the theoretical ones. This puts some constraints on future theoretical calculation of the line.

Key Words:   Sun: flares -- Sun: X-rays -- line: profiles

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A Study on the Relationship between the Orbital Lifetime and Inclination of Low Lunar Satellites

Hai-Hong Wang1,2 and Lin Liu1,2

1 Department of Astronomy, Nanjing University, Nanjing 210093; xhliao@nju.edu.cn
2 Institute for Space Environment and Astrodynamics, Nanjing University, Nanjing 210093

A detailed theoretical analysis on the orbital lifetime and orbital inclination of a Low Moon-Orbiting satellite (LMOs) and the `stable areas' of long orbital lifetime are given. Numerical simulations under the real force model were carried out, which not only validate the theoretical analysis and also give some valuable results for the orbit design of the LMOs.

Key Words:   celestial mechanics -- Low-Moon-Orbiting satellite -- orbital lifetime

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ChJAA, 2005, Vol.5, No.6

Chinese Journal of Astronomy and Astrophysics: Online Edition


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