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

2008, Vol.8, No.4 (August 20, 2008)



Extragalactic Astronomy

Astrophysical Processes


The Sun


A Critical Review of the Evidence for M32 being a Compact Dwarf Satellite of M31 rather than a More Distant Normal Galaxy

C. Ke-shih Young 1,2,3,4, Malcolm J. Currie 5, Robert J. Dickens 5, A-Li Luo 1 and Tong-Jie Zhang 6

1 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China
2 Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China
3 Department of Physics, University of Hong Kong, Hong Kong, China
4 School of Physics, University of New South Wales, Sydney 2052, Australia; cky@bat.phys.unsw.edu.au
5 Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, Great Britain
6 Department of Astronomy, Beijing Normal University, Beijing 100875, China

Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope (HST) based stellar population studies which have resolved red-giant branch (RGB) and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32's anomalously high central velocity dispersion for a dwarf galaxy (several times that of either NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which suggest that M32 is more than twice as distant as M31) and also requires an elaborate physical explanation for M32's inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by: (1) a central velocity dispersion typical of intermediate galaxies, (2) the published planetary nebula observations, and (3) known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary. This suggests that current understanding of some relevant fields is still very far from adequate.

Key Words:   galaxies: individual: M32 -- galaxies: distances and redshifts -- galaxies: dwarf -- galaxies: elliptical and lenticular, cD -- galaxies: fundamental parameters

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Statistics of Superluminal Motion in Active Galactic Nuclei

Yong-Wei Zhang and Jun-Hui Fan

Center for Astrophysics, Guangzhou University, Guangzhou 510006, China; fjh@gzhu.edu.com

We have collected an up-to-date sample of 123 superluminal sources (84 quasars, 27 BL Lac objects and 12 galaxies) and calculated the apparent velocities $(\beta_{\rm
app})$ for 224 components in the sources with the $\Lambda$-CDM model. We checked the relationships between their proper motions, redshifts, $\beta_{\rm app}$ and 5GHz flux densities. Our analysis shows that the radio emission is strongly boosted by the Doppler effect. The superluminal motion and the relativistic beaming boosting effect are, to some extent, the same in active galactic nuclei.

Key Words:   galaxies: jets -- galaxies: general -- BL Lacertae objects: active -- quasars: data analysis

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Simultaneous Multi-Wavelength Observations of the TeV Blazar Mrk 421 during February - March, 2003: X-Ray and NIR Correlated Variability

Alok C. Gupta 1,3, B. S. Acharya 2, Debanjan Bose 2, Varsha R. Chitnis 2 and Jun-Hui Fan 1

1 Center for Astrophysics, Guangzhou University, Guangzhou 510006, China; acgupta30@gmail.com

2 Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai - 400 005, India

3 Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital - 263129, India

We report the result of simultaneous multi-wavelength observations of the TeV blazar Mrk 421 during February - March 2003. We observed Mrk 421 using the Pachmarhi Array of Cerenkov Telescopes (PACT) of Tata Institute of Fundamental Research at Pachmarhi, India. Other simultaneous data were taken from the literature and public data archives. We have analyzed the high quality X-ray (2-20keV) observations from the NASA Rossi X-Ray Timing Explorer (RXTE). We obtained a possible correlated variability between X-ray and J band (1.25$\mu$) near infrared (NIR) wavelength. This is the first case of X-ray and NIR correlated variability in Mrk 421 or any high energy peaked (HBL) blazar. The correlated variability reported here indicates a similar origin for the NIR and X-ray emissions. The emission is not affected much by the environment of the surrounding medium of the central engine of Mrk 421. The observations are consistent with the shock-in-jet model for the emissions.

Key Words:   galaxies: active -- galaxies: blazars: general -- galaxies: blazars: individual: Mrk 421

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Hyperaccretion after the Blandford-Znajek Process: A New Model for GRBs with X-Ray Flares Observed in Early Afterglows

Wei-Hua Lei Ding-Xiong Wang Yuan-Chuan Zou and Lei Zhang

Department of Physics, Huazhong University of Science and Technology, Wuhan 430074, China leiwh@hust.edu.cn

We propose a three-stage model with Blandford-Znajek (BZ) and hyperaccretion process to interpret the recent observations of early afterglows of Gamma-Ray Bursts (GRBs). In the first stage, the prompt GRB is powered by a rotating black hole (BH) invoking the BZ process. The second stage is a quiet stage, in which the BZ process is shut off, and the accretion onto the BH is depressed by the torque exerted by the magnetic coupling (MC) process. Part of the rotational energy transported by the MC process from the BH is stored in the disk as magnetic energy. In the third stage, the MC process is shut off when the magnetic energy in the disk accumulates and triggers magnetic instability. At this moment, the hyperaccretion process may set in, and the jet launched in this restarted central engine generates the observed X-ray flares. This model can account for the energies and timescales of GRBs with X-ray flares observed in early afterglows.

Key Words:   accretion, accretion disks -- black hole physics -- magnetic fields -- gamma-rays: bursts

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Ring-Shaped Jets in Gamma-Ray Bursts

Ming Xu, Yong-Feng Huang and Si-Wei Kong

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

When the axis of a gamma-ray burst (GRB) does not coincide with the spin axis of its source, there may result a ring-shaped jet. Using some refined jet dynamics, we calculate multi-wavelength afterglow light curves for such ring-shaped jets. In the R-band we find an obvious break in the afterglow light curve due to the beaming effect and the break is affected by many parameters, such as the electron energy fraction $\xi_{e}$, the magnetic energy fraction $\xi_{B}^{2}$, the width of ring $\Delta\theta$ and the medium number density n. The overall light curve can be divided into three power-law stages, i.e., an ultra-relativistic stage, an after-break stage and a deep Newtonian stage. For each stage the power-law index is larger in the ring-shaped jet than in the corresponding conical jet.

Key Words:   gamma rays: bursts -- ISM: jets and outflows
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Asteroseismic Analysis of $\alpha$ Cen B: Preliminary Tests of Effects of Rotation and Interior Magnetic Field in the Solar-like Star

Yan-Ke Tang 1,3, Shao-Lan Bi 2,1 Ning Gai 1,3 and Hua-Yin Xu 1

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences China; tangyanke@ynao.ac.cn; bisl@bnu.edu.cn
2 Department of Astronomy Beijing Normal University, Beijing 100875, China

3 Graduate School of Chinese Academy of Sciences, Beijing 100049, China


Taking into consideration the effects of rotation and interior magnetic field during the lifetime of the star, we reconstruct the model of $\alpha$ Cen B to satisfy the latest non-asteroseismic and asterosei We find that the effects can induce a change of about 0.3 $\mu$Hz in the large frequency spacings and can speed up the star's evolution. The model of $\alpha$ Cen B has thereby been improved.

Key Words:   stars: oscillations -- stars: interiors -- stars: individual ($\alpha$ Cen B)

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First Mapping Observations of Two Possible Cloud Collision Candidates IRAS 02459+6029 and 05363+3127

Bei Xin and Jun-Jie Wang

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China xinpei@hep.com.cn


The first mapping observations of the cold infrared sources IRAS 02459+6029 and 05363+3127 in the molecular lines 12CO(1-0), 13CO(1-0) and C18O(1-0) were made using the 13.7m millimeter wave telescope in Qinghai. Both the integrated intensity maps and position-velocity diagrams show that each has two components adjacent in both space and velocity which means possible cloud-cloud collisions in the two regions. The near-infrared color-color diagram from the 2MASS database reveals that the density of YSOs in the colliding site is much higher than in the surrounding regions. The results appear to indicate that star forming activities have taken place in the two regions due to the cloud-cloud collision. We conclude that both sources are cloud collision candidates.

Key Words:   stars: formation -- ISM: clouds

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High Spatial Resolution X-Ray Spectroscopy of Cas A with Chandra

Xue-Juan Yang 1,2, Fang-Jun Lu 1 and Li Chen 2

1 Particle Astrophysics Center, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China; yangxj@mail.ihep.ac.cn

2 Department of Astronomy, Beijing Normal University, Beijing 100875, China

We present high spatial resolution X-ray spectroscopy of the supernova remnant Cassiopeia A with the Chandra observations. The X-ray emitting region of this remnant was divided into 38 x 34 pixels of 10$\arcsec\times$ 10$\arcsec$ each. Spectra of 960 pixels were created and fitted with an absorbed two component non-equilibrium ionization model. From the results of the spectral analysis we obtained maps of absorbing column density, temperatures, ionization ages, and the abundances of Ne, Mg, Si, S, Ca and Fe. The Si, S and possibly Ca abundance maps show obvious jet structures, while Fe does not follow the jet but seems to be distributed perpendicular to it. The abundances of Si, S and Ca show tight correlations between one another over a range of about two dex. This suggests that they are ejecta from explosive O-burning and incomplete Si-burning. Meanwhile, the Ne abundance is well correlated with that of Mg, indicating them to be the ashes of explosive C/Ne burning. The Fe abundance is positively correlated with that of Si when the latter is lower than 3 times the solar value, and is negatively correlated when higher. We suggest that such a two phase correlation is due to the different ways in which Fe was synthesized.

Key Words:   ISM: supernova remnants --ISM: individual: Cassiopeia A

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A Test on Different Types of the Time Curve of Hardness Ratio of Gamma-Ray Bursts based on the Curvature Effect

Lan-Wei Jia

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

We analyzed a sample of 66 gamma-ray bursts (GRBs) and statistically confirmed the prediction on the time curve of the hardness ratio of GRBs made by Qin et al. based on the curvature effect. In their analysis, GRB pulses are divided into three types according to the shape of their raw hardness ratio (RHR) time curves, defined as to include the background counts to the signal counts, so as to make use of counts within small time intervals. Of the three types, very hard sources exhibit a perfect pulse-like profile (type 1), hard bursts possess a pulse-like profile with a dip in the decay phase (type 2), and soft bursts show no pulse-like profile but have only a dipped profile (type 3). In terms of the conventional hardness ratio, type 3 sources are indeed generally softer than those of type 1 and type 2, in agreement with the prediction. We found that the minimum value of RHR is sensitive in distinguishing the different types. We propose that GRB pulses can be classified according to the minimum value of RHR and that the different type sources may be connected with different strengths of the shock or/and the magnetic field.

Key Words:   gamma-rays: bursts -- gamma-rays: observations -- methods: statistical

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A Photometric Study of the W UMa-Type Contact Binary RZ Com

Jia-Jia He 1,2,3 and Sheng-Bang Qian 1,2

1 National Astronomical Observatories / Yunnan Observatory, Chinese Academy of Sciences, Kunming 650011, China; hejiajiacn@gmail.com

2 United Laboratory of Optical Astronomy, Chinese Academy of Sciences (ULOAC), Beijing 100012, China

3 Graduate School of Chinese Academy of Sciences, Beijing 100049, China

We present results of CCD photometric observations of the short-period W UMa-type contact binary system, RZ Com. The light curve of the binary has changed from W-subtype to A-subtype from 1998 to 2003, then back to W-subtype in 2004. An analysis was carried out using the 2003 version of the Wilson-Devinney code. It is confirmed that RZ Com is a low-degree, overcontact $f=20.1\%$ $(\pm7.4\%)$ binary system with a high inclination of $i=81.\dg
40$ $(\pm0.\dg 40)$, and a mass ratio q=2.351 $(\pm0.031)$. Combining four newly determined times of light minimum with others in the literature, the variations in orbital period is examined. A small-amplitude oscillation (A=0.0065d), with a period of 41.5 year, is discovered superimposed on a long-term increase at rate dP/dt=+3.97 x 10-8d yr-1. The period oscillation can be explained either by the light-time effect due to the presence of an unseen third body, or by cycles of magnetic activity on the components. Combining our photometric solution with the spectroscopic elements obtained by Mclean & Hilditch, the absolute dimensions of RZ Com are: M1=1.14 $(\pm0.19)M_{\odot}$, M2=0.50 $(\pm0.09)M_{\odot}$, R1=1.12 $(\pm0.01)R_{\odot}$, R2=0.78 $(\pm0.01)R_{\odot}$ and A=2.41 $(\pm0.02)R_{\odot}$.

Key Words:   stars: binaries: close -- stars: binaries: eclipsing -- stars: individual: RZ Com
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Historical Dataset Reconstruction and a Prediction Method of Solar 10.7 cm Radio Flux

Juan Zhao 1 and Yan-Ben Han 2

1 Department of Astronomy, Beijing Normal University, Beijing 100875, China; zj@bnu.edu.cn
2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China

We reconstruct the developing history of solar 10.7cm radio flux (F10.7) since 1848, based on the yearly sunspot number and the variations. A relationship between the maximum and the linear regression slope of the first 3 years starting from minimum of the solar cycle is considered. We put forward a method of predicting the maximum of F10.7 by means of the slope-maximum relationship. Running tests for cycles 19 to 23 indicate that the method can properly predict the peak of F10.7.

Key Words:   Sun: activity -- Sun: radio radiation -- Sun: sunspots

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A Running Average Method for Predicting the Size and Length of a Solar Cycle

Zhan-Le Du, Hua-Ning Wang and Li-Yun Zhang

National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China zldu@bao.ac.cn

The running correlation coefficient between the solar cycle amplitudes and the max-max cycle lengths at a given cycle lag is found to vary roughly in a cyclical wave with the cycle number, based on the smoothed monthly mean Group sunspot numbers available since 1610. A running average method is proposed to predict the size and length of a solar cycle by the use of the varying trend of the coefficients. It is found that, when a condition (that the correlation becomes stronger) is satisfied, the mean prediction error (16.1) is much smaller than when the condition is not satisfied (38.7). This result can be explained by the fact that the prediction must fall on the regression line and increase the strength of the correlation. The method itself can also indicate whether the prediction is reasonable or not. To obtain a reasonable prediction, it is more important to search for a running correlation coefficient whose varying trend satisfies the proposed condition, and the result does not depend so much on the size of the correlation coefficient. As an application, the peak sunspot number of cycle 24 is estimated as $140.4\pm 15.7$, and the peak as May $2012\pm11$ months.

Key Words:   Sun: activity -- Sun: sunspots -- Sun: general
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ChJAA, 2008, Vol.8, No.4

Chinese Journal of Astronomy and Astrophysics: Online Edition


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