2002, Vol.2, No.2 (April 20, 2002)


Contents


On the Evolution of the Lower Energy Cutoff of Nonthermal Electrons in Solar Flares
Wei-Qun Gan, You-Ping Li and Jin Chang ........................................
Abstract | | PDF file (132 KB) | PS file *.gz  (162 KB) 



p.103

Expected Number Counts of Radio Galaxy Clusters

Wei Zhou  ......................................................................
Abstract | | PDF file (155 KB) | PS file *.gz  (153 KB) 


p.106

Expectation for the X-ray Galactic Halo
Zhi-Ying Huo ..................................................................
Abstract | | PDF file (147 KB) | PS file *.gz  (167 KB) 


p.112

Variability of Soft X-ray Spectral Shape in Blazars Observed by ROSAT

Lin-Peng Cheng, Yong-Heng Zhao and Jian-Yan Wei ..............................
Abstract | | PDF file (317 KB) | PS file *.gz  (455 KB)


p.117

Estimating the Metallicity of Old Star Clusters in M33

Jun Ma,Xu Zhou,Hong Wu,Jian-Sheng Chen,Zhao-Ji Jiang,Sui-Jian Xue and Jin Zhu ...
Abstract | | PDF file (302 KB) | PS file *.gz  (1024 KB)  


p.127

Radio Emission from Globular Clusters

Xiao-Hui Sun and Jin-Lin Han  .............................................  
Abstract | | PDF file (1627 KB) | PS file *.gz  (3415 KB)  



p.133

Pulsars in FIRST Observations

Xiang-Hua Li and Jin-Lin Han .............................................. 
Abstract | | PDF file (146 KB) | PS file *.gz  (150 KB) 


p.146

Planet Host Stars: Mass, Age and Kinematics

Yu-Qin Chen and Gang Zhao  ..................................................
Abstract | | PDF file (195 KB) | PS file *.gz  (254 KB) 


p.151

A Two-Temperature Supernova Fallback Disk Model for Anomalous X-ray
Pulsars
Ye Lu and K. S. Cheng ...................................................... 
Abstract | | PDF file (154 KB) | PS file *.gz  ( 66 KB) 



p.161

On the Carbon-Star Status of Five Stars in a New Carbon Star Catalog
Pei-Sheng Chen and Yi-Fei Gao ..............................................  
Abstract | | PDF file (138 KB) | PS file *.gz  (181 KB) 


p.169

Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms

Hui Li  ...................................................................... 
Abstract | | PDF file (750 KB) | PS file *.gz  (1118 KB) 



p.174

Wavelet Cleaning of Solar Dynamic Radio Spectrograms

Robert A. Sych and Yi-Hua Yan ...............................................
Abstract | | PDF file (2337 KB) | PS file *.gz  (2889 KB)


p.183



Abstract


On the Evolution of the Lower Energy Cutoff of Nonthermal Electrons in Solar Flares


Wei-Qun Gan, You-Ping Li and Jin Chang


E-mail:  wqgan@pmo.ac.cn 

Abstract

Using the method recently developed by Gan et al. (2001a, 2002), We investigate the time variation of the lower energy cutoff (Ec) of nonthermal electrons for three BATSE/CGRO hard X-ray events. The result shows that Ec changes with time, from smaller before the peak flux, to larger at the peak, and then back to smaller after the peak. Such a variation of Ec, being a preliminary conclusion for the first time, should be checked in the future by using data with a higher energy resolution.

Key words: Sun: hard X-rays --- Sun: gamma-rays --- Sun: flares --- Sun: particles

PDF file (132 KB) | gzipped PS file (162KB) | Back to Contents



Expected Number Counts of Radio Galaxy Clusters

Wei Zhou

E-mail:  zw@class2.bao.ac.cn   

Abstract

Clusters of galaxies may contain radio sources if they still experience successive mergers at present. This has been confirmed by radio observations that about 30% of nearby clusters possess radio halos. We present a theoretical prediction of radio cluster counts using a semi-analytic approach which incorporates the empirical correlation between radio power and dynamical mass of clusters, and the cluster mass function described by the Press-Schechter formalism. The total population of radio clusters over the whole sky and their redshift distribution are given.

Key words: cosmology: theory --- galaxies: cluster: general --- radio sources: extended

PDF file (155 KB) | gzipped PS file (153 KB) | Back to Contents



Expectation for the X-ray Galactic Halo

Zhi-Ying Huo

E-mail: huo@class2.bao.ac.cn   

Abstract

We present an estimate of the strength and spectrum of the X-ray background from the warm gas associated with the Galactic halo. This investigation is motivated primarily by the recent detection of a spatially variable soft X-ray component towards the north Galactic polar cap by Kuntz et al. (2001), suggesting that the warm gas heated by gravitational shocks of the Galactic halo may produce a significant contribution to the soft X-ray sky. Another purpose of the study is to refine the recent theoretical prediction of the X-ray spectrum from the Galactic halo by Xue (2001) who adopted an ideal and simple isothermal model for the gas and dark matter distributions of the Galactic halo. We use the universal density profile for the dark matter distributions of the Galactic halo to evaluate the X-ray properties of the warm gas either in hydrostatic equilibrium with, or tracing the underlying gravitational potential of the Galaxy. It has been shown that our prediction is consistent with the measured soft X-ray component towards the north Galactic polar cap if the gas fraction is taken to be $\sim$0.005.


Key words: cosmology: diffuse radiation --- Galaxy: formation --- X-rays: galaxies

PDF file (147 KB) | gzipped PS file (167 KB) | Back to Contents


Variability of Soft X-ray Spectral Shape in Blazars Observed by ROSAT

Lin-Peng Cheng,Yong-Heng Zhao and Jian-Yan Wei

E-mail:  clp@lamost.bao.ac.cn 

Abstract

In previous paper we have shown that the soft X-ray spectra of two types of Seyfert 1 galaxies behave statistically differently with increasing intensity. In order to see how the spectrum of blazars changes, we made plots of Hardness Ratio 1 versus Count Rates (HR1-Cts) for 18 blazars observed by ROSAT/PSPC. According to our criteria, ten showed a positive HR1-Cts correlation, two a negative correlation, and the remaining six, no clear correlation. Thus, most blazars of our sample show a hardening spectrum during overall flux increase, though some vary randomly. By investigating the photon index of these objects and different radiation theories, we argue that relative dominance between the synchrotron and inverse Compton emission in the soft X-ray band can well account for the differing spectral behaviours and that the different spectral variations might represent a sequence of synchrotron peaked frequency.

Key words: galaxies: active --- galaxies: X-ray --- blazar: spectrum

PDF file (317 KB) | gzipped PS file (455 KB) | Back to Contents


Estimating the Metallicity of Old Star Clusters in M33

Jun Ma, Xu Zhou, Hong Wu, Jian-Sheng Chen, Zhao-Ji Jiang,Sui-Jian Xue and Jin Zhu


E-mail: majun@vega.bac.pku.edu.cn 
  
Abstract

Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from -0.14 to -2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.

Key words: galaxies: individual (M33) --- galaxies: evolution --- galaxies: star clusters

PDf file (302 KB) | gzipped PS file (1024 KB) | Back to Contents


Radio Emission from Globular Clusters

Xiao-Hui Sun, Jin-Lin Han and Guo-Jun Qiao

E-mail: xhsun@ns.bao.ac.cn   

Abstract

Radio emission of globular clusters is studied by analyzing the VLA radio survey data of the NVSS and FIRST. We find that 13 clusters have radio sources within their half-mass radii of clusters. Sources detected previously in NGC 7078 and NGC 6440 are identified. Pulsars in NGC 6121, NGC 6440 and NGC 7078 cannot be detected because of the insufficient survey sensitivity and resolution. There may be a pulsar in the core of Terzan 1. The nature of the extended radio source near the core of NGC 6440 remains unclear. In the core of a globular cluster, there may be many neutron stars or an intermediate mass black hole, but this cannot be clarified with the current radio observations.

Key words: globular clusters: general --- pulsars: general --- radio continuum: general

PDF file (1627 KB) | gzipped PS file (3415 KB)| Back to Contents


Pulsars in FIRST Observations

Xiang-Hua Li and Jin-Lin Han 

E-mail: xhli@ns.bao.ac.cn   

Abstract

We identify 16 pulsars from the Survey of Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. By comparing the source positions with those in the PSR catalog, we obtain better determined positions of PSR J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of PSR J0751+1807, J1012+5307, and J1640+2224. The proper motions of the other ten pulsars are consistent with the catalog values.

Key words: pulsar: general --- stars: neutron

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Planet Host Stars: Mass, Age and Kinematics

Yu-Qin Chen and Gang Zhao


E-mail: cyq@yac.bao.ac.cn 

Abstract

We determine the mass, age and kinematics of 51 extra-solar planet host stars. The results are then used to search for signs of connection of the data with metallicity and to investigate the population nature. We find that the increase in mean metallicity with stellar mass is similar to that in normal field stars, so it seems unsuitable to use this relation as a constraint on the theory of planet formation. The age and kinematic distributions seem to favour the metallicity of extra-solar planet host stars being initial. Although the kinematic data of these stars indicate their origin from two populations -- the thin and the thick disks, kinematics may not help in the maintenance of the planet around the host. Stars with planets, brown dwarfs or stellar companions are sorted into three groups and re-investigated separately for their formation mechanism. The main results indicate that stars with M2 < 25 MJ have [Fe/H] > -0.1 and a wide period range, but there are no other differences. Thus, there does not seem to be any physically distinguishable characteristics among the three star groups.

Key words: stars: masses, ages --- stars: kinematics --- planetary system 

PDF file (195 KB) | gzipped PS file (254 KB) | Back to Contents


A Two-Temperature Supernova Fallback Disk Model for Anomalous X-ray Pulsars

Ye Lu and K. S. Cheng


E-mail: ly@yac.bao.ac.cn    

Abstract

We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars(AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10-6--10-5$M_{\odot}$ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.

Key words: pulsars: general --- pulsars --- stars: neutron --- X-rays: stars --- accretion disk --- instability

PDF file (154 KB) | gzipped PS file ( 66 KB) | Back to Contents


On the Carbon-Star Status of Five Stars in a New Carbon Star Catalog

Pei-Sheng Chen and Yi-Fei Gao


E-mail: ym990715@public.km.yn.cn    

Abstract

We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10µm silicate features in absorption and the 1612 MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygen-rich stars must be done with caution, because, in general, it has only a statistical meaning.

Key words: stars: AGB --- stars: carbon --- infrared: stars

PDF file (138 KB) | gzipped PS file (181 KB) | Back to Contents

Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms

Hui Li


E-mail: lihui@mail.pmo.ac.cn    

Abstract

Projection effects in Huairou solar vector magnetograms are corrected by transferring or mapping the observed vector magnetogram in the image plane to the heliographic plane (planar correction) and to the heliospheric coordinate system (spherical correction). The magnetograms after the correction are considerably different. The planar correction and the spherical correction lead to slightly different magnetic configurations, especially when the active region involved is far from the disk center. We also discuss the effects of the corrections on magnetic activity parameters, such as magnetic shear, current helicity, etc. It is shown that the neutral line is obviously distorted after the mapping. The mapping generally decreases the average shear angle on the neutral line by several degrees when the active region is in the eastern hemisphere, and increases it when in the western hemisphere. In most of the cases studied, the correction reduces the current helicity imbalance, and sometimes even changes its sign. It is found that the current helicity imbalance may change its sign in its evolution when there are apparent fluxes emerging from the lower photosphere. The corrections increase the noise level of Bz greatly, and decrease the noise level of Bt slightly. The accuracy of the magnetic field measurement at Huairou is estimated to be better than 20 G and 150 G for the longitudinal and the transverse component, respectively.

Key words: Sun: magnetic fields --- Sun: activity --- Sun: photosphere

PDF file (750 KB) | gzipped PS file (1118 KB) | Back to Contents

Wavelet Cleaning of Solar Dynamic Radio Spectrograms

Robert A. Sych and Yi-Hua Yan

E-mail: sych@iszf.irk.ru 

Abstract

By applying the state-of-the-art mathematical apparatus, the wavelet transformation, we explore the possibility of a dynamic cleaning of raw data obtained with the Chinese solar radio spectrographs over a wide wavelength range (from 0.7 to 7.6 GHz). We consider the problem of eliminating the interference caused by combination rates of data sampling (10–20 ms), and the low-frequency interference (4 –30 s) caused by the receiving equipment changing its characteristics with time. It is shown that the best choice to reconstruct a signal suffering from amplitude, frequency and phase instabilities, is by means of wavelet transformation at both high and low frequencies. We analysed observational data which contained interferences of nonsolar origin such as instrumental effects and other man-made signals. A subsequent comparison of the reference data obtained with the acousto-optical receiver of the Siberian Solar Radio Telescope (SSRT) with the ``cleaned'' spectra confirms the correctness of this approach.

Key words: Sun: radio radiation --- methods: data analysis

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ChJAA, 2002, Vol.2, No.2

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

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Chinese Academy of Sciences, P.R. China. This Journal or parts thereof, may not be
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