2002, Vol.2, No.3 (June 20, 2002)


Contents

Letter
Extragalactic astronomy
  • Positions and Spectral Energy Distributions of 41 Star Clusters in M33   p.197
    Jun Ma, Xu Zhou, Jian-Sheng Chen, Hong Wu, Zhao-Ji Jiang, Sui-Jian Xue and Jin Zhu
    Abstract | | PDF file (915 KB) | PS file *.gz  (2221 KB) 
  • The Variability of Hardness Ratio 1 observed by ROSAT: Narrow-Line Seyfert 1 Galaxies versus Broad-Line Seyfert 1 Galaxies   p.207
    Lin-Peng Cheng, Jian-Yan Wei and Yong-Heng Zhao 
    Abstract | | PDF file (317 KB) | PS file *.gz  (532 KB) 
Stellar cluster
  • Determination of the Proper Motions and Membership of the Globular Cluster M3 and of its Orbit in the Galaxy  p.216
    Zhen-Yu Wu, Jia-Ji Wang and Li Chen  
    Abstract | | PDF file (302 KB) | PS file *.gz  (456 KB)
The Galaxy
  • History of Star Formation and Chemical Enrichment in the Milky Way Disk   p.226
    Rui-Xiang Chang, Cheng-Gang Shu and Jin-Liang Hou 
    Abstract | | PDF file (378 KB) | PS file *.gz  (673 KB)  
Stars
  • Near-Infrared Imaging Observations of the Orion A-W Star Forming Region   p.260
    Jun-Jie Wang 
    Abstract | | PDF file (585 KB) | PS file *.gz  (510 KB) 
The Sun
  • Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions   p.266
    Chang-Xi Zhang, G. B. Gelfreikh and Jing-Xiu Wang  
    Abstract | | PDF file (486 KB) | PS file *.gz  (503 KB) 
  • Line Broadening in a Limb Flare: Derivation of Macro-turbulent Velocity Fields   p.277
    Ying Liu and Ming-De Ding  
    Abstract | | PDF file (236 KB) | PS file *.gz  (396 KB) 
  • An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz   p.287
    Xing-Feng Yu and Jin-Xing Yao   
    Abstract | | PDF file (167 KB) | PS file *.gz  (193 KB) 


Abstract


IRAS 01005+7910: a High Galactic Latitude Post-AGB Star


Jing-Yao Hu


E-mail:  hjy@bao.ac.cn 

Abstract

IRAS 01005+7910 is a cold IRAS source. We present its optical identification, photometric and spectroscopic observation results. Its optical counterpart is classified as a B2Ie star with V magnitude 10.85. Its H$\alpha$ line shows the P Cygni profile. According to its location in the Galaxy (b=16.6), we consider it to be a post-AGB star or a proto-planetary nebula.

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Positions and Spectral Energy Distributions of 41 Star Clusters in M33

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

E-mail:  majun@vega.bac.pku.edu.cn   

Abstract

We present accurate positions and multi-color photometry for 41 star clusters detected by Melnick & D'odorico in the nearby spiral galaxy M33 as a part of the BATC Color Survey of the sky in 13 intermediate-band filters from 3800 to 10000 Å. The coordinates of the clusters are found from the HST Guide Star Catalog. By aperture photometry, we obtain the spectral energy distributions of the clusters. Using the relations between the BATC intermediate-band system and UBVRI broadband system, we derive their V magnitudes and BV colors and find that most of them are blue, which is consistent with previous findings.

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The Variability of Hardness Ratio 1 observed by ROSAT: Narrow-Line Seyfert 1 Galaxies versus Broad-Line Seyfert 1 Galaxies

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

E-mail:   clp@lamost.bao.ac.cn  

Abstract

We examined the correlation between the ROSAT Hardness Ratio 1 and Count Rates eight Narrow-line Seyfert 1 Galaxies (NLS1s) and 14 Broad-line Seyfert1 Galaxies (BLS1s). We found that six of the NLS1s show a positive HR1-CTs correlation, and seven of the BLS1s, a negative correlation. The other two NLS1s and seven BLS1s do not show any clear HR1-CTs correlation. Thus, the spectral behavior is statistically different for the NLS1s and BLS1s. The different behaviors can possibly be interpreted in terms of a stable `soft excess' that is strong in NLS1s and weak in BLS1s, plus a power law component, common to both, which softens with increasing flux.

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Determination of the Proper Motions and Membership of the Globular
Cluster M3 and of its Orbit in the Galaxy

Zhen-Yu Wu, Jia-Ji Wang and Li Chen

E-mail:  wuzy@center.shao.ac.cn 

Abstract

We examine 14 plates of the globular cluster M3 (NGC 5272) taken with the 40 cm refractor at the Sheshan station of Shanghai Astronomical Observatory. The plates span over a period of about 77 years. The positions and absolute proper motions of eight stars in the Hipparcos Catalogue and of 49 stars in the Tycho-2 Catalogue are used as the reference frame. The astrometric reduction is made with the central overlapping principle. The absolute proper motions of 534 stars in a region of about 100'×100' around the cluster are measured. With the new proper motion data the membership probabilities of the stars are determined. The average absolute proper motion obtained for the cluster is -0.06±0.30 mas yr-1 in R.A. and -2.6±0.30 mas  yr-1 in Decl. By combining this result with the known distance and radial velocity of the cluster, we also obtained the Galactic orbit of M3 for a chosen three-component Galactic potential.

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History of Star Formation and Chemical Enrichment in the Milky Way Disk

Rui-Xiang Chang,Cheng-Gang Shu and Jin-Liang Hou


E-mail:  crx@center.shao.ac.cn 
  
Abstract

Based on a physical treatment of the star formation law similar to that given by Efstathiou, we have improved our two-component chemical evolution model for the Milky Way disk. Two gas infall rates are compared, one exponential, one Gaussian. It is shown that the star formation law adopted in this paper depends more strongly on the gas surface density than that in Chang et al. It has large effects on the history of star formation and gas evolution of the whole disk. In the solar neighborhood, the history of chemical evolution and star formation is not sensitive to whether the infall rate is Gaussian or exponential. For the same infall time scale, both forms predict the same behavior for the current properties of the Galactic disk. The model predictions do depend on whether or not the infall time scale varies with the radius, but current available observations cannot decide which case is the more realistic. Our results also show that it would be inadequate to describe the gradient evolution along the Galactic disk by only one word ``flatter'' or ``steeper'', as was suggested by Hou et al. and Chiapinni et al. We point out that both the absolute value and the evolution of the abundance gradient may be different in the inner and outer regions.

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An Exact Anisotropic Quark Star Model

M. K. Mak and T. Harko

E-mail:  mkmak@vtc.edu.hk  

Abstract

We present an exact analytical solution of the gravitational field equations describing a static spherically symmetric anisotropic quark matter distribution. The radial pressure inside the star is assumed to obey a linear equation of state, while the tangential pressure is a complicated function of the radial coordinate. In order to obtain the general solution of the field equations a particular density profile inside the star is also assumed. The anisotropic pressure distribution leads to an increase in the maximum radius and mass of the quark star, which in the present model is around three solar masses.

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Near-Infrared Imaging Observations of the Orion A-W Star Forming Region

Jun-Jie Wang 

E-mail:  wangjj@bao.ac.cn    

Abstract

We carried out near-infrared imaging observations of the Ori A-W region using the Italian 1.5 m TIRGO infrared telescope at Gornergrat. A group of infrared objects is visible on the K band image, including an IRAS source (IRS 1). From its IRAS flux density the IRAS luminosity is derived to be 45 $L_{\odot}$, which shows that IRS 1 is a low-mass protostar. By superimposing the position of the VLA H2O maser on the K image, we can identify the less evolved object IRS 1 as the excitation source of the H2O maser, within a projected distance of 470 AU. This would be evidence that the maser effect is associated with the youngest phase of stellar evolution. The first probable HH object candidate in the Ori A-W region is discovered from the H2O S(1)  1 – 0 observation. Comparing the position of the H2O maser with the direction of the molecular hydrogen emission in the region, we suggest that the observed H2O maser could be tracing the circumstellar disk of IRS 1.

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Magnetic Field Strengths and Structures from Radio Observations of
Solar Active Regions


Chang-Xi Zhang, G. B. Gelfreikh and Jing-Xiu Wang


E-mail:  zhcx@vega.bac.pku.edu.cn   

Abstract

Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at  $\lambda$ = 1.76 cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggests that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at  $\lambda$ = 1.76 cm. Analysing the I-maps, we
identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.

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Line Broadening in a Limb Flare: Derivation of Macro-turbulent Velocity Fields

Ying Liu and Ming-De Ding


E-mail: dmd@nju.edu.cn 

Abstract

The line profiles of H$\alpha$ in a limb flare on 1998 November 11 appear to be unusually broadened. It is considered that macro-turbulence (or macroscopic mass motions) may be one of the main causes. We use an inversion technique to extract the probability distribution of the line-of-sight velocity in the flare. There exist some differences between the velocity distributions deduced from H$\alpha$ and from Ca II  $\lambda$8542, which may be because the two lines depend differently on the temperature and velocity. Since the loop density is high, we obtain a rather short cooling time (several tens of seconds) from the hot X-ray loops to the cool loops visible in H$\alpha$. Possible origins of the large scale motions are discussed.

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An Electron Density Model above the Sunspot from a Mapping of NOAA 7260 at 17 GHz

Xing-Feng Yu and Jin-Xing Yao


E-mail: pmoyxf@263.net      

Abstract

The brightness temperature distribution of microwave emission in a solar active region generally shows a ring structure, with a dip at the centre. However, no dip was found in the Nobeyama Radioheliograph left handed circular polarization (LCP) image on 1992 August 18; instead, there was a peak. This is a completely LCP source with zero right-handed circular polarization (RCP). We examine this structure in terms of the joint effect of gyroresonance and bremsstrahlung mechanism with a raised electron density above the central part of the sunspot, and the commonly assumed temperature and vertical dipole magnetic field models. The raised electron density is found to be 1.4×1011 cm-3 at the chromosphere base.

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ChJAA, 2002, Vol.2, No.3

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

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