2001, Vol.1, No.6 (December 20, 2001)


Contents



1RXS J232953.9+062814: a New SU UMa Dwarf Nova below the Period Minimum
Jian-Yan Wei, Xiao-Jun Jiang, Da-Wei Xu, Ai-Ying Zhou and Jing-Yao Hu ....... p.483
Abstract | | PDF file (152 KB) | PS file *.gz (193 KB)  

Gamma-ray Bursts: a Probe of Black Holes
Wei Wang and Yong-Heng Zhao  ................................................. p.487
Abstract | | PDF file (189 KB) | PS file *.gz (118 KB) 

Gamma-ray Emission from the $\gamma$-ray-loud BL Lac Objects

Guang-Zhong Xie,Ben-Zhong Dai, En-Wei Liang and Zhao-Hua Xie  ................ p.494
Abstract | | PDF file (176 KB) | PS file *.gz (103 KB)  

Optical Identifications of Companion Soft X-ray Sources of Mrk 231
Hong Wu, Zu-Gan Deng and Xiao-Yang Xia ......................................  p.501
Abstract | | PDF file (212 KB) | PS file *.gz (2311 KB) 

Multi-frequency VLBI Observations of NRAO 150
Yong-Jun Chen, Dong-Rong Jiang and Fu-Jun Zhang .............................  p.507
Abstract | | PDF file (196 KB) | PS file *.gz (436 KB)  

Infall and Outflow Activities in the Be star FY CMa
Hui-Lai Cao  ................................................................   p.514
Abstract | | PDF file (332 KB) | PS file *.gz (329 KB)  

On the Zebra Structure in the Frequency Range near 3 GHz
G. P. Chernov, L. V. Yasnov,Yi-Hua Yan and Qi-Jun Fu   ......................   p.525
Abstract | | PDF file (319 KB) | PS file *.gz (8399 KB)  

A Correlation between Proton Events and H$\alpha$ Flares and its Possible Interpretation
Kim Jik Su, Yuan-Yong Deng, Kim Kum Sok and Kim Jin Song  ...................  p.537
Abstract | | PDF file (238 KB) | PS file *.gz (226 KB)  

Close Approaches of Potentially Hazardous Asteroids during Two Centuries
Jiang-Hui Ji and Lin Liu ...................................................  p.549
Abstract | | PDF file (141 KB) | PS file *.gz (51 KB)  

The Coudé Echelle Spectrograph for the Xinglong 2.16-m Telescope
Gang Zhao and Hong-Bin Li  ..................................................  p.555
Abstract | | PDF file (195 KB) | PS file *.gz (306 KB)  

Steps Towards a Fully Automated Classification and Redshift-measurement 
Pipeline for LAMOST Spectra. I. Continuum level and wavelength estimation 
for galaxies

A-Li Luo and Yong-Heng Zhao  ................................................  p.563
Abstract | | PDF file (223 KB) | PS file *.gz (412 KB)  



Abstract


1RXS J232953.9+062814: a New SU UMa Dwarf Nova below the Period Minimum

Jian-Yan Wei, Xiao-Jun Jiang, Da-Wei Xu,Ai-Ying Zhou and Jing-Yao Hu

E-mail: wjy@bao.ac.cn 

Abstract

1RXS J232953.9+062814 was identified as a cataclysmic variable by Wei et al. (1999). Four low-resolution spectra of 1RXS J232953.9+062814 were obtained with the 2.16-m telescope of the National Astronomical Observatories, of which two were at outburst, and two were at quiescence. The system is about 16.8 B and 16.5 V at quiescence, and 12.6 B and 12.6 V at outburst. The quiescent spectra were dominated by double-peaked Balmer emissions, which indicates a hydrogen-rich system with a high-inclination accretion disc. MgH and TiO absorption bands appeared in the quiescent spectrum which implies a companion with a spectral type of early M dwarf. If we take it as an M0 dwarf, then the system is located at a distance of 350 pc with a proper motion velocity 150 km s-1. The superhump period of 0.046311 days was confirmed by our V photometry. The short period and the hydrogen-rich nature reveal that this system is another SU Ursae Majoris-type dwarf nova below the period minimum after V485 Centauri. 1RXS J232953.9+062814 is one of the most important systems for studying the evolutionary scenario of cataclysmic variables since it is much brighter than V485 Cen.

Key words: stars: dwarf novae --- stars: cataclysmic variables: individual:  1RXS J232953.9 +062814

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Gamma-ray Bursts: a Probe of Black Holes

Wei Wang and Yong-Heng Zhao

E-mail:  wwang@lamost.bao.ac.cn 

Abstract

There is strong evidence for the existence of black holes (BHs) in some X-ray binaries and in most galactic nuclei based on different types of measurement, but black holes have not been definitely identified for the lack of very firm observational evidence up to now. Because direct evidence for BHs should come from determination of strong gravitational redshift, we expect an object can fall into the region near the BH horizon where radiation can be detected. Therefore the object must be a compact star such as a neutron star (NS), and intense astrophysical processes will release highly energetic radiation that is transient and fast-varying. These characteristics may point to the observed gamma-ray bursts (GRBs). Recent observations of iron lines suggest that afterglows of GRBs show properties similar to those observed in active galactic nuclei (AGNs), implying that the GRBs may originate from intense events related to black holes. A model for GRBs and afterglows is proposed here to obtain the range of gravitational redshifts (zg) of GRBs with known cosmological redshifts. Here, we provide a new method that, with a search for high-energy emission lines (X- or $\gamma$-rays) in GRBs, one can determine the gravitational redshift. We expect zg to be 0.5 or even larger, so we can rule out the possibility of other compact objects such as NSs, and identify the central progenitors of GRBs as black holes.

Key words: black hole physics --- accretion, accretion disks --- gamma rays: burst

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Gamma-ray Emission from the $\gamma$-ray-loud BL Lac Objects

Guang-Zhong Xie,Ben-Zhong Dai, En-Wei Liang and Zhao-Hua Xie

E-mail:  gzxie@public.km.yn.cn 

Abstract

Using the HST observation data of BL Lac objects by Urry et al. and $\gamma$-ray observation data, we find that there is a correlation between $F_{\gamma}$ and FOnuclei for $\gamma$-ray-loud BL Lac objects (correlation coefficients: $\gamma$ = 0.63, p = 4.0 ×10-2), but no correlation between $F_{\gamma}$ and Fhost, where FOnuclei and FOhost are the fluxes of nuclei and host galaxy in V-band. For 19 $\gamma$-ray-loud BL Lac objects with observed spectral index in multi-wavebands, the spectral index correlations between any two bands are as follow: (1) there is a strong correlation between $\alpha_{\gamma}$ and $\alpha_K$ for 15 BL Lac  objects ( $\gamma$ = 0.84, p = 3.11× 10-4); (2) the correlation between $\alpha_{\gamma}$ and $\alpha_O$ for 12 BL Lac objects is $\gamma$ = 0.82, p = 1.5 × 10-3; (3) there is no correlation between $\alpha_{\gamma}$ and $\alpha_X$ for 16 BL Lac objects. The results, together with characteristic double-humped shape of their SEDs, show that the synchrotron self-Compton mechanism might be a main mechanism for the $\gamma$-ray emission of the BL Lac objects. The electrons emitting IR and optical radiation via synchrotron are also responsible for upscattering these photons to $\gamma$-rays, and a variability in IR-optical regime should be accompanied by a change in the $\gamma$-rays.

Key words: gamma rays --- BL Lacertae objects: general

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Optical Identifications of Companion Soft X-ray Sources of Mrk 231

Hong Wu, Zu-Gan Deng and Xiao-Yang Xia


E-mail:   wu@vega.bac.pku.edu.cn 

Abstract

We present optical identification results for four ROSAT PSPC soft X-ray companions of Mrk 231 based on the deep BATC 6660 Å -band image and the optical spectra obtained by the 60/90-cm Schmidt telescope and the 2.16-m telescope at the Xinglong Station, NAOC. Three optical counterparts are quasars with redshifts z > 1 and the remaining X-ray source is probably a background galaxy cluster. Therefore, none of these soft X-ray companions are physically connected with the central X-ray source Mrk 231. Incorporating the previous results of Arp 220 and Mrk 273 (Xia et al. 1998, 1999), we suggest that the apparent soft X-ray associations with ULIRGs are chance coincidence in most cases.

Key words: galaxies: individual (Mrk 231) --- X-rays: galaxies --- quasars

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Multi-frequency VLBI Observations of NRAO 150

Yong-Jun Chen, Dong-Rong Jiang and Fu-Jun Zhang


E-mail: cyj@center.shao.ac.cn 

Abstract

We present multi-frequency, high resolution, radio structures of NRAO 150 with VLBA and EVN array respectively, both of which show a very collimated one-sided jet structure beyond an angular distance of 80 mas. Model fitting is performed for observations at 2.3 GHz and 8.4 GHz which reveal the source to be consisting of several components at position angle $\sim$ 30$\circ$. According to the light curves at 4.8 GHz, 8.0 GHz and 14.5 GHz an outburst is currently occurring in its rising stage, which suggests that a new component is probably in the course of forming. Spectral analysis reveals that the new component probably has a higher spectral index. The maximum proper motion of $\sim$0.46 mas yr-1 is expected if we suppose that the new component is moving away from core at the beginning of the flaring.

Key words: galaxies: active --- galaxies: radio source: individual: NRAO 150 --- radio structure: galaxies

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Infall and Outflow Activities in the Be star FY CMa

Hui-Lai Cao


E-mail:  caohl@bao.ac.cn 

Abstract

Unusual activity of outflow mass motion connected with infall events was recorded for the B0.5 IVe star FY CMa in February 1987 from both archival IUE spectrograms of circumstellar N resonance lines and optical spectra of H$\alpha$ and He I $\lambda$5876Å  emission lines which showed inverse P Cygni-type profiles. We estimate the mass loss rate using ultraviolet Si resonance lines with expanding atmosphere modeling calculations, and describe how the radial pressure performs the dominant role in accelerating the stellar wind. We attempt to give a qualitative explanation for the activity observed for FY CMa in terms of circumstellar matter raining down to the star.

Key words: line: profiles --- stars: activity --- stars: emission-line, Be --- 
circumstellar matter --- stars: mass-loss --- ultraviolet: stars

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On the Zebra Structure in the Frequency Range near 3 GHz

G. P. Chernov, L. V. Yasnov,Yi-Hua Yan and Qi-Jun Fu

E-mail: yyh@bao.ac.cn 

Abstract

We present 19 cases of zebra pattern structure (ZPS) and fiber bursts (FB) in radio bursts in frequency range around 3 GHz, and one such case in the range 5.2--7.6 GHz, using the new microwave spectrometer of NAOC between 2.6--3.8 and 5.2--7.6 GHz (China, Huairou station) with high resolution (10 MHz and 8 ms). The FB and ZPS have about the same spectral parameters: the frequency bandwidth of emission stripes $\Delta f\sim$20 MHz, the frequency separation between the emission and the neighboring low frequency absorption $-\Delta f_{ea}\sim$30 MHz and the frequency separation between emission stripes (when a periodic structure persists) $\Delta f_s\sim$60−70 MHz. Therefore we consider both these fine structures to be whistler manifestations, i.e., interactions of plasma electrostatic waves with whistler waves (generated by the same fast particles with loss-cone anisotropy) $l + w \rightarrow t$. The duration of the fiber bursts of about 2 s corresponds to whistler waves propagating undamped at about 2 s, which requires a whistler increment <0.5 s-1. In the frequency range 3--7 GHz the relation between the ratios of plasma to cyclotron frequencies and whistler to cyclotron frequencies is almost independent of the decrement of whistler electron damping. This finding is used to obtain the magnetic field strength in the region of generation. For a reasonable value of electron temperature (2--20 MK), we find B = 125--190 G when the electron density is (8−18) × 1010 cm-3 and B = 520--610 G when the electron density is (35--60)× 1010 cm-3. In two remarkable events, 1998-04-15 and 2000-10-29, the right-hand polarization is strong for all the fine structures and corresponds to ordinary wave.

Key words: Sun: radio radiation --- Sun: activity

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A Correlation between Proton Events and H$\alpha$ Flares and its Possible Interpretation

Kim Jik Su, Yuan-Yong Deng, Kim Kum Sok and Kim Jin Song


E-mail: dyy@sun10.bao.ac.cn 

Abstract

Comparing space proton event data obtained during 1970--1980 with their identified  H$\alpha$ flare signatures we discover a peculiar correlation between them, according to which weak and small H$\alpha$ flares can also produce proton events, and we reveal a characteristic ``triangle" distribution of H$\alpha$ flares accompanying proton events. In order to explain such feature of proton events, we accept the acceleration mechanism by DC electric field. To deduce the parallel electric field we use the electric current helicity (or force-free parameter $\alpha$) determined by the Huairou vector magnetograph. A comparison of $E_{\Vert}$ with $E_{\bot}$) shows that the former is negligible in flaring sites. We show that in the flaring current sheet ion-anisotropy is generated, and it, in turn, gives rise to ion-anisotropic instability which competes with electric acceleration to give one possibility: the acceleration by DC electric field or annihilation of the built-up energy. The competition of DC acceleration and ion-anisotropic instability annihilation in the current sheet gives a possible explanation for the above-mentioned ``triangle" character of the distribution.

Key words: Sun: flares --- Sun: particle emission

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Close Approaches of Potentially Hazardous Asteroids during Two Centuries

Jiang-Hui Ji and Lin Liu

E-mail: jijh@pmo.ac.cn 

Abstract

Asteroids are the most important small bodies in the solar system and the near-earth asteroids (NEAs) are of especial concern to the world. The reason is that they will make close approaches to the earth in the near future. We use a reasonable dynamical model and an efficient computing method to calculate the orbits of over 160 Potentially Hazardous Asteroids (PHAs) for two centuries.

Key words: celestial mechanics --- asteroids --- Earth

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The Coudé  Echelle Spectrograph for the Xinglong 2.16-m Telescope

Gang Zhao and Hong-Bin Li

E-mail: zg@orion.bao.ac.cn 

Abstract

A brief description of the NAO coudé echelle spectrograph mounted on the 2.16-m telescope at Xinglong station is given. This echelle spectrograph is located at the coudиж focus with a prism cross disperser. The echelle image covers the spectral region from 330 to 1100 nm displayed in 80 spectral orders in one exposure through two light beams. With a slit height of 2 mm, spectral orders are separated by 15 to 23 pixels in blue region and by 7 to 19 pixels in red region. Alternatively, two additional resolution modes corresponding to different focal length cameras with resolving power R =16 000, 170 000 in the blue beam and R = 13 000, 170 000 in the red beam could be provided by this spectrograph. The bias, dark, wavelength calibration, flat field and science exposure are described in details. The limiting magnitude for 1 hour exposure with an S/N ratio of 100 scales to V = 9.5 in the red path and to V = 7.2 in the blue path.

Key words: instrumentation: spectrographs --- methods: observational --- techniques: spectroscopic

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Steps Towards a Fully Automated Classification and Redshift-measurement 
Pipeline for LAMOST Spectra. I. Continuum level and wavelength estimation 
for galaxies


A-Li Luo and Yong-Heng Zhao

E-mail: lal@lamost.bao.ac.cn 

Abstract

The Large Sky-Area Multi-Object Spectroscopic Telescope (LAMOST) under construction by the National Astronomical Observatories will yield up to four thousand multi-fiber spectra of stars and galaxies per field. The present series of papers describes the automated data-reduction pipeline currently being designed in order to cope with the anticipated flood of spectrographic data. In this preliminary paper, we present an automated method for estimating the continuum level, the positions of strong lines and the 4000Å break in galaxy spectra. In order to obtain detailed information on the continuum, we use a wavelet filter bank. After continuum fitting, our software searches for a 4000Å break and distinguishes between emission-line galaxies (ELGs)and non-ELGs according to whether the break is small or large. It then searches for strong lines and measures the intensities of emission lines and the equivalent widths of absorption lines. For non-ELGs, the absorption lines are identified automatically yielding redshift measurements.

Key words: methods: data analysis --- techniques: spectroscopic --- galaxies: emission lines -- galaxies: absorption lines

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ChJAA, 2001, Vol.1, No.6

Chinese Journal of Astronomy and Astrophysics: Online Edition

http://www.chjaa.org 

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