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1968년 ~ 2024년까지 1,211 건의 한국천문학회지를 격월간 확인하실 수 있습니다.
- The Korean Astronomical Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-4614 (ISSN : 1225-4614)
1225-4614
- DB구축현황 : 1,211건 (DB Construction : 1,211 Articles)
총 게시글 1,211건
페이지 59/122
581
- HALLMAN ERIC J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.593-596
- 2004
- 원문 바로보기
We introduce a method of identifying evidence of shocks in the X-ray emitting gas in clusters of galaxies. Using information from synthetic observations of simulated clusters, we do a blind search of the synthetic image plane. The locations of likely shocks found using this method closely match those of shocks identified in the simulation hydrodynamic data. Though this method assumes nothing about the geometry of the shocks, the general distribution of shocks as a function of Mach number in the cluster hydrodynamic data can be extracted via this method. Characterization of the cluster shock distribution is critical to understanding production of cosmic rays in clusters and the use of shocks as dynamical tracers.
582
- NARASIMHA D.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.355-359
- 2004
- 원문 바로보기
Differential Faraday Rotation measurements between the images of same background source, of multiply-imaged gravitational lens systems can be effectively used to provide a valuable probe to establish the existence of large-scale ordered magnetic fields in lensing galaxies as well as galaxy clusters. Estimates of the magnetic field in lens galaxies, based on the radio polarization measurements do not appear to show any clear evidence for evolution with redhsift of the coherent large scale magnetic field between redshift of 0.9 and the present epoch. However, our method clearly establishes the presence of coherent large scale magnetic field in giant ellitpical galaxies.
583
- RICHER M. G.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.269-272
- 2004
- 원문 바로보기
We present the first results of a wide field survey for planetary nebulae throughout M31 undertaken at the KPNO 0.9m telescope with the Mosaic camera. So far, images in [O III]<TEX>$\lambda$</TEX>5007 and its continuum filter have been analyzed. Our survey appears to be at least <TEX>$90\%$</TEX> complete to about 2 mag below the peak of the planetary nebula luminosity function. Over 900 planetary nebulae candidates have been found within a 12 square degree area.
584
- BOHRINGER HANS
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.361-369
- 2004
- 원문 바로보기
Galaxy clusters as the densest and most prominent regions within the large-scale structure can be used as well characterizable laboratories to study astrophysical processes on the largest scales. X-ray observations provide currently the best way to determine the physical properties of galaxy clusters and the environmental parameters that describe them as laboratories. We illustrate this use of galaxy clusters and the precision of our understanding of them as laboratory environments with several examples. Their application to determine the matter composition of the Universe shows good agreement with results from other methods and is therefore a good test of our understanding. We test the reliability of mass measurements and illustrate the use of X-ray diagnostics to study the dynamical state of clusters. We discuss further studies on turbulence in the cluster ICM, the interaction of central AGN with the radiatively cooling plasma in cluster cooling cores and the lessons learned from the ICM enrichment by heavy elements.
585
- BRUNETTI GIANFRANCO
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.493-500
- 2004
- 원문 바로보기
The existence and extent of non-thermal phenomena in galaxy clusters is now well established. A key question in our understanding of these phenomena is the origin of the relativistic electrons which may be constrained by the modelling of the fine radio properties of radio halos and of their statistics. In this paper we argue that present data favour a scenario in which the emitting electrons in the intracluster medium (ICM) are reaccelerated in situ on their way out. An overview of turbulent-particle acceleration models is given focussing on recent time-dependent calculations which include a full coupling between particles and MHD waves.
586
- KIM WOONG-TAE
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.243-248
- 2004
- 원문 바로보기
Disk galaxies abound with intermediate-scale structures such as OB star complexes, giant clouds, and dust spurs in a close geometrical association with spiral arms. Various mechanisms have been proposed as candidates for their origin, but a comprehensive theory should encompass fundamental physical agents such as self-gravity, magnetic fields, galactic differential rotation, and spiral arms, all of which are known to exist in disk galaxies. Recent numerical simulations incorporating all these physical processes show that magneto-Jeans instability (MJI), in which magnetic tension resists the stabilizing Coriolis force of galaxy rotation, is much more powerful than swing-amplification or the Parker instability in forming self-gravitating intermediate-scale structures. The MJI occurring in shearing and expanding flows off spiral arms rapidly forms structures elongated along the direction perpendicular to the arms, remarkably similar to dust spurs seen in HST images of spiral galaxies. In highly nonlinear stages, these spurs fragment to form bound clumps, possibly evolving into bright arm and interarm H II regions, suggesting that all these intermediate-scale structures in spiral galaxies probably share a common dynamical origin.
587
- SHEEN YUN-KYEONG
- Journal of the Korean astronomical society = 천문학회지
- 37, n.2
- pp.87-90
- 2004
- 원문 바로보기
Spectrophotometry of the night sky over Mount Bohyun is presented for the nearly entire visible wavelengths of <TEX>$3600{\~}$8600{\AA}$</TEX>. The data was obtained under moonless clear sky in February 2004 with the 1.8-m telescope and the long slit spectrograph. The sky spectrum shows a number of strong emission lines originated from light pollution, especially due to high pressure sodium lamps. When compared to the night sky of Kitt Peak, our sky continuum is 1 to 2 magnitude brighter at all wavelengths, the worst being around the broad emission region near 6000<TEX>${\AA}$</TEX>. The night sky spectrum presented here with almost complete line identifications is a useful reference for arc-independent wavelength calibrations to check the gravity flexure of the spectrograph and the wavelength shift between FeNeArHe arc frames and science frames.
588
- OH SU YEON
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.151-157
- 2004
- 원문 바로보기
It is investigated quantitative relations between the magnetic storm magnitude and the solar wind parameters such as the Interplanetary Magnetic Field (hereinafter, IMF) magnitude (B), the southward component of IMF (Bz), and the dynamic pressure during the main phase of the magnetic storm with focus on the role of the interplanetary shock (hereinafter, IPS) in order to build the space weather fore-casting model in the future capable to predict the occurrence of the magnetic storm and its magnitude quantitatively. Total 113 moderate and intense magnetic storms and 189 forward IPSs are selected for four years from 1998 to 2001. The results agree with the general consensus that solar wind parameter, especially, Bz component in the shocked gas region plays the most important role in generating storms (Tsurutani and Gonzales, 1997). However, we found that the correlations between the solar wind parameters and the magnetic storm magnitude are higher in case the storm happens after the IPS passing than in case the storm occurs without any IPS influence. The correlation coefficients of B and <TEX>$BZ_(min)$</TEX> are specially over 0.8 while the magnetic storms are driven by IPSs. Even though recently a Dst prediction model based on the real time solar wind data (Temerin and Li, 2002) is made, our correlation test results would be supplementary in estimating the prediction error of such kind of model and in improving the model by using the different fitting parameters in cases associated with IPS or not associated with IPS rather than single fitting parameter in the current model.
589
- KAASTRA JELLE S.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.375-379
- 2004
- 원문 바로보기
In this paper I give an overview of the detection of emission from the warm-hot intergalactic medium (WHIM) in the outer parts of clusters of galaxies. The evidence for the presence of soft excess X-ray emission in 7 out of 21 clusters is summarized, and it is demonstrated that several of these clusters show the signatures of thermal emission in the outer parts. A strong signature is the presence of redshifted O VII emission at 0.57 keV. In the central parts, several clusters show also a soft excess, but m this case the observations cannot well discriminate between a thermal or non-thermal origin of the soft X-ray excess.
590
- MOON Y.-J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.1
- pp.41-53
- 2004
- 원문 바로보기
It has been a big mystery what drives filament eruptions and flares. We have studied in detail an X1.8 flare and its associated filament eruption that occurred in NOAA Active Region 9236 on November 24,2000. For this work we have analyzed high temporal (about 1 minute) and spatial (about 1 arcsec) resolution images taken by Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory, Hoc centerline and blue wing (<TEX>$-0.6{\AA}$</TEX>) images from Big Bear Solar Observatory, and 1600 <TEX>${\AA}$</TEX> UV images by the Transition Region and Corona Explorer (TRACE). We have found that there were several transient brightenings seen in H<TEX>$\alpha$</TEX> and, more noticeably in TRACE 1600 <TEX>${\AA}$</TEX> images around the preflare phase. A closer look at the UV brightenings in 1600 <TEX>${\AA}$</TEX> images reveals that they took place near one end of the erupting filament, and are a kind of jets supplying mass into the transient loops seen in 1600 <TEX>${\AA}$</TEX>. These brightenings were also associated with canceling magnetic features (CMFs) as seen in the MDI magnetograms. The flux variations of these CMFs suggest that the flux cancellation may have been driven by the emergence of the new flux. For this event, we have estimated the ejection speeds of the filament ranging from 10 to 160 km <TEX>$s^{-1}$</TEX> for the first twenty minutes. It is noted that the initiation of the filament eruption (as defined by the rise speed less than 20 km <TEX>$s^{-1}$</TEX>) coincided with the preflare activity characterized by UV brightenings and CMFs. The speed of the associated LASCO CME can be well extrapolated from the observed filament speed and its direction is consistent with those of the disturbed UV loops associated with the preflare activity. Supposing the H<TEX>$\alpha$</TEX>/UV transient brightenings and the canceling magnetic features are due to magnetic reconnect ion in the low atmosphere, our results may be strong observational evidence supporting that the initiation of the filament eruption and the preflare phase of the associated flare may be physically related to low-atmosphere magnetic reconnection.