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- 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 55/122
541
- O'NEILL SEAN M.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.605-609
- 2004
- 원문 바로보기
We present a set of high-resolution 3D MHD simulations exploring the evolution of light, supersonic jets in cluster environments. We model sets of high- and low-Mach jets entering both uniform surroundings and King-type atmospheres and propagating distances more than 100 times the initial jet radius. Through complimentary analyses of synthetic observations and energy flow, we explore the detailed interactions between these jets and their environments. We find that jet cocoon morphology is strongly influenced by the structure of the ambient medium. Jets moving into uniform atmospheres have more pronounced backflow than their non-uniform counterparts, and this difference is clearly reflected by morphological differences in the synthetic observations. Additionally, synthetic observations illustrate differences in the appearances of terminal hotspots and the x-ray and radio correlations between the high- and low-Mach runs. Exploration of energy flow in these systems illustrates the general conversion of kinetic to thermal and magnetic energy in all of our simulations. Specifically, we examine conversion of energy type and the spatial transport of energy to the ambient medium. Determination of the evolution of the energy distribution in these objects will enhance our understanding of the role of AGN feedback in cluster environments.
542
- ENBLIN TORSTEN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.5
- pp.439-446
- 2004
- 원문 바로보기
A critical discussion of our knowledge about extragalactic cosmic rays and magnetic fields is at-tempted. What do we know for sure? What are our prejudices? How do we confront our models with the observations? How can we assess the uncertainties in our modeling and in our observations? Unfortunately, perfect answers to these questions can not be given. Instead, I describe efforts I am involved in to gain reliable information about relativistic particles and magnetic fields in extragalactic space.
543
- SANCHEZ-SALCEDO F. J.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.205-210
- 2004
- 원문 바로보기
The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.
544
- HYUNG SIEK
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.273-279
- 2004
- 원문 바로보기
Chemical compositions of planetary nebulae are of interest for a study of the late stage of stellar evolution and for elemental contributions to the interstellar medium of reprocessed elements since possibly a large fraction of stars in 0.8 - 8 <TEX>$M_{\bigodot}$</TEX> range go through this stage. One of the methods for getting chemical composition is a construction of theoretical photoionization models, which involves geometrical complexities and a variety of physical processes. With modelling effort, one can analyze the high dispersion and find the elemental abundances for a number of planetary nebulae. The model also gives the physical parameter of planetary nebula and its central star physical parameter along with the knowledge of its evolutionary status. Two planetary nebulae, NGC 7026 and Hu 1-2, which could have evolved from about one solar mass progenitor stars, showed radically different chemical abundances: the former has high chemical abundances in most elements, while the latter has extremely low abundances. We discuss their significance in the light of the evolution of our Galaxy.
545
- BOHIGAS JOAQUIN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.281-284
- 2004
- 원문 바로보기
Optical imaging and spectroscopy of G353.2+0.9, the brightest part of the giant H II region NGC 6357, shows that this H II region is optically thin, contains <TEX>${\~}300\;M_{\bigodot}$</TEX> of ionized gas and is probably expanding into the surrounding medium. Its chemical composition is similar to that found in other H II regions at similar galactocentric distances if temperature fluctuations are significant. The inner regions are probably made of thin shells and filaments, whereas extended slabs of material, maybe shells seen edge-on, are found in the periphery. The radio continuum and H<TEX>$\alpha$</TEX> emission maps are very similar, indicating that most of the optical nebula is not embedded in the denser regions traced by molecular gas and the presence of IR sources. About <TEX>$10^{50}$</TEX> UV photons per second are required to produce the H<TEX>$\beta$</TEX> flux from the 1l.3'<TEX>${\times}$</TEX>10' region surrounding the Pis 24 cluster that is south of G353.2+0.9. Most of the energy powering this region is produced by the 03-7 stars in Pis 24. Most of the 2MASS sources in the field with large infrared excesses are within G353.2+0.9, indicating that the most recent star forming process occured within it. The formation of Pis 24 preceded and caused the formation of this new generation of stars and may be responsible for the present-day morphology of the entire NGC 6357 region.
546
- 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.
547
- KIM S.-L.
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.143-149
- 2004
- 원문 바로보기
We present photometric results for four new variable stars discovered in the vicinity of the ZZ Ceti-type pulsating white dwarf BR Cam. Observations were performed on 5 nights in November 2003 using the 1.8m telescope at Bohyunsan Optical Astronomy Observatory with no filter, on 3 nights in December 2003 using the 0.61m telescope at Sobaeksan Optical Astronomy Observatory with V, I filters, and on 3 nights in October 2004 using the 1.0m telescope at Mt. Lemmon Optical Astronomy Observatory with V, I filters. We estimated their periods from the phase-match technique for one eclipsing binary and the multiple frequency analysis for three pulsating stars. By considering the light curve shape, period and amplitude difference between two passbands, we classified the objects by their variability types as follows: V1 (USNO-A2.0 1425-05691757) is a W UMa-type eclipsing binary with an orbital period of <TEX>$0^d.4641$</TEX>; V2 (USNO-A2.0 1425-05703335) is a multi-periodic <TEX>$\delta$</TEX> Set-type pulsating star with a dominant period of <TEX>$0^d.0649$</TEX>; V3 (USNO-A2.0 1425-05699659) is also a <TEX>$\delta$</TEX> Set-type pulsating star with a period of <TEX>$0^d.1408$</TEX>; and V 4 (USNO-A2.0 1425-05707705) is a RR Lyr-type pulsating star with a period of <TEX>$0^d.2643$</TEX>.
548
- BOHIGAS JOAQUIN
- Journal of the Korean astronomical society = 천문학회지
- 37, n.4
- pp.285-288
- 2004
- 원문 바로보기
Near-infrared imaging photometry supplemented by optical spectroscopy and narrow-band imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and the neighboring compact H II region S 128N associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an 07 star close to its center. A new spectroscopic distance of 9.4 kpc is derived, very similar to the kinematic distance to the nebula. This implies a galactocentric distance of 13.5 kpc and z = 550 pc. The region is optically thin with abundances close to those predicted by galactocentric gradients. The <TEX>$JHK_s$</TEX> images show that S 128N contains several infrared point sources and nebular emission knots with large near-infrared excesses. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and <TEX>$K_s$</TEX> show the presence of a small cluster of B-type stars, mainly associated with S 128N. The <TEX>$JHK_s$</TEX> photometric properties together with the characteristics of the other objects in the vicinity suggest that Sh 2-128 and S 128N constitute a single complex formed from the same molecular cloud, with ages <TEX>${\~}10^6$</TEX> and < <TEX>$3 {\times} 10^5$</TEX> years respectively. No molecular hydrogen emission was detected at 2.12 <TEX>${\mu}m$</TEX>. The origin of this remote star forming region is an open problem.
549
- 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.
550
- 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.