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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 61/119
601
- KIM D.-C.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.159-165
- 2003
- 원문 바로보기
Optical (R) and near-infrared (K') images of the IRAS 1-Jy sample of 118 ultraluminous infrared galaxies have been studied. All but one object in the 1-Jy sample show signs of strong tidal interaction/merger. Most of them harbor a single disturbed nucleus and are therefore in the later stages of a merger event. Single-nucleus ULIGs show a broad distribution in host magnitudes with significant overlap with those of quasars. The same statement applies to R - K' colors in ULIG and quasar hosts. An analysis of the surface brightness profiles of the host galaxies in single-nucleus sources reveals that about <TEX>$35\%$</TEX> of the Rand K' surface brightness profiles are well fit by an elliptical-like <TEX>$R^{1/4}$</TEX>-law, while only <TEX>$2\%$</TEX> are well fit by an exponential disk. Another <TEX>$38\%$</TEX> of the single-nucleus systems are fit equally well with an exponential or de Vaucouleurs profile. Elliptical-like hosts are most common among merger remnants with Seyfert 1 nuclei (<TEX>$83\%$</TEX>) and Seyfert 2 optical characteristics (<TEX>$69\%$</TEX>). The mean effective radius of these ULIGs is 4.80 <TEX>$\pm$</TEX> 1.37 kpc at Rand 3.48 <TEX>$\pm$</TEX> 1.39 kpc at K'. These values are in excellent agreement with recent quasar measurements obtained at H with HST. The hosts of elliptical-like 1-Jy systems follow with some scatter the same <TEX>${\mu}e - r_e$</TEX> relation, giving credence to the idea that some of these objects may eventually become elliptical galaxies if they get rid of their excess gas or transform this gas into stars.
602
- RYU DONGSU
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.105-110
- 2003
- 원문 바로보기
Recent observations of galaxy clusters in radio and X-ray indicate that cosmic rays and magnetic fields may be energetically important in the intracluster medium. According to the estimates based on theses observational studies, the combined pressure of these two components of the intracluster medium may range between <TEX>$10\%{\~}100\%$</TEX> of gas pressure, although their total energy is probably time dependent. Hence, these non-thermal components may have influenced the formation and evolution of cosmic structures, and may provide unique and vital diagnostic information through various radiations emitted via their interactions with surrounding matter and cosmic background photons. We suggest that shock waves associated with cosmic structures, along with individual sources such as active galactic nuclei and radio galaxies, supply the cosmic rays and magnetic fields to the intracluster medium and to surrounding large scale structures. In order to study 1) the properties of cosmic shock waves emerging during the large scale structure formation of the universe, and 2) the dynamical influence of cosmic rays, which were ejected by AGN-like sources into the intracluster medium, on structure formation, we have performed two sets of N-body /hydrodynamic simulations of cosmic structure formation. In this contribution, we report the preliminary results of these simulations.
603
- PARK MYEONG-GU
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.97-103
- 2003
- 원문 바로보기
We now have more than 70 multiple image gravitational lens systems. Since gravitational lensing occurs through gravitational distortions in cosmic space, cosmological informations can be extracted from multiple image systems. Specifically, Hubble constant can be determined by the time delay mea-surement, curvature of the universe can be measured by the distribution of image separations in lens systems, and limits on matter density and cosmological constant can be set by the statistics of gravitationallens systems. Uncertainties, however, still exist in various steps, and results may be taken with some caution. Larger systematic survey and better understanding of galaxy properties would definitely help.
604
- HAMED ABDEL-HAMID
- Journal of the Korean astronomical society = 천문학회지
- 36, n.2
- pp.49-54
- 2003
- 원문 바로보기
CCD observations in V, I and H<TEX>$\alpha$</TEX> for NGC 3389 are used to present photometry of 61 HII regions. Their positions, diameters and absolute luminosities have been determined. The luminosity and size distribution functions of the HII regions in NGC 3389 are discussed.
605
- KANG SANGJUN
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.75-80
- 2003
- 원문 바로보기
When a bright astronomical object (source) is gravitationally lensed by a foreground mass (lens), its image appears to be located at different positions. The lens equation describes the relations between the locations of the lens, source, and images. The lens equation used for the description of the lensing behavior caused by a lens system composed of multiple masses has a form with a linear combination of the individual single lens equations. In this paper, we examine the validity of the linear nature of the multi-lens equation based on the general relativistic point of view.
606
- LEE HEE-WON
- Journal of the Korean astronomical society = 천문학회지
- 36, n.2
- pp.55-60
- 2003
- 원문 바로보기
In Lee, Kang & Byun (2001) the discovery of Raman scattered 6545 A feature was reported in symbiotic stars and the planetary nebula M2-9. The broad emission feature around 6545 A is formed as a result of Raman scattering of He II n = 6 <TEX>$\to$</TEX> n = 2 photons by atomic hydrogen. In this paper, we introduce a method to compute the equivalent width of He II <TEX>$\lambda$</TEX> 1025 line and present an optical spectrum of the symbiotic star RR Telescopii as an example for a detailed illustration. In this spectrum, we pay attention to the broad H<TEX>$\alpha$</TEX> wings and the Raman scattered He II 6545 feature. The broad Ha wings are also proposed to be formed through Raman scattering of continuum around Ly<TEX>$\beta$</TEX> by Lee (2000), and therefore we propose that the equivalent width of the He II <TEX>$\lambda$</TEX> 1025 emission line is obtained by a simple comparison of the strengths of the 6545 feature and the broad H<TEX>$\alpha$</TEX> wings. We prepare a template H<TEX>$\alpha$</TEX> wing profile from continuum radiation around Ly<TEX>$\beta$</TEX> with the neutral scattering region that is supposed to be responsible for the formation of Raman scattered He II 6545 feature. Isolation of the 6545 feature that is blended with [N II] <TEX>$\lambda$</TEX> 6548 is made by using the fact that [N II] <TEX>$\lambda$</TEX> 6584 is always 3 times stronger than [N II] <TEX>$\lambda$</TEX> 6548. We also fit the 6545 feature by a Gaussian which has a width 6.4 times that of the He II <TEX>$\lambda$</TEX> 6527 line. A direct comparison of these two features for RR Tel yields the equivalent width <TEX>$EW_{Hel025} = 2.3{\AA}$</TEX> of He II <TEX>$\lambda$</TEX> 1025 line. Even though this far UV emission line is not directly observable due to heavy interstellar extinction, nearby He II lines such as He II <TEX>$\lambda$</TEX> 1085 line may be observed using far UV space instruments, which will verify this calculation and hence the origins of various features occurring in spectra around H<TEX>$\alpha$</TEX>.
607
- GOODE PHILIP R.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.125-133
- 2003
- 원문 바로보기
New Jersey Institute of Technology (NJIT), in collaboration with the University of Hawaii (UH), is upgrading Big Bear Solar Observatory (BBSO) by replacing its principal, 65 cm aperture telescope with a modern, off-axis 1.6 m clear aperture instrument from a 1.7 m blank. The new telescope offers a significant incremental improvement in ground-based infrared and high angular resolution capabilities, and enhances our continuing program to understand photospheric magneto-convection and chromospheric dynamics. These are the drivers for what is broadly called space weather - an important problem, which impacts human technologies and life on earth. This New Solar Telescope (NST) will use the existing BBSO pedestal, pier and observatory building, which will be modified to accept the larger open telescope structure. It will be operated together with our 10 inch (for larger field-of-view vector magnetograms, Ca II K and Ha observations) and Singer-Link (full disk H<TEX>$\alpha$</TEX>, Ca II K and white light) synoptic telescopes. The NST optical and software control design will be similar to the existing SOLARC (UH) and the planned Advanced Technology Solar Telescope (ATST) facility led by the National Solar Observatory (NSO) - all three are off-axis designs. The NST will be available to guest observers and will continue BBSO's open data policy. The polishing of the primary will be done in partnership with the University of Arizona Mirror Lab, where their proof-of-concept for figuring 8 m pieces of 20 m nighttime telescopes will be the NST's primary mirror. We plan for the NST's first light in late 2005. This new telescope will be the largest aperture solar telescope, and the largest aperture off-axis telescope, located in one of the best observing sites. It will enable new, cutting edge science. The scientific results will be extremely important to space weather and global climate change research.
608
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.155-161
- 2003
- 원문 바로보기
In this article I review the past and current status of solar astronomy in Korea and present some future prospects. Along with a brief historical account on the introduction of modern astronomy to Korea, I describe in detail how solar astronomy in Korea has developed since its birth about 20 years ago. With education of solar astronomers at domestic universities and collaboration with foreign scientists in China, Japan and the U. S., there has been a rapid growth of solar physics in Korea in the past decade. For further advance of solar astronomy in Korea, Korean solar astronomers have to build their own observing facilities and develop instrumentation programs. Also it is very important to bring up manpower competent for these projects.
609
- GARY DALE E.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.135-143
- 2003
- 원문 바로보기
Solar radio astronomy is about to undergo a revolution with the advent of a new radio synthesis array, the Frequency Agile Solar Radiotelescope (FASR). The array will consist of more than 100 antennas (5000 baselines), and will be designed to meet the special challenges of solar imaging. It will produce high-quality images at hundreds of frequencies in the range 20 MHz-24 GHz. We briefly describe the plans for the instrument, and then concentrate on the range of science that is expected to be addressed, using current state-of-the-art solar radio observations and modeling to illustrate FASR performance. We end with an assessment of the current status of the instrument, and plans for future.
610
- CHANG HEON-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.81-87
- 2003
- 원문 바로보기
It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A<TEX>$\ast$</TEX> for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A<TEX>$\ast$</TEX>, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order <TEX>$10^{-4}$</TEX>, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A<TEX>$\ast$</TEX> and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v <TEX>$\le$</TEX> 100 MHz.