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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 63/122
621
- SKUMANICH A.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.1-5
- 2003
- 원문 바로보기
In an early paper Skumanich suggested the existence of a scaling law relating the mean sunspot magnetic field with the square-root of the photospheric pressure. This was derived from an analysis of a variety of theoretical spot models including those by Yun (1968). These were based on the Schliiter-Temesvary (S- T) similarity assumption. To answer criticisms that such modeling may have unphysical (non-axial maxima) solutions, the S-T model was revisited, Moon et al. (1998), with an improved vector potential function. We consider here the consequences of this work for the scaling relation. We show that by dimensionalizing the lateral force balance equation for the S- T model one finds that a single parameter enters as a characteristic value of the solution. This parameter yields Skumanich's scaling directly. Using an observed universal flux-radius relation for dark solar magnetic features (spots and pores) for comparison, we find good to fair agreement with Yun's characteristic value, however the Moon et al. values deviate significantly.
622
- MIN KYOUNG W.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.109-115
- 2003
- 원문 바로보기
We report the results of the ionospheric measurement obtained from the instruments on board the Korea Multi-Purpose Satellite - 1 (KOMPSAT-l). We observed a deep electron density trough in the nighttime equatorial ionosphere during the great magnetic storm on 15 July 2000. We attribute the phenomena to the up-lifted F-layer caused by the enhanced eastward electric field, while the spacecraft passed underneath the layer. We also present the results of our statistical study on the equatorial plasma bubble formation. We confirm the previous results regarding its seasonal and longitudinal dependence. In addition, we obtain new statistical results of the bubble temperature variations. The whole data set of measurement for more than a year is compared with the International Reference Ionosphere (IRI). It is seen that the features of the electron density and temperature along the magnetic equator are more prominent in the KOMPSAT-l observations than in the IRI model.
623
- 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.
624
- 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.
625
- 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>.
626
- CHANG HEON-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 36, n.2
- pp.67-72
- 2003
- 원문 바로보기
The basic objective of helioseismology is to determine the structure and the dynamics of the Sun by analysing the frequency spectrum of the solar oscillations. Accurate frequency measurements provide information that enables us to probe the solar interior structure and the dynamics. Therefore the frequency of the solar oscillation is the most fundamental and important information to be extracted from the solar oscillation observation. This is why many efforts have been put into the development of accurate data analysis techniques, as well as observational efforts. To test one's data analysis method, a realistic artificial data set is essential because the newly suggested method is calibrated with a set of artificial data with predetermined parameters. Therefore, unless test data sets reflect the real solar oscillation data correctly, such a calibration is likely incomplete and a unwanted systematic bias may result in. Unfortunately, however, commonly used artificial data generation algorithms insufficiently accommodate physical properties of the stochastic excitation mechanism. One of reason for this is that it is computaionally very expensive to solve the governing equation directly. In this paper we discuss the nature of solar oscillation excitation and suggest an efficient algorithm to generate the artificial solar oscillation data. We also briefly discuss how the results of this work can be applied in the future studies.
627
- 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.
628
- LEE MYUNG GYOON
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.189-212
- 2003
- 원문 바로보기
I review the current status of understanding when, how long, and how giant elliptical galaxies formed, focusing on the globular clusters. Several observational evidences show that massive elliptical galaxies formed at z > 2 (> 10 Gyr ago). Giant elliptical galaxies show mostly a bimodal color distribution of globular clusters, indicating a factor of <TEX>$\approx$</TEX> 20 metallicity difference between the two peaks. The red globular clusters (RGCs) are closely related with the stellar halo in color and spatial distribution, while the blue globular clusters (BGCs) are not. The ratio of the number of the RGCs and that of the BGCs varies depending on galaxies. It is concluded that the BGCs might have formed 12-13 Gyr ago, while the RGCs and giant elliptical galaxies might have formed similarly 10-11 Gyr ago. It remains now to explain the existence of a gap between the RGC formation epoch and the BGC formation epoch, and the rapid metallicity increase during the gap (<TEX>${\Delta}t{\approx}$</TEX> 2 Gyr). If hierarchical merging can form a significant number of giant elliptical galaxies > 10 Gyr ago, several observational constraints from stars and globular clusters in elliptical galaxies can be explained.
629
- 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.
630
- 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.