모달창 닫기
- 홈으로 이동
1968년 ~ 2025년까지 1,227 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 : 1,227건 (DB Construction : 1,227 Articles)
총 게시글 1,227건
페이지 67/123
661
- CHOI CHUL-SUNG
- Journal of the Korean astronomical society = 천문학회지
- 36, n.2
- pp.73-73
- 2003
- 원문 바로보기
Proof correction to the equation in the third paragraph of the DISCUSSION AND CONCLUSION has not been carried faithfully to the published version of the paper. The corrected equation should read <TEX>${\approx}10^{-3}\;M_8^4/^3(N_{\ast}/10^6\;pc^{-3})({\sigma}/300 km\;s^{-l})^{-l}(r/r_t)\;yr^{-1}$</TEX>, where Ms is the mass of the SMBH in units of <TEX>$10^8\;M_{\bigodot}$</TEX>, <TEX>$\sigma$</TEX> is the virial velocity of the stars, <TEX>$r_t$</TEX> is the tidal radius of the SMBH. This estimates the frequency that a star would pass within a sphere with the radius r from the SMBH, rather than the frequency of the tidal disruption event. Therefore, it increases with the mass of the SMBH. However, the loss cone effect should also be taken into account, which reduces the actual event rate. Here, we adopted a factor of one hundred to consider the deficiency from the isotrophic rate. The authors sincerely regret this error.
662
- AHN SANG-HYEON
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.145-148
- 2003
- 원문 바로보기
P-Cygni type Ly<TEX>$\alpha$</TEX> from starburst galaxies, either nearby galaxies or Lyman Break galaxies, are believed to be formed by galactic outflows such as galactic supershells or galactic superwinds. We develope a Monte Carlo code to calculate the Ly<TEX>$\alpha$</TEX> line transfer in a galactic supershell which is expanding and formed of uniform and dusty neutral hydrogen gas. The escape of Ly<TEX>$\alpha$</TEX> photons from the system is achieved by a number of back-scatterings. A series of emission peaks are formed by back-scatterings. When we observe P-Cygni type Ly<TEX>$\alpha$</TEX> emissions of starforming galaxies, we can usually see merely singly-peaked emission. Hence the secondary and the tertiary emission humps should be destroyed. In order to do this, dust should be spatially more extended into the inner cavity than neutral supershell. We find that the kinematic information of the expanding supershell is conserved even in dusty media. We discuss the astrophysical applications of our results.
663
- PEARSON CHRIS
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.249-260
- 2003
- 원문 바로보기
ASTRO-F is the next generation Japanese infrared space mission of the Institute of Space and Astronautical Science. ASTRO-F will be dedicated to an All Sky Survey in the far-infrared in 4 bands from 50-200microns with 2 additional mid-infrared bands at 9microns and 20microns. This will be the first all sky survey in the infrared since the ground breaking IRAS mission almost 20 years ago and the first ever survey at 170microns. The All Sky Survey should detect 10's of millions of sources in the far-infrared bands most of which will be dusty luminous and ultra-luminous star forming galaxies, with as many as half lying at redshifts greater than unity. In this contribution, the ASTRO-F mission and its objectives are reviewed and many of the mission expectations are discussed.
664
- HIEI E.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.45-47
- 2003
- 원문 바로보기
A white light flare was observed at the limb on 16 August 1989 in He 10830 <TEX>${\AA}$</TEX> spectra, H<TEX>$\alpha$</TEX> slit jaw photo-grams, and white light filter-grams of <TEX>${\lambda}=5600{\AA}{\pm}800{\AA}$</TEX>. The kernels of the white light flare are not spatially related with Ha brightenings, suggesting that the flare energy would be released at the photosphere.
665
- ANN HONG BAE
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.241-248
- 2003
- 원문 바로보기
Owing to several observational evidences and theoretical predictions for morphological evolution of galaxies, it is now widely accepted that galaxies do evolve from late types to early ones along the Hubble sequence. It is also well established that non-axisymmetric potentials of bar-like or oval mass distributions can change the morphology of galaxies significantly during the Hubble time. Here, we review the observational and theoretical grounds of the secular evolution driven by bar-like potentials, and present the results of SPH simulations for the response of the gaseous disks to the imposed potentials to explore the secular evolution in the central regions of barred galaxies.
666
- SANDERS D. B.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.149-158
- 2003
- 원문 바로보기
Deep surveys at mid-infared through submillimeter wavelengths indicate that a substantial fraction of the total luminosity output from galaxies at high redshift (z > 1) emerges at wavelengths 30 - 300<TEX>${\mu}m$</TEX>. In addition, much of the star formation and AGN activity associated with galaxy building at these epochs appears to reside in a class of luminous infrared galaxies (LIGs), often so heavily enshrouded in dust that they appear as 'blank-fields' in deep optical/UV surveys. Here we present an update on the state of our current knowledge of the cosmic evolution of LIGs from z = 0 to z <TEX>$\~$</TEX> 4 based on the most recent data obtained from ongoing ground-based redshift surveys of sources detected in ISO and SCUBA deep fields. A scenario for the origin and evolution of LIGs in the local Universe (z < 0.3), based on results from multiwavelength observations of several large complete samples of luminous IRAS galaxies, is then discussed.
667
- AHN BYUNG-HO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.93-99
- 2003
- 원문 바로보기
Various attempts have been made to explain the: pronounced seasonal and universal time (UT) variations of geomagnetic indices. As one of such attempts, we analyze the hourly-averaged auroral electroject indices obtained during the past 20 years. The AU and AL indices maximize during summer and equinoctial months, respectively. By normalizing the contribution of the solar conductivity enhancement to the AU index, or to the eastward electrojet, it is found that the AU also follows the same semiannual variation pattern of the AL index, suggesting that the electric field is the main modulator of the semiannual magnetic variation. The fact that the variation pattern of the yearly-mean AU index follows the mirror image of the AL index provides another indication that the electric field is the main modulator of magnetic disturbance. The pronounced UT variations of the auroral electrojet indices are also noted. To determine the magnetic activity dependence, the probability of recording a given activity level of AU and AL during each UT is examined. The UT variation of the AL index, thus obtained, shows a maximum at around 1200-1800 UT and a minimum around 0000-0800 UT particularly during winter. It is closely associated with the rotation of the geomagnetic pole around the rotational axis, which results in the change of the solar-originated ionospheric conductivity distribution over the polar region. On the other hand the UT variation is prominent during disturbed periods, indicating that the latitudinal mismatch between the AE stations and the auroral electrojet belt is responsible for it. Although not as prominent as the AL index, the probability distribution of the AU also shows two UT peaks. We confirm that the Dst index shows more prominent seasonal variation than the AE indices. However, the UT variation of the Dst index is only noticeable during the main phase of a magnetic storm. It is a combined result of the uneven distribution of the Dst stations and frequent developments of the partial ring current and substorm wedge current preferentially during the main phase.
668
- CHAE JONGCHUL
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.33-41
- 2003
- 원문 바로보기
Recent observations have shown that coronal magnetic fields in the northern (southern) hemisphere tend to have negative (positive) magnetic helicity. There has been controversy as to whether this hemispheric pattern is of surface or sub-surface origin. A number of studies have focused on clarifying the effect of the surface differential rotation on the change of magnetic helicity in the corona. Meanwhile, recent observational studies reported the existence of transient shear flows in active regions that can feed magnetic helicity to the corona at a much higher rate than the differential rotation does. Here we propose that such transient shear flows may be driven by the torque produced by either the axial or radial expansion of the coronal segment of a twisted flux tube that is rooted deeply below the surface. We have derived a simple relation between the coronal expansion parameter and the amount of helicity transferred via shear flows. To demonstrate our proposition, we have inspected Yohkoh soft X-ray images of NOAA 8668 in which strong shear flows were observed. As a result, we found that the expansion of magnetic fields really took place in the corona while transient shear flows were observed in the photosphere, and the amount of magnetic helicity change due to the transient shear flows is quantitatively consistent with the observed expansion of coronal magnetic fields. The transient shear flows hence may be understood as an observable manifestation of the pumping of magnetic helicity out of the interior portions of the field lines driven by the expansion of coronal parts as was originally proposed by Parker (1974).
669
- KIM SAM
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.21-31
- 2003
- 원문 바로보기
ASTRO-F /FIS will carry out all sky survey in the wavelength from 50 to 200 <TEX>${\mu}m$</TEX>. At far infrared, stars and galaxies may not be good calibration sources because the IR fluxes could be sensitive to the dust shell of stars and star formation activities of galaxies. On the other hand, asteroids could be good calibration sources at far infrared because of rather simple spectral energy distribution. Recent progresses in thermal models for asteroids enable us to calculate the far infrared flux fairly accurately. We have derived the Bond albedos and diameters for 559 asteroids based on the IRAS and ground based optical data. Using these thermal parameters and standard thermal model, we have calculated the spectral energy distributions of asteroids from 10 to 200 <TEX>${\mu}m$</TEX>. We have found that more than <TEX>$70\%$</TEX> of our sample asteroids have flux errors less than <TEX>$10\%$</TEX> within the context of the best fitting thermal models. In order to assess flux uncertainties due to model parameters, we have computed SEDs by varing external parameters such as emissivity, beaming parameter and phase integral. We have found that about 100 asteroids can be modeled to be better than <TEX>$5.8\%$</TEX> of flux uncertainties. The systematic effects due to uncertainties in phase integral are not so important.
670
- Lee, Chang-Won
- Journal of the Korean astronomical society = 천문학회지
- 36, n.4
- pp.271-282
- 2003
- 원문 바로보기
We present results of a <TEX>$H^{13}CN$</TEX> J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of <TEX>$-1.6^{\circ}{\le}{\iota}{\le}2^{\circ}$</TEX> and <TEX>$-0.23^{\circ}{\le}b{\le}0.30^{\circ}$</TEX> with 2' grid resolution. The <TEX>$H^{13}CN$</TEX> emissions show similar distribution and velocity structures to those of the <TEX>$H^{12}CN$</TEX> emissions, but are found to better trace the feature saturated with <TEX>$H^{12}CN$</TEX> (1-0). The bright components among multi-components of <TEX>$H^{12}CN$</TEX> line profiles usually appear in the <TEX>$H^{13}CN$</TEX> line while most of the dynamically forbidden, weak <TEX>$H^{12}CN$</TEX> components are seldom detected in the <TEX>$H^{13}CN$</TEX> line. We also present results of other complementary observations in <TEX>$^{12}CO$</TEX> (J=1-0) and <TEX>$^{13}CO$</TEX> (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of <TEX>$H^{12}CN$</TEX> and <TEX>$H^{13}CN$</TEX> relative to <TEX>$H_2$</TEX> in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within <TEX>$[{\iota}]{\le}6^{\circ}$</TEX> is estimated to be <TEX>${\~}2 {\times}10^7\;M_{\bigodot}$</TEX> using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few <TEX>$10^5$</TEX> to <TEX>${\~}10^7\;M_{\bigodot}$</TEX> All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km <TEX>$s^{-1}$</TEX>) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.