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 38/123
371
- Hasan, M. Khayrul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.5
- pp.107-123
- 2009
- 원문 바로보기
We investigate the wave properties for isothermal plasma state around to the de Sitter black hole's horizon using 3+1 split of spacetime. The corresponding Fourier analyzed perturbed perfect GRMHD equations are used to obtain the complex dispersion relations. We obtain the real values of the wave number k, from these relations, which are used to evaluate the quantities like phase and group velocities etc. These have been analyzed graphically in the neighborhood of the horizon.
372
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.155-159
- 2009
- 원문 바로보기
In order to determine color excess in the <TEX>$uvby\beta$</TEX> color system for high amplitude <TEX>$\delta$</TEX> Scuti stars, reddening free <TEX>$[m_1]$</TEX>, <TEX>$[c_1]$</TEX>, and <TEX>$\beta$</TEX> indices data were obtained from the existing literature for 21 stars. Then, the three intrinsic relations of <TEX>$(b-y)_0$</TEX> - <TEX>$[m_1]$</TEX>, <TEX>$(b-y)_0$</TEX> - <TEX>$[c_1]$</TEX>, and <TEX>$(b-y)_0$</TEX> - <TEX>$\beta$</TEX> were investigated. Among these, it was shown that the <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relation is the most useful. By establishing intrinsic <TEX>$(b-y)_0$</TEX>-<TEX>$[c_1]$</TEX> relations for six reddening calibration stars, color excesses of other stars were determined.
373
- Shanmugarju, A.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.55-60
- 2009
- 원문 바로보기
The properties of SOHO/LASCO CMEs are subjected to projection effects. Their dependence on the source position is important to be studied. Our main aim is to study the dependence of CME properties on helio-longitude and latitude using the CMEs associated with type IIs observed by Wind/WAVES spacecraft (Deca-hecta metric type IIs - DH type IIs). These CMEs were identified as a separate population of geo-effective CMEs. We considered the CMEs associated with the Wind/WAVE type IIs observed during the period January 1997 - December 2005. The source locations of these CMEs were identified using their associated GOES X-ray flares and listed online. Using their locations and the cataloged properties of CMEs, we carried out a study on the dependence of CME properties on source location. We studied the above for three groups of CMEs: (i) all CMEs, (ii) halo and non-halo CMEs, and (iii) limb and non-limb CMEs. Major results from this study can be summarized as follows. (i) There is a clear dependence of speed on both the longitude and latitude; while there is an increasing trend with respect to longitude, it is opposite in the case of latitude. Our investigations show that the longitudinal dependence is caused by the projection effect and the latitudinal effect by the solar cycle effect. (ii) In the case of width, the disc centered events are observed with more width than those occurred at higher longitudes, and this result seems to be the same for latitude. (iii) The dependency of speed is confirmed on the angular distance between the sun-center and source location determined using both the longitude and latitude. (iv) There is no dependency found in the case of acceleration. (v) Among all the three groups of CMEs, the speeds of halo CMEs show more dependency on longitude. The speed of non-halo and non-limb CMEs show more dependency on latitude. The above results may be taken into account in correcting the projection effects of geo-effective CMEs.
374
- Yoo, Kye-Hwa
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.93-103
- 2009
- 원문 바로보기
This article reports the spectral behavior of CH Cygni, using data obtained in October 2005 and June 2006. In these epochs, CH Cygni showed emission lines of H I, Fe II, [Fe II], [O III], [N II], [Ne III] and [S II]. Many of these lines were more enhanced since 2004. The underlying M-type spectrum was removed to get the intrinsic emission profile, and the resulting profiles were deconvoluted into several Gaussian components. Also, the radial velocities for all the lines that appeared in these spectra of CH Cygni were measured. The resultant lines were compared with each other and with those obtained in 2004; the findings are explained in terms of an accretion disk and jets.
375
- Kim, Sang-Chul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.135-144
- 2009
- 원문 바로보기
We present JHK near-infrared photometric study for the old open cluster (OC) Trumpler 5 (Tr 5), based on the 2MASS data. From the color-magnitude diagrams of Tr 5, we have located the position of the red giant clump (RGC) stars, and used the mean magnitude of the RGC stars in K-band to estimate the distance to Tr 5, d = <TEX>$3.1{\pm}0.1$</TEX> kpc (<TEX>$(m-M)_0$</TEX> = <TEX>$12.46{\pm}0.04$</TEX>). From fitting the theoretical isochrones of Padova group, we have estimated the reddening, metallicity, and age : E(B-V) = <TEX>$0.64{\pm}0:05$</TEX>, [Fe/H] = <TEX>$-0.4{\pm}0.1$</TEX> dex, and t = <TEX>$2.8{\pm}0.2$</TEX> Gyr (log t = <TEX>$9.45{\pm}0.04$</TEX>), respectively. These parameters generally agree well with those obtained from the previous studies on Tr 5 and confirms that this cluster is an old OC with metallicity being metal-poorer than solar abundance, located in the anti-Galactic center region.
376
- Kim, Do-Eon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.33-37
- 2009
- 원문 바로보기
We propose a diagnostic that can resolve the planet/binary degeneracy of central perturbations in caustic-crossing high-magnification microlensing events. The diagnostic is based on the difference in the morphology of perturbation inside the central caustics induced by a planet and a wide-separation binary companion. We find that the contours of excess exhibit a concentric circular pattern around the caustic center for the binary-lensing case, while the contours are elongated or off-centered for the planetary case. This difference results in the distinctive features of the individual lens populations in the residual of the trough region between the two peaks of the caustic crossings, where the shape of the residual is symmetric for binary lensing while it tends to be asymmetric for planetary lensing. We determine the ranges of the planetary parameters for which the proposed diagnostic can be used. The diagnostic is complementary to previously proposed diagnostics in the sense that it is applicable to caustic-crossing events with small finite-source effect.
377
- Jang, Min-Hwan
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.175-184
- 2009
- 원문 바로보기
A method of estimating the lower bound of coronal magnetic field strength in the neighborhood of an ejecting plasmoid is presented. Based on the assumption that the plasma ejecta is within a magnetic island, an analytical expression for the force acting on the ejecta is derived. The method is applied to a limb coronal mass ejection event, and a lower bound of the magnetic field strength just below the CME core is estimated. The method is expected to provide useful information on the strength of reconnecting magnetic field if applied to X-ray plasma ejecta.
378
- Kim, Do-Eon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.39-45
- 2009
- 원문 바로보기
We investigate the degeneracy in the pattern of central microlensing perturbations of a pair of planetary systems where the planets are located from the primary with projected separations in units of the Einstein radius s and <TEX>$s^{-1}$</TEX>, respectively. From this, we confirm the fact that although alike, the patterns of central perturbations induced by a close (s < 1) planet and a wide (s > 1) planet are not identical and the degree of difference depends on the planet/primary mass ratio and the planet-primary separation. We find that the difference can be greater than 5% for planetary systems with lensing parameters located in the parameter space of (1/1.8 < |s| < 1.8, q > <TEX>$5{\times}10^{-3}$</TEX>), (1/1.3 < |s| < 1.3, q > <TEX>$1{\times}10^{-3}$</TEX>), and (1/1.2 < |s| < 1.2, q > <TEX>$5{\times}10^{-4}$</TEX>), where q represents the planet/primary mass ratio. Although this range occupies a small fraction of the entire parameter space of planetary systems, we predict that the chance of resolving the close/wide degeneracy would not be meager considering that the planet detection efficiency is higher for planets with resonant separations (s <TEX>$\sim$</TEX> 1) and heavier masses. We also find that the differences between the perturbation patterns are basically caused by the effect of the planetary caustic. This explains the tendency of the perturbation difference where (1) the difference increases as the planet/primary mass ratio increases and the separation approaches the Einstein radius, (2) the region of major difference is confined within the region around the line connecting the central and the planetary caustics, and (3) a wide (close) planetary system has a more extended central perturbation region toward the (opposite) direction of the planet.
379
- Lee, Dae-Hee
- Journal of the Korean astronomical society = 천문학회지
- 42, n.6
- pp.145-153
- 2009
- 원문 바로보기
We present measurements of diffuse interstellar <TEX>$H_2$</TEX> absorption lines in the continuum spectra of 10 early-type stars. The data were observed with the Berkeley Extreme and Far-Ultraviolet Spectrometer (BEFS) of the ORFEUS telescope on board the ORFEUS-SPAS I and II space-shuttle missions in 1993 and 1996, respectively. The spectra extend from the interstellar cutoff at 912 <TEX>$\AA$</TEX> to about 1200 <TEX>$\AA$</TEX> with a resolution of ~ 3000 and statistical signal-to-noise ratios between 10 and 65. Adopting Doppler broadening velocities from high-resolution optical observations, we obtain the <TEX>$H_2$</TEX> column densities of rotational levels J' = 0 through 5 for each line of sight. The kinetic temperatures derived from J' = 0 and 1 states show a small variation around the mean value of 80 K, except for the component toward HD 219188, which has a temperature of 211 K. Based on a synthetic interstellar cloud model described in our previous work, we derive the incident UV intensity IUV and the hydrogen density <TEX>$n_H$</TEX> of the observed components to be -0.4 <TEX>$\leq$</TEX> log <TEX>$I_{UV}\leq2.2$</TEX> and <TEX>$6.3{\leq}n_H2500cm^{-3}$</TEX>, respectively.
380
- Son, Dong-Hoon
- Journal of the Korean astronomical society = 천문학회지
- 42, n.5
- pp.125-134
- 2009
- 원문 바로보기
We investigated the circumnuclear region of the Seyfert 2 galaxy NGC 5728, using the CFHT 3.6 m OASIS <TEX>$[S_{II}]$</TEX>, <TEX>$[O_{III}]$</TEX> & <TEX>$H\beta$</TEX> spectral images complemented with the IUE spectra. The physical condition of the circumnuclear zone has been derived: the gas density (indicated by <TEX>$[S_{II}]$</TEX>6716/31 ratio) around the C core is generally similar to that around the NW core, i.e., <TEX>$\sim500cm^{-3}$</TEX>. However, there appears to be evidence of a higher density shell in front of the NW core, <TEX>$\sim10^4cm^{-3}$</TEX> at -250 km <TEX>$s^-1$</TEX>. The IUE <TEX>$Si_{III}$</TEX>]1892/<TEX>$C_{III}$</TEX>]1909 ratio implies a possible presence of a broad emission region of gas densities of <TEX>$\sim10^{10}cm^{-3}$</TEX>. The SE cone and surrounding area show several prominent features, while the NW cone does not show any particular structure: we identified three prominent blobs in the SE cone and one possible candidate in the NW cone. The outflow activities exist within the relatively large conic opening angle. We discussed the possibility of inflow or outflow activities of blobs found in the circumnuclear region of NGC 5728. The gas around two cores, two cones, and several blobs, is likely to be excited by the AGN hot source(s).