모달창 닫기
- 홈으로 이동
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 34/119
331
- 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.
332
- 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.
333
- 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.
334
- Suh, Kyung-Won
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.81-91
- 2009
- 원문 바로보기
We make a new catalog of AGB stars in our Galaxy from the sources listed in the Infrared Astronomical Satellite (IRAS) point source catalog (PSC) compiling the lists of previous works with verifying processes. We verify the class identification of AGB stars into oxygen-rich and carbon-rich stars using the information from recent investigations. For the large sample of AGB stars, we present infrared two-color diagrams from the observations at near infrared bands and IRAS PSC. On the two-color diagrams, we plot the tracks of theoretical radiative transfer model results with increasing dust shell optical depths. Comparing the observations with the theoretical tracks, we discuss the meaning of the infrared two-color diagrams.
335
- Oh, Seung-Kyung
- Journal of the Korean astronomical society = 천문학회지
- 42, n.2
- pp.17-26
- 2009
- 원문 바로보기
We estimate the enclosed mass profile in the central 10 pc of the Milky Way by analyzing the infrared photometry and the velocity observations of dynamically relaxed stellar population in the Galactic center. HST/NICMOS and Gemini Adaptive Optics images in the archive are used to obtain the number density profile, and proper motion and radial velocity data were compiled from the literature to find the velocity dispersion profile assuming a spherical symmetry and velocity isotropy. From these data, we calculate the the enclosed mass and density profiles in the central 10 pc of the Galaxy using the Jeans equation. Our improved estimates can better describe the exact evolution of the molecular clouds and star clusters falling down to the Galactic center, and constrain the star formation history of the inner part of the Galaxy.
336
- Nouh, M.I.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.47-54
- 2009
- 원문 바로보기
In this paper we present an independent FORTRAN code for calculating LTE-plane-parallel model atmospheres. The transfer equation has been solved using Avrett and Loeser method. It is shown that, using an approximate non-gray temperature distribution together with the iteration factors method (Simonneau and Crivellari) for correcting the temperature distribution reduce the number of iteration required to achieve the condition of radiative equilibrium. Preliminary results for pure helium model atmospheres are presented.
337
- Chae, Jong-Chul
- Journal of the Korean astronomical society = 천문학회지
- 42, n.3
- pp.61-69
- 2009
- 원문 바로보기
Transverse velocity vectors can be determined from a pair of images successively taken with a time interval using an optical flow technique. We have tested the performance of the new technique called NAVE (non-linear affine velocity estimator) recently implemented by Chae & Sakurai using real image data taken by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) aboard the Hinode satellite. We have developed two methods of estimating the errors in the determination of velocity vectors, one resulting from the non-linear fitting <TEX>${\sigma}_{\upsilon}$</TEX> and the other <TEX>${\epsilon}_u$</TEX> resulting from the statistics of the determined velocity vectors. The real error is expected to be somewhere between <TEX>${\sigma}_{\upsilon}$</TEX> and <TEX>${\epsilo</TEX><TEX>n}_u$</TEX>. We have investigated the dependence of the determined velocity vectors and their errors on the different parameters such as the critical speed for the subsonic filtering, the width of the localizing window, the time interval between two successive images, and the signal-to-noise ratio of the feature. With the choice of <TEX>$v_{crit}$</TEX> = 2 pixel/step for the subsonic filtering, and the window FWHM of 16 pixels, and the time interval of one step (2 minutes), we find that the errors of velocity vectors determined using the NAVE range from around 0.04 pixel/step in high signal-to-noise ratio features (S/N <TEX>$\sim$</TEX> 10), to 0.1 pixel/step in low signa-to-noise ratio features (S/N <TEX>$\sim$</TEX> 3) with the mean of about 0.06 pixel/step where 1 pixel/step corresponds roughly to 1 km/s in our case.
338
- Oh, Seung-Kyung
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.105-105
- 2009
- 원문 바로보기
339
- Moon, Y.J.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.2
- pp.27-32
- 2009
- 원문 바로보기
Recently, we suggested a CME earthward direction parameter as an important geoeffective parameter that has been demonstrated by front-side halo CME data. In this study, we present the geometrical implication of this parameter by comparing with the parameters from a CME cone model. Major results from this study can be summarized as follows. First, we derive an analytic relationship between the cone model parameters(the half angular width of a cone and the angle between the cone axis and the plane of sky) and the earthward direction parameter. Second, we demonstrate a close relationship between the earthward direction parameter and the cone axis angle using 32 front-side full halo CMEs. Third, we found that there is noticeable inconsistency between the cone axis angles estimated from the cone model fitting to the CMEs and from their associated flare positions, implying that the flare position should not be considered as a good earthward direction parameter. Finally we present several advantages of our earthward direction parameter in terms of the forecast of a geomagnetic storm based on CME parameters.
340
- Abdel-Rahman, H.I.
- Journal of the Korean astronomical society = 천문학회지
- 42, n.4
- pp.71-79
- 2009
- 원문 바로보기
In this paper, statistical distribution functions are developed for distance determination of stellar groups. This method depends on the assumption that absolute magnitudes and apparent magnitudes follow a Gaussian distribution function. Due to the limits of the integrands of the frequency function of apparent and absolute magnitudes, we introduce Case A, B, and C Gaussian distributions. The developed approaches have been implemented to determine distances to some clusters and stellar associations. The comparison with the distances derived by different authors reveals good agreement.