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1968년 ~ 2024년까지 1,201 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 : 1,201건 (DB Construction : 1,201 Articles)
총 게시글 1,201건
페이지 35/121
341
- Isayev, Alexander A.
- Journal of the Korean astronomical society = 천문학회지
- 43, n.5
- pp.161-168
- 2010
- 원문 바로보기
Magnetars are neutron stars possessing a magnetic field of about <TEX>$10^{14}-10^{15}$</TEX> G at the surface. Thermodynamic properties of neutron star matter, approximated by pure neutron matter, are considered at finite temperature in strong magnetic fields up to <TEX>$10^{18}$</TEX> G which could be relevant for the inner regions of magnetars. In the model with the Skyrme effective interaction, it is shown that a thermodynamically stable branch of solutions for the spin polarization parameter corresponds to the case when the majority of neutron spins are oriented opposite to the direction of the magnetic field (i.e. negative spin polarization). Moreover, starting from some threshold density, the self-consistent equations have also two other branches of solutions, corresponding to positive spin polarization. The influence of finite temperatures on spin polarization remains moderate in the Skyrme model up to temperatures relevant for protoneutron stars. In particular, the scenario with the metastable state characterized by positive spin polarization, considered at zero temperature in Phys. Rev. C 80, 065801 (2009), is preserved at finite temperatures as well. It is shown that, above certain density, the entropy for various branches of spin polarization in neutron matter with the Skyrme interaction in a strong magnetic field shows the unusual behavior, being larger than that of the nonpolarized state. By providing the corresponding low-temperature analysis, we prove that this unexpected behavior should be related to the dependence of the entropy of a spin polarized state on the effective masses of neutrons with spin up and spin down, and to a certain constraint on them which is violated in the respective density range.
342
- 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.
343
- 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.
344
- 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.
345
- 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.
346
- 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.
347
- 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.
348
- 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.
349
- 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.
350
- 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.