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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
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1001
- LA DAILE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.61-65
- 1995
- 원문 바로보기
We discuss a model4-dimensional Friedmann cosmology which may have evolved from a model of 4+D dimensions which admits spontaneous compactification of D dimensions (or N-dimensional variants of the Brans-Dicke (BD) theory). The BD parameter appearing in dimensional reduction is negative <TEX>$-1<\omega<0$</TEX> (for the N-dimensional variants of the BD theory, <TEX>$-1.5{\leq}{\omega})$</TEX>. We find that if there had been inflationary transtion to the standard big-bang model, the Universe can undergoe a polar-type expansion during when the gravitational coupling becomes negative. The unique feature is that for the negative w, the density parameter of the post-inflationary Universe falls in a range 0<0<1 even if the Universe is geometrically flat (k = 0).
1002
- PARK SEOK JAE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.71-75
- 1995
- 원문 바로보기
In the previous work we made a long term evolution code for the central black hole in an active galactic nucleus under the assumption that the Blandford-Znajek process is the source of the emission. Using our code we get the evolution of the angular velocity of the precession for a supermassive black hole. We consider a hole at the center of an axisymmetric, ellipsoidal galactic nucleus. Our numerical results show that, only for the cases such that the stellar density or the mass of the black hole is large enough, the precession of the black hole - presumably the precession of the galactic jet - is interestingly large.
1003
- Jung, Jae-Hun
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.109-117
- 1995
- 원문 바로보기
The morphology and strength of the primordial magnetic field which is generated spontaneously in the early universe are studied for three models: (1) inflation (2) primordial magnetized bubble and (3) primordial turbulence models, We calculate the power spectra of magnetic field that are scale-free and proportional to <TEX>$k^{1.5},k^{3{\sim}4}$</TEX> and <TEX>$k^{2/3}$</TEX>, respectively. The configurations of magnetic field having these power spectra are visualized. To constrain the present strength of the primordial magnetic field we calculate the anisotropy of the microwave background radiation in Bianchi type I universe with globally homogeneous magnetic field. From the COBE limit of the quadrupole moment of <TEX>$({\delta}T/T)_{l=2}$</TEX> the present strength of horizen-scale magnetic fields <TEX>$B_p$</TEX> is constrained to be less than <TEX>$9{\times}10^{-8}G$</TEX>.
1004
- KIM KWANG TAE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.15-30
- 1995
- 원문 바로보기
A velocity inhomogeneity, which is defined as a regional preponderence of either radial or tangential orbits, is searched with a new technique for the Coma cluster of galaxies. It is found within <TEX>$\~2h^{-1}$</TEX> Mpc from the cluster center that the Coma shows conspicuous inhomogeneities in velocity and that the inhomogeneities are real at a <TEX>$99\%$</TEX> level of confidence. Even in the central region (7' - 30' from the center), zones that are dominated by radial and tangential orbits are distinguishable. Defining the cluster's 'equator' as the direction defined by the Coma-A1367 supercluster, tangential orbits dominate the 'polar' zones in the central region. Galaxies that are located in 30'-100' also inhomogeneous in velocity in that the 'polar' zones are mostly radial while the rest is nearly homogeneous. These results indicate that the Coma galaxies are exceedingly more radial in orbit, implying that merging or infalls are either still going on or an earlier virialization is likely to have occurred preferentially near the 'equator'. Incorporating the velocity inhomogeneity into mass estimators, the most appropriate mass is turned out to be <TEX>$0.4\times10^{15}h^{-1}M_\bigodot(R\;\leq\;0.6h^{-1} Mpc),\;and\;1.0\times10^{15}h^{-1} M_\bigodot(R\;\leq\;2.1h^{-1}Mpc)$</TEX>. The corresponding mass to blue light ratio on the average is <TEX>$\~$</TEX>300h. These estimates are consistent with Merritt (1987) and Hughes (1989) and the MILE is seemed to favour the mass-follows-light models than the uniform spread of dark matter throughout the cluster.
1005
- LEE MYUNG GYOON
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.31-43
- 1995
- 원문 바로보기
We present UBVRI CCD photometry of the Type Ie supernova SN 19941 in M51 which was discovered on April 2, 1994 (UT). UBVRI CCD photometry of SN 1994 I were obtained for the period of the first two months from April 4, 1994, using the Seoul National University Observatory 60 cm telescope. The light curves of SN 19941 show several interesting features: (a) SN 19941 reaches the maximum brightness at B-band on April 8.23 (B = 13.68 mag), at V-band on April 9.10 (V = 12.89 mag), and at I-band on April 10.32 (I = 12.48 mag); (b) The light curves around the maximum brightness are much narrower than those of other types of supernovae; (c) The light curves after the peak decline more steeply than those of other types of supernovae; and (d) The colors get redder from <TEX>$(V-R){\approx}0.2 mag ((V - I){\approx} 0.3 mag, (B - V){\approx}0.7 mag)$</TEX> on April 4 to <TEX>$(V-R){\approx}0.6 mag ((V-1){\approx}0.9 mag, (B-V){\approx}1.3 mag)$</TEX> on April 18. Afterwards (V - R) colors get bluer slightly <TEX>$(by\~0.005 mag/day)$</TEX>, while (V-I) colors stay almost constant around <TEX>$(V-1){\approx}1.0 mag$</TEX>. The color at the maximum brightness is (B-V)=0.9 mag, which is <TEX>$\~1$</TEX>mag redder than the mean color of typical Type la supernovae at the maximum brightness. The light curves of SN 1994I are similar to those of the Type Ie supernova SN 1962L in NGC 1073. Adopting the distance modulus of <TEX>$(m-M)_0 = 29.2 mag$</TEX> and the reddening of E(B - V) = 0.45 mag [Iwamoto et al. 1994, preprint for ApJ], we derive absolute magnitudes at the maximum brightness of SN 1994I, Mv(max) = -17.7 mag and MB(max) = -17.4 mag. This result shows that SN 1994I was <TEX>$\~2$</TEX>mag fainter at the maximum brightness compared with typical Type Ia supernovae. A narrower peak and faster decline after the maximum in the light curve of SN 1994I compared with other types of supernovae indicate that the progenitor of SN 1994I might be a lower mass star compared with those of other types of supernovae.
1006
- Kim, Seung-Lee
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.197-208
- 1995
- 원문 바로보기
Real time CCD differential photometry was performed for BT Cnc in Praesepe cluster from February to March, 1994. New 885 differential V magnitudes were obtained for thirteen nights. From the frequency analysis, we have detected two distinct pulsational frequencies of <TEX>$f_1$</TEX>=9.7783c/d and <TEX>$f_2$</TEX>=7.0153c/d. The first frequency is nearly equal to the previous result(Breger 1980), but the second one is much different. Our reanalysis of the previous data obtained by Guerrero el al.(1979) indicates that the previous result of <TEX>$f_s$</TEX>=5.95c/d might be uncertain; it was not detected in the power spectrum. Also it turns out that our second frequency could not be fitted to the previous data and the reanalyzed frequency(<TEX>$f_2$</TEX>=7.8813c/d) of the previous data was poor-fitted to our data. Therefore we suggest that the second frequency which might be newly excited in the nonradial mode, has been changed over the last eighteen years.
1007
- Yoon, Tae-Sam
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.245-253
- 1995
- 원문 바로보기
We have analyzed the time series of Ca II H,K and <TEX>${\lambda}8498$</TEX> line profiles taken for a sunspot (SPO 5007) with the Echelle spectrograph attached to Vacuum Tower Telescope at Sacramento Peak Solar Observatory. Each set of spectra was taken simultaneously for 20 minutes at a time interval of 30 seconds. A total of 40 photographic films for each line was scanned by a PDS at Korea Astronomy Observatory. The central peak intensity of Ca II H (<TEX>$I_{max}$</TEX>), the intensity measured at <TEX>${\Delta}{\lambda}=-0.1{\AA}$</TEX> from the line center of <TEX>${\lambda}8498(I_{{\lambda}8489})$</TEX>, the radial velocity (<TEX>$V_r$</TEX>) and the Doppler width (<TEX>${\Delta}{\lambda}_D$</TEX>) estimated from Ca II H have been measured to study the dynamical behaviors of the sunspot chromosphere. Fourier analysis has been carried out for these measured quantities. Our main results are as follows: (1) We have confirmed the 3-minute oscillation being dominant throughout the umbra. The period of oscillations jumps from 180 sec in the umbra to 500 to 1000 sec in the penumbra. (2) The nonlinear character of the umbral oscillation is noted from the observed sawtooth shaped radial velocity fluctuations with amplitudes reaching up to <TEX>$5{\sim}6\;km/sec$</TEX>. (3) The spatial distribution of the maximum powers shows that the power of oscillations is stronger in the umbra than in the penumbra. (4) The spatial distributions of the time averaged < <TEX>$I_{max}$</TEX> > and < <TEX>$V_r$</TEX> > across the spot are found to be nearly axially symmetric, implying that the physical quantities derived from the line profiles of Ca II H and <TEX>${\lambda}8498$</TEX> are inherently associated with the geometry of the magnetic field distribution of the spot. (5) The central peaks of the CaII H emission core lead the upward motions of the umbral atmosphere by <TEX>$90^{\circ}$</TEX>, while no phase delay is found in intensities between <TEX>$I_{max}$</TEX> and <TEX>$I_{{\lambda}8498}$</TEX>, suggesting that the umbral oscillation is of standing waves.
1008
- LA DAILE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.67-70
- 1995
- 원문 바로보기
In contrast to conventional belief that extended inflation ends when the Universe percolates, we find inflation may continue at least many Hubble times even after the Universe percolates. What is observed is that inflation will not stop unless the global equation of state changes from inflationary one into radiation one. Thus the energy density of shorter wavelength gravitational waves induced by bubble collision at near the end of inflation should be at least Order <TEX>$(10^2)\~O(10^3)$</TEX> times greater than previous estimation of Turner and Wilcek(TW).
1009
- LEE SANG-WOO
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.77-87
- 1995
- 원문 바로보기
An attempt has been made to analyze time series of <TEX>$H_\alpha,\;H_\beta,\;and\; H_\gamma$</TEX> line profiles taken from a 3B/X6.1 flare which occurred on Oct. 27, 1991 in an active region, NOAA 6891. A total of 22 sets of <TEX>$H_\alpha,\;H_\beta,\;and\; H_\gamma$</TEX> taken with a low and non-uniform time resolution of 10-40 seconds were scanned by PDS with absolute intensity calibration to derive the physical characteristics of the material in the flare chromosphere. Our . results are as follows: (1) The lower Balmer lines observed during the flare activity are broadened by Stark effect. (2) At the peak of the flare activity, the electron temperature of the Balmer line emitting region reaches up to 35000K and its geometrical thickness increases to a scale of <TEX>$10^4km$</TEX>, suggesting that high energy particles penetrate deep into the photospheric level.
1010
- Ryu, Dong-Su
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.223-243
- 1995
- 원문 바로보기
We describe the implementation of a multi-dimensional numerical code to solve the equations for idea! magnetohydrodynamics (MHD) in cylindrical geometry. It is based on an explicit finite difference scheme on an Eulerian grid, called the Total Variation Diminishing (TVD) scheme, which is a second-order-accurate extension of the Roe-type upwind scheme. Multiple spatial dimensions are treated through a Strang-type operator splitting. Curvature and source terms are included in a way to insure the formal accuracy of the code to be second order. The constraint of a divergence-free magnetic field is enforced exactly by adding a correction, which involves solving a Poisson equation. The Fourier Analysis and Cyclic Reduction (FACR) method is employed to solve it. Results from a set of tests show that the code handles flows in cylindrical geometry successfully and resolves strong shocks within two to four computational cells. The advantages and limitations of the code are discussed.