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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
- KIM YONG-HA
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.89-95
- 1995
- 원문 바로보기
We examined a total of 166 images of <TEX>$3.5{\mu}m\;H_3^+$</TEX> emission in the auroral regions of Jupiter observed with the Protocam on IRTF in 1991 and 1992, and found that 30 images contain a clearly isolated small emission patch in the vicinity of the northern auroral regions. Two different time sequences of the images show the small patches at the dusk limb in the range of System III longitudes from <TEX>$270^{\circ}\;through\;0^{\circ}\;to\;90^{circ}$</TEX>. The small patches in one sequence of the images, which were taken at 10 phase between <TEX>$240^{\circ}\;and\;260^{\circ}$</TEX>, may be related to the 10 flux tube, similarly suggested by Connerney et al. (1993). However, the small patches in the other sequence are separated from Io as much as <TEX>$80^{\circ}$</TEX> in longitude. The positions of the small patches in both sequences are deviated equatorward from the 10 footprint oval by <TEX>$5^{\circ}-8^{\circ}$</TEX> latitude in the longitudinal range of <TEX>$270^{\circ}-360^{\circ}$</TEX>. A significant modification is required in current Jovian magnetic field models near the Jupiter's surface if the small patches are produced at the foot of the 10 flux tube.
1009
- Lee, Myung-Gyoon
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.169-175
- 1995
- 원문 바로보기
Deep V I CCD photometry of the Pegasus dwarf irregular galaxy shows that the tip of the red giant branch (RGB) is located at I = <TEX>$21.15{\pm}0.10$</TEX> mag and (V - I) = <TEX>$1.58{\pm}0.03$</TEX>. Using the I magnitude of the tip of the RGB (TRGB), the distance modulus of the Pegasus galaxy is estimated to be <TEX>$(m\;-\;M)_o\;=\;25.13{\pm}0.11$</TEX> mag (corresponding to a distance of d = <TEX>$1060{\pm}50$</TEX> kpc). This result is in a good agreement with the recent distance estimate based on the TRGB method by Aparicio [1994, ApJ, 437, L27],<TEX>$ (m\;-\;M)_o$</TEX> = 24.9 (d = 950 kpc). However, our distance estimate is much smaller than that based on the Cepheid variable candidates by Hoessel et al.[1990, AJ, 100, 1151], <TEX>$(m\;-\;M)_o\;=\;26.22{\pm}0.20$</TEX> (d = <TEX>$1750{\pm}160$</TEX> kpc) mag. The color-magnitude diagram illustrates that the Cepheid candidates used by Hoessel et al.are not located in the Cepheid instability strip, but in the upper part of the giant branch. This result shows that the Cepheid candidates studied by Hoessel et al.are probably not Cepheids, but other types of variable stars. Taking the average of our distance estimate and Aparicio's, the distance to the Pegasus galaxy is d= <TEX>$1000{\pm}80$</TEX> kpc. Considering the distance and velocity of the Pegasus galaxy with respect to the center of the Local Group, we conclude that the Pegasus galaxy is probably a member of the Local Group.
1010
- KIM KWANG TAE
- Journal of the Korean astronomical society = 천문학회지
- 28, n.1
- pp.1-13
- 1995
- 원문 바로보기
A list of radio sources in the field of Abell 2256 is presented at 1420 MHz. Also presented is the source count based on the list. This source count is taken with the sources above <TEX>$7\sigma$</TEX> level at 1420 MHz. The overall characteristics of the count is consistent with that of a field where no galaxy cluster presents. The excess of radio sources due to the cluster is examined in the source count but it turned out to be unnoticiable as expected.