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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 103/123
1021
- Ann, Hong-Bae
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.209-221
- 1995
- 원문 바로보기
We have examined bulge morphology of 104 bright barred galaxies, using V-band surface photometry based on the Kiso Schmidt plates. By measuring the bulge ellipticity and bulge-disk misalignment, we have classified bulges into four morphological types: sphere, oblate spheroid, triaxial ellipsoid, and pseudo triaxial ellipsoid. About half of the observed galaxies are found to have triaxial bulges with mean ellipticity of 0.24. They are distributed uniformly along the Hubble sequence.
1022
- Lee, Sang-Gak
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.139-146
- 1995
- 원문 바로보기
The bright part of the halo luminosity function is derived from a sample of the 233 NLTT propermotion stars, which are selected by the 220 km/ see of cutoff velocity in transverse to rid the contamination by the disk stars and corrected for the stars omitted in the sample by the selection criterion. It is limited to the absolute magnitude range of <TEX>$M_v=4-8$</TEX>, but is based on the largest sample of halo stars up to now. This luminosity function provides a number density of <TEX>$2.3{\cdot}10^{-5}pc^{-3}$</TEX> and a mass density of <TEX>$2.3{\cdot}10^{-5}M_{o}pc^{-3}$</TEX> for 4 < <TEX>$M_v$</TEX> < 8 in the solar neighborhood. These are not sufficient for disk stability. The kinematics of the sample stars are < U > = - 7 km/sec, < V > = - 228 km/sec, and < W > = -8 km/sec with (<TEX>${\sigma_u},{\sigma_v},{\sigma_w}$</TEX>) = (192, 84, 94) km/sec. The average metallicity of them is [Fe/H] = <TEX>$- 1.7{\pm}0.8$</TEX>. These are typical values for halo stars which are selected by the high cutoff velocity. We reanalyze the luminosity function for a sample of 57 LHS proper-motion stars. The newly derived luminosity function is consistent with the one derived from the NLTT halo stars, but gives a somewhat smaller number density for the absolute magnitude range covered by the LF from NLTT stars. The luminosity function based on the LHS stars seems to have a dip in the magnitude range corresponding to the Wielen Dip, but it also seems to have some fluctuations due to a small number of sample stars.
1023
- Park, Seok-Jae
- Journal of the Korean astronomical society = 천문학회지
- 28, n.2
- pp.147-152
- 1995
- 원문 바로보기
An axisymmetric, stationary electrodynamic model of the central engine of an active galactic nucleus has been well formulated by Macdonald and Thorne. In this model the relativistic region around the central black hole must be filled by highly conducting plasma. We analyze plasma wave propagation in this region and discuss the results. We find that the ionosphere cannot exist right outside of the event horizon of the black hole. Another interesting aspect is that certain resonance phenomena can occur in this case.
1024
- 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.
1025
- 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.
1026
- 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.
1027
- 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.
1028
- 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>.
1029
- 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).
1030
- SEON KWANG IL
- Journal of the Korean astronomical society = 천문학회지
- 27, n.1
- pp.45-53
- 1994
- 원문 바로보기
We present the calculation of X -ray spectra produced through Compton scattering of soft X-rays by hot electrons in the spherical shell geometry, using fully relativistic Monte Carlo simulation. With this model, we show that the power-law component, which has been observed in the low luminosity state of low-mass X-ray binaries (LMXBs), is explained physically. From a spectral. analysis, we find that spectral hardness is mainly due to the relative contribution of scattered component. In addition, we see that Wi en spectral features appear when the plasma is optically thick, especially in the high energy range, <TEX>$E{\gtrsim}100keV$</TEX>. We suggest that after a number of scattering the escape probability approaches an asymptotic form depending on the geometry of the scattering medium rather than on the initial photon spectrum.