간행물
천문학회지 KCI 등재 SCOPUS Journal of The Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 반년간
- ISSN 1225-4614 (Print)2288-890X (Online)
- 수록기간 1968 ~ 2024
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
제28권 제1호 (1995년 4월) 10건
1.
1995.04
구독 인증기관 무료, 개인회원 유료
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 7σ 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.
4,500원
2.
1995.04
구독 인증기관 무료, 개인회원 유료
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 ~2h-1 Mpc from the cluster center that the Coma shows conspicuous inhomogeneities in velocity and that the inhomogeneities are real at a 99% 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 0.4×1015h-1M⊙ (R ≤ 0.6h-1 Mpc),and 1.0\times10×15h-1 M⊙ (R≤ 2.1h-1Mpc). The corresponding mass to blue light ratio on the average is ~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.
4,900원
3.
1995.04
구독 인증기관 무료, 개인회원 유료
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 (V-R) ≈ 0.2 mag ((V - I) ≈ 0.3 mag, (B - V) ≈ 0.7 mag) on April 4 to (V-R)≈ 0.6 mag ((V-1) ≈0.9 mag, (B-V) ≈ 1.3 mag) on April 18. Afterwards (V - R) colors get bluer slightly (by ~0.005 mag/day), while (V-I) colors stay almost constant around (V-1) ≈ 1.0 mag. The color at the maximum brightness is (B-V)=0.9 mag, which is ~1 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 (m-M)0 = 29.2 mag 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 ~2 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.
4,500원
4.
1995.04
구독 인증기관 무료, 개인회원 유료
In the best observed Pleiades cluster, the luminosity function(LF) and mass function(MF) for main sequence(MS) stars extended to Mv ≈ 15.5(V≈21) are very similar to the initial luminosity function(ILF) and initial mass function(IMF) for field stars in the solar neighborhood showing a bump at log m≃-0.05 and a dip at log m ≃ -0.12. This dip is equivalent to the Wielen dip appearing in the LF for the field stars. The occurence of these bump and dip is independent of adopted mass-luminosity relation(MLR) . and their characteristics could be explained by a time-dependent bimodal IMF. The model with this IMF gives a total cluster mass of ~700M⊙, ~25 brown dwarfs and ~3 white dwarfs if the upper mass limit of progenitor of white dwarf is greater than 4.5M⊙. The cluster age on the basis of LF for brightest stars is given by ~ 8×107yr and all stars in the cluster lie along the single age sequence in the C-M diagram without showing a large dispersion from the sequence.
4,800원
5.
1995.04
구독 인증기관 무료, 개인회원 유료
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 -1< ω < 0 (for the N-dimensional variants of the BD theory, -1.5≤ω). 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).
4,000원
6.
1995.04
구독 인증기관 무료, 개인회원 유료
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 (102)~O(103) times greater than previous estimation of Turner and Wilcek(TW).
3,000원
7.
1995.04
구독 인증기관 무료, 개인회원 유료
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.
4,000원
8.
1995.04
구독 인증기관 무료, 개인회원 유료
An attempt has been made to analyze time series of Hα, Hβ, and Hɤ 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 Hα, Hβ, and Hɤ 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 ~104km, suggesting that high energy particles penetrate deep into the photospheric level.
4,200원
9.
1995.04
구독 인증기관 무료, 개인회원 유료
We examined a total of 166 images of 3.5 μm H3+ 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 270° through 0° to 90°. The small patches in one sequence of the images, which were taken at 10 phase between 240° and 260°, 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 80° in longitude. The positions of the small patches in both sequences are deviated equatorward from the 10 footprint oval by 5° - 8° latitude in the longitudinal range of 270° - 360°. 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.
4,000원
10.
1995.04
구독 인증기관 무료, 개인회원 유료
The stability of the geometrically thin, two-temperature hot accretion disk is studied. The general criterion for thermal instability is derived from the linear local analyses, allowing for advective cooling and dynamics in the vertical direction. Specifically, classic unsaturated Comptonization disk is analysed in detail. We find five eigen-modes: (1) Heating mode grows in thermal time scale, (5/3)(αω)-1, where alpha is the viscosity parameter and w the Keplerian frequency. (2) Cooling mode decays in time scale, (2/5)(Te/Ti)(αω)-1, where Te and Ti are the electron and ion temperatures, respectively. (3) Lightman-Eardley viscous mode decays in time scale, (4/3)(Λ/H)2(αω)-1, where Λ is the wavelength of the perturbation and H the unperturbed disk height. (4) Two vertically oscillating modes oscillate in Keplerian time scale, (3/8)1/2ω-1 with growth rate ∝(H/Λ)2. The inclusion of dynamics in the vertical direction does not affect the thermal instability, adding only the oscillatory modes which gradually grow for short wavelength modes. Also, the advective cooling is not strong enough to suppress the growth of heating modes, at least for geometrically thin disk. Non-linear development of the perturbation is followed for simple unsaturated Compton disk: depending on the initial proton temperature perturbation, the disk can evolve to decoupled state with hot protons and cool electrons, or to one-temperature state with very cool protons and electrons.
4,200원
