간행물
천문학논총 KCI 등재 Publications of the Korean Astronomical Society
- 발행기관 한국천문학회
- 자료유형 학술지
- 간기 연3회
- ISSN 1225-1534 (Print)2287-6936 (Online)
- 수록기간 1984 ~ 2023
- 주제분류 자연과학 > 천문학 자연과학 분류의 다른 간행물
- 십진분류KDC 440DDC 520
권호리스트/논문검색
Volume 7 (1992년 12월) 21건
1.
1992.12
구독 인증기관 무료, 개인회원 유료
We may consider the following three fundamental epistemological questions concerning cosmology. Can cosmology at last understand the origin of the universe? Can computers at last create? Can life be formed at last synthetically? These questions are in some sense related to the liar paradox containing the self-reference and, therefore. may not be answered by recursive processes in finite time. There are, however. various implications such that the chaos may break the trap of the self-reference paradox. In other words, Goedel's incompleteness theorem would not apply to chaos, even if the chaos can be generated by recursive processes. Internal relations among cosmology, epistemology and chaos must be investigated in greater detail.
4,000원
2.
1992.12
구독 인증기관 무료, 개인회원 유료
The power spectrum of the galaxy distribution is accurately measured up to wavelengths over 100h−1 100h−1 Mpc from the CfA 1 and 2 catalogs. We find that our results agree with power spectra calculated by others from smaller samples of optical, radio and infrared galaxies. The power spectrum of an open CDM model (Ωh Ωh = 0.2 and δ8 δ8 = 1; see below for definitions) best approximates the observed power spectrum. The power spectrum of the standard COM model (Ωh Ωh = 0.5 and δ8 δ8 = 1) is inconsistent with the observed one at the 99% confidence level. Our best estimation of the corresponding correlation function in real space is ξ(r)=(r/6.2h−1Mpc)−1.8 ξ(r)=(r/6.2h−1Mpc)−1.8 for r < 20h−1 20h−1 Mpc.
4,000원
3.
1992.12
구독 인증기관 무료, 개인회원 유료
We investigated the "tilting" of the Universe, i.e., a non-Doppler origin of the dipole moment of the cosmic background radiation (CBR). Superhorizon-sized isocurvature, rotational and true vacuum bubble perturbations are considered. We show that the more natural way of the "tilting" the Universe is via the true vacuum bubble perturbation. Nevertheless, due to the small filling fraction of the bubbles of viable extended inflationary models, we find that the probability of the real occurrence in the Universe is quite insignificant.
4,000원
4.
1992.12
구독 인증기관 무료, 개인회원 유료
Recent redshift surveys suggest that most galaxies may be distributed on the surfaces of bubbles surrounding large voids. To investigate the quantitative consistency of this qualitative picture of large-scale structure, we study analytically the clustering properties of galaxies in a universe filled with spherical shells. In this paper, we report the results of the calculations for the spatial and angular two-point correlation functions of galaxies. With ∼20 ∼20 of galaxies in clusters and a power law distribution of shell sizes, nsh(R)∼R−α nsh(R)∼R−α , α≃4 α≃4 , the observed slope and amplitude of the spatial two-point correlation function ξgg(r) ξgg(r) can be reproduced. (It has been shown that the same model parameters reproduce the enhanced cluster two-point correlation function, ξcc(r) ξcc(r) ). The corresponding angular two-point correlation function w(θ) w(θ) is calculated using the relativistic form of Limber's equation and the Schecter-type luminosity function. The calculated w(θ θ ) agrees with the observed one quite well on small separations (θ≲2deg θ≲2deg ).
4,000원
5.
1992.12
구독 인증기관 무료, 개인회원 유료
Dark matter in various size of scales is reviewed briefly. The evidence of dark matter in dwarf spheroidal galaxies is still uncertain. However there is no doubt about the existence of dark matter in larger scales. Many proposed candidates for dark matter are still speculative. Several possibilities of direct detection of dark matter are proposed.
4,000원
6.
1992.12
구독 인증기관 무료, 개인회원 유료
A velocity inhomogeneity, which is the regional preponderence of either radial or tangential orbits, is searched with the new technique proposed by Kim (1992) for Coma, Hydra I, and Abell 2256 cluster of galaxies. Conspicuous inhomogeneities are found in the Coma and A2256 which X-ray isophotes are indicative for their underlying potentials being ellipitcal in shape, Even in their central regions, zones that are dominated by radial orbits are clearly distinguishable from that of the tangential orbits, and defining the cluster 'equator' as the direction of maximum elongation of the X-ray isophotes, radial orbits dominate along this direction whereas tangential orbits dominate the 'polar' zones. Merger events that are evidenced in X-ray observations occur in the equatorial zones of Coma and A2256, suggesting preponderence of radial orbits in the zones, which is in good agreement with their velocity structures. On the other hand, the inhomogeneity in Hydra I turns out to be insignificant in the central regions and this is just what is expected from a cluster whose X-ray isophotes is nearly circular. The velocity distribution in regions further out, however, shows significant inhomogeneity and this seems to support the previous results that this cluster is likely to have substructures and velocity anisotropy.
4,300원
7.
1992.12
구독 인증기관 무료, 개인회원 유료
The nonlinear stochastic behavior of chaotic inflation is characterized by the 'scaling' effect. Using a simple criterion for the appearance of scaling behavior in the λϕ4 λϕ4 inflation model, we show explicitly that in this limit the onset of the scaling regime does not require any special initial conditions and that it is independent of the self-coupling constant λ λ . Non-Gaussian statistics in adiabatic fluctuations are important only for super-horizon scales and the scaling regime does not lead to any significant statistical properties on currently observable scales. However, the scaling effect gives some cosmological consequences very different from what we expect in the naive diffusion approximation for quantum fluctuations. The classical (deterministic) treatment of the inflation field (essentially a quantum mechanical object.) becomes valid towards the end of inflation.
4,200원
8.
1992.12
구독 인증기관 무료, 개인회원 유료
We have systematically investigated the X-ray spectra of normal galaxies, by using the Imaging Proportional Counter (IPC) data in the Einstein data base. We employed the X-ray color-color plot as well as the standard model fitting method which requires higher signal to noise ratio. We discuss X-ray emission mechanisms in terms of their spectral properties and the signature of cooling flows which are most likely present in X-ray bright early type galaxies. On the average, fits to absorbed thermal spectra show that the X-ray emission temperature of spirals is higher than that of ellipticals. This is consistent with our understanding that accreting binaries are a major X-ray source in spirals, while extended gaseous halos are present in ellipticals. The emission temperature becomes lower with increasing X-ray to optical luminosity ratio in E and S0 galaxies. This result is what we would expect if the emission of X-ray faint early type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. We also find a cool, self-absorbed core in some early type galaxies, which directly indicates the presence of cooling flows in such galaxies.
4,000원
9.
1992.12
구독 인증기관 무료, 개인회원 유료
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 and the equations of magnetohydrodynamics are then satisfied. In this paper we analyze magnetohydrodynamic wave propagation in this region. We find that there are three distinct types of waves - the Alfven wave and two magnetosonic waves. The wave equations turn out to be not very different from those in nonrelativistic case except they are redshifted.
4,000원
10.
1992.12
구독 인증기관 무료, 개인회원 유료
New and improved data on the gravitational lens systems discovered so far are compared with the theoretical predictions of Gott, Park, and Lee (1989, GPL). Systems lensed by a single galaxy, compatible with assumptions of GPL, support flat or near-flat geometry for the universe. But the statistical uncertainty is too large to draw any definite conclusion. We need more lens systems. Also, the probability of multiple image lensing and mean separation of the images averaged over the source distribution are calculated for various cosmological models. Multiple-image lens systems and radio ring systems are compared with the predictions. Although the data reject exotic cosmological models, it cannot discriminate among conventional Friedmann models yet.
4,000원
11.
1992.12
구독 인증기관 무료, 개인회원 유료
Recent spectroscopic observations indicate concentration of dark masses in the nuclei of nearby galaxies. This has been usually interpreted as the presence of massive black holes in these nuclei. Alternative explanations such as the dark cluster composed of low mass stars (brown dwarfs) or dark stellar remnants are possible provided that these systems can be stably maintained for the age of galaxies. For the case of low mass star cluster, mass of individual stars can grow to that of conventional stars in collision time scale. The requirement of collision time scale being shorter than the Hubble time gives the minimum cluster size. For typical conditions of M31 or M32, the half-mass radii of dark clusters can be as small as 0.1 arcsecond. For the case of clusters composed of stellar remnants, core-collapse and post-collapse expansion are required to take place in longer than Hubble time. Simple estimates reveal that the size of these clusters also can be small enough that no contradiction with observational data exists for the clusters made of white dwarfs or neutron stars. We then considered the possible outcomes of interactions between the black hole and the surrounding stellar system. Under typical conditions of M31 or M32, tidal disruption will occur every 103 103 to 104 104 years. We present a simple scenario for the evolution of stellar debris based on basic principles. While the accretion of stellar material could produce large amount of radiation so that the mass-to-light ratio can become too small compared to observational values it is too early to rule out the black hole model because the black hole can consume most of the stellar debris in time scale much shorter than mean time between two successive tidal disruptions. Finally we outline recent effort to simulate the process of tidal disruption and subsequent evolution of the stellar debris numerically using Smoothed Particle Hydrodynamics technique.
4,000원
12.
1992.12
구독 인증기관 무료, 개인회원 유료
The most favourable possibilities to observe the phenomena of gravitational lensing are the high amplification events and the time delay between the images. These effects provide us the information to determine the Hubble parameter and the matter distribution in the universe. The image properties due to micro-lensing also is of an importance to find out the size and the structure of the source.
4,000원
13.
1992.12
구독 인증기관 무료, 개인회원 유료
This paper presents a cosmological perturbation analysis in a Newtonian framework, using the Newtonian multi component version of the relativistic covariant equations. This work considers the fully nonlinear evolution of the perturbations, and is generalized to multicomponent systems and imperfect fluids. Known nonlinear solutions are presented in a general framework. Quasi-nonlinear analysis, considering both the compressible and rotational modes, is presented, including cases already known in the literature. The Fourier space representation of the conservation equations is also derived in a general context, with various decompositions of the velocity field. Commonly accepted cosmogonical frameworks are critically examined in the context of nonlinear evolution. This work may be regarded as the Newtonian counterpart of a recently presented general relativistic covariant formulation.
9,300원
14.
1992.12
구독 인증기관 무료, 개인회원 유료
We determined the efficiencies of the aperture. beam and forward spillover and scattering of 13.7 m radio telescope at Daeduk Radio Astronomy Observatory through the observations of the planets and Moon. The main panels adjustments were carried out on September 1991 and the improvements in the efficiencies were checked by comparing the observations made before and after the panel adjustments. The efficiencies were turned out to be 0.35, 0,47 and 0.83 at 115.27 GHz for the aperture, beam and forward scattering and spillover. respectively. These marked nearly a factor of two upgrade of the efficiencies previously measured.
4,000원
15.
1992.12
구독 인증기관 무료, 개인회원 유료
We observed a total of 14 Mira variables as well as 4 late type variable stars for their SiO ν=1 ν=1 , J = 2 - 1 maser lines from April 1989 to November 1990 with the 13.7 m radio telescope at Daeduk Radio Astronomy Observatory. The maser intensity variations were the prime objective of the observations which well covered the periods of the variations. The origion of the variations were studied by comparing wi th those previousely measured in optical and infrared(IR) wavelengths and we confirmed that the intensity variations were in good correlation with those in V magnitude and IR intensity as previousely found in former investigators in general. However, for a few sources, we could find the missing maxima. The intensities themselves also were in good correlation with SiO ν=1 ν=1 , J = 1 - 0 maser intensities observed in Yebes as expected. The good correlations indicate that the pumping source of the SiO maser is likely to be the IR emission in the masing regions and the "missing maxima" that are apparent in two particular sources are considered to relate wi th the strength of shocks arising from the eruptive mass-loss from central stars.
4,300원
16.
1992.12
구독 인증기관 무료, 개인회원 유료
서울대 천문학과(SNU)의 Washington 측광계를 사용하여 관측한 자료와 ADC (Astronomical Data Center)의 자료를 분석함으로써 SNU Washington 측광계를 표준화 시켰다. SNU Washington 측광계중에서 C필터에 나타나는 적색광 누출은 V필터와의 결합을 통해 보정했으며, 그 최대값은 K0형에서 약 0m.14 0m.14 까지 이른다. ADC의 자료분석 결과 G. K형 별들에 대해 중원소 측광지수와 중원소함량과 서로 잘 일치함을 알 수 있었고. 주계열성의 경우 온도 측광지수와 온도와는 좋은 관계를 보임을 알 수 있었다. 또한 (M−T2 M−T2 )과 (M−T1 M−T1 ) 평면상에서는 중원소함량과 광도계급에 무관한 좋은 온도관계를 나타냄을 알았다. 그리고 이 측광계의 장점으로 나타난 CN지수와 CN 특이성과는 특별한 관계를 찾기가 어려웠고, 이 측광계만으로는 상도계급의 구분을 다른 측광계 만큼 분명하게 결정짓기가 어려웠다. 그러나 표면중력과이 측광계의 색지수와의 관계를 본 결과 초거성, 거성, 주계열성을 비교적 잘 구분해 낼 수 있었다.
5,800원
17.
1992.12
구독 인증기관 무료, 개인회원 유료
Paper I (김강민외. 1991) 에서 만든 초증감처리 장치를 보완하여 실용적으로 천체관측에 이용할 수 있도록 초증감처리 장치를 완성하였다. 초증감처리 장치의 주된 보완 내용으로는 진공처리조의 오븐 기능의 보완, 굽기통 (baking box) 사용, 농도쐐기마스크의 교체 및 현상의 균질도를 높이기 위한 자동현상기의 준비등이다. 8 % 수소 혼합가스를 채운 굽기처리에 의한 시험적인 초증감처리 결과, 일정한 초증감처리 시간에 대해 굽기온도를 높게 할수록 감도증가량은 커졌으며, IIIa-J 의 경우 4.8∼15.3 4.8∼15.3 배, 103a-0 의 경우 1.5∼2.1 1.5∼2.1 배의 감도증가를 보였다. 이 때의 안개농도는 0.1 이하의 낮은 값을 보였다.
5,100원
18.
1992.12
구독 인증기관 무료, 개인회원 유료
우리 은하계내 field RR Lyrae 변광성의 관측자료(GCVS 4th ed. )의 특성과 이들의 공간분포 및 증원소함량 분포를 조사하였다 이들의 공간분포에서 scale height 가 H = 0.6 kpc 인 원반(thick)형과 H = 2.2 kpc 인 헬로형의 두 성분으로 나타난다. 그리고 증원소함량의 은하중심거리와 은하정면거리에 따른 변화율은 각각 d[Fe/H]/dr = −0.013∼−0.020/kpc −0.013∼−0.020/kpc (r≤20kpc r≤20kpc ), d[Fe/H]/d|Z| = -0.034 /kpc (|Z|≤10kpc |Z|≤10kpc ) 이다. 이러한 공간분포와 증원소함량의 기울기 변화는 구상성단의 경우와 비슷하게 이증진화모형을 나타낸다. 그러나 증원소함랑의 빈도분포로 보아 field RR Lyrae 변광성이 모두 구상성단에서 기원되었다고 보기는 어렵다.
6,000원
19.
1992.12
구독 인증기관 무료, 개인회원 유료
A model for the distribution of stars in the disk and the spheroid of our Galaxy is reexamined from an edge-on view of the Galaxy obtained by selecting infrared sources from the IRAS Point Source Catalog. The sources are counted as a function of galactic latitude. longitude and 12μm 12μm apparent magnitude. The source counts are reasonably separated into the disk component and the spheroid component contributions and each of the contributions is further interpreted as a convolution of a spatial density distribution and a luminosity function based on the least-square fit method. The spatial density of the disk component has an exponential radial scale length of hR∼2.6kpc hR∼2.6kpc and the vertical distribution follows a canonical sech2 sech2 law with a scale height hz∼240pc hz∼240pc . The distribution of the spheroid component can be represented by an oblate spheriod with an axis ratio k∼0.61 k∼0.61 and a de Vaucouleurs' r1/4 r1/4 law with an effective radius of Re∼120pc Re∼120pc . The steep density gradient of the spheroid component is consistent with that of late M giants in the central bulge. The luminosity functions of the disk and the spheroid component stars resemble respectively those of the K luminosity function of disk M giants (Garwood and Jones 1986) and the bolometric luminosity function of M giants in bulge fields (Frogel et al, 1990).
6,000원
20.
1992.12
구독 인증기관 무료, 개인회원 유료
1992년 1년 동안 월 평균 14.3일간 흑점을 관측하여 총 172일간 관측하였으며 매일 평균 6.1개의 흑점군과 45.8개의 흑점이 관측되어 년 평균 흑점 상대수 97.9를 얻었다. 이 기간동안 297개의 흑점군이 출현하여 1041개의 흑점군이 관측되었으며 태양 북반구보다 남반구에 약 55%이상의 흑점이 더 많이 나타나 1990년, 1991년에 이어 점점 더 남반구의 태양 활동이 북반구보다 더욱더 활성적이었음을 보여준다.
4,000원
1
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