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
제29권 제S호 (1996년 12월) 178건
41.
1996.12
구독 인증기관·개인회원 무료
In this paper, we present observations of absorption line spectrum of QSO 1225+317 with resolution of 18 km sec-1. Four possible new heavy element line systems are identified. The properties of Lyman α forest lines are discussed.
42.
1996.12
구독 인증기관·개인회원 무료
VRI bands CCD photometric observations of the BL Lac object OJ 287 have been carried out during the period from October, 1994 to May, 1996. OJ 287 underwent two major outbursts during our observations. The first peak (V14.0 mag.) occurred in the first half of November, 1994 and faded out to 16.5 mag within 150 days. The second peak (14.0 mag.) was observed in late December, 1995. The latter peak continued at nearly the same brightness until May, 1996. Such a long lasting outburst has never been reported for OJ 287. Color indices (V - R and V-I) remained nearly constant during the outbursts.
43.
1996.12
구독 인증기관·개인회원 무료
44.
1996.12
구독 인증기관 무료, 개인회원 유료
J. E. HESSER, P. B. STETSON, W. E. HARRISM, M. BOLTE, T. A. SMECKER-HANE, D. A. VANDENBERG, R. A. BELL, H. E. BOND, S. VAN DEN BERGH, R. D. MCCLURE, G. G. FAHLMAN, H. B. RICHER
We review observational evidence bearing on the formation of a prototypical large spiral galaxy, the Milky Way. New ground- and space-based studies of globular star clusters and dwarf spheroidal galaxies provide a wealth of information to constrain theories of galaxy formation. It appears likely that the Milky Way formed by an combination of rapid, dissipative collapse and mergers, but the relative contributions of these two mechanisms remain controversial. New evidence, however, indicates that initial star and star cluster formation occurred simultaneously over a volume that presently extends to twice the distance of the Magellanic Clouds.
4,000원
45.
1996.12
구독 인증기관 무료, 개인회원 유료
The case for a massive black hole in the center of the Galaxy is reassessed using improved modeling techniques and observational data. A dark mass of ~2 ×10 6 M⊙ is present within 0.2 pc of the Galactic center. However, the available data can be modeled, without appealing to a massive black hole, using an extended distribution of dark stellar remnants (neutron stars and stellar mass black holes) provided that the stellar initial mass function in the central parsec is deficient in stars less massive than ~1 M⊙. Such a situation may be a natural consequence of repeated gas build-up followed by starbursts in the central region. A clear distinction between this and the massive central black hole model cannot be made using red giant tracers outside 0.2 pc due to uncertainties in the radial velocity dispersion distribution. The cluster of massive early-type emission-line stars in the central parcsec more effectively probe the mass distribution close to Sgr A *, but their small number and partial rotational support complicate mass determinations. Proper motion determinations for stars within 0.5' of Sgr A * may be the most effective means of unambiguously determining the mass distribution in the immediate vicinity of the Galactic center.
3,000원
46.
1996.12
구독 인증기관·개인회원 무료
Snapshots of eight SA and standard fields from low to high galactic latitudes were made using the KPNO 0.9m 2K × 2K CCD with a limiting magnitude from 19 to 22.5. The purpose of this study is to determine the vertical distribution of stars with respect to Galactic latitude and z-distance in comparison with the model simulation between intermediate population to the 'thick disk' component of scale height of a few kpc. Comparison of the preliminary results between observed and model simulation for 3 of the S fields shows good agreement both in V-mag and B- V color distributions. A bimodal distribution in B- V at high galactic latitude seems to be represented by a halo and 'thick disk' dwarf in the blue and by a normal disk dwarf population in the red.
47.
1996.12
구독 인증기관·개인회원 무료
Beijing-Arizona-Taipei-Connecticut (BATC) survey is a long term project to map the spectral energy distribution of various objects using 15 intermediate band filters and aims to cover about 450 sq degrees of northern sky. The SED information, combined with image structure information, is used to classify objects into several stellar and galaxy categories as well as QSO candidates. In this paper, we present a preliminary setup of robust data reduction procedure recently developed at NCU and also briefly discuss general classification scheme: redshift estimate, and automatic detection of variable objects.
48.
1996.12
구독 인증기관·개인회원 무료
The solar neighbourhood is the starting point for studies of the structure and evolution of the Galactic disk. Yet, our knowledge of the relative frequencies, distances, ages, chemical abundances, velocities, and birthplaces of the nearby stars is severely incomplete. We have determined complete, homogeneous, and precise such data for a kinematically unbiased sample of ~12,000 local F and G dwarf stars and describe a first, significant result from it.
49.
1996.12
구독 인증기관 무료, 개인회원 유료
The results on the deep low dispersion (1250 Å/mm at Hɤ, 30° < I < 165°, 195° < I < 210°, |b| < 5°; 7000Å/mm at A band, 50° < I < 115°, b=0°, b=±3.5°) spectral surveys of the MILKY WAY are presented. More than 2250 carbon stars were identified among them 1440 new ones. The C/M5+ ratio increases from 0.02 to 0.3 when longitude varies from 30° to 210°. On the basis of A GENERAL CATALOG OF GALACTIC COOL CARBON STARS the surface distribution of carbon stars has been studied.
3,000원
50.
1996.12
구독 인증기관·개인회원 무료
We present the systematic variations of Hβ index of simple stellar populations due to horizontal-branch (HB) stars. Most of the previous works have been done without careful considerations of HB stars. Since the Balmer line strengths are very sensitive to the temperature, including the HB stars are quite important. We found that the strength of H,6 index is strongly affected by HB stars, and hence the age estimation without careful consideration of the variation of HB morphology with metallicity and age would underestimate the ages of ellipticals.
51.
1996.12
구독 인증기관·개인회원 무료
We present a new photometric study of the globular cluster NGC288 in Stromgren u, v, b, y, and Hβ system. This cluster is known to have an intermediate metallicity but its color-magnitude diagram has a pure blue horizontal branch, which is a signature of metal poor stellar population. We compare our dataset with Bergbusch's (1993) in both field size and CMD to see whether different photometry system would determine the same physical parameters of a cluster. Demarque and Yi's isochrones (1996, private communication) were applied to Bergbusch's dataset, and we obtained distance modulus of (m - M) = 14.9 ± 0.2, color excess of E(B - V) = 0.03, and age of 1.5±3 Gyr. Vandenberg's (1985) isochrones for Stromgren system were also applied to Bergbusch's and our data. We find that the isochrone fits to different photometric systems give rather in consist ant solutions. The source of this discrepancy may become clear when the Demarque and Yi's isochrones for Johnson system are converted to those of Stromgren system. We note that Kurucz model atmospheres provide a useful ground for this conversion work as well as theoretical study of Stromgren characteristics of globular cluster stars.
52.
1996.12
구독 인증기관·개인회원 무료
The first large-format CCD color-magnitude diagram (CMD) in the B and V passbands is presented for the Galactic globular cluster M53 (NGC 5024). We have discovered 117 new blue straggler (BS) candidates in the field of M53. The analysis of bright BS stars (V <19.0) clearly shows a bimodal radial distribution, with a high frequency in the inner and outer regions. The distribution is similar to that found in M3, a globular cluster with similar central density and concentration.
53.
1996.12
구독 인증기관·개인회원 무료
54.
1996.12
구독 인증기관·개인회원 무료
55.
1996.12
구독 인증기관·개인회원 무료
Two-component models (normal star and degenerate star components) are the simplest realization of clusters with a mass spectrum because the high mass stars quickly evolve off leaving degenerate stars behind, while low mass stars survive for a long time as main-sequence stars. In the present study we examine the post-collapse evolution of globular clusters using two-component Fokker-Planck models that include three-body binary heating. We confirm that a simple parameter є ≡ (Etot/trh)/(Ec/trc) well describes the occurrence of gravothermal oscillations of two-component clusters. Also, we find that the degree of instability depends on the steepness of the mass function such that clusters with a steeper mass function are less exposed to instability.
56.
1996.12
구독 인증기관·개인회원 무료
We have estimated a metal abundance of [Fe/H]= -0.04 ± 0.05 dex, a reddening of E(B- V)= 0.28 mag, an age of 1.1 ± 0.1 Gyr, and a distance of 2.5 ± 0.2 kpc for NGC 1245 using the Washington filter system.
57.
1996.12
구독 인증기관·개인회원 무료
We have estimated a metal abundance of [Fe/H]= -0.48 ± 0.14 dex, a reddening of E(B- V)= 0.30 mag, an age of 2.0 ± 0.4 Gyr, and a distance of 7.9 ± 0.8 kpc for Tombaugh 2 using the Washington filter system.
58.
1996.12
구독 인증기관·개인회원 무료
The results of observations of a dozen OB stellar associations made with the ultraviolet space telescope Glazar is presented.
59.
1996.12
구독 인증기관 무료, 개인회원 유료
We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform (Bu), random (Br), and total (Bt) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of Bt is 4.2 μG and we adopt Bu ~2.2 and Br ~3.6 μG. Bt is higher in spiral arms, reaching ~5.9 μG. Bt is higher for smaller RGal, reaching ~8.0 μG for RGal = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.
3,000원
60.
1996.12
구독 인증기관 무료, 개인회원 유료
Magnetic fields correlated on several kiloparsec scales are seen in spiral galaxies. Their origin could be due to the winding up of a primordial cosmological field or due to amplification of a small seed field by a turbulent galactic dynamo. Both options have difficulties: There is no known battery mechanism for producing the required primordial field. Equally the turbulent dynamo may self destruct before being able to produce the large scale field, due to excess generation of small scale power. The current status of these difficulties is discussed. The resolution could depend on the nature of the saturated field produced by the small scale dynamo. We argue that the small scale fields do not fill most of the volume of the fluid and instead concentrate into intermittent ropes, with their peak value of order equipartition fields, and radii much smaller than their lengths. In this case these fields neither drain significant energy from the turbulence nor convert eddy motion of the turbulence on the outer scale to wave like motion. This preserves the diffusive effects needed for the large scale dynamo operation.
3,000원
