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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
페이지 82/122
811
- LEE YOUNG-WOOK
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.49-51
- 1996
- 원문 바로보기
New population synthesis models, with the effects of metallicity spread and the horizontal-branch (HB) morphology, provide a way to break the well-known age-metallicity degeneracy in the analysis of the integrated light of elliptical galaxies. Our models suggest that the far- UV radiation of these systems is dominated by a minority population of metal-poor, hot HB stars and their post-HB progeny, while the optical radiation is dominated by a metal-rich population. The systematic variation of UV upturn depends on the contribution from metal-poor, hot HB stars and their post-HB progeny, which in turn depends on the ages of old stellar populations in galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. Our models also suggest that the strenghth of H<TEX>$\beta$</TEX> index is strongly affected by HB stars, and hence previous age estimation without detailed modeling of the HB would underestimate the ages of ellipticals by <TEX>$\~$</TEX>7 Gyr.
812
- CHOE SEUNG-URN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.93-105
- 1996
- 원문 바로보기
We have solved the radiative transfer problem using a Sobolev approximation with an escape probability method in case of the supersonic expansion of a stellar envelope to an ambient medium. The radiation from the expanding envelope turns out to produce a P-Cygni type profile. In order to investigate the morphology of the theoretical P-Cygni type profile, we have treated <TEX>$V_\infty,\;V_{sto},\;\beta$</TEX> (parameters for the velocity field), it and E(parameter for collisional effect) as model parameters. We have investigated that the velocity field and the mass loss rate affect the shapes of the P-Cygni type profiles most effectively. The secondarily important factors are <TEX>$V_\infty,\;V_{sto}$</TEX>. The collisional effect tends to make the total flux increased but not so much in magnitude. We have infered some physical parameters of 68 Cyg, HD24912, and <TEX>$\xi$</TEX> persei such as <TEX>$V_\infty,\;M$</TEX> from the model calculation, which shows a good agreenment with the observational results.
813
- HIREMATH K. M.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.313-314
- 1996
- 원문 바로보기
Assuming that the solar activity and the solar cycle phenomena may be manifestations of global torsional MHD oscillations, we compute the Alfven wave travel times along the field lines in the five models of magnetic field described in the following text. For all these models, we compute standard deviation and it's ratio to mean Alfvenic wave travel times. The last two models yield the smallest relative bandwidth for the frequencies of the MHD oscillations. However, the last model is the only admissible one which can sustain global Alfvenic oscillations with well defined frequency for the fundamental mode
814
- KIM SEUNG-LEE
- Journal of the Korean astronomical society = 천문학회지
- 29, n.1
- pp.31-41
- 1996
- 원문 바로보기
We present results of time-series CCD photometry for 178 stars in the young open cluster M29 (=NGC6913). Total 1036 V-band CCD frames were collected for five nights between August 12 and September 13, 1994. The photometric precision is about 7.6 mmag for 9th-10th mag stars in M29 with exposure times of 30 seconds. From the dispersion diagram and the light curves, one detached eclipsing binary (HD194378) and two suspected variables are newly discovered. <TEX>$A\;\gamma\;Cas$</TEX> type variable, V1322 Cyg, which has been known as a member of M29, did not show any light variations during the period of present observations, indicating that it passed the steady phase without the eruption during our observing runs.
815
- WEE SUN-OK
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.181-194
- 1996
- 원문 바로보기
We present a study of the metallicity of the old open cluster NGC 1245 , based on the Washington CCD photometry obtained using the 0.6 m telescope at the Sobaeksan Observatory, Korea. NGC 1245 has been known to be a unique cluster among the known open clusters in the sense that the previous metallicity estimates for this cluster are much larger <TEX>$(by\;\sigma)$</TEX> than the value expected from the radial metallicity gradient of the old open clusters in Our galaxy. We have estimated the metallicity of the cluster red giants using the four color-color diagrams, obtaining a value for the mean metallicity of <TEX>$[Fe/H] = -0.04\pm0.05$</TEX> dex. The total error including the error of the metallicity calibration, 0.15 dex, is 0.16 dex. The metallicity estimate of NGC 1245 we have obtained in this study is smaller than previous estimates, and is consistent with the radial metallicity gradient of the old open clusters, showing that the mean metallicity of NGC 1245 is not abnormally high. The reddening, distance, and age of the cluster have also been derived using the isochrones based on the convective overshooting models: the reddening <TEX>$E(B-V) = 0.28\pm0.03$</TEX>; the distance <TEX>$d = 2.5\pm0.2 kpc$</TEX> (the corresponding galactocentric distance is RGC = 10.7 kpc, and the distance from the galactic plane is z = -0.4 kpc); and the age <TEX>$t = 1.1\pm0.1 Gyrs$</TEX>.
816
- SUN AIQUN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.397-398
- 1996
- 원문 바로보기
Large field spectrographs are severely influenced by atmospheric refraction. LAMOST is a large field multi-object spectroscopy telescope with <TEX>$5^{\circ}$</TEX> field of view, f/5 focus ratio and 20m focal length. There will be 4000 fibers simultaneous on it's <TEX>$\phi$</TEX>1.75m focal plane. Here we discuss the atmospheric refraction effects on LAMOST in two hands. One is the effect of differential refraction across the field, another is the effect of atmospheric dispersion. According to the calculation, we find that: 1. The largest deviation from center within the field is 4.;32' during a 1.5-hour integration at <TEX>$80^{\circ}$</TEX> declination. 2. The directions of deviation are complex, so the deviations can't be decreased by rotating the field. We also give out the atmospheric dispersions.
817
- CHEN ALFRED B.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.123-124
- 1996
- 원문 바로보기
Snapshots of eight SA and standard fields from low to high galactic latitudes were made using the KPNO 0.9m 2K <TEX>$\times$</TEX> 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.
818
- CANNON RUSSELL
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.367-370
- 1996
- 원문 바로보기
Construction of the 'Two-degree Field' (2dF) instrument on the Anglo-Australian Telescope (AAT) is now virtually complete and commissioning is well underway. The key components are described. Several recent milestones are reported, including the first scientific results. Future prospects and plans are discussed.
819
- MINN YOUNG KEY
- Journal of the Korean astronomical society = 천문학회지
- 29, n.1
- pp.75-81
- 1996
- 원문 바로보기
We mapped the <TEX>$^{13}CO$</TEX> line in the dark nebula L134 using the 14-m Taeduck radio telescope with a 57 arcsec beam and one beam spacing. The cloud has a spherical shape with an intensity peak ridge extended from the northwest to the southeast directions. The halfwidth and the radial velocity of the lines peak at the region of the cloud center. The radial velocity decreases from the cloud center towards the north and south directions. The integrated line intensity distributions in the space-velocity plane show some structure and a velocity gradient. The <TEX>$^{13}CO$</TEX> and <TEX>$H_2CO$</TEX> clouds and dark clouds are closely related in space in shape, outer boundary, and intensity peak positions. The <TEX>$^{13}CO$</TEX> integrated line intensity is linearly proportional to the visual extinction.
820
- CHA SEUNG-HOON
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.253-254
- 1996
- 원문 바로보기
To understand the dynamical structures of stellar wind bubble, one and two-dimensional calculations has been performed. Using FCT Code with cooling effects and assuming constant mass loss rate and ambient medium density, we could divide stellar winds into the regime of slow and fast winds. The slow wind driven bubble shows initially radiative and becomes partially radiative bubble in which shocked stellar wind zone is still adiabatic. In contrast., the fast wind driven bubble shows initially fully adiabatic and becomes adiabatic bubbles with radiative outer shell. We also determine analytically the onset of thin-shell formation time in case of fast wind driven bubble with power-law energy injection and ambient density structure. We solve the line transfer problem with numerical results in order to calculate line profile of [OIII] forbidden line.