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- 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 93/123
921
- KOO BON-CHUL
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.183-186
- 1996
- 원문 바로보기
We report the results of H I 21-cm and molecular line studies of the shocked interstellar gas in the W51 complex. We present convincing evidences suggesting that the shocked gas has been produced by the interaction of the W51C supernova remant (SNR) with a large molecular cloud, Our results show that W51C is the second SNR with direct evidences for the shocked cloud material.
922
- WU XUEJUN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.41-42
- 1996
- 원문 바로보기
A possible cosmic X-ray background(XRB) radiation related to original antimatter is considered. If the universe is made of separating domains of antimatter and matter, the photons produced by the annihilation of electron-positron and proton-antiproton on the last scattering surface would reach us in the energy <TEX>$\~$</TEX>0.45 keV and <TEX>$\~$</TEX>60 keV respectively because of the redshift. The spectrums of X-ray radiation from annihilation are deduced and a possible observational figure is described also.
923
- GUHATHAKURTA PURAGRA
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.63-64
- 1996
- 원문 바로보기
The nature of distant faint blue field galaxies remains a mystery, despite the fact that much attention has been devoted to this subject in the last decade. Galaxy counts, particularly those in the optical and near ultraviolet bandpasses, have been demonstrated to be well in excess of those expected in the 'no-evolution' scenario. This has usually been taken to imply that galaxies were brighter in the past, presumably due to a higher rate of star formation. More recently, redshift surveys of galaxies as faint as B<TEX>$\~$</TEX>24 have shown that the mean redshift of faint blue galaxies is lower than that predicted by standard evolutionary models (de-signed to fit the galaxy counts). The galaxy number count data and redshift data suggest that evolutionary effects are most prominent at the faint end of the galaxy luminosity function. While these data constrain the form of evolution of the overall luminosity function, they do not constrain evolution in individual galaxies. We are carrying out a series of observations as part of a long-term program aimed at a better understanding of the nature and amount of luminosity evolution in individual galaxies. Our study uses the luminosity-linewidth relation (Tully-Fisher relation) for disk galaxies as a tool to study luminosity evolution. Several studies of a related nature are being carried out by other groups. A specific experiment to test a 'no-evolution' hypothesis is presented here. We have used the AUTOFIB multifibre spectro-graph on the 4-metre Anglo-Australian Telescope (AAT) and the Rutgers Fabry-Perot imager on the Cerro Tolalo lnteramerican Observatory (CTIO) 4-metre tele-scope to measure the internal kinematics of a representative sample of faint blue field galaxies in the red-shift range z = 0.15-0.4. The emission line profiles of [OII] and [OIII] in a typical sample galaxy are significantly broader than the instrumental resolution (100-120 km <TEX>$s^{-l}$</TEX>), and it is possible to make a reliable de-termination of the linewidth. Detailed and realistic simulations based on the properties of nearby, low-luminosity spirals are used to convert the measured linewidth into an estimate of the characteristic rotation speed, making statistical corrections for the effects of inclination, non-uniform distribution of ionized gas, rotation curve shape, finite fibre aperture, etc.. The (corrected) mean characteristic rotation speed for our distant galaxy sample is compared to the mean rotation speed of local galaxies of comparable blue luminosity and colour. The typical galaxy in our distant sample has a B-band luminosity of about 0.25 L<TEX>$\ast$</TEX> and a colour that corresponds to the Sb-Sd/Im range of Hub-ble types. Details of the AUTOFIB fibre spectroscopic study are described by Rix et al. (1996). Follow-up deep near infrared imaging with the 10-metre Keck tele-scope+ NIRC combination and high angular resolution imaging with the Hubble Space Telescope's WFPC2 are being used to determine the structural and orientation parameters of galaxies on an individual basis. This information is being combined with the spatially resolved CTIO Fabry-Perot data to study the internal kinematics of distant galaxies (Ing et al. 1996). The two main questions addressed by these (preliminary studies) are: 1. Do galaxies of a given luminosity and colour have the same characteristic rotation speed in the distant and local Universe? The distant galaxies in our AUTOFIB sample have a mean characteristic rotation speed of <TEX>$\~$</TEX>70 km <TEX>$s^{-l}$</TEX> after correction for measurement bias (Fig. 1); this is inconsistent with the characteristic rotation speed of local galaxies of comparable photometric proper-ties (105 km <TEX>$s^{-l}$</TEX>) at the > <TEX>$99\%$</TEX> significance level (Fig. 2). A straightforward explanation for this discrepancy is that faint blue galaxies were about 1-1.5 mag brighter (in the B band) at z <TEX>$\~$</TEX> 0.25 than their present-day counterparts. 2. What i
924
- ZHU XINGFEN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.109-110
- 1996
- 원문 바로보기
925
- CHEN JIAN-SHENG
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.407-407
- 1996
- 원문 바로보기
926
- LEE SEE-WOO
- Journal of the Korean astronomical society = 천문학회지
- 29, n.1
- pp.53-62
- 1996
- 원문 바로보기
31 white dwarfs in 10 open clusters are examined, and their maximum mass and the upper mass limit of their progenitors are obtained as <TEX>$1.22\pm0.02M_{\bigodot}\;and\;7.2\pm0.4M_{\bigodot}$</TEX> respectively, suggesting that the upper mass limit of white dwarfs is less than <TEX>8M_{\bigodot}$</TEX> The final mass of white dwarfs shows no clear correlation with the initial mass of their progenitors, and it is found that a deficient gap of initial mass exists between <TEX>$\~4\;and\;~5.2M_{\bigodot}$</TEX>. This gap seems to correspond to the mass range for carbon detonation or deflagration. The total expected numbers of white dwarfs are <TEX>$11\~22$</TEX> in Hyades with 7 known white dwarfs and 17 in Praesepe with 8 known white dwarfs. These known white dwrfs are all younger than the others in both clusters. But one known white dwarf in Pleiades is older one among <TEX>$2\~3$</TEX> expected white dwarfs.
927
- KOZHANOV T. S.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.27-29
- 1996
- 원문 바로보기
We describe the formation of large-scale inhomogeneous structure of expa-nding Universe on the basic of two components system-usual nonrelativistic particles and dark matter, with taking into account their interaction.
928
- KOZAI YOSHIHIDE
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.351-354
- 1996
- 원문 바로보기
In this paper it is explained how most of asteroids can avoid very close approach to Jupiter, to the earth for earth orbit crossing asteroids, and to Neptune for Kuiper-belt asteroids by mechanisms which work also for Neptune-Pluto system. In fact the mutual distance of the planets cannot become very small as the critical argument librates around <TEX>$180^{\circ}$</TEX> because of 2:3 mean motion resonance and the argument of perihelion of Pluto librates around <TEX>$90^{\circ}$</TEX>. And it is found that among nearly 40 Kuiper-belt asteroids discovered in recent years <TEX>$40\%$</TEX> have orbits similar to Pluto. For main-belt asteroids the distribution with respect to the semi-major axes has peculiar characteristics and the author tries to explain how their peaks and gaps are created. It is also found that <TEX>$30\%$</TEX> of 80 earth orbit crossing asteroids which have minimum perihelion distances less than 1.04AU have no chance to collide with the earth. Still <TEX>$30\%$</TEX> of them have a few probability to collide with the earth as they have dynamical characteristics of short-periodic comets.
929
- WIRAMIHARDJA SUHARDJA D.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.265-266
- 1996
- 원문 바로보기
930
- WU XUE-BING
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.231-232
- 1996
- 원문 바로보기
The local instabilities of accretion disks were extensively studied, with the considerations of radial advection, thermal diffusion and different disk geometry, dominated pressure and optical depth. Two inertial-acoustic modes in a geometrically thin, radiative cooling dominated disk depart from each other if very little advection is included. A geometrically slim, advection-dominated disk is found to be always stable if it is optically thin. However, if it is optically thick, the thermal diffusion has no effect on the stable viscous mode but has a significant contribution to enhance the thermal instability.