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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 95/122
941
- 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.
942
- ZHU XINGFEN
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.109-110
- 1996
- 원문 바로보기
943
- 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
944
- YERSHOV V. N.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.427-428
- 1996
- 원문 바로보기
The Struve astrometric satellite which is being developed at Pulkovo Observatory in cooperation with Krasno-yarsk Institute of Applied Mechanics, S.I. Vavilov's State Optical Institute and some others space instrumentation institutes, will produce observations of a second epoch for the Hipparcos stars. The project is devoted to maintaining the Hipparcos coordinate system as well as extending it to a density of <TEX>$\approx$</TEX> 100 stars per square degree. Possibilities of submilliarcsecond accuracy of observations with single aperture on-board telescopes are discussed. Requirements to the optical scheme and to the dynamic properties of the spacecraft are formulated. CCD and microchannel plates are discussed as a focal assembly detectors.
945
- LIU HANPING
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.175-176
- 1996
- 원문 바로보기
946
- IYE MASANORI
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.371-374
- 1996
- 원문 바로보기
An updated project status review of the Japan 8m telescope, Subaru, scheduled for its first light in the second quater of 1998 atop Mauna Kea is given.
947
- YOON SO-YOON
- Journal of the Korean astronomical society = 천문학회지
- 29, n.2
- pp.119-136
- 1996
- 원문 바로보기
To examine the effect of neighboring galaxies on the gravitational lensing statistics, we performed numerical simulations of lensing by many galaxies. The models consist of a galaxy in the rich cluster like Coma, or a galaxy surrounded by field galaxies in <TEX>$\Omega_0 = 1$</TEX> universe with <TEX>$\Omega_{gal} = 0.1,\;\Omega_{gal} = 0.3\;or\;\Omega_{gal}=1.0\;,\;where\;\Omega_{gal}$</TEX> is the total mass in galaxies. Field galaxies either have the same mass or follow Schechter luminosity function and luminosity-velocity relation. Each lensing galaxy is assumed to be singular isothermal sphere (SIS) with finite cutoff radius. In most simulations, the lensing is mainly due to the single galaxy. But in <TEX>$\Omega_{gal} = 3$</TEX> universe, one out of five simulations have 'collective lensing' event in which more than two galaxies collectively produce multiple images. These cases cannot be incorporated into the simple 'standard' lensing statistics calculations. In cases where 'collective lensing' does not occur, distribution of image separation changes from delta function to bimodal distribution due to shear induced by the surrounding galaxies. The amount of spread in the distribution is from a few <TEX>$\%\;up\;to\;50\%$</TEX> of the mean image separation in case when the galaxy is in the Coma-like cluster or when the galaxy is in the field with <TEX>$\Omega_{gal} = 0.1\;or\;\Omega_{gal}=0.3.$</TEX> The mean of the image separation changes less than <TEX>$5\%$</TEX> compared with a single lens case. Cross section for multiple image lensing turns out to be relatively insensitive to the presence of the neighboring galaxies, changing less than <TEX>$5\%$</TEX> for Coma-like cluster and <TEX>$\Omega_{gal}=0.1,\;0.3$</TEX> universe cases. So we conclude that Coma-like cluster or field galaxies whose total mass density <TEX>$\Omega_{gal}<0.3$</TEX> do not significantly affect the probability of multiple image lensing if we exclude the 'collective lensing' cases. However, the distribution of the image separations can be significantly affected especially if the 'collective lensing' cases are included. Therefore, the effects of surrounding galaxies may not be negligible when statistics of lensing is used to deduce the cosmological informations.
948
- WIRAMIHARDJA SUHARDJA D.
- Journal of the Korean astronomical society = 천문학회지
- 29, n.suppl1
- pp.265-266
- 1996
- 원문 바로보기
949
- 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.
950
- 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.