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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 64/123
631
- KOO BON-CHUL
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.43-48
- 2003
- 원문 바로보기
We introduce and describe performance of the 6-meter telescope of Seoul Radio Astronomy Observatory (SRAO). All the softwares and instruments except the antenna structure and its driving system are developed for ourselves. The SIS mixer type receiver resulted in the receiver noise temperature less than 50 K (DSB) over the whole 3-mm radio window. An autocorrelation spectrometer, developed first in Korea, provides maximum 50 MHz band width over 1024 channels. Antenna surface is measured and adjusted using template method and radio holography which resulted in a superb surface accuracy bet-ter than 30<TEX>${\mu}m$</TEX>. Accordingly, the aperture and beam efficiences amount to <TEX>$70\%$</TEX> and <TEX>$75\%$</TEX>, respectively, largely independent of frequency in the 85 - 115 GHz range. It is also found that telescope pointing errors are less than 10' in both azimuth and elevation and that antenna gain is almost constant against elevation greater than <TEX>$20^{\circ}$</TEX>, without adjusting sub-reflector position. The SRAO 6-meter telescope is now fully operational and all these characteristics verify that observations are carried out with high precision and fidelity.
632
- KIM DONG-WOO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.213-222
- 2003
- 원문 바로보기
We review recent observational results on early type galaxies obtained with high spatial resolution Chandra data. With its unprecedented high spatial resolution, Chandra reveals many intriguing features in early type galaxies which were not identified with the previous X-ray missions. In particular, various fine structures of the hot ISM in early type galaxies are detected, for example, X-ray cavities which are spatially coincident with radio jets/lobes, indicating the interaction between the hot ISM and radio jets. Also point sources (mostly LMXBs) are individually resolved down to Lx = a few x <TEX>$10^{37}\;erg\;sec^{-1}$</TEX> and it is for the first time possible to unequivocally investigate their properties and the X-ray luminosity function. After correcting for incompleteness, the XLF of LMXBs is well reproduced by a single power law with a slope of -1.0 - -1.5, which is in contrast to the previous report on the existence of the XLF break at Lx, Eddington = 2 x <TEX>$10^{38}\;erg\;sec^{-1}$</TEX> (i.e., Eddington luminosity of a neutron star binary). Carefully considering both detected and undetected, hidden populations of point sources we further discuss the XLF of LMXBs and the metal abundance of the hot ISM and their impact on the properties of early type galaxies.
633
- DING M. D.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.49-54
- 2003
- 원문 바로보기
We introduce the two-dimensional spectral observations of solar flares using the Solar Tower Tele-scope of Nanjing University, China. In particular, we introduce three typical events and the methods used to analyze the data. (1) The flare of November 11, 1998, which is a limb flare. We derive the temperature and density within the flaring loop using non-LTE calculations. The results show that the loop top may be hotter and denser than other parts of the loop, which may be a result of magnetic reconnect ion above the loop. (2) The flare of March 10, 2001, which is a white-light flare that shows an emission enhancement at the near infrared continuum. We propose a model of non-thermal electron beam heating plus backwarming to interpret the observations. (3) The flare of September 29, 2002, which shows unusual line asymmetries at one flare kernel. The line asymmetries are caused by an upward moving plasma that is accelerated and heated during the flare development.
634
- ZHANG XIAOLEI
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.223-239
- 2003
- 원문 바로보기
It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the whole have failed to reproduce the most important statistical and internal properties of galaxies. The secular evolution mechanism reviewed in this paper has the potential to overcome most of the known difficulties of the existing theories to provide a natural and coherent explanation of the properties of present day as well as high-redshift galaxies.
635
- MOON Y.-J.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.2
- pp.61-66
- 2003
- 원문 바로보기
We have examined the relationship between the speeds of coronal mass ejections (CMEs) and the GOES X-ray peak fluxes of associated flares. Noting that previous studies were possibly affected by projection effects and random association effects, we have considered two sets of carefully selected CME-flare events: four homologous events and four well-observed limb events. In the respective samples, good correlations are found between the CME speeds and the GOES X-ray peak fluxes of the associated flares. A similarly good correlation is found for all eight events of both samples when the CME speeds of the homologous events are corrected for projection effect. Our results suggest that a close relationship possibly exists between CME kinematics and flaring processes.
636
- JANG M.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.145-149
- 2003
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LIST is the Lyman-<TEX>$\alpha$</TEX> Imaging Solar Telescope, a project funded by the Korean government to fly on the second Korean Science and Technology research Satellite (STSat-2) due to launch in December 2005. The Principal Investigator is Dr. Minhwan Jang of Kyung-Hee University and of the Space Payload Research Center (SPARC), a consortium of Korean universities and institutions formed to develop scientific research projects in space. The purpose of the LIST project is to design, build, and operate an instrument on STSat-2 which will make images of the Sun from Earth orbit at the wavelength of the Hydrogen Lyman-a emission line at 121.6 nm. LIST has a simple design concept comprised of a small telescope to image the full disk of the Sun onto a CCD detector and a set of filters to isolate the 121.6 nm wavelength.
637
- BONG SU-CRAN
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.29-36
- 2003
- 원문 바로보기
Quiescent solar radiation, at microwave spectral regime, is dominated by gyroresonant and thermal Bremsstrahlung radiations from hot electrons residing in solar active region corona. These radiations are known to provide excellent diagnostics on the coronal temperature, density, and magnetic field, provided that spatially resolved spectra are available from observations. In this paper we present an imaging spectroscopy implemented for a bipolar active region, AR 7912, using the multifrequency interferometric data from the Owens Valley Solar Array (OVSA), as processed with a new imaging technique, so-called Spatio-Spectral Maximum Entropy Method (SSMEM). From the microwave maps at 26 frequencies in the range of 1.2-12.4 GHz at both right- and left-circular polarizations, we construct spatially resolved brightness spectra in every reconstructed pixel of about 2 arcsec interval. These spectra allowed us to determine 2-D distribution of electron temperature, magnetic field of coronal base, and emission measure at the coronal base above the active region. We briefly compare the present result with existing studies of the coronal active regions.
638
- LEE SANGWOO
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.21-27
- 2003
- 원문 바로보기
In the present study, we have investigated morphology and evolution of small-scale Ha dynamic features on the quiet sun by analyzing video magnetograms and high resolution Ha images simultaneously taken for 5 hours at Big Bear Solar Observatory on April 18, 1997. From comparisons between time sequential longitudinal magnetograms and H<TEX>$\alpha$</TEX> images covering <TEX>$150' {\times} 150'$</TEX>, several small-scale H<TEX>$\alpha$</TEX> dynamic features have been observed at a site of magnetic flux cancellation. A close relationship between such features and cancelling magnetic fluxes has been revealed temporarily and spatially. Our results support that material injection by chromospheric magnetic reconnect ion may be essential in supporting numerous small-scale H<TEX>$\alpha$</TEX> dynamical absorption features, being in line with recent observational studies showing that material injection by chromospheric magnetic reconnect ion is essential for the formation of solar filaments.
639
- SCOVILLE NICK
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.167-175
- 2003
- 원문 바로보기
There is accumulating evidence for a strong link between nuclear starbursts and AGN. Molecular gas in the central regions of galaxies plays a critical role in fueling nuclear starburst activity and feeding central AGN. The dense molecular ISM is accreted to the nuclear regions by stellar bars and galactic interactions. Here we describe recent observational results for the OB star forming regions in M51 and the nuclear star burst in Arp 220 - both of which have approximately the same rate of star formation per unit mass of ISM. We suggest that the maximum efficiency for forming young stars is an Eddington-like limit imposed by the radiation pressure of newly formed stars acting on the interstellar dust. This limit corresponds to approximately 500 <TEX>$L_{\bigodot} / M_{\bigodot}$</TEX> for optically thick regions in which the radiation has been degraded to the NIR. Interestingly, we note that some of the same considerations can be important in AGN where the source of fuel is provided by stellar evolution mass-loss or ISM accretion. Most of the stellar mass-loss occurs from evolving red giant stars and whether their mass-loss can be accreted to a central AGN or not depends on the radiative opacity of the mass-loss material. The latter depends on whether the dust survives or is sublimated (due to radiative heating). This, in turn, is determined by the AGN luminosity and the distance of the mass-loss stars from the AGN. Several AGN phenomena such as the broad emission and absorption lines may arise in this stellar mass-loss material. The same radiation pressure limit to the accretion may arise if the AGN fuel is from the ISM since the ISM dust-to-gas ratio is the same as that of stellar mass-loss.
640
- Taniguchi, Yoshiaki
- Journal of the Korean astronomical society = 천문학회지
- 36, n.4
- pp.283-283
- 2003
- 원문 바로보기
The first sentence in the second paragraph of INTRODUCTION, 'The first discovery of a galaxy beyond z=5 was reported by Weymann et al. (1998); HDF 4-470.3 at z=5.60.' should be read as 'The first discovery of a galaxy beyond z=5 was reported by Dey et al. (1998); 0140+326 RD1 at z=5.34'. The authors sincerely regret this error.