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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 64/122
631
- GOODE PHILIP R.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.125-133
- 2003
- 원문 바로보기
New Jersey Institute of Technology (NJIT), in collaboration with the University of Hawaii (UH), is upgrading Big Bear Solar Observatory (BBSO) by replacing its principal, 65 cm aperture telescope with a modern, off-axis 1.6 m clear aperture instrument from a 1.7 m blank. The new telescope offers a significant incremental improvement in ground-based infrared and high angular resolution capabilities, and enhances our continuing program to understand photospheric magneto-convection and chromospheric dynamics. These are the drivers for what is broadly called space weather - an important problem, which impacts human technologies and life on earth. This New Solar Telescope (NST) will use the existing BBSO pedestal, pier and observatory building, which will be modified to accept the larger open telescope structure. It will be operated together with our 10 inch (for larger field-of-view vector magnetograms, Ca II K and Ha observations) and Singer-Link (full disk H<TEX>$\alpha$</TEX>, Ca II K and white light) synoptic telescopes. The NST optical and software control design will be similar to the existing SOLARC (UH) and the planned Advanced Technology Solar Telescope (ATST) facility led by the National Solar Observatory (NSO) - all three are off-axis designs. The NST will be available to guest observers and will continue BBSO's open data policy. The polishing of the primary will be done in partnership with the University of Arizona Mirror Lab, where their proof-of-concept for figuring 8 m pieces of 20 m nighttime telescopes will be the NST's primary mirror. We plan for the NST's first light in late 2005. This new telescope will be the largest aperture solar telescope, and the largest aperture off-axis telescope, located in one of the best observing sites. It will enable new, cutting edge science. The scientific results will be extremely important to space weather and global climate change research.
632
- GARY DALE E.
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.135-143
- 2003
- 원문 바로보기
Solar radio astronomy is about to undergo a revolution with the advent of a new radio synthesis array, the Frequency Agile Solar Radiotelescope (FASR). The array will consist of more than 100 antennas (5000 baselines), and will be designed to meet the special challenges of solar imaging. It will produce high-quality images at hundreds of frequencies in the range 20 MHz-24 GHz. We briefly describe the plans for the instrument, and then concentrate on the range of science that is expected to be addressed, using current state-of-the-art solar radio observations and modeling to illustrate FASR performance. We end with an assessment of the current status of the instrument, and plans for future.
633
- YUN HONG SIK
- Journal of the Korean astronomical society = 천문학회지
- 36, n.suppl1
- pp.155-161
- 2003
- 원문 바로보기
In this article I review the past and current status of solar astronomy in Korea and present some future prospects. Along with a brief historical account on the introduction of modern astronomy to Korea, I describe in detail how solar astronomy in Korea has developed since its birth about 20 years ago. With education of solar astronomers at domestic universities and collaboration with foreign scientists in China, Japan and the U. S., there has been a rapid growth of solar physics in Korea in the past decade. For further advance of solar astronomy in Korea, Korean solar astronomers have to build their own observing facilities and develop instrumentation programs. Also it is very important to bring up manpower competent for these projects.
634
- Lee, Chang-Won
- Journal of the Korean astronomical society = 천문학회지
- 36, n.4
- pp.271-282
- 2003
- 원문 바로보기
We present results of a <TEX>$H^{13}CN$</TEX> J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of <TEX>$-1.6^{\circ}{\le}{\iota}{\le}2^{\circ}$</TEX> and <TEX>$-0.23^{\circ}{\le}b{\le}0.30^{\circ}$</TEX> with 2' grid resolution. The <TEX>$H^{13}CN$</TEX> emissions show similar distribution and velocity structures to those of the <TEX>$H^{12}CN$</TEX> emissions, but are found to better trace the feature saturated with <TEX>$H^{12}CN$</TEX> (1-0). The bright components among multi-components of <TEX>$H^{12}CN$</TEX> line profiles usually appear in the <TEX>$H^{13}CN$</TEX> line while most of the dynamically forbidden, weak <TEX>$H^{12}CN$</TEX> components are seldom detected in the <TEX>$H^{13}CN$</TEX> line. We also present results of other complementary observations in <TEX>$^{12}CO$</TEX> (J=1-0) and <TEX>$^{13}CO$</TEX> (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of <TEX>$H^{12}CN$</TEX> and <TEX>$H^{13}CN$</TEX> relative to <TEX>$H_2$</TEX> in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within <TEX>$[{\iota}]{\le}6^{\circ}$</TEX> is estimated to be <TEX>${\~}2 {\times}10^7\;M_{\bigodot}$</TEX> using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few <TEX>$10^5$</TEX> to <TEX>${\~}10^7\;M_{\bigodot}$</TEX> All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km <TEX>$s^{-1}$</TEX>) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.
635
- TANIGUCHI YOSHIAKI
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.123-144
- 2003
- 원문 바로보기
The 8m class telescopes in the ground-based optical astronomy together with help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to observe forming galaxies beyond red shift z = 5. In particular, more than twenty Ly<TEX>$\alpha$</TEX>-emitting galaxies have already been found at z > 5. These findings provide us with useful hints to investigate how galaxies formed and then evolved in the early universe. Further, detailed analysis of Ly<TEX>$\alpha$</TEX> emission line profiles are useful in exploring the nature of the intergalactic medium because the trailing edge of cosmic reionization could be close to z <TEX>$\~$</TEX> 6 -7, at which forming galaxies have been found recently. We also discuss the importance of superwinds from forming galaxies at high redshift, which has an intimate relationship between galaxies and the intergalactic medium. We then give a review of early cosmic star formation history based on recent progress in searching for Ly<TEX>$\alpha$</TEX>-emitting young galaxies beyond red shift 5.
636
- CHANG HEON-YOUNG
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.81-87
- 2003
- 원문 바로보기
It is suggested that a flying-by star in a hot accretion disk may cool the hot accretion disk by the Comptonization of the stellar emission. Such a stellar cooling can be observed in the radio frequency regime since synchrotron luminosity depends strongly on the electron temperature of the accretion flow. If a bright star orbiting around the supermassive black hole cools the hot disk, one should expect a quasi-periodic modulation in radio, or even possible an anti-correlation of luminosities in radio and X-rays. Recently, the unprecedentedly accurate infrared imaging of the Sagittarius A<TEX>$\ast$</TEX> for about ten years enables us to resolve stars around it and thus determine orbital parameters of the currently closest star S2. We explore the possibility of using such kind of observation to distinguish two quite different physical models for the central engine of the Sagittarius A<TEX>$\ast$</TEX>, that is, a hot accretion disk model and a jet model. We have attempted to estimate the observables using the observed parameters of the star S2. The relative difference in the electron temperature is a few parts of a thousand at the epoch when the star S2 is near at the pericenter. The relative radio luminosity difference with and without the stellar cooling is also small of order <TEX>$10^{-4}$</TEX>, particularly even when the star S2 is near at the pericenter. On the basis of our findings we tentatively conclude that even the currently closest pass of the star S2 is insufficiently close enough to meaningfully constrain the nature of the Sagittarius A<TEX>$\ast$</TEX> and distinguish two competing models. This implies that even though Bower et al. (2002)have found no periodic radio flux variations in their data set from 1981 to 1998, which is naturally expected from the presence of a hot disk, a hot disk model cannot be conclusively ruled out. This is simply because the energy bands they have studied are too high to observe the effect of the star S2 even if it indeed interacts with the hot disk. In other words, even if there is a hot accretion disk the star like S2 has imprints in the frequency range at v <TEX>$\le$</TEX> 100 MHz.
637
- AHN KYUNGJIN
- Journal of the Korean astronomical society = 천문학회지
- 36, n.3
- pp.89-95
- 2003
- 원문 바로보기
Observations of dark matter dominated dwarf and low surface brightness disk galaxies favor density profiles with a flat-density core, while cold dark matter (CDM) N-body simulations form halos with central cusps, instead. This apparent discrepancy has motivated a re-examination of the microscopic nature of the dark matter in order to explain the observed halo profiles, including the suggestion that CDM has a non-gravitational self-interaction. We study the formation and evolution of self-interacting dark matter (SIDM) halos. We find analytical, fully cosmological similarity solutions for their dynamics, which take proper account of the collisional interaction of SIDM particles, based on a fluid approximation derived from the Boltzmann equation. The SIDM particles scatter each other elastically, which results in an effective thermal conductivity that heats the halo core and flattens its density profile. These similarity solutions are relevant to galactic and cluster halo formation in the CDM model. We assume that the local density maximum which serves as the progenitor of the halo has an initial mass profile <TEX>${\delta}M / M {\propto} M^{-{\epsilon}$</TEX>, as in the familiar secondary infall model. If <TEX>$\epsilon$</TEX> = 1/6, SIDM halos will evolve self-similarly, with a cold, supersonic infall which is terminated by a strong accretion shock. Different solutions arise for different values of the dimensionless collisionality parameter, <TEX>$Q {\equiv}{\sigma}p_br_s$</TEX>, where <TEX>$\sigma$</TEX> is the SIDM particle scattering cross section per unit mass, <TEX>$p_b$</TEX> is the cosmic mean density, and <TEX>$r_s$</TEX> is the shock radius. For all these solutions, a flat-density, isothermal core is present which grows in size as a fixed fraction of <TEX>$r_s$</TEX>. We find two different regimes for these solutions: 1) for <TEX>$Q < Q_{th}({\simeq} 7.35{\times} 10^{-4}$</TEX>), the core density decreases and core size increases as Q increases; 2) for <TEX>$Q > Q_{th}$</TEX>, the core density increases and core size decreases as Q increases. Our similarity solutions are in good agreement with previous results of N-body simulation of SIDM halos, which correspond to the low-Q regime, for which SIDM halo profiles match the observed galactic rotation curves if <TEX>$Q {\~} [8.4 {\times}10^{-4} - 4.9 {\times} 10^{-2}]Q_{th}$</TEX>, or <TEX>${\sigma}{\~} [0.56 - 5.6] cm^2g{-1}$</TEX>. These similarity solutions also show that, as <TEX>$Q {\to}{\infty}$</TEX>, the central density acquires a singular profile, in agreement with some earlier simulation results which approximated the effects of SIDM collisionality by considering an ordinary fluid without conductivity, i.e. the limit of mean free path <TEX>${\lambda}_{mfp}{\to} 0$</TEX>. The intermediate regime where <TEX>$Q {\~} [18.6 - 231]Q_{th}$</TEX> or <TEX>${\sigma}{\~} [1.2{\times}10^4 - 2.7{\times}10^4] cm^2g{-1}$</TEX>, for which we find flat-density cores comparable to those of the low-Q solutions preferred to make SIDM halos match halo observations, has not previously been identified. Further study of this regime is warranted.
638
- CHAE JONGCHUL
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.33-41
- 2003
- 원문 바로보기
Recent observations have shown that coronal magnetic fields in the northern (southern) hemisphere tend to have negative (positive) magnetic helicity. There has been controversy as to whether this hemispheric pattern is of surface or sub-surface origin. A number of studies have focused on clarifying the effect of the surface differential rotation on the change of magnetic helicity in the corona. Meanwhile, recent observational studies reported the existence of transient shear flows in active regions that can feed magnetic helicity to the corona at a much higher rate than the differential rotation does. Here we propose that such transient shear flows may be driven by the torque produced by either the axial or radial expansion of the coronal segment of a twisted flux tube that is rooted deeply below the surface. We have derived a simple relation between the coronal expansion parameter and the amount of helicity transferred via shear flows. To demonstrate our proposition, we have inspected Yohkoh soft X-ray images of NOAA 8668 in which strong shear flows were observed. As a result, we found that the expansion of magnetic fields really took place in the corona while transient shear flows were observed in the photosphere, and the amount of magnetic helicity change due to the transient shear flows is quantitatively consistent with the observed expansion of coronal magnetic fields. The transient shear flows hence may be understood as an observable manifestation of the pumping of magnetic helicity out of the interior portions of the field lines driven by the expansion of coronal parts as was originally proposed by Parker (1974).
639
- Ann, Hong-Bae
- Journal of the Korean astronomical society = 천문학회지
- 36, n.4
- pp.261-270
- 2003
- 원문 바로보기
We have conducted a V-band CCD surface photometry of 68 disk galaxies to analyze the bulge morphology of nearby spirals. We classify bulges into four types according to their ellipticities and the misalignments between the major axis of the bulge and those of the disk and the bar: spherical, oblate, pseudo triaxial, and triaxial. We found that one third of the bulges are triaxial and they are preponderant in barred galaxies. The presence of the triaxial bulges in a significant fraction of unbarred galaxies as well as in barred galaxies might support the secular evolution hypothesis which postulates that the bar driven mass inflow leads to the formation of triaxial bulges and the destruction of bars when sufficient mass is accumulated in the central regions.
640
- KIM SAM
- Journal of the Korean astronomical society = 천문학회지
- 36, n.1
- pp.21-31
- 2003
- 원문 바로보기
ASTRO-F /FIS will carry out all sky survey in the wavelength from 50 to 200 <TEX>${\mu}m$</TEX>. At far infrared, stars and galaxies may not be good calibration sources because the IR fluxes could be sensitive to the dust shell of stars and star formation activities of galaxies. On the other hand, asteroids could be good calibration sources at far infrared because of rather simple spectral energy distribution. Recent progresses in thermal models for asteroids enable us to calculate the far infrared flux fairly accurately. We have derived the Bond albedos and diameters for 559 asteroids based on the IRAS and ground based optical data. Using these thermal parameters and standard thermal model, we have calculated the spectral energy distributions of asteroids from 10 to 200 <TEX>${\mu}m$</TEX>. We have found that more than <TEX>$70\%$</TEX> of our sample asteroids have flux errors less than <TEX>$10\%$</TEX> within the context of the best fitting thermal models. In order to assess flux uncertainties due to model parameters, we have computed SEDs by varing external parameters such as emissivity, beaming parameter and phase integral. We have found that about 100 asteroids can be modeled to be better than <TEX>$5.8\%$</TEX> of flux uncertainties. The systematic effects due to uncertainties in phase integral are not so important.