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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 42/122
411
- Migenes, V.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.127-129
- 2007
- 원문 바로보기
It is well known that water vapor maser emission at 22.2 GHz is associated with the earliest stages of both low- and high-mass star formation and it can be considered a reliable diagnostic of their evolutionary state. Bright Rimmed Clouds (BRCs) are clouds that have been compressed by an external ionization-shock front which focuses the neutral gas into compact globules. The boundary layer between the neutral gas and the gas ionized by the incident photons is often called 'bright rim' but the clumps are sometimes classified also as speck globules or cometary globules depending on their appearance. Small globules with bright rims have been considered to be potential sites of star formation and have been studied in several individual regions. We present results from high resolution VLA observations searching for new candidates of recent star formation in bright-rimmed clouds/globules associated with IRAS point sources.
412
- Richer, Michael G.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.183-186
- 2007
- 원문 바로보기
The spectroscopic properties of bright extragalactic planetary nebulae are reviewed, considering primarily their chemical abundances and their internal kinematics. Low-resolution spectroscopy is used to investigate how the precursor stars of bright planetary nebulae modify their original composition through nucleosynthesis and dredge up. At present, the evidence indicates that oxygen and neon abundances usually remain unchanged, helium abundances are typically enhanced by less than 50%, while nitrogen enhancements span a very wide range. Interpreting these changes in terms of the masses of their progenitor stars implies that the progenitor stars typically have masses or order <TEX>$1.5M_{\bigodot}$</TEX> or less, though no models satisfactorily explain the nitrogen enrichment. High-resolution spectroscopy is used to study the internal kinematics of bright planetary nebulae in Local Group galaxies. At first sight, the expansion velocities are remarkably uniform, with a typical expansion velocity of 18 km/s and a range of 8-28 km/s, independent of the progenitor stellar population. Upon closer examination, bright planetary nebulae in the bulge of M31 expand slightly faster than their counterparts in M31's disk, a result that may extend generally to the planetary nebulae arising from old and young stellar populations. There are no very strong correlations between expansion velocity and global nebular properties, except that there are no large expansion velocities at the highest <TEX>$H{\beta}$</TEX> luminosities (i.e., the youngest objects never expand rapidly). These results independently suggest that bright planetary nebulae arise from a similar mass range in all galaxies. Nonetheless, there are good reasons to believe that bright planetary nebulae do not arise from identical progenitor stars in all galaxies.
413
- Ann, H.B.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.9-16
- 2007
- 원문 바로보기
We examine the morphology and luminosity distribution of a strongly warped spiral galaxy PGC 20348 by conducting a detailed BVI CCD surface photometry using BOAO 1.8m telescope. The radial surface brightness shows a break at warp radius <TEX>$(r_{\omega})$</TEX> with a shallow gradient in the inner disk and a steeper gradient in the outer disk. The luminosity of east side of the disk is <TEX>${\sim}0.5$</TEX> mag fainter than the west side at r > <TEX>$r_{\omega}$</TEX>. The reason for the asymmetric luminosity distribution is thought to be the asymmetric flarings that result in the formation of a large diffuse region at the edge of the east disk and a smaller diffuse region at the west disk. The vertical luminosity profiles show a thick disk component whose scale heights increase with increasing galactocentric distances. The warp of PGC 20348 seems to be made by the tidal interactions with the two massive companion galaxies since the flarings and radial increase of disk scale heights are thought to be general properties of tidally perturbed disks. According to the colors of the two clumps inside the diffuse region at the edge of the east disk, they seem to be sites of active star formation triggered by tidal forces from the companion galaxies.
414
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.83-89
- 2007
- 원문 바로보기
A new type of object called 'Very Low Luminosity Objects (VeLLOs)' has been discovered by the Spitzer Space Telescope. VeLLOs might be substellar objects forming by accretion. However, some VeLLOs are associated with strong outflows, indicating the previous existence of massive accretion. The thermal history, which significantly affects the chemistry, between substellar objects with a continuous low accretion rate and objects in a quiescent phase after massive accretion (outburst) must be greatly different. In this study, the chemical evolution has been calculated in an episodic accretion model to show that CO and <TEX>$N_2H^+$</TEX> have a relation different from starless cores or Class 0/I objects. Furthermore, the <TEX>$CO_2$</TEX> ice feature at <TEX>$15.2{\mu}m$</TEX> will be a good tracer of the thermal process in VeLLOs.
415
- Santikkan, Alfredo
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.165-169
- 2007
- 원문 바로보기
The numerical simulations associated with the interaction of High Velocity Clouds (HVC) with the Magnetized Galactic Interstellar Medium (ISM) are a powerful tool to describe the evolution of the interaction of these objects in our Galaxy. In this work we present a new project referred to as Theoretical Virtual i Observatories. It is oriented toward to perform numerical simulations in real time through a Web page. This is a powerful astrophysical computational tool that consists of an intuitive graphical user interface (GUI) and a database produced by numerical calculations. In this Website the user can make use of the existing numerical simulations from the database or run a new simulation introducing initial conditions such as temperatures, densities, velocities, and magnetic field intensities for both the ISM and HVC. The prototype is programmed using Linux, Apache, MySQL, and PHP (LAMP), based on the open source philosophy. All simulations were performed with the MHD code ZEUS-3D, which solves the ideal MHD equations by finite differences on a fixed Eulerian mesh. Finally, we present typical results that can be obtained with this tool.
416
- Oh, Su-Yeon
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.37-37
- 2007
- 원문 바로보기
417
- Nejad-Asghar, Mohsen
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.29-36
- 2007
- 원문 바로보기
The smoothed particle hydrodynamics (SPH) method is applied to construct the dispersion of fluctuations in quasi-hydrostatic configuration of an isothermal self-gravitating slab. The uncertainty of the implementation is evaluated, and a novel technique (acceleration error) is proposed to weaken this uncertainty. The two-fluid quasi-hydrostatic diffusion of small fluctuations is used to support the importance of the acceleration error. The results show that the uncertainty converges to a few percent by increasing of the SPH particle numbers. Considering the acceleration error weakens the uncertainty, and prohibits the serious dynamical consequences in slow dispersion of fluctuation in the quasi-hydrostatic evolution of the slab.
418
- Lee, Jeong-Eun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.107-111
- 2007
- 원문 바로보기
The original environment of the solar system can be inferred by studying the oxygen isotope ratios in the Sun as well as in primitive meteorites and comets. The oxygen isotopic fractionation measured in primitive meteorites is mass-independent, which can be explained by the isotopic-selective photodissociation of CO. The isotopic-selective photodissociation model in a collapsing cloud by Lee et al. (2007) imply the birth of the Sun in a stellar cluster with an enhanced radiation field, which is consistent with the inferred presence of <TEX>$^{60}Fe$</TEX>.
419
- Kim, Hyo-Sun
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.17-28
- 2007
- 원문 바로보기
We present wide-field <TEX>$JHK_s$</TEX>-band photometric observations of the three compact H II regions G48.9-0.3, G49.0-0.3, and G49.2-0.3 in the active star-forming region W51B. The star clusters inside the three compact H II regions show the excess number of stars in the <TEX>$J-K_s$</TEX> histograms compared with reference fields. While the mean color excess ratio <TEX>$(E_{J-H}/E_{H-K_s})$</TEX> of the three compact H II regions are similar to <TEX>${\sim}2.07$</TEX>, the visual extinctions toward them are somewhat different: <TEX>${\sim}17$</TEX> mag for G48.9-0.3 and G49.0-0.3; <TEX>${\sim}23$</TEX> mag for G49.2-0.3. Based on their sizes and brightnesses, we suggest that the age of each compact H II region is <TEX>${\leq}2\;Myr$</TEX>. The inferred total stellar mass, <TEX>${\sim}1.4{\times}10^4M_{\odot}$</TEX>, of W51B makes it one of the most active star forming regions in the Galaxy with the star formation efficiency of <TEX>${\sim}10%$</TEX>.
420
- Kim, Sung-Soo S.
- Journal of the Korean astronomical society = 천문학회지
- 40, n.4
- pp.153-155
- 2007
- 원문 바로보기
We have analyzed H and <TEX>$K_s$</TEX>-band images of the Arches cluster obtained using the NIRC2 instrument on Keck with the laser guide star adaptive optics (LGS AO) system. With the help of the LGS AO system, we were able to obtain the deepest ever photometry for this cluster and its neighborhood, and derive the background-subtracted present-day mass function (PDMF) down to <TEX>$1.3M_{\bigodot}$</TEX> for the 5'-9' annulus of the cluster. We find that the previously reported turnover at <TEX>$6M_{\bigodot}$</TEX> is simply due to a local bump in the mass function (MF), and that the MF continues to increase down to our 50 % completeness limit (<TEX>$1.3M_{\bigodot}$</TEX>) with a power-law exponent of <TEX>${\Gamma}$</TEX> = -0.91 for the mass range of 1.3 < M/<TEX>$M_{\bigodot}$</TEX> < 50. Our numerical calculations for the evolution of the Arches cluster show that the <TEX>${\Gamma}$</TEX> values for our annulus increase by 0.1-0.2 during the lifetime of the cluster, and thus suggest that the Arches cluster initially had <TEX>${\Gamma}$</TEX> of <TEX>$-1.0{\sim}-1.1$</TEX>, which is only slightly shallower than the Salpeter value.