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1968년 ~ 2023년까지 1,187 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 : 1,187건 (DB Construction : 1,187 Articles)
총 게시글 1,187건
페이지 40/119
391
- 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.
392
- 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.
393
- Oh, Su-Yeon
- Journal of the Korean astronomical society = 천문학회지
- 40, n.1
- pp.37-37
- 2007
- 원문 바로보기
394
- 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>.
395
- 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.
396
- 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>.
397
- Lee, Sung-Ho
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.151-155
- 2006
- 원문 바로보기
Long slit spectrometers are widely used in optical and infrared bands in astronomy. Absolute flux calibration for extended sources, however, is not straightforward, because a portion of the radiation energy from a flux calibration star is blocked by the narrow slit width. Assuming that the point spread function(PSF) of the star is circularly symmetric, we develop a robust method to extrapolate the detected stellar flux to the unobscured flux using the measured PSF along the slit-length direction. We apply this method to our long slit data and prove that the uncertainty of the absolute flux calibration is less than a few percents.
398
- Chi Seung-Youp
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.9-17
- 2006
- 원문 바로보기
In an attempt to investigate star formation activity and statistical properties of clumps of high Galactic latitude clouds (HLCs), we mapped the Polaris Flare region, PF121.3+25.5, in <TEX>$^{12}CO\;and\;^{13}CO$</TEX> J = 1 - 0 using SRAO 6-m telescope and also observed its 12 <TEX>$^{13}CO$</TEX> peak positions in CS J = 2 - 1 with TRAO 14-m telescope. <TEX>$^{13}CO$</TEX> integrated intensity map shows clearly its clumpy structure and the locations of clumps well agree with <TEX>$^{12}CO$</TEX>morphology. CS line is not detected toward the 12 <TEX>$^{13}CO$</TEX> peak positions, so we can conclude there are no dense <TEX>$(\sim10^4\;cm^{-3})$</TEX> in this region. We decomposed 105 clumps from <TEX>$^{13}CO$</TEX> map using GAUSSCLUMPS algorithm. The mass of clumps ranges from <TEX>$7.8\;M_{\odot}\;to\;7.4{\times}10^{-2}\;M_{\odot}$</TEX> with a total mass of <TEX>$66.4\;M_{\odot}$</TEX> The mass spectrum follows a power law, dN/dM <TEX>${\propto}\;M^{-\alpha}$</TEX> with a power index of <TEX>${\alpha}=1.91{\pm}0.13$</TEX>. The virial masses of clumps are in the range of <TEX>$10{\sim}100M_{LTE}$</TEX> and so these clumps are considered to be gravitationally unbound.
399
- Kim, Chul-Hee
- Journal of the Korean astronomical society = 천문학회지
- 39, n.4
- pp.125-128
- 2006
- 원문 바로보기
In order to determine the precise effective temperature and surface gravity of warm stars, all synthetic spectral lines in the wavelength range of <TEX>$4000-5700{\AA}$</TEX> with T=6000-7750 K, and log g=3.5, 4.0, and 4.5 for [M/H]=0.0, <TEX>$V_{rot}$</TEX>=10 km <TEX>$s^{-1}$</TEX>, and <TEX>$V_{tubl}$</TEX>=2 km <TEX>$s^{-1}$</TEX> were calculated using the SYNSPEC package(Hubeny, et al., 1995) and the Kurucz(1995) model. Then, the depth-ratios for all line pairs were investigated and we selected two and six depth-ratios appropriate for the surface gravity and temperature indicators, respectively. We plotted six grids with X- and Y-axes for the depth-ratios of surface gravity and temperature, respectively, for the simultaneous estimation of these two atmospheric parameters. This method was applied to the spectum of <TEX>$\delta$</TEX> Scu for the determination of its temperature and surface gravity simultaneously.
400
- Lee Min-Young
- Journal of the Korean astronomical society = 천문학회지
- 39, n.1
- pp.1-7
- 2006
- 원문 바로보기
We present the results of a highly sensitive (<TEX>${\sim}10$</TEX> mK rms) survey toward the central parts of 22 barred spiral galaxies in <TEX>$^{12}CO(1-0)$</TEX> line using the NRAO 12m telescope at Kitt Peak. Seven of the target galaxies were detected in CO; NGC 3686 has been detected with CO for the first time. We estimated central CO fluxes of <TEX>$50{\sim}1000\;Jy\;km\;s^{-1}$</TEX> and molecular gas masses of <TEX>$10^7{\sim}10^8\;M_{\odot}$</TEX> for those galaxies.