• 천문학회지
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• 제26권1호
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• pp.73-78
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• 1993

We have mapped the $C_3H_2\;2_{12}-1_{01}$ transition line toward the Sgr A molecular cloud on a 1' grid spacing and derived $C_3H_2$ column densities of $3\~7\times10^{14}\;cm^{-2}$ for molecular clouds of Sgr A. The fractional abundances of $C_3H_2$ relative to $H_2$ are obtained to be $3\~6\times10^{-9}$, which are slightly lower than that for the cold dark cloud TMC-1 but are enhanced by factors of 5-60 compared to those for Sgr B2 and the Orion extended ridge. We also estimate from the $C_3H_2$ column densities total masses of $\~10^6\; M_\bigodot$ for two clouds (M - 0.13 - 0.08 and M - 0.02 - 0.07), which are thought to be close to the virial equilibrium. We suggest that the large abundance of $C_3H_2$ in Sgr A may be partly due to the activities of the Galactic center.

• 천문학회보
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• 제35권1호
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• pp.68.1-68.1
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• 2010

We focus on two Galactic molecular clouds that are located in wholly different environments and both are observed by FIMS instrument onboard STSAT-1. The Draco cloud is known as a translucent molecular cloud at high Galactic latitude. The FUV spectra show important ionic lines of C IV, Si IV+O IV], Si II* and Al II, indicating the existence of hot and warm interstellar gases in the region. The enhanced C IV emission inside the Draco cloud region is attributable to the turbulent mixing of the interacting cold and warm/hot media, which is supported by the detection of the O III] emission line and the $H{\alpha}$ feature in this region. The Si II* emission covers the remainder of the region outside the Draco cloud, in agreement with previous observations of Galactic halos. Additionally, the H2 fluorescent map is consistent with the morphology of the atomic neutral hydrogen and dust emission of the Draco cloud. In the Aquila Rift region near Galactic plane, FIMS observed that the FUV continuum emission from the core of the Aquila Rift suffers heavy dust extinction. The entire field is divided into three sub-regions that are known as the- "halo," "diffuse," and "star-forming" regions. The "diffuse" and "star-forming" regions show various prominent H2 fluorescent emission lines, while the "halo" region indicates the general ubiquitous characteristics of H2. The CLOUD model and the FUV line ratio are included here to investigate the physical conditions of each sub-region. Finally, the development of an infrared imaging system known as the MIRIS instrument onboard STSAT-3 is briefly introduced. It can be used in WIM studies through $Pa{\alpha}$ observations.

• 천문학회보
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• 제44권2호
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• pp.68.3-68.3
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• 2019

We present the preliminary results on the formation of star clusters by cloud-cloud collision. For this purpose, we perform sub-parsec scale, radiation-hydrodynamic simulations of giant molecular clouds using a sink particle algorithm. The simulations include photo-ionization, direct radiation pressure, and non-thermal radiation pressure from infrared and Lyman alpha photons. We confirm that radiation feedback from massive stars suppresses accretion onto sink particles. We examine the collision-induced star formation and discuss the possibility on the formation of a globular cluster.

• 천문학회지
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• 제29권spc1호
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• pp.183-186
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• 1996

We report the results of H I 21-cm and molecular line studies of the shocked interstellar gas in the W51 complex. We present convincing evidences suggesting that the shocked gas has been produced by the interaction of the W51C supernova remant (SNR) with a large molecular cloud, Our results show that W51C is the second SNR with direct evidences for the shocked cloud material.

• 천문학회지
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• 제27권1호
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• pp.31-44
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• 1994

The 4.8GHz formaldehyde absorption line in the dark clouds in M17 and NGC 2024 regions has been mapped. In both nebulae, we detected two $H_2CO$ line components. In M17, the 24km $S^{-1}$ cloud is closely associated with the HII region located in front of the radio continuum source, and the 19km $S^{-1}$ cloud is associated with the visual dark clouds with a larger extent which are closer to us. The 19km $S^{-1}$ cloud has a mass motion approaching to the HII region. In both clouds, a velocity gradient from the north-east to the south-west directions is observed. The linewidth has no variation indicating no collapsing motion. In NGC 2024, the 9km $S^{-1}$ feature is extended along the dark bar in front of the bright nebula and a weak second component at 13km $S^{-1}$ is confined to the immediate vicinity of the radio source. Indications are that the 9km $S^{-1}$ cloud is physically associated with the dark bar and the 13km $S^{-1}$ cloud is located behind the radio source. The angular extent, the column density, and the total mass of the clouds are derived. The radial velocities of other molecular lines observed in these clouds are compared.

• 천문학회지
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• 제41권5호
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• pp.139-145
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• 2008

The molecular cloud, embedding AFGL 2591, has a "head-and-tail" structure with a total mass of ${\sim}\;1800\;M_{\odot}$, about half of the mass (${\sim}\;900\;M_{\odot}$) in the head (size ${\sim}\;1.2\;pc$ in diameter), and another half in the envelope (${\sim}\;3.5\;pc$ in the east-west direction). We found a new cloud in the direction toward north-east from AFGL 2591 (projected distance ${\sim}\;2.4\;pc$), which is probably associated with the AFGL 2591 cloud. The $^{12}CO$ spectrum clearly shows a blue-shifted high-velocity wing at around the velocity $-20\;{\sim}\;-10\;km\;s^{-1}$, but it is not clear whether this high-velocity component has a bipolar nature in our observations. The observed CN spectra also show blue-shifted wing component but the existence of the red-shifted component is not clear, either. In some CN and HCN spectra, the highvelocity components appear as a different velocity component, not a broad line-wing component. The dense cores, traced by CN and HCN, exist in the 'head' of the AFGL 2591 cloud with an elongated morphology roughly in the north-south direction with a size of about 0.5 pc. The abundance ratio between CN and HCN is found to be about 2 - 3 within the observed region, which may suggest a possibility that this core is being affected by the embedded YSOs or by possible shocks from outside.

• 천문학회보
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• 제44권1호
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• pp.43.3-43.3
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• 2019

Magnetic fields play an important role in supporting molecular clouds against gravitational collapse. The measured magnetic field strengths in molecular clods enable us to see the effect of magnetic fields in star-forming regions. People have used the Chandrasekhar and Fermi (CF) method to estimate magnetic field strength from observational quantities of molecular cloud density, turbulent velocity and polarization angle dispersion. However, previous studies obtained just one magnetic field strength over the quite large region of a molecular cloud by using the CF method. We here suggest a way to estimate magnetic field strength distribution in Orion A region. We used 450 and 850-micron polarization data of James Clerk Maxwell Telescope (JCMT). Magnetic field strengths were estimated in two wavelengths with 4 pixel resolutions of 16, 20, 24 and 28". Through statistical analysis, we proved the difference of magnetic field strengths between two wavelengths were caused by the difference of their beam sizes. Additionally, we calculated the radii of curvature of polarization segments to select a best pixel resolution for estimating the magnetic field distribution. The pixel resolution should be larger than a radius of curvature. We selected that 20 or 24" pixel resolutions are good choices towards Orion A region.

• 천문학회지
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• 제35권2호
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• pp.97-103
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• 2002

We have mapped 1 $deg^2$ region toward a high latitude cloud MBM 40 in the J = 1 - 0 transition of $^{12}CO$ and $^{13}CO$, using the 3 mm SIS receiver on the 14 m telescope at Taeduk Radio Astronomy Observatory. We used a high resolution autocorrelator to resolve extremely narrow CO linewidths of the molecular gas. Though the linewidth of the molecular gas is very narrow (FWHP < 1 km $s^{-1}$ ), it is found that there is an evident velocity difference between the middle upper part and the lower part of the cloud. Their spectra for both of $^{12}CO$ and $^{13}CO$ show blue wings, and the position-velocity map shows clear velocity difference of 0.4 km $s^{-1}$ between two parts. The mean velocity of the cloud is 3.1 km $s^{-1}$. It is also found that the linewidths at the blueshifted region are broader than those of the rest of the cloud. We confirmed that the visual extinction is less than 3 magnitude, and the molecular gas is translucent. We discussed three mass estimates, and took a mass of 17 solar masses from CO integrated intensity using a conversion factor $2.3 {\times} 10^{20} cm^{-2} (K\;km s^{-1})^{-1}$. Spatial coincidence and close morphological similarity is found between the CO emission and dust far-infrared (FIR) emission. The ratio between the 100 f.Lm intensity and CO integrated intensity of MBM 40 is 0.7 (MJy/sr)/(K km $s^{-1}$), which is larger than those of dark clouds, but much smaller than those of GMCs. The low ratio found for MBM 40 probably results from the absence of internal heating sources, or significant nearby external heating sources.

• 천문학회지
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• 제49권6호
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• pp.255-259
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• 2016

We estimate the fractal dimension of the ${\rho}$ Ophiuchus Molecular Cloud Complex, associated with star forming regions. We selected a cube (${\upsilon}$, l, b) database, obtained with J = 1-0 transition lines of $^{12}CO$ and $^{13}CO$ at a resolution of 22" using a multibeam receiver system on the 14-m telescope of the Five College Radio Astronomy Observatory. Using a code developed within IRAF, we identified slice-clouds with two threshold temperatures to estimate the fractal dimension. With threshold temperatures of 2.25 K ($3{\sigma}$) and 3.75 K ($5{\sigma}$), the fractal dimension of the target cloud is estimated to be D = 1.52-1.54, where $P{\propto}A^{D/2}$, which is larger than previous results. We suggest that the sampling rate (spatial resolution) of observed data must be an important parameter when estimating the fractal dimension, and that narrower or wider dispersion around an arbitrary fit line and the intercepts at NP = 100 should be checked whether they relate to firms noise level or characteristic structure of the target cloud. This issue could be investigated by analysing several high resolution databases with different quality (low or moderate sensitivity).

• 천문학회보
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• 제30권2호
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• pp.78.2-78.2
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• 2005