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Observations of the CH<sub>3</sub>OH 4<sub>2</sub>-5<sub>1</sub> E Line Toward the Sgr B2 Region
Minh, Young-Chol,Kim, Sang-Joon The Korean Space Science Society 2011 Journal of Astronomy and Space Sciences Vol.28 No.1
The $CH_3OH$ $4_2-5_1$ E transition was observed toward the Sgr B2 region, including the Principal Cloud and its surroundings. This methanol transition shows an extended emission along the 2'N cloud, which is believed to be colliding with the Principal Cloud and may trigger the massive star formation in this cloud. This extended methanol emission may also suggest that the 2'N cloud is under shocks. We derive total methanol column density $N(CH_3OH)\;=\;2.9{\pm}0.3{\times}10^{14}\;cm^{-2}$ toward the peak position of the extended emission. The fractional abundance of methanol is about 10.9, relative to the estimated total $H_2$ abundance, which is similar to the methanol abundances in quiet gas phase.
Minh, Young Chol,Liu, Hauyu Baobab,Ho, Paul T. P.,Hsieh, Pei-Ying,Su, Yu-Nung,Kim, Sungsoo S.,Wright, Melvyn IOP Publishing 2013 The Astrophysical journal Vol.773 No.1
<P>Ammonia (3, 3) and (6, 6) transitions have been observed using the Green Bank Telescope toward the Sgr A region. The gas is mainly concentrated in 50 km s(-1) and 20 km s(-1) clouds located in a plane inclined to the galactic plane. These 'main' clouds appear to be virialized and influenced by the expansion of the supernova remnant Sgr A East. The observed emission shows very complicated features in the morphology and velocity structure. Gaussian multi-component fittings of the observed spectra revealed that various 'streaming' gas components exist all over the observed region. These components include those previously known as 'streamers' and 'ridges,' but most of these components appear not to be directly connected to the major gas condensations (the 50 km s(-1) and 20 km s(-1) clouds). They are apparently located out of the galactic plane, and they may have a different origin than the major gas condensations. Some of the streaming components are expected to be sources that feed the circumnuclear disk of our Galactic center directly and episodically. They may also evolve differently than major gas condensations under the influence of the activities of the Galactic center.</P>
CHEMICAL DIAGNOSTICS OF THE MASSIVE STAR CLUSTER-FORMING CLOUD G33.92+0.11. III. $^{13}$CN AND DCN
Young Chol Minh,Hauyu Baobab Liu 한국천문학회 2019 Journal of The Korean Astronomical Society Vol.52 No.3
Using ALMA observations of the $^{13}$CN and DCN lines in the massive star-forming region G33.92+0.11A, we investigate the CN/HCN abundance ratio, which serves as a tracer of photodissociation chemistry, over the whole observed region. Even considering the uncertainties in calculating the abundance ratio, we find high ratios ($\gg$1) in large parts of the source, especially in the outer regions of star-forming clumps A1, A2, and A5. Regions with high CN/HCN ratios coincide with the inflows of accreted gas suggested by \citet{liu15}. We conclude that we found strong evidence for interaction between the dense gas clumps and the accreted ambient gas which may have sequentially triggered the star formation in these clumps.
Minh, Young Chol,Liu, Hauyu Baobab,Chen, Huei-Ru Vivien The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.3
In the molecular cloud G33.92+0.11A, massive stars are forming sequentially in dense cores, probably due to interaction with accreted gas. Cold dense gas, which is likely the pristine gas of the cloud, is traced by DCN line and dust continuum emission. Clear chemical differences were observed in different source locations and for different velocity components in the same line of sight. Several distinct gas components coexist in the cloud: the pristine cold gas, the accreted dense gas, and warm turbulent gas, in addition to the star-forming dense clumps. Filaments of accreted gas occur in the northern part of the A1 and A5 clumps, and the velocity gradient along these features suggests that the gas is falling toward the cloud and may have triggered the most recent star formation. The large concentration of turbulent gas in the A2 clump seems to have formed mainly through disturbances from the outside.
SMA OBSERVATIONS OF THE HOT CORES OF DR21(OH)
Minh, Young Chol,Chen, Huei-Ru,Su, Yu-Nung,Liu, Sheng-Yuan The Korean Astronomical Society 2012 Journal of The Korean Astronomical Society Vol.45 No.6
Using the Submillimeter Array (SMA), we identified two bright hot subcores, MM1a and MM1b (size ~ 1" and mass ~ 0.5 $M_{\odot}$) separated by about 1.600, in the 230 GHz continuum emission toward the massive star-forming region DR21(OH). Both display typical hot core characteristics but have slightly different chemical properties. For example, highly saturated species show stronger emission toward MM1a and seem to be evaporating directly from the grain mantles. In contrast, simple sulfur-bearing species have brighter emission at MM1b. These features indicate that MM1a is at an earlier stage than MM1b, and the small-scale chemical differences between these two cores may result from the age difference of the order of $10^4$ years.