• Journal of The Korean Astronomical Society
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• v.34 no.3
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• pp.157-166
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• 2001

The molecular cloud associated with the H II region S301 has been mapped in the J = 1-0 transitions of $^{12}CO$ and $^{13}CO$ using the 13.7 m radio telescope of Taeduk Radio Astronomy Observatory. The cloud is elongated along the north-south direction with two strong emission components facing the H II region. Its total mass is $8.7 {\times} 10^3 M{\bigodot}$. We find a velocity gradient of the molecular gas near the interface with the optical H II region, which may be a signature of interaction between the molecular cloud and the H II region. Spectra of CO, CS, and HCO+ exhibit line splitting even in the densest part of the cloud and suggests the clumpy structure. The radio continuum maps show that the ionzed gas is distributed with some asymmetry and the eastern part of the H II region is obscured by the molecular cloud. We propose that the S301 H II region is at the late stage of the champagne phase, but the second generation of stars has not yet been formed in the postshock layer.

• Journal of The Korean Astronomical Society
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• v.34 no.3
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• pp.167-179
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• 2001

A molecular line survey towards the UC H II region G34.3+0.15 from 155.3 to 165.3GHz has been conducted with the TRAO 14-m radio telescope. Combined with our previous observations from 84.7 to 115.6GHz and 123.5 to 155.3GHz (Paper I), the spectral coverage of this survey in G34.3+0.15 now runs from 85 to 165 GHz. From these latest observations, a total of 18 lines from 6 species were detected. These include four new lines corresponding to ${\Delta}$J = 0, ${\Delta}$K = 1 transitions of the $CH_3OH$ E-type species, and two new lines corresponding to transitions from $SO_2$ and $HC_3N$. These 6 new lines are $CH_3OH$[1(1) - 1(0)E], $CH_3OH$[2(1) - 2(0)E], $CH_3OH$[3(1) - 3(0)E], $CH_3OH$[4(1) - 4(0)E], $SO_2$[14(1, 13) -14(0, 14)] and $HC_3N$[18 -17]. We applied a rotation diagram analysis to derive rotation temperatures and column densities from the methanol transitions detected, and combined with NRAO 12-m data from Slysh et al. 1999. Applying a two-component fit, we find a cold component with temperature 13-16K and column density $3.3-3.4 {\times} 10^{14} cm^{-2}$, and a hot component with temperature 64 - 83K and column density $9.3{\times}10^{14} - 9.7 {\times} 10^{14} cm^{-2}$. On the other hand, applying just a one-component fit yields temperatures in the 47 -62 K range and column densities from $7.5-1.1 {\times} 10^{15} cm^{-2}$.

• Publications of The Korean Astronomical Society
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• v.16 no.1
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• pp.15-20
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• 2001

We observed the thermal transitions of SiO (J=I-0, 2-1) and $^{29}SiO$ (J=l-O) toward the Sgr A molecular clouds. The distribution and the velocity structure of SiO are very similar to previous results for 'quiet' interstellar molecules. We think· that the SiO has been well mixed with other molecules such as $H_2$ which may indicate that the formation of Sgr A molecular clouds was affected by the activities, such as shock waves or energetic photons, from the Galactic center in large scales. The total column density of SiO is about $4.1\times10^{14} cm^{-2}$ and the fractional abundance $SiO/H_2$ appears to be about 10 times larger than those of other clouds in the central region of our galaxy. The derived values are thought to be lower limits since the optical depths of the observed SiO lines are not very thin. The formation of SiO has been known to be critically related to shocks, and our results provide informative data on the environment of our Galactic center.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.219-222
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• 2005

We present the high-resolution (2"-4") images of the molecular envelopes surrounding the evolved stars, V Hya, VY CMa, and ${\pi}^1$ Gru observed with the Submillimeter Array. The CO J=2-1 and 3-2 images of the carbon star V Hya show that the circumstellar structure of this star consists of three kinematic components; there is a flattened disk-like envelope that is expanding with a velocity of ${\~}16 km\;s^{-1}$, the second component is the medium-velocity wind having a deprojected velocity of 40-120 km $s^{-l}$ moving along the disk plane, and the third one is the bipolar molecular jet having an extreme velocity of 70-185 km $s^{-l}$. The axis of this high velocity jet is perpendicular to the plane of the disk-like envelope. We found that the circumstellar structure of the S-star ${\pi}^1$ Gru traced by the CO J =2-1 resembles that of V Hya quite closely; the star is surrounded by the expanding disk-like envelope and is driving the medium-velocity wind along the disk plane. We also obtained the excellent images of VY CMa with the CO and $^{13}CO$ J=2-1 and $SO\;6_5-5_4$ lines. The maps of three molecular lines show that the envelope has a significant velocity gradient in the east-west direction, suggesting that the envelope surrounding VY CMa is also flattened and expanding along its radial direction. The high-resolution images obtained with the SMA show that some AGB stars are associated with the asymmetric mass loss including the equatorial wind and bipolar jet.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.33-41
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• 2005

We have conducted observations toward the molecular cloud associated with the H II region Sh 156 in $^{13}CO$(J = 1-0), $C^{18}O$(J = 1-0), and CS(J = 2 -1) using the TRAO 14 m telescope. Combining with existing $^{12}CO$(J = 1- 0) data of the Outer Galaxy Survey, we delineated the physical properties of the cloud. We found that there is a significant sign of interaction between the H II region and the molecular gas. We estimated the masses of the molecular cloud, using three different techniques; the most plausible mass is estimated to be $1.37 {\times} 10^5 M_{\bigodot}$, using a conversion factor of $X = 1.9 {\times} 10^{20}\;cm^{-2} (K\;km\;s^{-1})^{-1}$, and this is similar to virial mass estimate. This implies that the cloud is gravitationally bound and in virial equilibrium even though it is closely associated with the H II region. In addition to existing outflow, we found several MSX and IRAS point sources associated with dense core regions. Thus, more star forming activities other than the existing H II region are also going on in this region.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.33.1-33.1
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• 2013

Galaxies undergo various processes in the cluster environment, which could affect their evolution. In particular, ram pressure due to intracluster medium (ICM) can effectively remove HI gas, which is a relatively diffuse form of interstellar medium (ISM). On the other hand, molecular gas is not expected to get easily stripped as atomic gas since it is denser and sitting well within the stellar disk in a deeper potential well. However, cluster galaxies are found to be redder and more passive in star formation activity compared to their field counterpart. This implies that molecular gas may also get affected somehow in dense environments. In this work, we investigate molecular gas properties of a sample of galaxies undergoing HI stripping due to the ICM. We present the 12/13 CO (2-1) data of four spiral galaxies in the Virgo cluster at different ram pressure stripping stages, obtained using the Sub Millimeter Array (SMA). CO morphology of the sample appears to be highly asymmetric and disturbed. Using the ratio of different lines, we probe the molecular gas temperature in different regions. We find higher gas temperature than the range normally found among field galaxies. We discuss how these distinct molecular gas properties may affect star formation and hence the evolution of the cluster galaxy population.

• Journal of The Korean Astronomical Society
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• v.31 no.2
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• pp.117-125
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• 1998

We have observed the 10-9 transitions of $HC_3N$ and its $^{13}C$ substitutes ($H^{13}CCCN,\;HC^{13}CCN$, and $HCC^{13}CN$), and the vibration ally excited 12-11 ($v_r=1$) $HC_3N$ transition toward the Sgr B2 molecular cloud. The observed $HC_3N$ emission shows an elongated shape around the Principal Cloud ($\~$4.5 pc in R.A. $\times$ 7.4 pc in Decl.). The optically thin $H^{13}CCCN$ line peaks around the (N) core and we derive the total column density $N(H^{13}CCCN) = 4 {\times}10^{13} cm^{-2}$ at this position. Toward the 2' N cloud which shows the peculiar chemistry, the $HC_3N$ lines show enhancements compared to the extended envelope. The shocks of the 2' N may have resulted in the enhancement of $HC_3N$. The hot component of $HC_3N$ is strongly concentrated around the (N) core and its HPW is $\~$0.9 pc in diameter. We derive the lower limit of the abundance ratio $N(HC_3N)/N(H^{13}CCCN)$ to be larger than 40 in most regions except the (M) and (N) cores. The fractionation processes of $^{13}C $at this region may not be as effective as previously reported.

• Journal of The Korean Astronomical Society
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• v.49 no.6
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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).

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.133-135
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• 2007

A survey project of TRAO with the fifteen beam array receiver system is presented. A multibeam array receiver system has been purchased from FCRAO, and is being installed on TRAO 14m telescope. The target region of the survey is from ${\iota}=120^{\circ}{\sim}137^{\circ},\;b=-1^{\circ}{\sim}+ 1^{\circ}$, and velocity resolution would be 1 km/sec after smoothing from the original resolution of $0.64km\;s^{-1}$ in the transition of J = 1-0 of $^{13}CO$. The survey region is a part of the $^{12}CO$ Outer Galaxy Survey(OGS), and would be an extension of the Bell Laboratories $^{13}CO$ Galactic Plane Survey. By combining with the existing $^{12}CO$ database of the Outer Galaxy Survey, we will derive physical properties of identified molecular clouds and will conduct and statistical analysis of the Outer Galalxy molecular clouds. Reduction process and analysis methods will be introduced.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.167-175
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• 2003

There is accumulating evidence for a strong link between nuclear starbursts and AGN. Molecular gas in the central regions of galaxies plays a critical role in fueling nuclear starburst activity and feeding central AGN. The dense molecular ISM is accreted to the nuclear regions by stellar bars and galactic interactions. Here we describe recent observational results for the OB star forming regions in M51 and the nuclear star burst in Arp 220 - both of which have approximately the same rate of star formation per unit mass of ISM. We suggest that the maximum efficiency for forming young stars is an Eddington-like limit imposed by the radiation pressure of newly formed stars acting on the interstellar dust. This limit corresponds to approximately 500 $L_{\bigodot} / M_{\bigodot}$ for optically thick regions in which the radiation has been degraded to the NIR. Interestingly, we note that some of the same considerations can be important in AGN where the source of fuel is provided by stellar evolution mass-loss or ISM accretion. Most of the stellar mass-loss occurs from evolving red giant stars and whether their mass-loss can be accreted to a central AGN or not depends on the radiative opacity of the mass-loss material. The latter depends on whether the dust survives or is sublimated (due to radiative heating). This, in turn, is determined by the AGN luminosity and the distance of the mass-loss stars from the AGN. Several AGN phenomena such as the broad emission and absorption lines may arise in this stellar mass-loss material. The same radiation pressure limit to the accretion may arise if the AGN fuel is from the ISM since the ISM dust-to-gas ratio is the same as that of stellar mass-loss.