Sgr A 분자운의 열적 SiO 천이선 관측연구

민영철,노덕규,김상준,MINH Y. C.,ROH D.-G.,KIM S. J.,OHISHI M. 한국천문학회 2001 天文學論叢 Vol.16 No.1

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.

IMAGING THE CIRCUMSTELLAR ENVELOPES AROUND EVOLVED STARS WITH THE SMA

HIRANO NAOMI,CHIU PO-JIAN,MULLER SEBASTIEN,TRUNG DINH-V The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2

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.

Blueshifted diffuse interstellar bands in the spectrum of HD 34078

Galazutdinov, G. A.,Manicò,, G.,Krełowski, J. Blackwell Science Ltd 2006 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.366 No.3

<P>ABSTRACT</P><P>In this paper, we report the very first observation of diffuse interstellar bands (DIBs) that, in the spectrum of HD 34078 (AE Aur), are blueshifted with respect to the normal position that they have in other objects, where the rest-wavelength velocity frame is determined using very sharp interstellar atomic lines or molecular features. Only reasonably narrow DIBs seemingly show this effect, which is absent in broader ones. The result is confirmed independently using three different spectrographs attached to two different telescopes.</P>

A SPECTRAL LINE SURVEY FROM 159.7 TO 164.7 GHZ TOWARD ORION-KL: THE DATA

LEE CHANG WON,CHO SE-HYUNG The Korean Astronomical Society 2002 Journal of The Korean Astronomical Society Vol.35 No.4

A spectral line survey is performed from 159.7 to 164.7 GHz toward Orion-KL, as an extension of our previous line survey from 138.3 to 150.7 GHz with the same 14 m radio telescope of Taeduk Radio Astronomy Observatory. Typical system temperatures were 260 - 1000 K to achieve a sensitivity of about 0.02 - 0.04 K in TA unit. A total of 63 line spectra are detected in this survey. Among them, 54 lines lines are found to be the first detections towards an astronomical source and only 9 spectral lines have been previously identified from other observations. Forty-eight of 54 lines are believed to be from the known transitions of the known molecules, while 6 lines are 'unidentified'. All detected lines are found to be from a total of 10 molecular species and their isotopic variants. The molecular species with most numerous detected transitions are $HCOOCH_3$ (22), followed by $CH_3OCH_3$ (7), $C_2H_5CN$ (7), and $SO_2$ (6). The LTE rotation diagram analysis using all homogeneous data with those from previous survey gives more reliable determination of physical quantities. The derived values of the rotation temperatures and column densities for $HCOOCH_3$, $CH_3OCH_3$, and $SO_2$ are are 75 $\~$ 197 K and $1.5 {\~}18 {\times} 10^{15}\;cm^{-2}$, respectively.

Physical properties of giant molecular clouds in the Large Magellanic Cloud

Hughes, A.,Wong, T.,Ott, J.,Muller, E.,Pineda, J. L.,Mizuno, Y.,Bernard, J.-P.,Paradis, D.,Maddison, S.,Reach, W. T.,Staveley-Smith, L.,Kawamura, A.,Meixner, M.,Kim, S.,Onishi, T.,Mizuno, N.,Fukui, Y. Blackwell Publishing Ltd 2010 Monthly notices of the Royal Astronomical Society Vol.406 No.3

<P>ABSTRACT</P><P>The Magellanic Mopra Assessment (MAGMA) is a high angular resolution <SUP>12</SUP>CO (<I>J</I>= 1 → 0) mapping survey of giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud using the Mopra Telescope. Here we report on the basic physical properties of 125 GMCs in the LMC that have been surveyed to date. The observed clouds exhibit scaling relations that are similar to those determined for Galactic GMCs, although LMC clouds have narrower linewidths and lower CO luminosities than Galactic clouds of a similar size. The average mass surface density of the LMC clouds is 50 M<SUB>⊙</SUB> pc<SUP>−2</SUP>, approximately half that of GMCs in the inner Milky Way. We compare the properties of GMCs with and without signs of massive star formation, finding that non-star-forming GMCs have lower peak CO brightness than star-forming GMCs. We compare the properties of GMCs with estimates for local interstellar conditions: specifically, we investigate the H <SMALL>I</SMALL> column density, radiation field, stellar mass surface density and the external pressure. Very few cloud properties demonstrate a clear dependence on the environment; the exceptions are significant positive correlations between (i) the H <SMALL>I</SMALL> column density and the GMC velocity dispersion, (ii) the stellar mass surface density and the average peak CO brightness and (iii) the stellar mass surface density and the CO surface brightness. The molecular mass surface density of GMCs without signs of massive star formation shows no dependence on the local radiation field, which is inconsistent with the photoionization-regulated star formation theory proposed by McKee. We find some evidence that the mass surface density of the MAGMA clouds increases with the interstellar pressure, as proposed by Elmegreen, but the detailed predictions of this model are not fulfilled once estimates for the local radiation field, metallicity and GMC envelope mass are taken into account.</P>

CO OBSERVATIONS OF A HIGH LATITUDE CLOUD MBM 40 WITH A HIGH RESOLUTION AUTOCORRELATOR

LEE YOUNGUNG,CHUNG HYUN SOO,KIM HYORYOUNG The Korean Astronomical Society 2002 Journal of The Korean Astronomical Society Vol.35 No.2

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.

VLA AMMONIA LINE OBSERVATIONS OF THE YOUNG STELLAR OBJECT IRAS 19550+3248

LEE Ho-GYU,KOO BON-CHUL,PARK YONG-SUN,HO PAUL T. P. The Korean Astronomical Society 2002 Journal of The Korean Astronomical Society Vol.35 No.2

We present the results of VLA $NH_3$ (1,1) and (2,2) line observations of the young-stellar object (YSO) IRAS 19550+3248. The integrated intensity map of the $NH_3$ (1,1) line shows that there are two ammonia cores in this region; core A which is associated with the YSO, and core B which is diffuse and located at the northeast of core A. Core A is compact and elongated along the east-west direction (0.07 pc$\times$0.05 pc) roughly perpendicular to the molecular outflow axis. Core B is diffuse and extended (0.18 pc$\times$0.07 pc). $NH_3$ (2,2) line is detected only toward core A, which indicates that it is hotter (~ 15 K), presumably due to the heating by the YSO. The $NH_3$ (1,1) line toward core A is wide (${\Delta}v{\ge} 3 km s^{-l}$) and appears to have an anomalous intensity ratio of the inner satellite hyperfine lines. The large line width may be attributed to the embedded YSO, but the hyperfine anomaly is difficult to explain. We compare the results of $NH_3$ observations with those of previous CS observations and find that the CS emission is detected only toward core A and is much more extended than the $NH_3$ emission.

SiO IN THE SGR B2 REGION

Minh, Y.C. The Korean Astronomical Society 2007 Journal of The Korean Astronomical Society Vol.40 No.3

The 2-1 and 5-4 transitions of SiO have been observed toward the Sgr B2 region, including the Principal Cloud(the GMC containing Sgr B2(M)) and its surroundings. The morphology and velocity structure of the SiO emission show a close resemblance with the HNCO Ring feature, identified by Minh & Irvine(2006), of about 10 pc in diameter, which may be expanding and colliding with the Principal Cloud. Three SiO clumps have been found around the Ring, with total column densities $N_{SiO}{\sim}1{\times}10^{14}cm^{-2}$ at the peak positions of these clumps. The fractional SiO abundance relative to $H_2$ has been estimated to be ${\sim}(0.5-1){\times}10^{-9}$, which is about two orders of magnitude larger than the quiet dense cloud values. Our SiO observational result supports the existence of an expanding ring, which may be triggering active star formations in the Principal Cloud.

[ N₂H⁺ ] OBSERVATIONS OF MOLECULAR CLOUD CORES IN TAURUS

TATEMATSU KEN'ICHI The Korean Astronomical Society 2005 Journal of The Korean Astronomical Society Vol.38 No.2

We report the millimeter-wave radio observations of molecular cloud cores in Taurus. The observed line is the $N_2H^+$ emission at 93 GHz, which is known to be less affected by molecular depletion. We have compared starless (IRAS-less) cores with star-forming cores. We found that there is no large difference between starless and star-forming cores, in core radius, linewidth, core mass, and radial intensity profile. Our result is in contrast with the result obtained by using a popular molecular line, in which starless cores are larger and less condensed. We suggest that different results mainly come from whether the employed molecular line is affected by depletion or not. We made a virial analysis, and found that both starless and star-forming cores are not far from the critical equilibrium state, in Taurus. Together with the fact that Taurus cores are almost thermally supported, we conclude that starless Taurus cores evolve to star formation without dissipating turbulence. The critical equilibrium state in the virial analysis corresponds to the critical Bonnor-Ebert sphere in the Bonnor-Ebert analysis (Nakano 1998). It is suggested that the initial condition of the molecular cloud cores/globules for star formation is close to the critical equilibrium state/critical Bonnor-Ebert sphere, in the low-mass star forming region.

HCN(1-0) OBSERVATIONS OF STARLESS CORES

J. SOHN,C. W. LEE,H. M. LEE,Y.-S. PARK,P. C. MYERS,Y. LEE,M. TAFALLA 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

We present a progress report on HCN(1-0) line observations toward starless cores to probe inwardmotions. We have made a single pointing survey toward the central regions of 85 starless cores andperformed mapping observations of 6 infall candidate starless cores. The distributions of the velocitydierence between HCN(1-0) hyperne lines and the optically thin tracer N2H+ (1-0) are signicantlyskewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to theblue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence thanCS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infallasymmetry seen in HCN(1-0) hyperne lines, CS(3-2), CS(2-1), DCO+ (2-1) and N2H+ observations.The HCN(1-0) F(0-1) with the least optical depth usually shows a similar intensity distribution to thatof N2H+ which closely traces the density distribution of the cores, indicating that HCN(1-0) is lesschemically aected and so believed to reect kinematics occurring in rather inner regions of the cores.Detailed radiative transfer model ts of the spectra are underway to analyze central infall kinematicsin starless cores.