MOLECULAR CORES OF THE HIGH-LATITUDE CLOUD MBM7

Y. C. MINH,H. G. KIM,S. J. KIM,P. BERGMAN,L. E. B. JOHANSSON 한국천문학회 2000 Journal of The Korean Astronomical Society Vol.33 No.1

We have investigated the properties of the high-latitude cloud MBM 7 using the 3 mm transitions of CO, CS, HCN, HCO+,C3H2,N2H+, and SiO. The molecular component of MBM 7 shows a very clumpy structure with a size of ≤0.5 pc, elongated along the northwest-southeast direction, perpendicularly to an extended HI component, which could be resulted from shock formation. We have derived physical properties for two molecular cores in the central region. Their sizes are 0.1-0.3 pc and masses 1-2 M⊙ having an average volume density ~2×10 3 cm-3 at the peak of molecular emission. We have tested the stability of the cores using the full version of the virial theorem and found that the cores are stabilized with ambient medium, and they are expected not to be dissipated easily without external perturbations. Therefore MBM 7 does not seem to be a site for new star formation. The molecular abundances in the densest core appear to be much less (by about one order of magnitude) than the 'general' dark cloud values. If the depletions of heavy elements are not significant in the HLCs compared with those in typical dark clouds, our results may suggest different chemical evolutionary stages or different chemical environments of the HLCs compared with dense dark clouds in the Galactic plane.

H2S 22,0-21,1 OBSERVATIONS TOWARD THE SGR B2 REGION

Y. C. MINH,W. M. IRVINE,S.-J. KIM 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

The H2S 22;0 21;1 line emission is observed to be strongly localized toward Sgr B2(M), and emissionsfrom other positions in the more extended SgrB2 region are almost negligible. H2S is thought to formeectively by the passage of the C-type shocks but to be quickly transformed to SO2 or other sulfurspecies (Pineau des For^ets et al. 1993). Such a shock may have enhanced the H2S abundance in SgrB2(M), where massive star formation is taking place. But the negligible emission of H2S from otherobserved positions may indicate that these positions have not been aected by shocks enough to produceH2S, or if they have experienced shocks, H2S may have transformed already to other sulfur-containingspecies. The SO2 222;20 221;21 line was also observed to be detectable only toward the (M) position.The line intensity ratios of these two molecules appear to be very similar at Sgr B2(M) and IRAS16239-2422, where the latter is a region of low-mass star formation. This may suggest that the shockenvironment in these two star-forming regions is similar and that the shock chemistry also proceeds ina similar fashion in these two dierent regions, if we accept shock formation of these two species.

[ H2S (22,0 - 21,1) ] OBSERVATIONS TOWARD THE SGR B2 REGIO

MINH Y. C.,IRVINE W. M.,KIM S.-J. The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

The $H_2S\;(2_{2,0} - 2_{1,1})$ line emission is observed to be strongly localized toward Sgr B2(M), and emissions from other positions in the more extended SgrB2 region are almost negligible. $H_2S$ is thought to form effectively by the passage of the C-type shocks but to be quickly transformed to $SO_2$ or other sulfur species (Pineau des Forets et al. 1993). Such a shock may have enhanced the $H_2S$ abundance in Sgr B2(M), where massive star formation is taking place. But the negligible emission of $H_2S$ from other observed positions may indicate that these positions have not been affected by shocks enough to produce $H_2S$, or if they have experienced shocks, $H_2S$ may have transformed already to other sulfur-containing species. The $SO_2\;22_{2,20} - 22_{1,21}$ line was also observed to be detectable only toward the (M) position. The line intensity ratios of these two molecules appear to be very similar at Sgr B2(M) and IRAS 16239-2422, where the latter is a region of low-mass star formation. This may suggest that the shock environment in these two star-forming regions is similar and that the shock chemistry also proceeds in a similar fashion in these two different regions, if we accept shock formation of these two species.

MOLECULAR CORES OF THE HIGH-LATITUDE CLOUD MBM7

MINH Y. C.,KIM H. G.,KIM S. J.,BERGMAN P.,JOHANSSON L. E. B. The Korean Astronomical Society 2000 Journal of The Korean Astronomical Society Vol.33 No.1

We have investigated the properties of the high-latitude cloud MBM 7 using the 3 mm transitions of CO, CS, HCN, $HCO^+,\;C_3H_2,\;N_2H^+$, and SiO. The molecular component of MBM 7 shows a very clumpy structure with a size of $\le$0.5 pc, elongated along the northwest-southeast direction, perpendicularly to an extended HI component, which could be resulted from shock formation. We have derived physical properties for two molecular cores in the central region. Their sizes are 0.1-0.3 pc and masses 1-2 M$\bigodot$ having an average volume density $\~2{\times}10^3 cm^{-3}$ at the peak of molecular emission. We have tested the stability of the cores using the full version of the virial theorem and found that the cores are stabilized with ambient medium, and they are expected not to be dissipated easily without external perturbations. Therefore MBM 7 does not seem to be a site for new star formation. The molecular abundances in the densest core appear to be much less (by about one order of magnitude) than the 'general' dark cloud values. If the depletions of heavy elements are not significant in the HLCs compared with those in typical dark clouds, our results may suggest different chemical evolutionary stages or different chemical environments of the HLCs compared with dense dark clouds in the Galactic plane.

OBSERVATIONS OF THE $J=1{\rightarrow}0$ TRANSITIONS OF $^{12}CO,\;^{13}CO\;and\;C^{18}O$ TOWARD OMC-1

SONG H. J.,CHUN M. S.,MINH Y. C. The Korean Astronomical Society 1993 Journal of The Korean Astronomical Society Vol.26 No.1

Using the Daeduk Radio Telescope, we have observed $J=1\rightarrow0$ transitions of 1$^{12}CO,\;^{13}CO\;and\;C^{18}O$ toward OMC-l. The column densities of $1\~5\times10^{17}\;cm^{-2}\;and\;1\~3\times10^{16}\;cm^{-2}$ have been derived, for $^{13}CO$ and $C^{18}O$, respectively, in the $11'\times11'$ region centered at Orion - KL. The double isotope ratio $[^{13}CO]/[C^{18}O]$ was found to be larger than the cosmic abundance ratio by factors of $2\~10$ which may result from the chemical fractionation effect.

High-resolution 3-μm spectra of Jupiter: Latitudinal spectral variations influenced by molecules, clouds, and haze

Kim, S.J.,Geballe, T.R.,Kim, J.H.,Jung, A.,Seo, H.J.,Minh, Y.C. Academic Press 2010 Icarus Vol.208 No.2

We present latitudinally-resolved high-resolution (R=37,000) pole-to-pole spectra of Jupiter in various narrow longitudinal ranges, in spectral intervals covering roughly half of the spectral range 2.86-3.53μm. We have analyzed the data with the aid of synthetic spectra generated from a model jovian atmosphere that included lines of CH<SUB>4</SUB>, CH<SUB>3</SUB>D, NH<SUB>3</SUB>, C<SUB>2</SUB>H<SUB>2</SUB>, C<SUB>2</SUB>H<SUB>6</SUB>, PH<SUB>3</SUB>, and HCN, as well as clouds and haze. Numerous spectral features of many of these molecular species are present and are individually identified for the first time, as are many lines of H<SUB>3</SUB><SUP>+</SUP> and a few unidentified spectral features. In both polar regions the 2.86-3.10-μm continuum is more than 10 times weaker than in spectra at lower latitudes, implying that in this wavelength range the single-scattering albedos of polar haze particles are very low. In contrast, the 3.24-3.53μm the weak polar and equatorial continua are of comparable intensity. We derive vertical distributions of NH<SUB>3</SUB>, C<SUB>2</SUB>H<SUB>2</SUB> and C<SUB>2</SUB>H<SUB>6</SUB>, and find that the mixing ratios of NH<SUB>3</SUB> and C<SUB>2</SUB>H<SUB>6</SUB> show little variation between equatorial and polar regions. However, the mixing ratios of C<SUB>2</SUB>H<SUB>2</SUB> in the northern and southern polar regions are ∼6 and ∼3 times, respectively, less than those in the equatorial regions. The derived mixing ratio curves of C<SUB>2</SUB>H<SUB>2</SUB> and C<SUB>2</SUB>H<SUB>6</SUB> extend up to the 10<SUP>-6</SUP> bar level, a significantly higher altitude than most previous results in the literature. Further ground-based observations covering other longitudes are needed to test if these mixing ratios are representative values for the equatorial and polar regions.

12CO, 13CO and C18O Observations toward OMC-1

H.J. Song,M.S. Chun,Y.C. Minh 한국천문학회 1992 天文學會報 Vol.17 No.-

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.

MOLECULAR CLOUD ASSOCIATED WITH AFGL 2591

Minh, Y.C.,Yang, Ji The Korean Astronomical Society 2008 Journal of The Korean Astronomical Society Vol.41 No.5

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.

SEARCH FOR $H_2COH+\;AND\;H_2^{13}CO$ IN DENSE INTERSTELLAR MOLECULAR CLOUDS

MINH Y. C.,IRVINE W. M.,MCGONAGLE D. The Korean Astronomical Society 1993 Journal of The Korean Astronomical Society Vol.26 No.2

We have searched for the 2 mm transitions of $H_2COH^+(2_{02}-1_{01})$ and $H_2\;^{13}CO(2_{02} - 1_{01},\; 2_{12}-1_{11},\;and\;2_{11}-1_{10})$ toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14 m telescope. None of the transitions have been detected except the $H_2\;^{13}CO$ transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion $(H_2COH^+)$, which are close to the abundances expected from ion-molecule chemistry.