Browsing by Subject "GOULD BELT SURVEY"

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  • Harju, Jorma; Sipilä, Olli; Brunken, Sandra; Schlemmer, Stephan; Caselli, Paola; Juvela, Mika; Menten, Karl M.; Stutzki, Juergen; Asvany, Oskar; Kaminski, Tomasz; Okada, Yoko; Higgins, Ronan (2017)
    We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 mu m) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on. board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against. far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T <18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of similar to 5. x. 10(5) yr for the core, with an uncertainty of similar to 2. x. 10(5) yr. The core material has probably been pre-processed for another 5. x. 10(5) years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+ para) fractional abundances of similar to 10(-9) in the outer envelope. This confirms the central role of H-3 + in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D-3(+) should be abundant in these conditions.
  • Harju, J.; Daniel, F.; Sipilä, O.; Caselli, P.; Pineda, J. E.; Friesen, R. K.; Punanova, A.; Guesten, R.; Wiesenfeld, L.; Myers, P. C.; Faure, A.; Hily-Blant, P.; Rist, C.; Rosolowsky, E.; Schlemmer, S.; Shirley, Y. L. (2017)
    Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D = NH3 similar to 0 : 4, NHD2 = NH2D similar to 0 : 2 and ND3 = NHD2 similar to 0 : 06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N-2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.
  • Juvela, Mika; Neha, Sharma; Mannfors, Emma; Saajasto, Mika; Ysard, Nathalie; Pelkonen, Veli-Matti (2020)
    Context. LDN 1642 is a rare example of a star-forming, high-latitude molecular cloud. The dust emission of LDN 1642 has already been studied extensively in the past, but its location also makes it a good target for studies of light scattering.Aims. We wish to study the near-infrared (NIR) light scattering in LDN 1642, its correlation with the cloud structure, and the ability of dust models to simultaneously explain observations of sub-millimetre dust emission, NIR extinction, and NIR scattering.Methods. We used observations made with the HAWK-I instrument to measure the NIR surface brightness and extinction in LDN 1642. These data were compared with Herschel observations of dust emission and, with the help of radiative transfer modelling, with the predictions calculated for different dust models.Results. We find, for LDN 1642, an optical depth ratio tau (250 mu m)/tau (J) approximate to 10(-3), confirming earlier findings of enhanced sub-millimetre emissivity. The relationships between the column density derived from dust emission and the NIR colour excesses are linear and consistent with the shape of the standard NIR extinction curve. The extinction peaks at A(J) = 2.6 mag, and the NIR surface brightness remains correlated with N(H-2) without saturation. Radiative transfer models are able to fit the sub-millimetre data with any of the tested dust models. However, these predict an NIR extinction that is higher and an NIR surface brightness that is lower than based on NIR observations. If the dust sub-millimetre emissivity is rescaled to the observed value of tau (250 mu m)/tau (J), dust models with high NIR albedo can reach the observed level of NIR surface brightness. The NIR extinction of the models tends to be higher than in the direct extinction measurements, which is also reflected in the shape of the NIR surface brightness spectra.Conclusions. The combination of emission, extinction, and scattering measurements provides strong constraints on dust models. The observations of LDN 1642 indicate clear dust evolution, including a strong increase in the sub-millimetre emissivity, which has not been fully explained by the current dust models yet.
  • Juvela, Mika; Guillet, Vincent; Liu, Tie; Ristorcelli, Isabelle; Pelkonen, Veli-Matti; Alina, Dana; Bronfman, Leonardo; Eden, David J.; Kim, Kee Tae; Koch, Patrick M.; Kwon, Woojin; Lee, Chang Won; Malinen, Johanna; Micelotta, Elisabetta; Montillaud, Julien; Rawlings, Mark G.; Sanhueza, Patricio; Soam, Archana; Traficante, Alessio; Ysard, Nathalie; Zhang, Chuan-Peng (2018)
    Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 mu m were combined with Planck 850 mu m (353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 mu m) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H-2) similar to 7 x 10(22) cm(-2), a minimum dust temperature of T similar to 12 K, and a mass of similar to 4300 M-circle dot for the area N(H-2) > 5 x 10(21) cm(-2). The estimated average value of the dust opacity spectral index is beta similar to 1.9. The ratio of sub-millimetre and J-band optical depths is tau (250 mu m)/tau(J) similar to 2.5 x 10(-3), more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p similar to 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H-2) > 2 x 10(22) cm(-2). The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above similar to 10(4) cm(-3) or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.
  • Eden, D. J.; Liu, Tie; Kim, Kee-Tae; Juvela, M.; Liu, S. -Y.; Tatematsu, K.; Di Francesco, J.; Wang, K.; Wu, Y.; Thompson, M. A.; Fuller, G. A.; Li, Di; Ristorcelli, I.; Kang, Sung-ju; Hirano, N.; Johnstone, D.; Lin, Y.; He, J. H.; Koch, P. M.; Sanhueza, Patricio; Qin, S. -L.; Zhang, Q.; Goldsmith, P. F.; Evans, N. J.; Yuan, J.; Zhang, C. -P.; White, G. J.; Choi, Minho; Lee, Chang Won; Toth, L. V.; Mairs, S.; Yi, H. -W.; Tang, M.; Soam, A.; Peretto, N.; Samal, M. R.; Fich, M.; Parsons, H.; Malinen, J.; Bendo, G. J.; Rivera-Ingraham, A.; Liu, H. -L.; Wouterloot, J.; Li, P. S.; Qian, L.; Rawlings, J.; Rawlings, M. G.; Feng, S.; Wang, B.; Li, Dalei; Liu, M.; Luo, G.; Marston, A. P.; Pattle, K. M.; Pelkonen, V. -M.; Rigby, A. J.; Zahorecz, S.; Zhang, G.; Bogner, R.; Aikawa, Y.; Akhter, S.; Alina, D.; Bell, G.; Bernard, J. -P.; Blain, A.; Bronfman, L.; Byun, D. -Y.; Chapman, S.; Chen, H. -R.; Chen, M.; Chen, W. -P.; Chen, X.; Chen, Xuepeng; Chrysostomou, A.; Chu, Y. -H.; Chung, E. J.; Cornu, D.; Cosentino, G.; Cunningham, M. R.; Demyk, K.; Drabek-Maunder, E.; Doi, Y.; Eswaraiah, C.; Falgarone, E.; Feher, O.; Fraser, H.; Friberg, P.; Garay, G.; Ge, J. X.; Gear, W. K.; Greaves, J.; Guan, X.; Harvey-Smith, L.; Hasegawa, T.; He, Y.; Henkel, C.; Hirota, T.; Holland, W.; Hughes, A.; Jarken, E.; Ji, T. -G.; Jimenez-Serra, I.; Kang, M.; Kawabata, K. S.; Kim, Gwanjeong; Kim, Jungha; Kim, Jongsoo; Kim, S.; Koo, B. -C.; Kwon, Woojin; Kuan, Y. -J.; Lacaille, K. M.; Lai, S. -P.; Lee, C. F.; Lee, J. -E.; Lee, Y. -U.; Li, H.; Lo, N.; Lopez, J. A. P.; Lu, X.; Lyo, A. -R.; Mardones, D.; McGehee, P.; Meng, F.; Montier, L.; Montillaud, J.; Moore, T. J. T.; Morata, O.; Moriarty-Schieven, G. H.; Ohashi, S.; Pak, S.; Park, Geumsook; Paladini, R.; Pech, G.; Qiu, K.; Ren, Z. -Y.; Richer, J.; Sakai, T.; Shang, H.; Shinnaga, H.; Stamatellos, D.; Tang, Y. -W.; Traficante, A.; Vastel, C.; Viti, S.; Walsh, A.; Wang, H.; Wang, J.; Ward-Thompson, D.; Whitworth, A.; Wilson, C. D.; Xu, Y.; Yang, J.; Yuan, Y. -L.; Yuan, L.; Zavagno, A.; Zhang, C.; Zhang, G.; Zhang, H. -W.; Zhou, C.; Zhou, J.; Zhu, L.; Zuo, P. (2019)
    We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850 mu m continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14.4 arcsec, significantly improving upon the 353 GHz resolution of Planck at 5 arcmin, and allowing for a catalogue of 3528 compact sources in 558 PGCCs. We find that the detected PGCCs have significant sub-structure, with 61 per cent of detected PGCCs having three or more compact sources, with filamentary structure also prevalent within the sample. A detection rate of 45 per cent is found across the survey, which is 95 per cent complete to Planck column densities of N-H2 > 5 x10(21) cm(-2). By positionally associating the SCOPE compact sources with young stellar objects, the star formation efficiency, as measured by the ratio of luminosity to mass, in nearby clouds is found to be similar to that in the more distant Galactic Plane, with the column density distributions also indistinguishable from each other.
  • Zhang, Chuan-Peng; Liu, Tie; Yuan, Jinghua; Sanhueza, Patricio; Traficante, Alessio; Li, Guang-Xing; Li, Di; Tatematsu, Ken'ichi; Wang, Ke; Lee, Chang Won; Samal, Manash R.; Eden, David; Marston, Anthony; Liu, Xiao-Lan; Zhou, Jian-Jun; Li, Pak Shing; Koch, Patrick M.; Xu, Jin-Long; Wu, Yuefang; Juvela, Mika; Zhang, Tianwei; Alina, Dana; Goldsmith, Paul F.; Toth, L.; Wang, Jun-Jie; Kim, Kee-Tae (2018)
    In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 Planck Galactic cold clumps (PGCCs) in the second quadrant of the Milky Way. Using the (CO)-C-13 and (CO)-O-18 J = 1-0 lines and 850 mu m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the (CO)-C-13 line and 850 mu m continuum maps, respectively. We made use of the Bayesian distance calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of m similar to r(1.67). At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency (similar to 3.0%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850 mu m cores are more turbulent, more optically thick, and denser than the (CO)-C-13 clumps for star formation candidates, suggesting that the 850 mu m cores are likely more appropriate future star formation candidates than the (CO)-C-13 clumps.