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Compressed Magnetic Field in the Magnetically Regulated Global Collapsing Clump of G9.62+0.19
Liu, Tie,Kim, Kee-Tae,Liu, Sheng-Yuan,Juvela, Mika,Zhang, Qizhou,Wu, Yuefang,Li, Pak Shing,Parsons, Harriet,Soam, Archana,Goldsmith, Paul F.,Su, Yu-Nung,Tatematsu, Ken’ichi,Qin, Sheng-Li,Garay, Guido American Astronomical Society 2018 ASTROPHYSICAL JOURNAL LETTERS - Vol.869 No.1
ALMA Reveals Sequential High-mass Star Formation in the G9.62+0.19 Complex
Liu, Tie,Lacy, John,Li, Pak Shing,Wang, Ke,Qin, Sheng-Li,Zhang, Qizhou,Kim, Kee-Tae,Garay, Guido,Wu, Yuefang,Mardones, Diego,Zhu, Qingfeng,Tatematsu, Ken’ichi,Hirota, Tomoya,Ren, Zhiyuan,Liu, Sheng-Yu American Astronomical Society 2017 The Astrophysical journal Vol.849 No.1
<P>Stellar feedback from high-mass stars (e.g., H II regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one subvirial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM1-MM12) detected by ALMA are at very different evolutionary stages, from the starless core phase to the UC H II region phase. Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The mass-velocity diagrams of the outflows associated with MM7/G and MM8/F can be well-fit by broken power laws. The mass-velocity diagram of the SiO outflow associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO, SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10) are massive starless core candidates whose masses are estimated to be larger than 25 M-circle dot, assuming a dust temperature of <= 20 K. The shocks from the expanding H II regions ('B' and 'C') to the west may have a great impact on the G9.62 clump by compressing it into a filament and inducing core collapse successively, leading to sequential star formation. Our findings suggest that stellar feedback from H II regions may enhance the star formation efficiency and suppress low-mass star formation in adjacent pre-existing massive clumps.</P>
Liu, Tie,Kim, Kee-Tae,Yoo, Hyunju,Liu, Sheng-yuan,Tatematsu, Ken’ichi,Qin, Sheng-Li,Zhang, Qizhou,Wu, Yuefang,Wang, Ke,Goldsmith, Paul F.,Juvela, Mika,Lee, Jeong-Eun,Tó,th, L. Viktor,Mardones, D American Astronomical Society 2016 The Astrophysical journal Vol.829 No.2
<P>We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z > 1) star forming galaxies (SFGs), indicating a constant gas depletion time of similar to 100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L-TIR) and molecular line luminosities (L-mol') of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L-TIR similar to 10(3) L-circle dot. These correlations become linear when extended to external galaxies. A bimodal behavior in the L-TIR-L-mol' correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and sigma(line)/sigma(vir). Such bimodal behavior may be due to evolutionary effects. The slopes of L-TIR-L-mol' correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L-TIR larger than L-TIR similar to 10(4.5) L-circle dot. High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M-clump-L-mol' and L-TIR-L-mol' relations.</P>
Liu, Tie,Li, Pak Shing,Juvela, Mika,Kim, Kee-Tae,Evans II, Neal J.,Francesco, James Di,Liu, Sheng-Yuan,Yuan, Jinghua,Tatematsu, Ken’ichi,Zhang, Qizhou,Ward-Thompson, Derek,Fuller, Gary,Goldsmith, Paul American Astronomical Society 2018 The Astrophysical journal Vol.859 No.2
<P>Magnetic field plays a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained owing to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 mu m with SCUBA-2/POL-2 at JCMT for the first time. The magnetic field tends to be perpendicular to the densest part of the main filament (F-M), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of similar to 50 mu G for F-M is obtained using the Davis-Chandrasekhar-Fermi method. Based on (CO)-C-13 (1-0) line observations, we suggest a formation scenario of F-M due to large-scale (similar to 10 pc) cloud-cloud collision. Using additional NH3 line data, we estimate that F-M will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F-M, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F-M are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F-M may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive (similar to 200 M-circle dot, collapsing starless clump candidate, 'c8,' in G035.39-00.33. The magnetic field surrounding 'c8' is likely pinched, hinting at an accretion flow along the filament.</P>
Qin, Sheng-Li,Schilke, Peter,Wu, Jingwen,Wu, Yuefang,Liu, Tie,Liu, Ying,Sá,nchez-Monge, Á,lvaro IOP Publishing 2015 The Astrophysical journal Vol.803 No.1
<P>We report on the Submillimeter Array (SMA) observations of molecular lines at 270 GHz toward the W3(OH) and W3(H2O) complex. Although previous observations already resolved the W3(H2O) into two or three subcomponents, the physical and chemical properties of the two sources are not well constrained. Our SMA observations clearly resolved the W3(OH) and W3(H2O) continuum cores. Taking advantage of the line fitting tool XCLASS, we identified and modeled a rich molecular spectrum in this complex, including multiple CH3CN and CH3OH transitions in both cores. HDO, C2H5CN, (OCS)-C-13, and vibrationally excited lines of HCN, CH3CN, and CH3OCHO were only detected in W3(H2O). We calculate gas temperatures and column densities for both cores. The results show that W3(H2O) has higher gas temperatures and larger column densities than W3(OH) as previously observed, suggesting physical and chemical differences between the two cores. We compare the molecular abundances in W3(H2O) to those in the Sgr B2(N) hot core, the Orion KL hot core, and the Orion Compact Ridge, and discuss the chemical origin of specific species. An east-west velocity gradient is seen in W3 (H2O), and the extension is consistent with the bipolar outflow orientation traced by water masers and radio jets. A north-south velocity gradient across W3(OH) is also observed. However, with current observations we cannot be assured whether the velocity gradients are caused by rotation, outflow, or radial velocity differences of the subcomponents of W3(OH).</P>
Liu, Tie,Kim, Kee-Tae,Juvela, Mika,Wang, Ke,Tatematsu, Ken’ichi,Francesco, James Di,Liu, Sheng-Yuan,Wu, Yuefang,Thompson, Mark,Fuller, Gary,Eden, David,Li, Di,Ristorcelli, I.,Kang, Sung-ju,Lin, Yuxin Published by the University of Chicago Press for t 2018 The Astrophysical journal Supplement series Vol.234 No.2
<P>The low dust temperatures (< 14 K) of Planck Galactic cold clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. 'TOP-SCOPE' is a joint survey program targeting similar to 2000 PGCCs in J = 1-0 transitions of CO isotopologues and similar to 1000 PGCCs in 850 mu m continuum emission. The objective of the 'TOP-SCOPE' survey and the joint surveys (SMT 10 m, KVN 21 m, and NRO 45 m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis, and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, length, and mean line mass (M/L) of the G26 filament are similar to 6200 M-circle dot, similar to 12 pc, and similar to 500 M-circle dot pc(-1), respectively. Ten massive clumps, including eight starless ones, are found along the filament. The most massive clump as a whole may still be in global collapse, while its denser part seems to be undergoing expansion owing to outflow feedback. The fragmentation in the G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, nonmagnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index (beta) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed owing to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.</P>
FOLLOW-UP OBSERVATIONS TOWARD PLANCK COLD CLUMPS WITH GROUND-BASED RADIO TELESCOPES
LIU, TIE,WU, YUEFANG,MARDONES, DIEGO,KIM, KEE-TAE,MENTEN, KARL M.,TATEMATSU, KEN,CUNNINGHAM, MARIA,JUVELA, MIKA,ZHANG, QIZHOU,GOLDSMITH, PAUL F,LIU, SHENG-YUAN,ZHANG, HUA-WEI,MENG, FANYI,LI, DI,LO, NA The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
The physical and chemical properties of prestellar cores, especially massive ones, are still far from being well understood due to the lack of a large sample. The low dust temperature (< 14 K) of Planck cold clumps makes them promising candidates for prestellar objects or for sources at the very initial stages of protostellar collapse. We have been conducting a series of observations toward Planck cold clumps (PCCs) with ground-based radio telescopes. In general, when compared with other star forming samples (e.g. infrared dark clouds), PCCs are more quiescent, suggesting that most of them may be in the earliest phase of star formation. However, some PCCs are associated with protostars and molecular outflows, indicating that not all PCCs are in a prestellar phase. We have identified hundreds of starless dense clumps from a mapping survey with the Purple Mountain Observatory (PMO) 13.7-m telescope. Follow-up observations suggest that these dense clumps are ideal targets to search for prestellar objects.
Discriminative Models for Automatic Acquisition of Translation Equivalences
Chun-Xiang Zhang,Sheng Li,Tie-Jun Zhao 대한전기학회 2007 International Journal of Control, Automation, and Vol.5 No.1
Translation equivalence is very important for bilingual lexicography, machine translation system and cross-lingual information retrieval. Extraction of equivalences from bilingual sentence pairs belongs to data mining problem. In this paper, discriminative learning methods are employed to filter translation equivalences. Discriminative features including translation literality, phrase alignment probability, and phrase length ratio are used to evaluate equivalences. 1000 equivalences randomly selected are filtered and then evaluated. Experimental results indicate that its precision is 87.8% and recall is 89.8% for support vector machine.
Wu, Yuefang,Liu, Tie,Qin, Sheng-Li IOP Publishing 2014 The Astrophysical journal Vol.791 No.2
<P>This work reports high spatial resolution observations toward the Orion KL region with high critical density lines of CH3CN (124-114) and CH3OH (8-1,8-70,7), as well as a continuum at similar to 1.3 mm band. The observations were made using the Atacama Large Millimeter/Submillimeter Array with a spatial resolution of similar to 1.'' 5 and sensitivity of about 0.07 K and similar to 0.18 K for continuum and line, respectively. The observational results showed that the gas in the Orion KL region consists of jet-propelled cores at the ridge and dense cores east and south of the region that are shaped like a wedge ring. The outflow has multiple lobes, which may originate from an explosive ejection, and is not driven by young stellar objects. Four infrared bubbles were found in the Spitzer/IRAC emissions. These bubbles, the distributions of the previously found H-2 jets, the young stellar objects, and molecular gas suggest that BN is the explosive center. The burst time was estimated to be similar to 1300 yr. At the same time, signatures of gravitational collapse toward Source I and the hot core were detected with material infall velocities of 1.5 km s(-1) and similar to 0.6 km s(-1), corresponding to mass accretion rates of 1.2 x 10-3M(circle dot)/yr and 8.0 x 10-5M(circle dot)/yr, respectively. These observations may support the belief that high-mass stars form via the accretion model, similar to their low-mass counterparts.</P>