Examinando por Autor "Wang, K."

Mostrando 1 - 4 de 4

Acceso Abierto
A Low-mass Cold and Quiescent Core Population in a Massive Star Protocluster
(IOP Science Publishing, 2021-04-29) Li, S.; Lu, X.; Zhang, Q.; Lee, C. W.; Sanhueza, P.; Beuther, H.; Jiménez Serra, I.; Qiu, K.; Palau, A.; Feng, S.; Pillai, T.; Kim, K. T.; Liu, H. L.; Girart, J. M.; Liu, T.; Wang, K.; Liu, H. B.; Li, D.; Lee, J. E.; Li, F.; Li, J.; Kim, S.; Yue, N.; National Natural Science Foundation of China (NSFC); National Research Foundation of Korea (NRF); European Research Council (ERC); Deutsche Forschungsgemeinschaft (DFG); Agencia Estatal de Investigación (AEI); Li, S. [0000-0003-1275-5251]; Lu, X. [0000-0003-2619-9305]; Zhang, Q. [0000-0003-2384-6589]; Lee, C. W. [0000-0002-3179-6334]; Sanhueza, P. [0000-0002-7125-7685]; Beuther, H. [0000-0002-1700-090X]; Jiménez Serra, I. [0000-0003-4493-8714]; Qiu, K. [0000-0002-5093-5088]; Palau, A. [0000-0002-9569-9234]; Feng, S. [0000-0002-4707-8409]; Pillai, T. [0000-0003-2133-4862]; Kim, K. T. [0000-0003-2412-7092]; Liu, H. L. [0000-0003-3343-9645]; Girart, J. M. [0000-0002-3829-5591]; Liu, T. [0000-0002-5286-2564]; Wang, J. [0000-0001-6106-1171]; Wang, K. [0000-0002-7237-3856]; Liu, H. B. [0000-0003-2300-2626]; Li, D. [0000-0003-3010-7661]; Lee, J. E. [0000-0003-3119-2087]; Li, F. [0000-0002-9832-8295]; Li, J. [0000-0003-3520-6191]; Kim, S. [0000-0001-9333-5608]; Yue, N. [0000-0003-0355-6875]
Pre-stellar cores represent the initial conditions of star formation. Although these initial conditions in nearby low-mass star-forming regions have been investigated in detail, such initial conditions remain vastly unexplored for massive star-forming regions. We report the detection of a cluster of low-mass starless and pre-stellar core candidates in a massive star protocluster-forming cloud, NGC 6334S. With the Atacama Large Millimeter/submillimeter Array (ALMA) observations at a ∼0.02 pc spatial resolution, we identified 17 low-mass starless core candidates that do not show any evidence of protostellar activity. These candidates present small velocity dispersions, high fractional abundances of NH2D, high NH3 deuterium fractionations, and are completely dark in the infrared wavelengths from 3.6 up to 70 μm. Turbulence is significantly dissipated and the gas kinematics are dominated by thermal motions toward these candidates. Nine out of the 17 cores are gravitationally bound, and therefore are identified as pre-stellar core candidates. The embedded cores of NGC 6334S show a wide diversity in masses and evolutionary stages.
Restringido
ALMA–IRDC: dense gas mass distribution from cloud to core scales
(Oxford Academics: Oxford University Press, 2021-03-22) Barnes, A. T.; Henshaw, J. D.; Fontani, F.; Pineda, J. E.; Cosentino, G.; Tan, J. C.; Caselli, P.; Jiménez Serra, I.; Law, C. Y.; Avison, A.; Bigiel, F.; Feng, S.; Kong, S.; Longmore, S. N.; Moser, L.; Parker, R. J.; Sánchez Monge, Á.; Wang, K.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); Deutsche Forschungsgemeinschaft (DFG); East Asia Core Observatories Association (EACOA); National Natural Science Foundation of China (NSFC); National Key Research and Development Program of China; Peking University; Avison, A. [0000-0002-2562-8609]
Infrared dark clouds (IRDCs) are potential hosts of the elusive early phases of high mass star formation (HMSF). Here, we conduct an in-depth analysis of the fragmentation properties of a sample of 10 IRDCs, which have been highlighted as some of the best candidates to study HMSF within the Milky Way. To do so, we have obtained a set of large mosaics covering these IRDCs with Atacama Large Millimeter/submillimeter Array (ALMA) at Band 3 (or 3 mm). These observations have a high angular resolution (∼3 arcsec; ∼0.05 pc), and high continuum and spectral line sensitivity (∼0.15 mJy beam−1 and ∼0.2 K per 0.1 km s−1 channel at the N2H+ (1 − 0) transition). From the dust continuum emission, we identify 96 cores ranging from low to high mass (M = 3.4−50.9 M⊙) that are gravitationally bound (αvir = 0.3−1.3) and which would require magnetic field strengths of B = 0.3−1.0 mG to be in virial equilibrium. We combine these results with a homogenized catalogue of literature cores to recover the hierarchical structure within these clouds over four orders of magnitude in spatial scale (0.01–10 pc). Using supplementary observations at an even higher angular resolution, we find that the smallest fragments (<0.02 pc) within this hierarchy do not currently have the mass and/or the density required to form high-mass stars. None the less, the new ALMA observations presented in this paper have facilitated the identification of 19 (6 quiescent and 13 star-forming) cores that retain >16 M⊙ without further fragmentation. These high-mass cores contain trans-sonic non-thermal motions, are kinematically sub-virial, and require moderate magnetic field strengths for support against collapse. The identification of these potential sites of HMSF represents a key step in allowing us to test the predictions from high-mass star and cluster formation theories.
Acceso Abierto
Singly and doubly deuterated formaldehyde in massive star-forming regions
(EDP Sciences, 2021-09-07) Zahorecz, S.; Jiménez Serra, I.; Testi, L.; Immer, K.; Fontani, F.; Caselli, P.; Wang, K.; Onishi, T.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); National Natural Science Foundation of China (NSFC); National Key Research and Development Program of China (NKRDPC); Zahorecz, S. [0000-0001-6149-1278]
Context. Deuterated molecules are good tracers of the evolutionary stage of star-forming cores. During the star formation process, deuterated molecules are expected to be enhanced in cold, dense pre-stellar cores and to deplete after protostellar birth. Aims. In this paper, we study the deuteration fraction of formaldehyde in high-mass star-forming cores at different evolutionary stages to investigate whether the deuteration fraction of formaldehyde can be used as an evolutionary tracer. Methods. Using the APEX SEPIA Band 5 receiver, we extended our pilot study of the J = 3 →2 rotational lines of HDCO and D2CO to eleven high-mass star-forming regions that host objects at different evolutionary stages. High-resolution follow-up observations of eight objects in ALMA Band 6 were performed to reveal the size of the H2CO emission and to give an estimate of the deuteration fractions HDCO/H2CO and D2CO/HDCO at scales of ~6″ (0.04–0.15 pc at the distance of our targets). Results. Our observations show that singly and doubly deuterated H2CO are detected towards high-mass protostellar objects (HMPOs) and ultracompact H II regions (UC H II regions), and the deuteration fraction of H2CO is also found to decrease by an order of magnitude from the earlier HMPO phases to the latest evolutionary stage (UC H II), from ~0.13 to ~0.01. We have not detected HDCO and D2CO emission from the youngest sources (i.e. high-mass starless cores or HMSCs). Conclusions. Our extended study supports the results of the previous pilot study: the deuteration fraction of formaldehyde decreases with the evolutionary stage, but higher sensitivity observations are needed to provide more stringent constraints on the D/H ratio during the HMSC phase. The calculated upper limits for the HMSC sources are high, so the trend between HMSC and HMPO phases cannot be constrained.
Acceso Abierto
The Chemical Structure of Young High-mass Star-forming Clumps. II. Parsec-scale CO Depletion and Deuterium Fraction of HCO+
(The Institute of Physics (IOP), 2020-10-01) Feng, S.; Li, D.; Caselli, P.; Du, F.; Lin, Y.; Sipilä, O.; Beuther, H.; Sanhueza, P.; Tatematsu, K.; Liu, Y.; Zhang, Q.; Wang, Y.; Hogge, T.; Jiménez Serra, I.; Lu, X.; Liu, T.; Wang, K.; Zhang, Y.; Zahorecz, S.; Li, G.; Liu, H. B.; Yuan, J.; National Natural Science Foundation of China (NSFC); Max-Planck-Gesellschaft (MPG); European Research Council (ERC); Chinese Academy of Sciences (CAS); Agencia Estatal de Investigación (AEI); Japan Society for the Promotion of Science (JSPS); Feng, S. [0000-0002-4707-8409]; Li, D. [0000-0003-3010-7661]; Caselli, P. [0000-0003-1481-7911]; Du, F. [0000-0002-7489-0179]; Lin, Y. [0000-0001-9299-5479; Sipilä, O. [0000-0002-9148-1625]; Beuther, H. [0000-0002-1700-090X]; Sanhueza, P. [0000-0002-7125-7685]; Tatematsu, K. [0000-0002-8149-8546]; Liu, S. Y. [0000-0003-4603-7119]; Zhang, Q. [0000-0003-2384-6589]; Wang, Y. [0000-0003-2226-4384]; Hogge, T. [0000-0002-7211-7078]; Jiménez Serra, I. [0000-0003-4493-8714]; Lu, X. [0000-0003-2619-9305]; Liu, T. [0000-0002-5286-2564]; Wang, K. [0000-0002-7237-3856]; Zhang, Z. Y. [0000-0002-7299-2876]; Zahorecz, S. [0000-0001-6149-1278]; Li, G. [0000-0003-3144-1952]; Liu, H. B. [0000-0003-2300-2626]; Yuan, J. [0000-0001-8060-3538]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The physical and chemical properties of cold and dense molecular clouds are key to understanding how stars form. Using the IRAM 30 m and NRO 45 m telescopes, we carried out a Multiwavelength line-Imaging survey of the 70 μm-dArk and bright clOuds (MIAO). At a linear resolution of 0.1–0.5 pc, this work presents a detailed study of parsec-scale CO depletion and HCO+ deuterium (D-) fractionation toward four sources (G11.38+0.81, G15.22–0.43, G14.49–0.13, and G34.74–0.12) included in our full sample. In each source with T < 20 K and nH ~ 104–105 cm−3, we compared pairs of neighboring 70 μm bright and dark clumps and found that (1) the H2 column density and dust temperature of each source show strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue lines and dense gas tracers, such as 1–0 lines of H13CO+ and DCO+, are anticorrelated; (3) the abundance ratio between C18O and DCO+ shows a strong correlation with the source temperature; (4) both the C18O depletion factor and D-fraction of HCO+ show a robust decrease from younger clumps to more evolved clumps by a factor of more than 3; and (5) preliminary chemical modeling indicates that chemical ages of our sources are ~8 × 104 yr, which is comparable to their free-fall timescales and smaller than their contraction timescales, indicating that our sources are likely dynamically and chemically young.