Examinando por Autor "Zhang, Q."

Mostrando 1 - 5 de 5

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.
Acceso Abierto
Chemical complexity in high-mass star formation An observational and modeling case study of the AFGL 2591 VLA 3 hot core
(EDP Sciences, 2019-11-08) Gieser, C.; Semenov, D.; Beuther, H.; Ahmadi, A.; Mottram, J. C.; Henning, T.; Beltrán, M. T.; Maud, L. T.; Bosco, F.; Leurini, S.; Peters, T.; Klaassen, P. D.; Kuiper, R.; Feng, S.; Urquhart, J. S.; Moscadelli, L.; Csengeri, T.; Lumsden, S.; Winters, J. M.; Suri, S.; Zhang, Q.; Pudritz, R.; Palau, A.; Menten, K. M.; Galván Madrid, R.; Wyrowski, F.; Schilke, P.; Sánchez Monge, A.; Linz, H.; Johnston, K. G.; Jiménez Serra, I.; Longmore, S.; Möller, T.; Deutsche Forschungsgemeinschaft (DFG); Agencia Estatal de Investigación (AEI); Ministerio de Economía y Competitividad (MINECO); European Research Council (ERC); Kuiper, R. [0000-0003-2309-8963]; Sánchez Monge, A. [0000-0002-3078-9482]; Galván Madrid, R. [0000-0003-1480-4643]; Leurini, S. [0000-0003-1014-3390]; Ahmadi, A. [0000-0003-4037-5248]; Semenov, D. [0000-0002-3913-7114]; Gieser, C. [0000-0002-8120-1765]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Aims. In order to understand the observed molecular diversity in high-mass star-forming regions, we have to determine the underlying physical and chemical structure of those regions at high angular resolution and over a range of evolutionary stages. Methods. We present a detailed observational and modeling study of the hot core VLA 3 in the high-mass star-forming region AFGL 2591, which is a target region of the NOrthern Extended Millimeter Array (NOEMA) large program CORE. Using NOEMA observations at 1.37 mm with an angular resolution of ~0″. 42 (1400 au at 3.33 kpc), we derived the physical and chemical structure of the source. We modeled the observed molecular abundances with the chemical evolution code MUSCLE (MUlti Stage ChemicaL codE). Results. With the kinetic temperature tracers CH3CN and H2CO we observe a temperature distribution with a power-law index of q = 0.41 ± 0.08. Using the visibilities of the continuum emission we derive a density structure with a power-law index of p = 1.7 ± 0.1. The hot core spectra reveal high molecular abundances and a rich diversity in complex molecules. The majority of the molecules have an asymmetric spatial distribution around the forming protostar(s), which indicates a complex physical structure on scales <1400 au. Using MUSCLE, we are able to explain the observed molecular abundance of 10 out of 14 modeled species at an estimated hot core chemical age of ~21 100 yr. In contrast to the observational analysis, our chemical modeling predicts a lower density power-law index of p < 1.4. Reasons for this discrepancy are discussed. Conclusions. Combining high spatial resolution observations with detailed chemical modeling allows us to derive a concise picture of the physical and chemical structure of the famous AFGL 2591 hot core. The next steps are to conduct a similar analysis for the whole CORE sample, and then use this analysis to constrain the chemical diversity in high-mass star formation to a much greater depth.
Acceso Abierto
Cloud–cloud collision as drivers of the chemical complexity in Galactic Centre molecular clouds.
(Oxford Academics: Blackwell Publishing, 2020-07-29) Zeng, S.; Zhang, Q.; Jiménez Serra, I.; Tercero, B.; Lu, X.; Martín Pintado, J.; De Vicente, P.; Rivilla, V. M.; Li, S.; European Research Council (ERC); Agencia Estatal de Investigación (AEI); European Commission (EC); Japan Society for the Promotion of Science (KAKENHI); De Vicente, P. [0000-0002-5902-5005]; Rivilla, V. M. [0000-0002-2887-5859]; Li, S. [0000-0003-1275-5251]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
G+0.693-0.03 is a quiescent molecular cloud located within the Sagittarius B2 (Sgr B2) star-forming complex. Recent spectral surveys have shown that it represents one of the most prolific repositories of complex organic species in the Galaxy. The origin of such chemical complexity, along with the small-scale physical structure and properties of G+0.693-0.03, remains a mystery. In this paper, we report the study of multiple molecules with interferometric observations in combination with single-dish data in G+0.693-0.03. Despite the lack of detection of continuum source, we find small-scale (0.2 pc) structures within this cloud. The analysis of the molecular emission of typical shock tracers such as SiO, HNCO, and CH3OH unveiled two molecular components, peaking at velocities of 57 and 75 km s(-1). They are found to be interconnected in both space and velocity. The position-velocity diagrams show features that match with the observational signatures of a cloud-cloud collision. Additionally, we detect three series of class I methanol masers known to appear in shocked gas, supporting the cloud-cloud collision scenario. From the maser emission we provide constraints on the gas kinetic temperatures (similar to 30-150 K) and H-2 densities (10(4)-10(5) cm(-2)). These properties are similar to those found for the starburst galaxy NGC 253 also using class I methanol masers, suggested to be associated with a cloud-cloud collision. We conclude that shocks driven by the possible cloud-cloud collision is likely the most important mechanism responsible for the high level of chemical complexity observed in G+0.693-0.03.
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.
Acceso Abierto
The Ionized Warped Disk and Disk Wind of the Massive Protostar Monoceros R2-IRS2 Seen with ALMA
(The Institute of Physics (IOP), 2020-07-13) Jiménez Serra, I.; Báez Rubio, A.; Martín Pintado, J.; Zhang, Q.; Rivilla, V. M.; Agencia Estatal de Investigación (AEI); European Research Council (ERC); Jiménez Serra, I. [0000-0003-4493-8714]; Zhang, Q. [0000-0003-2384-6589]; Rivilla, V. M. [0000-0002-2887-5859]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Theories of massive star formation predict that massive protostars accrete gas through circumstellar disks. Although several cases have been found already thanks to high angular-resolution interferometry, the internal physical structure of these disks remains unknown, in particular whether they present warps or internal holes, as observed in low-mass protoplanetary disks. Here, we report very high angular-resolution observations of the H21 alpha radio recombination line carried out in Band 9 with the Atacama Large Millimeter/submillimeter Array (beam of 80 mas x 60 mas, or 70 au x 50 au) toward the IRS2 massive young stellar object in the Monoceros R2 star-forming cluster. The H21 alpha line shows maser amplification, which allows us to study the kinematics and physical structure of the ionized gas around the massive protostar down to spatial scales of similar to 1-2 au. Our ALMA images and 3D radiative transfer modeling reveal that the ionized gas around IRS2 is distributed in a Keplerian circumstellar disk and an expanding wind. The H21 alpha emission centroids at velocities between -10 and 20 km s(-1)deviate from the disk plane, suggesting a warping for the disk. This could be explained by the presence of a secondary object (a stellar companion or a massive planet) within the system. The ionized wind seems to be launched from the disk surface at distances similar to 11 au from the central star, consistent with magnetically-regulated disk wind models. This suggests a similar wind-launching mechanism to that recently found for evolved massive stars such as MWC349A and MWC922.