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- Taniguchi, Kotomi, et al.
(författare)
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Carbon-chain chemistry in the interstellar medium
- 2024
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Ingår i: Astrophysics and Space Science. - 1572-946X .- 0004-640X. ; 369:4
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Forskningsöversikt (refereegranskat)abstract
- The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and >130 such species have been identified to date, making up ∼43% of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Larger species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C60 and C70), which may be related to the formation of the carbon-chain molecules, have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of the ISM in most galaxies. Recently, two line survey projects toward Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how future facilities may answer them.
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| 2. |
- Taniguchi, Kotomi, et al.
(författare)
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Chemical Differentiation around Five Massive Protostars Revealed by ALMA: Carbon-chain Species and Oxygen/Nitrogen-bearing Complex Organic Molecules
- 2023
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Ingår i: Astrophysical Journal, Supplement Series. - 1538-4365 .- 0067-0049. ; 267:1
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Tidskriftsartikel (refereegranskat)abstract
- We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC5N (J = 35-34) line has been detected from three MYSOs, where nitrogen (N)-bearing COMs (CH2CHCN and CH3CH2CN) have been detected. The HC5N spatial distributions show compact features and match with a methanol (CH3OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC5N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC5N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs.
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| 3. |
- Taniguchi, Kotomi, et al.
(författare)
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Digging into the Interior of Hot Cores with the ALMA (DIHCA). III. The Chemical Link between NH 2 CHO, HNCO, and H 2 CO
- 2023
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 950:1
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Tidskriftsartikel (refereegranskat)abstract
- We have analyzed the NH2CHO, HNCO, H2CO, and CH3CN (13CH3CN) molecular lines at an angular resolution of ∼0.″3 obtained by the Atacama Large Millimeter/submillimeter Array Band 6 toward 30 high-mass star-forming regions. The NH2CHO emission has been detected in 23 regions, while the other species have been detected toward 29 regions. A total of 44 hot molecular cores (HMCs) have been identified using the moment 0 maps of the CH3CN line. The fractional abundances of the four species have been derived at each HMC. In order to investigate pure chemical relationships, we have conducted a partial correlation test to exclude the effect of temperature. Strong positive correlations between NH2CHO and HNCO (ρ = 0.89) and between NH2CHO and H2CO (0.84) have been found. These strong correlations indicate their direct chemical links; dual-cyclic hydrogen addition and abstraction reactions between HNCO and NH2CHO and gas-phase formation of NH2CHO from H2CO. Chemical models including these reactions can reproduce the observed abundances in our target sources.
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| 4. |
- Taniguchi, Kotomi, et al.
(författare)
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Vibrationally Excited Lines of HC3N Associated with the Molecular Disk around the G24.78+0.08 A1 Hypercompact H ii Region
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 931:2
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Tidskriftsartikel (refereegranskat)abstract
- We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of the hypercompact H ii region G24.78+0.08 A1 (G24 HC H ii) and report the detection of vibrationally excited lines of HC3N (v (7) = 2, J = 24 - 23). The spatial distribution and kinematics of a vibrationally excited line of HC3N (v (7) = 2, J = 24 - 23, l = 2e) are found to be similar to the CH3CN vibrationally excited line (v (8) = 1), which indicates that the HC3N emission is tracing the disk around the G24 HC H ii region previously identified by the CH3CN lines. We derive the (CH3CN)-C-13/(HCCCN)-C-13 abundance ratios around G24 and compare them to the CH3CN/HC3N abundance ratios in disks around Herbig Ae and T Tauri stars. The (CH3CN)-C-13/(HCCCN)-C-13 ratios around G24 (similar to 3.0-3.5) are higher than the CH3CN/HC3N ratios in the other disks (similar to 0.03-0.11) by more than 1 order of magnitude. The higher CH3CN/HC3N ratios around G24 suggest that the thermal desorption of CH3CN in the hot dense gas and efficient destruction of HC3N in the region irradiated by the strong UV radiation are occurring. Our results indicate that the vibrationally excited HC3N lines can be used as a disk tracer of massive protostars at the HC H ii region stage, and the combination of these nitrile species will provide information of not only chemistry but also physical conditions of the disk structures.
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