| 1. |
- Taniguchi, KotomiFF, et al.
(författare)
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Carbon Chain Chemistry in Hot-core Regions around Three Massive Young Stellar Objects Associated with 6.7 GHz Methanol Masers
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 908:1
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Tidskriftsartikel (refereegranskat)abstract
- We have carried out observations of CCH (N = 1 - 0), CH3CN (J = 5 - 4), and three C-13 isotopologues of HC3N (J = 10 - 9) toward three massive young stellar objects (MYSOs), G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Nobeyama 45 m radio telescope. Combined with previous results on HC5N, the column density ratios of N(CCH)/N(HC5N), hereafter the CCH/HC5N ratios, in the MYSOs are derived to be similar to 15. This value is lower than that in a low-mass warm carbon chain chemistry (WCCC) source by more than one order of magnitude. We compare the observed CCH/HC5N ratios with hot-core model calculations. The observed ratios in the MYSOs can be best reproduced by models when the gas temperature is similar to 85 K, which is higher than in L1527, a low-mass WCCC source (similar to 35 K). These results suggest that carbon-chain molecules detected around the MYSOs exist at least partially in higher temperature regions than those in low-mass WCCC sources. There is no significant difference in column density among the three C-13 isotopologues of HC3N in G12.89+0.49 and G16.86-2.16, while (HCCCN)-C-13 is more abundant than the others in G28.28-0.36. We discuss carbon-chain chemistry around the three MYSOs based on the CCH/HC5N ratio and the C-13 isotopic fractionation of HC3N.
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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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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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