A molecule-rich torus-like structure in the 21 $μ$m source IRAS 23304+6147
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arXiv
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| Natura: | Preprint |
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2025
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| author | Sun, Hao-Min Zhang, Yong Ouyang, Xu-Jia Qin, Sheng-Li Nakashima, Junichi Qiu, Jian-Jie Li, Xiao-Hu |
| author_facet | Sun, Hao-Min Zhang, Yong Ouyang, Xu-Jia Qin, Sheng-Li Nakashima, Junichi Qiu, Jian-Jie Li, Xiao-Hu |
| contents | A long-standing enigma in observational astronomy is the identification of the so-called 21 $μ$m feature in a subset of envelopes of post-asymptotic giant branch (post-AGB) stars. Identifying this transient feature is important for understanding the chemical processes during the brief post-AGB phase and the enrichment of the interstellar medium. Understanding the structures and chemical environments of these objects is a prerequisite for such an endeavor. We investigate the structure of the circumstellar envelope and the spatial distribution of gas-phase molecules in the 21 $μ$m source IRAS 23304+6147, aiming to explor the potential physicochemical conditions required for the emergence of the 21 $μ$m feature. Molecular line observations toward IRAS 23304+6147 at the 1.3 mm band were performed using the Northern Extended Millimeter Array. A morpho-kinematic model was built to reproduce the observed $^{13}$CO images and to decipher the structures of the nebula. The imaging results reveal an elliptically elongated shell with an equatorial density enhancement (or a torus-like structure),and in detail how the various molecules distribute in the envelope. The nebular morphology points to a binary system in which the ultraviolet radiation from the companion may trigger photochemistry in the inner regions. The torus-like structure exhibits an enrichment of linear carbon-chain molecules and a depletion of silicon-bearing molecules. The chemically stratified structure of $^{13}$CN, HC$_3$N, and C$_4$H represents an observational evidence of the internal radiation that initiates photochemistry. The carbon-rich torus-like structure probably offers a conducive environment for the formation of dust and complex molecules implicated in the rare 21 $μ$m emission. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_12054 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A molecule-rich torus-like structure in the 21 $μ$m source IRAS 23304+6147 Sun, Hao-Min Zhang, Yong Ouyang, Xu-Jia Qin, Sheng-Li Nakashima, Junichi Qiu, Jian-Jie Li, Xiao-Hu Astrophysics of Galaxies Solar and Stellar Astrophysics A long-standing enigma in observational astronomy is the identification of the so-called 21 $μ$m feature in a subset of envelopes of post-asymptotic giant branch (post-AGB) stars. Identifying this transient feature is important for understanding the chemical processes during the brief post-AGB phase and the enrichment of the interstellar medium. Understanding the structures and chemical environments of these objects is a prerequisite for such an endeavor. We investigate the structure of the circumstellar envelope and the spatial distribution of gas-phase molecules in the 21 $μ$m source IRAS 23304+6147, aiming to explor the potential physicochemical conditions required for the emergence of the 21 $μ$m feature. Molecular line observations toward IRAS 23304+6147 at the 1.3 mm band were performed using the Northern Extended Millimeter Array. A morpho-kinematic model was built to reproduce the observed $^{13}$CO images and to decipher the structures of the nebula. The imaging results reveal an elliptically elongated shell with an equatorial density enhancement (or a torus-like structure),and in detail how the various molecules distribute in the envelope. The nebular morphology points to a binary system in which the ultraviolet radiation from the companion may trigger photochemistry in the inner regions. The torus-like structure exhibits an enrichment of linear carbon-chain molecules and a depletion of silicon-bearing molecules. The chemically stratified structure of $^{13}$CN, HC$_3$N, and C$_4$H represents an observational evidence of the internal radiation that initiates photochemistry. The carbon-rich torus-like structure probably offers a conducive environment for the formation of dust and complex molecules implicated in the rare 21 $μ$m emission. |
| title | A molecule-rich torus-like structure in the 21 $μ$m source IRAS 23304+6147 |
| topic | Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2503.12054 |