Observations of Molecular CN toward S-type Asymptotic Giant Branch Stars

Abstract S-type asymptotic giant branch (AGB) stars are defined by their carbon-to-oxygen (C/O) ratio approaching unity. However, observations of circumstellar molecules in these stars are limited and challenging. In this study, we used the James Clerk Maxwell Telescope to search for cyanide (CN) in 12 selected S-type AGB stars, with only 4 of these stars displaying CN spectral line signals. The column density and fractional abundance of CN were calculated assuming local thermodynamic equilibrium, and the average CN-to-hydrogen-cyanide (HCN) abundance ratio of the four sources is about 0.036. We investigate, for the first time, the relationship between CN and HCN fractional abundances in all types of AGB stars, finding that the ratio is similar in O-rich and S-type stars, while those in C-rich stars are quite different. This result supports the idea that the level of HCN photodissociation plays a crucial role in determining the CN abundance in the circumstellar envelopes of AGB stars at various stages of their evolution.

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Publication Details

Journal
The Astronomical Journal
Published
2024-11-25
DOI
https://doi.org/10.3847/1538-3881/ad8ba6
Citations
1
Primary Topic
Astrophysics and Star Formation Studies
Type
article
Field-Weighted Citation Impact
0.33

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Observations of Molecular CN toward S-type Asymptotic Giant Branch Stars

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Observations of Molecular CN toward S-type Asymptotic Giant Branch Stars

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article en
1 citations

Abstract

Abstract S-type asymptotic giant branch (AGB) stars are defined by their carbon-to-oxygen (C/O) ratio approaching unity. However, observations of circumstellar molecules in these stars are limited and challenging. In this study, we used the James Clerk Maxwell Telescope to search for cyanide (CN) in 12 selected S-type AGB stars, with only 4 of these stars displaying CN spectral line signals. The column density and fractional abundance of CN were calculated assuming local thermodynamic equilibrium, and the average CN-to-hydrogen-cyanide (HCN) abundance ratio of the four sources is about 0.036. We investigate, for the first time, the relationship between CN and HCN fractional abundances in all types of AGB stars, finding that the ratio is similar in O-rich and S-type stars, while those in C-rich stars are quite different. This result supports the idea that the level of HCN photodissociation plays a crucial role in determining the CN abundance in the circumstellar envelopes of AGB stars at various stages of their evolution.

The Astronomical JournalVol. 168(6)
National Science Foundation, Natural Science Foundation of Xinjiang Province, National Astronomical Research Institute of Thailand, Leverhulme Trust, National Natural Science Foundation of China, Academia Sinica, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, Natural Science Foundation of Xinjiang, Science and Technology Facilities Council
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Openalex Percentile: Top 33%
Astrophysics and Star Formation Studies
0.33
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