The Dustiest Galactic S Stars: Mid-Infrared Spectra from SOFIA/FORCAST
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arXiv
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2024
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| author | Kraemer, Kathleen E. Sloan, G. C. Ramirez, Ramses M. |
| author_facet | Kraemer, Kathleen E. Sloan, G. C. Ramirez, Ramses M. |
| contents | We present spectra of 12 of the reddest, and hence dustiest, S stars in the Milky Way, observed with the FORCAST grisms on SOFIA. S stars are asymptotic giant branch (AGB) stars with C/O$\sim$1, so their molecular and dust chemistries are dominated by neither O nor C, often leading to atypical spectral features from their molecules and dust grains. All of the stars in our sample have strong dust emission features at 10--11 $μ$m, but the shape of the feature in most of the stars differs from the shapes commonly observed in either oxygen-rich or carbon-rich AGB stars. Two stars also show the 13 $μ$m feature associated with crystalline alumina. Two have a water absorption band at $\sim$6.5--7.5 $μ$m, and a third has a tentative detection, but only one of these three has the more common SiO absorption band at 7.5 $μ$m. Three others show a red 6.3 $μ$m emission feature from complex hydrocarbons consistent with ``Class C'' objects, and in a fourth it appears at 6.37 $μ$m, redder than even the standard Class C hydrocarbon feature. Class C spectra typically indicate complex hydrocarbons which have been less processed by UV radiation, resulting in more aliphatic bonds relative to aromatic bonds. None of the S stars shows a strong 11.3 $μ$m hydrocarbon feature, which is also consistent with the presence of aliphatic hydrocarbons. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2409_20316 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | The Dustiest Galactic S Stars: Mid-Infrared Spectra from SOFIA/FORCAST Kraemer, Kathleen E. Sloan, G. C. Ramirez, Ramses M. Solar and Stellar Astrophysics Astrophysics of Galaxies We present spectra of 12 of the reddest, and hence dustiest, S stars in the Milky Way, observed with the FORCAST grisms on SOFIA. S stars are asymptotic giant branch (AGB) stars with C/O$\sim$1, so their molecular and dust chemistries are dominated by neither O nor C, often leading to atypical spectral features from their molecules and dust grains. All of the stars in our sample have strong dust emission features at 10--11 $μ$m, but the shape of the feature in most of the stars differs from the shapes commonly observed in either oxygen-rich or carbon-rich AGB stars. Two stars also show the 13 $μ$m feature associated with crystalline alumina. Two have a water absorption band at $\sim$6.5--7.5 $μ$m, and a third has a tentative detection, but only one of these three has the more common SiO absorption band at 7.5 $μ$m. Three others show a red 6.3 $μ$m emission feature from complex hydrocarbons consistent with ``Class C'' objects, and in a fourth it appears at 6.37 $μ$m, redder than even the standard Class C hydrocarbon feature. Class C spectra typically indicate complex hydrocarbons which have been less processed by UV radiation, resulting in more aliphatic bonds relative to aromatic bonds. None of the S stars shows a strong 11.3 $μ$m hydrocarbon feature, which is also consistent with the presence of aliphatic hydrocarbons. |
| title | The Dustiest Galactic S Stars: Mid-Infrared Spectra from SOFIA/FORCAST |
| topic | Solar and Stellar Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2409.20316 |