论文标题
S型明星W AQL的碳富含碳富含碳环境
The surprisingly carbon-rich environment of the S-type star W Aql
论文作者
论文摘要
W AQL是一个渐近巨型分支（AGB）恒星，其大气元素丰度比C/O $ \ $ $ \ $ 0.98 $ 0.98，报告了M型（C/O $ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$> $ $> $ $> $ 1）AGB星之间的中间物中间的分子丰度。尽管我们对其偶发信封（CSE）的化学含量的理解目前相当有限，但这种中间状态被认为是S型恒星的典型特征。我们使用Apex望远镜在频率范围159-268 GHz的频率范围内进行了观察，并通过将可用的光谱与一些研究良好的AGB恒星进行比较，并基于SIC2的旋转图分析。我们得出的结论是，W AQL的CSE似乎比C型AGB恒星更接近于M型AGB恒星。特别是，我们检测到C2H，SIC2，SIN和HC3N的发射，以前仅检测到C型恒星CSE的分子。基于CSE气态成分的化学性质，该结论在文献中的报道中进一步支持了大气分子带的存在以及典型的C型AGB恒星的粉尘物种的光谱特征。尽管我们的观察结果主要是在CSE的外部区域中进行痕量物种，但我们的结论与S型星的内风的最新化学平衡模型紧密相匹配：S型星的内风：S型星的大气和室内化学化学可能类似于C-Type AGB星星的大气和与M型AGB恒星更接近的C-Type AGB星星。需要进一步对S型星体气态性质化学的观察性研究来表征其对大气C/O的依赖性。 AGB恒星CSE的非平衡化学模型需要解决特定的S型恒星和由大气C/O范围诱导的化学品种。
W Aql is an asymptotic giant branch (AGB) star with an atmospheric elemental abundance ratio C/O$\approx$0.98 and reported circumstellar molecular abundances intermediate between those of M-type (C/O$<$1) and C-type (C/O$>$1) AGB stars. This intermediate status is considered typical for S-type stars, although our understanding of the chemical content of their circumstellar envelopes (CSEs) is currently rather limited. We performed observations in the frequency range 159-268 GHz with the APEX telescope and make abundance estimates through comparison to available spectra towards some well-studied AGB stars and based on rotational diagram analysis in the case of SiC2. We conclude that W Aql's CSE appears considerably closer to that of a C-type AGB star than to that of an M-type AGB star. In particular, we detect emission from C2H, SiC2, SiN, and HC3N, molecules previously only detected towards the CSEs of C-type stars. This conclusion, based on the chemistry of the gaseous component of the CSE, is further supported by reports in the literature on the presence of atmospheric molecular bands and spectral features of dust species typical for C-type AGB stars. Although our observations mainly trace species in the outer regions of the CSE, our conclusion matches closely that based on recent chemical equilibrium models for the inner wind of S-type stars: the atmospheric and circumstellar chemistry of S-type stars likely resembles that of C-type AGB stars much more closely than that of M-type AGB stars. Further observational investigation of the gaseous circumstellar chemistry of S-type stars is required to characterise its dependence on the atmospheric C/O. Non-equilibrium chemical models of the CSEs of AGB stars need to address the particular class of S-type stars and the chemical variety that is induced by the range in atmospheric C/O.
