AGB星中的含硫分子I：硫化氢的存在
Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
摘要：
通过对各种含硫分子的（亚）毫米发射谱线的调查，我们的目标是确定哪些分子是不同类型AGB星中硫的主要载体。在本文中，第一个系列，我们调查的发生H $_2$ S AGB拱星信封，并确定其丰度，在可能的情况下。我们用APEX望远镜观测了20颗具有不同质量损失率和不同化学类型的AGB星，寻找了5种关键含硫分子CS、SiS、SO、SO $_2$和H $_2$ S的转动跃迁线。在这里，我们提出了我们的结果H $_2$ S，包括检测，非检测和详细的辐射转移模型的检测线。我们比较结果的基础上不同的描述H $_2$ S的分子激发和不同的丰度分布，包括那些来自化学建模结果。我们检测到H $_2$ S对五个AGB星，所有这些都有高质量损失率的$\dot{M}\geq 5\times 10^{-6}M_\odot$年$^{-1}$和富氧。H $_2$ S在碳或S型恒星中没有被探测到，这些恒星的质量损失范围相似。对于我们的样本中的恒星与检测，我们发现峰值o-H $_2$ S丰度相对于H $_2$之间的$4\times 10^{-7}$和$2.5\times 10^{-5}$。总的来说，我们的结论是H $_2$ S可以发挥重要作用，在富氧AGB星具有较高的质量损失率，但不太可能发挥关键作用，在其他化学类型的恒星或较低的质量损失率的富氧星。对于V1300 Aql和GX Mon这两个源，H $_2$ S很可能是拱星包层中主要的含硫分子。
英文摘要：
Through a survey of (sub-)millimetre emission lines of various sulphur-bearing molecules, we aim to determine which molecules are the primary carriers of sulphur in different types of AGB stars. In this paper, the first in a series, we investigate the occurrence of H$_2$S in AGB circumstellar envelopes and determine its abundance, where possible. We have surveyed 20 AGB stars with a range of mass-loss rates and of different chemical types using the APEX telescope to search for rotational transition lines of five key sulphur-bearing molecules: CS, SiS, SO, SO$_2$ and H$_2$S. Here we present our results for H$_2$S, including detections, non-detections and detailed radiative transfer modelling of the detected lines. We compare results based on different descriptions of the molecular excitation of H$_2$S and different abundance distributions, including those derived from chemical modelling results. We detected H$_2$S towards five AGB stars, all of which have high mass-loss rates of $\dot{M}\geq 5\times 10^{-6}M_\odot$ yr$^{-1}$ and are oxygen-rich. H$_2$S was not detected towards the carbon or S-type stars that fall in a similar mass-loss range. For the stars in our sample with detections, we find peak o-H$_2$S abundances relative to H$_2$ between $4\times 10^{-7}$ and $2.5\times 10^{-5}$. Overall, we conclude that H$_2$S can play a significant role in oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a key role in stars of other chemical types or the lower mass-loss rate oxygen-rich stars. For two sources, V1300 Aql and GX Mon, H$_2$S is most likely the dominant sulphur-bearing molecule in the circumstellar envelope.
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