Circumstellar molecular composition of the oxygen-rich AGB star IK Tauri - I. Observations and LTE chemical abundance analysis
Circumstellar molecular composition of the oxygen-rich AGB star IK Tauri - I. Observations and LTE chemical abundance analysis
复制标题
富氧 AGB 星 IK Tauri 的星周分子组成 - I. 观测和 LTE 化学丰度分析
DOI：
--
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
L. Decin
中科院分区：
文献类型：
--
作者：
Hyun;F. Wyrowski;K. Menten;L. Decin
上下文。在(亚)毫米波长范围内的分子谱线可以提供关于渐近巨星分支恒星周围恒星包层中的物理和化学条件的重要信息。目标。本文的目的是研究富氧星IkTau周围星际包层中的分子组成。方法：研究方法。我们使用APEX望远镜在三个观察期内观测了几个(亚)毫米波段的IK Tau。为了确定12个CO(3-2)排放的空间分布，进行了测绘观测。为了约束星周包层的物理条件，用非局域热力学平衡辐射传输程序模拟了多条旋转的CO发射线。在局部热力学平衡的假设下，得到了其他分子的转动温度和丰度。结果。一颗富氧的渐近巨星在亚毫米波长范围内被观测到。检测到包括脉泽线在内的12个分子物种的34个跃迁。测定了包膜的动力学温度，估算了分子的分子丰度分数。将推导的分子丰度与文献中的观测和模型进行了比较，除SO2外，其余的分子丰度在10倍以内，几乎比化学模型预测的分子丰度高100倍。结论。从这项研究中，我们发现，IkTau是一个很好的实验室，可以用来研究具有(亚)毫米波长分子线的富氧星周围的星际包络条件。我们还可以从这项研究中预计，与只有较低跃迁线的简单LTE分析相比，具有较低和较高跃迁线的非LTE分析可以更真实地解释星周包层中的分子。特别是，用一个简单的具有幂函数结构的扩展包络模型可以很好地再现观测到的CO谱线轮廓。
Context. Molecular lines in the (sub)millimeter wavelength range can provide important information about the physical and chemical conditions in the circumstellar envelopes around asymptotic giant branch stars. Aims. The aim of this paper is to study the molecular composition in the circumstellar envelope around the oxygen-rich star IK Tau. Methods. We observed IK Tau in several (sub)millimeter bands using the APEX telescope during three observing periods. To determine the spatial distribution of the 12 CO(3-2) emission, mapping observations were performed. To constrain the physical conditions in the circumstellar envelope, multiple rotational CO emission lines were modeled using a nonlocal thermodynamic equilibrium radiative transfer code. The rotational temperatures and the abundances of the other molecules were obtained assuming local thermodynamic equilibrium. Results. An oxygen-rich asymptotic giant branch star has been surveyed in the submillimeter wavelength range. Thirty four transitions of twelve molecular species, including maser lines, were detected. The kinetic temperature of the envelope was determined, and the molecular abundance fractions of the molecules were estimated. The deduced molecular abundances were compared with observations and modeling from the literature and agree within a factor of 10, except for SO 2 , which is found to be almost a factor 100 stronger than predicted by chemical models. Conclusions. From this study, we found that IK Tau is a good laboratory for studying the conditions in circumstellar envelopes around oxygen-rich stars with (sub)millimeter-wavelength molecular lines. We could also expect from this study that the molecules in the circumstellar envelope can be explained more faithfully by non-LTE analysis with lower and higher transition lines than by simple LTE analysis with only lower transition lines. In particular, the observed CO line profiles could be well reproduced by a simple expanding envelope model with a power-law structure.