在富氧AGB恒星的风中寻找一氧化铝
Search for aluminium monoxide in the winds of oxygen-rich AGB stars
摘要：
一氧化铝（AlO）很可能从富氧恒星周围的气体中有效地耗尽，形成氧化铝簇和尘埃种子。它存在于演化恒星的扩展大气层中是由光学光谱学推导出来的。最近，在超巨星VY CMa和富氧渐近巨星分支（AGB）恒星o Cet（Mira A）周围的长波长处也发现了AlO气体。为了寻找AlO，我们挖掘了APEX，IRAM 30米望远镜，Herschel/HIFI，SMA和ALMA获得的数据，这些数据主要用于研究其他分子物种。我们在这里报告的观测AlO对样本的八个富氧AGB星在不同的旋转过渡，一些恒星高达7。我们提出了明确的检测到的一个旋转过渡的AlO O O Cet和R Aqr，和试探性的检测一个过渡的R Dor和O Cet，和两个IK Tau和W Hya。所呈现的WX Psc、R Cas和TX Cam的光谱没有显示出AlO的特征。对于o Cet，R Aqr和IK Tau，我们发现AlO（N=9-8）的发射可能跟踪风的内部，只有几十个AU，那里的气体还没有达到它的终极速度。在o Cet和R Aqr的情况下，对AlO发射的结论性探测证实了AGB星流出物中存在AlO气体。初步检测进一步证实了这一点。由于本研究中提出的大多数观测结果都是在考虑到其他物种比AlO发射更强的情况下获得的，因此结合高角分辨率的高灵敏度观测将提高我们对AlO存在和行为的理解。从目前的数据集，我们不能肯定地得出结论，是否有一个直接的相关性之间的风属性和检测率的AlO排放。我们希望这项研究可以作为一个刺激，以执行样本研究中寻找富氧流出的AlO。
英文摘要：
Aluminium monoxide, AlO, is likely efficiently depleted from the gas around oxygen-rich evolved stars to form alumina clusters and dust seeds. Its presence in the extended atmospheres of evolved stars has been derived from optical spectroscopy. More recently, AlO gas was also detected at long wavelengths around the supergiant VY CMa and the oxygen-rich asymptotic giant branch (AGB) star o Cet (Mira A). In search of AlO, we mined data obtained with APEX, the IRAM 30m telescope, Herschel/HIFI, SMA, and ALMA, which were primarily aimed at studying other molecular species. We report here on observations of AlO towards a sample of eight oxygen-rich AGB stars in different rotational transitions, up to seven for some stars. We present definite detections of one rotational transition of AlO for o Cet and R Aqr, and tentative detections of one transition for R Dor and o Cet, and two for IK Tau and W Hya. The presented spectra of WX Psc, R Cas, and TX Cam show no signature of AlO. For o Cet, R Aqr, and IK Tau, we find that the AlO(N=9-8) emission likely traces the inner parts of the wind, out to only a few tens of AU, where the gas has not yet reached its terminal velocity. The conclusive detections of AlO emission in the case of o Cet and R Aqr confirm the presence of AlO gas in outflows of AGB stars. The tentative detections further support this. Since most of the observations presented in this study were obtained with stronger emission from other species than AlO in mind, observations with higher sensitivity in combination with high angular resolution will improve our understanding of the presence and behaviour of AlO. From the current data sets we cannot firmly conclude whether there is a direct correlation between the wind properties and the detection rate of AlO emission. We hope that this study can serve as a stimulus to perform sample studies in search of AlO in oxygen-rich outflows.
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