ALMA observations of TiO2 around VY Canis Majoris
ALMA observations of TiO2 around VY Canis Majoris
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ALMA 对大犬座 VY 周围 TiO2 的观测
DOI：
10.1051/0004-6361/201525990
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发表时间：
2015
影响因子：
6.5
通讯作者：
E. Humphreys
中科院分区：
文献类型：
--
作者：
E. Beck;W. Vlemmings;S. Muller;J. Black;E. O’Gorman;A. Richards;A. Baudry;M. Maercker;L. Decin;E. Humphreys
上下文二氧化钛（TiO 2）是一种难熔物质，可能在富氧演化恒星周围的尘埃凝结序列中发挥关键作用。迄今为止，气相TiO 2仅在红超巨星VY CMa的复杂环境中被检测到。目标。我们的目标是限制VY CMa周围的TiO 2的分布和激发，以澄清其在粉尘形成中的作用。方法.我们分析了从阿尔马科学验证数据中提取的TiO 2的光谱和通道图。结果我们检测到15个跃迁的TiO 2，并首次空间分辨的发射。这些地图展示了一个高度cluerous，各向异性流出，其中二氧化钛排放可能跟踪气体暴露于恒星辐射场。一个加速的双极状结构被发现，大致东向西，其中蓝色的组件运行到一个固体连续组件周围，并打破了。在一些过渡中可以看到西南方向的明显尾巴，与光学和近红外线中看到的特征一致。结论.我们发现，一个显着的一部分二氧化钛仍然在尘埃形成区以外的气相中，并建议，这种物种可能只发挥了很小的作用，在尘埃冷凝过程中周围的极端富氧的演化恒星，如VY CMa。
Context. Titanium dioxide, TiO2, is a refractory species that could play a crucial role in the dust-condensation sequence around oxygen-rich evolved stars. To date, gas phase TiO2 has been detected only in the complex environment of the red supergiant VY CMa. Aims. We aim to constrain the distribution and excitation of TiO2 around VY CMa in order to clarify its role in dust formation. Methods. We analyse spectra and channel maps for TiO2 extracted from ALMA science verification data. Results. We detect 15 transitions of TiO2, and spatially resolve the emission for the first time. The maps demonstrate a highly clumpy, anisotropic outflow in which the TiO2 emission likely traces gas exposed to the stellar radiation field. An accelerating bipolar-like structure is found, oriented roughly east-west, of which the blue component runs into and breaks up around a solid continuum component. A distinct tail to the south-west is seen for some transitions, consistent with features seen in the optical and near-infrared. Conclusions. We find that a significant fraction of TiO2 remains in the gas phase outside the dust-formation zone and suggest that this species might play only a minor role in the dust-condensation process around extreme oxygen-rich evolved stars like VY CMa.