The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an
The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an
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快速旋转的 Be 星 Achernar 的极风。
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
A. D. D. Souza
中科院分区：
文献类型：
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作者：
P. Kervella;A. D. D. Souza
这些恒星显示出质量损失和星周包层（CSE）的证据，从紫外共振线，近红外过量和偶发性氢发射线的存在。这些包层的几何形状仍然不确定，尽管人们通常认为它们是由恒星赤道周围的圆盘和炎热的极地风形成的。我们在红外角尺度上对快速旋转的Be星Achernar的近距离环境进行了探测，以约束可能的极态CSE的几何形状。我们利用VINCI/VLTI波束合并器在H和K波段获得了Achernar的长基线干涉观测，使用了不同的望远镜配置和基线长度，具有较大的方位角覆盖。观测到的极向可见性测量值明显低于单独恒星光球的可见性函数，特别是在低空间频率。这表明存在一个沿恒星极向延伸的不对称漫射CSE。我们拟合了一个由两部分组成的简单模型：一个二维椭圆高斯叠加在一个均匀的椭圆上，代表快速旋转恒星的扭曲光球。我们清楚地探测到沿恒星极轴延伸的CSE，以及恒星光球的旋转变平。与恒星光球相比，CSE测量的相对近红外通量为5%。它的角尺寸受到现有数据的松散约束：$2.7 pm 1.3$ mas和$17.6 pm 4.9$ mas。这种CSE可能与来自恒星热极帽的辐射压力驱动的风的自由-自由发射有关。
Be stars show evidence of mass loss and circumstellar envelopes (CSE), from UV resonance lines, near-IR excesses and the presence of episodic hydrogen emission lines. The geometry of these envelopes is still uncertain, though it is often assumed that they are formed by a disk around the stellar equator and a hot polar wind. We probe the close environment of the fast rotating Be star Achernar at angular scales of a few mas in the infrared, in order to constrain the geometry of a possible polar CSE. We obtained long-baseline interferometric observations of Achernar with the VINCI/VLTI beam combiner in the $H$ and $K$ bands, using various telescope configurations and baseline lengths with a large azimuthal coverage. The observed visibility measurements along the polar direction are significantly lower than the visibility function of the photosphere of the star alone, in particular at low spatial frequencies. This points at the presence of an asymmetric diffuse CSE elongated along the polar direction of the star. We fit to our data a simple model consisting of two components: a 2D elliptical Gaussian superimposed on a uniform ellipse representing the distorted photosphere of the fast rotating star. We clearly detect a CSE elongated along the polar axis of the star, as well as the rotational flattening of the stellar photosphere. The relative near-IR flux measured for the CSE compared to the stellar photosphere is 5\%. Its angular dimensions are loosely constrained by the available data$2.7 pm 1.3$ mas and $17.6 pm 4.9$ mas. This CSE could be linked to free-free emission from the radiative pressure driven wind originating from the hot polar caps of the star.