arXiv 1507.059162015-07-23astro-ph.EPastro-ph.SR

光学氢吸收与引导热木星HD 189733 b的薄弓形激波一致

Optical hydrogen absorption consistent with a thin bow shock leading the hot Jupiter HD 189733b

P. Wilson Cauley, Seth Redfield, Adam G. Jensen, Travis Barman, Michael Endl, William D. Cochran

备注：: 10 pages, 5 figures, see http://pwcastro.com/research for an animation of the transiting bow shock
DOI：: 10.1088/0004-637X/810/1/13

摘要：

弓形激波是一种普遍存在的天体物理现象，它是由物体超音速通过气体引起的。最近，热木星系外行星HD 189733 b和WASP 12-b的紫外线金属跃迁中的过境前吸收被解释为是由行星弓形激波中压缩的材料引起的。在这里，我们提出了一个强大的检测时间分辨过境前，以及在运输中，吸收签名周围的热木星系外行星HD 189733 b使用高光谱分辨率观测几个氢巴耳末线。凌日前特征的线形和时间序列吸收的形状对系外行星周围扩展结构的形态和物理特征提供了最强的约束。在途测量证实了以前的外逸层H-α探测，尽管这里测量的吸收深度低了约50%。凌日前的吸收特征发生在预测的光学凌日前125分钟，从行星到恒星盘的投影线性距离为7.2行星半径。在巴耳末线中观察到的吸收强度指示光学上厚但物理上小的几何形状。我们将此信号建模为行星弓形激波的早期进入。如果弓形激波是由行星磁层介导的，那么从模型中导出的大间隔距离表明赤道行星磁场强度为28 G。更好地了解系外行星的磁场强度对于理解这些磁场在行星演化中的作用以及宜居带内行星上生命的潜在发展至关重要。

英文摘要：

Bow shocks are ubiquitous astrophysical phenomena resulting from the supersonic passage of an object through a gas. Recently, pre-transit absorption in UV metal transitions of the hot Jupiter exoplanets HD 189733b and WASP12-b have been interpreted as being caused by material compressed in a planetary bow shock. Here we present a robust detection of a time-resolved pre-transit, as well as in-transit, absorption signature around the hot Jupiter exoplanet HD 189733b using high spectral resolution observations of several hydrogen Balmer lines. The line shape of the pre-transit feature and the shape of the time series absorption provide the strongest constraints on the morphology and physical characteristics of extended structures around an exoplanet. The in-transit measurements confirm the previous exospheric H-alpha detection although the absorption depth measured here is ~50% lower. The pre-transit absorption feature occurs 125 minutes before the predicted optical transit, a projected linear distance from the planet to the stellar disk of 7.2 planetary radii. The absorption strength observed in the Balmer lines indicates an optically thick, but physically small, geometry. We model this signal as the early ingress of a planetary bow shock. If the bow shock is mediated by a planetary magnetosphere, the large standoff distance derived from the model suggests a large equatorial planetary magnetic field strength of 28 G. Better knowledge of exoplanet magnetic field strengths is crucial to understanding the role these fields play in planetary evolution and the potential development of life on planets in the habitable zone.

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