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arXiv 1306.2311astro-ph.SRastro-ph.EP
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热木星HD 189733 b在X射线波长上的凌日观测

Transit observations of the Hot Jupiter HD 189733b at X-ray wavelengths

K. Poppenhaeger, J. H. M. M. Schmitt, S. J. Wolk

摘要:

我们提出了新的X射线观测获得的钱德拉ACIS-S的HD 189733系统,包括一个K-型恒星的轨道上的凌日热木星和一个M-型恒星的同伴。我们报告的软X射线探测行星过境的过境深度显着大于观察到的光学。X射线数据支持6 - 8%的通过深度,而宽带光学通过深度为2.41%。虽然我们能够排除这种深凌的几种可能的恒星起源,但需要额外的观测来完全排除日冕不均匀性影响结果的可能性。从现有的数据,我们解释了深X射线过境所造成的薄外部行星大气是透明的光学波长,但足够密集,是不透明的X射线。X射线的半径似乎比在远紫外线波长下观测到的半径要大,这很可能是由于外层大气中的高温,在这种高温下,氢大部分被电离。此外,我们还首次在X射线中探测到恒星伴星HD 189733 B,其X射线光度log LX = 26.67 erg/s。我们发现,伴星的磁活动水平与行星主恒星的活动水平不一致。这种差异可能是由热木星和它的主星之间的潮汐相互作用造成的。

英文摘要:

We present new X-ray observations obtained with Chandra ACIS-S of the HD 189733 system, consisting of a K-type star orbited by a transiting Hot Jupiter and an M-type stellar companion. We report a detection of the planetary transit in soft X-rays with a significantly larger transit depth than observed in the optical. The X-ray data favor a transit depth of 6-8%, versus a broadband optical transit depth of 2.41%. While we are able to exclude several possible stellar origins for this deep transit, additional observations will be necessary to fully exclude the possibility that coronal inhomogeneities influence the result. From the available data, we interpret the deep X-ray transit to be caused by a thin outer planetary atmosphere which is transparent at optical wavelengths, but dense enough to be opaque to X-rays. The X-ray radius appears to be larger than the radius observed at far-UV wavelengths, most likely due to high temperatures in the outer atmosphere at which hydrogen is mostly ionized. We furthermore detect the stellar companion HD 189733B in X-rays for the first time with an X-ray luminosity of log LX = 26.67 erg/s. We show that the magnetic activity level of the companion is at odds with the activity level observed for the planet-hosting primary. The discrepancy may be caused by tidal interaction between the Hot Jupiter and its host star.

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