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arXiv 1502.07489astro-ph.EP
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哈勃Space Telescope观测WASP-12 b的NUV transit

Hubble Space Telescope observations of the NUV transit of WASP-12b

J. D. Nichols, G. A. Wynn, M. Goad, R. D. Alexander, S. L. Casewell, S. W. H Cowley, M. R. Burleigh, J. T. Clarke, D. Bisikalo

摘要:

我们提出了四个紧密间隔的NUV凌日的热类星体的系外行星WASP-12 b使用HST/COS的新的观测,显着增加了观测到的NUV光曲线相对于以前的观测的相位分辨率,同时最大限度地减少系统的时间变化。我们观察到显着过量的NUV吸收过境期间,平均归一化过境流量的$F_\mathrm{norm}\simeq0.97$,即$\simeq$ 2-5 $σ$深于光学过境水平的$\simeq0.986$均匀的恒星盘(确切的置信水平取决于所使用的归一化方法)。我们进一步观察到一个不对称的过境形状,这样的合并后的流量是整体$\simeq$ 2-3 $σ$高于合并前的值,其特征是在合并前和过境水平之间的计数率的快速变化。我们没有发现早期进入NUV过境的证据所建议的早期HST观测。然而,我们表明,NUV计数率观察之前的光学过境是高度可变的,但总体$\simeq$ 2.2-3.0 $σ$低于过境后的值和可比的深度光学过境,可能形成一个可变区域的NUV吸收至少相位$ϕ\simeq$ 0.83,受数据覆盖范围的限制。

英文摘要:

We present new observations of four closely-spaced NUV transits of the hot Jupiter-like exoplanet WASP-12b using HST/COS, significantly increasing the phase resolution of the observed NUV light curve relative to previous observations, while minimising the temporal variation of the system. We observe significant excess NUV absorption during the transit, with mean normalised in-transit fluxes of $F_\mathrm{norm}\simeq0.97$, i.e. $\simeq$2-5 $σ$ deeper than the optical transit level of $\simeq0.986$ for a uniform stellar disk (the exact confidence level depending on the normalisation method used). We further observe an asymmetric transit shape, such that the post-conjunction fluxes are overall $\simeq$2-3 $σ$ higher than pre-conjunction values, and characterised by rapid variations in count rate between the pre-conjunction and out of transit levels. We do not find evidence for an early ingress to the NUV transit as suggested by earlier HST observations. However, we show that the NUV count rate observed prior to the optical transit is highly variable, but overall $\simeq$2.2-3.0 $σ$ below the post-transit values and comparable in depth to the optical transit, possibly forming a variable region of NUV absorption from at least phase $ϕ\simeq$0.83, limited by the data coverage.

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