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arXiv 1401.4464astro-ph.EP
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用哈勃Space Telescope测量的系外行星CoRoT-2b的1.1-1.7微米光谱

The Emergent 1.1-1.7 Micron Spectrum of the Exoplanet CoRoT-2b as Measured Using the Hubble Space Telescope

Ashlee Wilkins, Drake Deming, Nikku Madhusudhan, Adam Burrows, Heather Knutson, Peter McCullough, Sukrit Ranjan

摘要:

我们用哈勃/WFC 3和G141棱镜在1.1-1.7 $μ$ m光谱区测量了极热木星CoRoT-2b的二次食。我们发现在这个波段上平均的食深等于百万分之$395^{+69}_{-45}$,相当于黑体温度为$1788\pm18$ K。我们研究和表征了几种WFC 3仪器效应,特别是Deming等人(2013)描述的“钩”现象。我们使用的数据从几个过境系外行星系统,找到一个定量的挂钩的振幅和曝光水平的一个给定的像素之间的关系。虽然这种关系的不确定性太大,使我们能够开发一个经验校正我们的数据,我们的研究提供了一个有用的指导,优化曝光水平在未来的WFC 3观测。我们用微分法推导出行星的光谱。行星与恒星的对比度在WFC 3带通内增加到较长波长,但没有水吸收或发射到85 ppm的$3σ$极限。WFC 3光谱的斜率明显小于最佳拟合黑体的斜率。我们比较所有现有的日食数据,这颗行星的黑体光谱,并从太阳丰度和富碳(C/O=1)模型的光谱。黑体光谱是完整数据集的可接受拟合。额外的连续不透明度,由于云或阴霾,和平坦的温度分布,是强有力的候选人,以产生准黑体光谱,并占的振幅的光学日食。我们的研究结果显示了这颗行星存在逆温的模糊证据。

英文摘要:

We have used Hubble/WFC3 and the G141 grism to measure the secondary eclipse of the transiting very hot Jupiter CoRoT-2b in the 1.1-1.7$μ$m spectral region. We find an eclipse depth averaged over this band equal to $395^{+69}_{-45}$ parts per million, equivalent to a blackbody temperature of $1788\pm18$K. We study and characterize several WFC3 instrumental effects, especially the "hook" phenomenon described by Deming et al. (2013). We use data from several transiting exoplanet systems to find a quantitative relation between the amplitude of the hook and the exposure level of a given pixel. Although the uncertainties in this relation are too large to allow us to develop an empirical correction for our data, our study provides a useful guide for optimizing exposure levels in future WFC3 observations. We derive the planet's spectrum using a differential method. The planet-to-star contrast increases to longer wavelength within the WFC3 bandpass, but without water absorption or emission to a $3σ$ limit of 85 ppm. The slope of the WFC3 spectrum is significantly less than the slope of the best-fit blackbody. We compare all existing eclipse data for this planet to a blackbody spectrum, and to spectra from both solar abundance and carbon-rich (C/O=1) models. A blackbody spectrum is an acceptable fit to the full dataset. Extra continuous opacity due to clouds or haze, and flattened temperature profiles, are strong candidates to produce quasi-blackbody spectra, and to account for the amplitude of the optical eclipses. Our results show ambiguous evidence for a temperature inversion in this planet.

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