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arXiv 1201.6573astro-ph.EP
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用HST/WFC3透射光谱探测HD 189733 b大气中的霾

Probing the haze in the atmosphere of HD 189733b with HST/WFC3 transmission spectroscopy

N. P. Gibson, S. Aigrain, F. Pont, D. Sing, J. -M. Désert, T. M. Evans, G. Henry, N. Husnoo, H. Knutson

摘要:

我们提出了哈勃太空望远镜近红外透射光谱的过境系外行星HD 189733 b,使用宽视场相机3。这包括两次凌日的时间序列光谱,用于测量行星半径的波长依赖性。这些观察旨在测试在光学波长处检测到的瑞利散射雾是否延伸到近红外,或者它是否变得透明,留下分子特征来主导透射光谱。由于饱和度和非线性影响光谱的最亮(中心)像素,因此仅从光谱的蓝色和红色端提取光变曲线,第一次访视分别对应于1.099-1.168 um和1.521-1.693 um的波长范围,第二次访视分别对应于1.082-1.128 um和1.514-1.671 um的波长范围。的光变曲线拟合使用高斯过程模型来解释仪器系统学,同时拟合的过境参数。这给出了蓝光和红光曲线的行星-恒星半径比值,分别为0.15650 \pm 0.00048和0.15634 \pm 0.00032(访视1)和0.15716 \pm 0.00078和0.15630 \pm 0.00037(访视2)(使用二次临边变暗定律)。在两次访问中测量的行星与恒星的半径比是一致的,并且我们没有看到如果在光学中观察到的薄雾在红外中变得透明时预期吸收下降的证据。这初步表明,霾主导了HD 189733 b的近红外波长的透射光谱,尽管需要更强大的观测来提供确凿的证据。

英文摘要:

We present Hubble Space Telescope near-infrared transmission spectroscopy of the transiting exoplanet HD 189733b, using Wide Field Camera 3. This consists of time-series spectra of two transits, used to measure the wavelength dependence of the planetary radius. These observations aim to test whether the Rayleigh scattering haze detected at optical wavelengths extends into the near-infrared, or if it becomes transparent leaving molecular features to dominate the transmission spectrum. Due to saturation and non-linearity affecting the brightest (central) pixels of the spectrum, light curves were extracted from the blue and red ends of the spectra only, corresponding to wavelength ranges of 1.099-1.168 um and 1.521-1.693 um, respectively, for the first visit, and 1.082-1.128 um and 1.514-1.671 um for the second. The light curves were fitted using a Gaussian process model to account for instrumental systematics whilst simultaneously fitting for the transit parameters. This gives values of the planet-to-star radius ratio for the blue and red light curves of 0.15650\pm0.00048 and 0.15634\pm0.00032, respectively, for visit one and 0.15716\pm0.00078 and 0.15630\pm0.00037 for visit 2 (using a quadratic limb darkening law). The planet-to-star radius ratios measured in both visits are consistent, and we see no evidence for the drop in absorption expected if the haze that is observed in the optical becomes transparent in the infrared. This tentatively suggests that the haze dominates the transmission spectrum of HD 189733b into near-infrared wavelengths, although more robust observations are required to provide conclusive evidence.

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