Transit是系外行星HD189733b的分光光度计。I.使用HST NICMOS寻找水源却发现雾霾
Transit spectrophotometry of the exoplanet HD189733b. I. Searching for water but finding haze with HST NICMOS
摘要：
介绍了哈勃空间望远镜对热木星HD 189733 b的近红外凌日测光。在五次透射期间用NICMOS仪器进行观察，其中三次透射用1.87微米的窄带滤光片进行，两次透射用1.66微米的窄带滤光片进行。我们的观测策略，使用窄带滤波器是不敏感的通常HST轨道内和轨道到轨道的测量系统误差，使我们能够准确和鲁棒地测量近红外波长的行星半径的依赖性。我们的测量未能再现Swain等人的吸收特征低于2微米的大气水在5西格玛的置信水平。我们在1.66微米处测量到行星与恒星的半径对比度为0.15498+/-0.00035，在1.87微米处测量到行星与恒星的半径对比度为0.15517+/-0.00019。我们的两个近红外行星半径值与在光学波长下观察到的亚微米霾粒子的瑞利散射预期水平非常一致，表明高层大气霾仍然主导着近红外透射光谱，超过至少低于2微米的气态分子物种的吸收。
英文摘要：
We present Hubble Space Telescope near-infrared transit photometry of the nearby hot-Jupiter HD189733b. The observations were taken with the NICMOS instrument during five transits, with three transits executed with a narrowband filter at 1.87 microns and two performed with a narrowband filter at 1.66 microns. Our observing strategy using narrowband filters is insensitive to the usual HST intra-orbit and orbit-to-orbit measurement of systematic errors, allowing us to accurately and robustly measure the near-IR wavelength dependance of the planetary radius. Our measurements fail to reproduce the Swain et al. absorption signature of atmospheric water below 2 microns at a 5-sigma confidence level. We measure a planet-to-star radius contrast of 0.15498+/-0.00035 at 1.66 microns and a contrast of 0.15517+/-0.00019 at 1.87 microns. Both of our near-IR planetary radii values are in excellent agreement with the levels expected from Rayleigh scattering by sub-micron haze particles, observed at optical wavelengths, indicating that upper-atmospheric haze still dominates the near-IR transmission spectra over the absorption from gaseous molecular species at least below 2 microns.
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