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The Very Low Albedo Of An Extrasolar Planet: Most Space-based Photometry Of Hd 209458

机译:太阳系外行星的极低反照率:Hd 209458的大多数天基光度法

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Measuring the albedo of an extrasolar planet provides insight into its atmospheric composition and its global thermal properties, including heat dissipation and weather patterns. Such a measurement requires very precise photometry of a transiting system, fully sampling many phases of the secondary eclipse. Space-based optical photometry of the transiting system HD 209458 from the MOST (Microvariablity and Oscillations of Stars) satellite, spanning 14 and 44 days in 2004 and 2005, respectively, allows us to set a sensitive limit on the optical eclipse of the hot exosolar giant planet in this system. Our best fit to the observations yields a flux ratio of the planet and star of 7 ± 9 ppm (parts per million), which corresponds to a geometric albedo through the MOST bandpass (400-700 nm) of A_g = 0.038 ± 0.045. This gives a 1 σ upper limit of 0.08 for the geometric albedo and a 3 σ upper limit of 0.17. HD 209458b is significantly less reflective than Jupiter (for which A_g would be about 0.5). This low geometric albedo rules out the presence of bright reflective clouds in this exoplanet's atmosphere. We determine refined parameters for the star and exoplanet in the HD 209458 system based on a model fit to the MOST light curve.
机译:测量太阳系外行星的反照率可以洞悉其大气成分及其整体热特性,包括散热和天气模式。这样的测量需要非常精密的运输系统光度学,对次食的许多相位进行完全采样。 2004年和2005年,MOST(恒星微变率和振荡)卫星传输系统HD 209458的空天光学测光分别跨越了14天和44天,这使我们能够对热的太阳系外行星的日食设置敏感极限这个系统中的巨型行星。我们与观测值的最佳拟合得出行星和恒星的通量比为7±9 ppm(百万分之一),这对应于通过MOST带通(400-700 nm)的几何反照率A_g = 0.038±0.045。这给出了几何反照率的1σ上限0.08和0.17的3σ上限。 HD 209458b的反射率明显低于木星(A_g约为0.5)。这种低几何反照率排除了系外行星大气中明亮的反射云的存在。我们根据适合于MOST光曲线的模型,确定HD 209458系统中恒星和系外行星的精确参数。

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