Sara Seager2014-03-17 4:49 PM

外太阳系巨行星穿越中的理论传输光谱 Theoretical Transmission Spectra During an Extrasolar Giant Planet Transit 

论文摘要

对HD 209458b的近期穿越观测(一个外太阳系行星环绕类太阳恒星)证实它是一个气体巨星且确定了它的轨道倾角为85°。这种倾角使得我们能够调查该行星的大气层。在本文中我们讨论了穿越过程中的行星传播光谱。该方法的基本原理是由于恒星通量能在行星边缘上穿过行星大气层,因而行星大气的吸收功能会在恒星通量上得到叠加。该方法中可行的行星可穿透大气层范围到恒星范围的比率极小(约为10的3-4个数量级); 必需要极强的行星光谱特征。我们使用封闭的外太阳系巨行星模型来估量有前景的吸收特质:即碱金属线;尤其是NaI和KI共振双峰以及HeI2③S- 2③P1083.0nm组线。如果成功的话,观测将约束视距的温度,压力和密度。尤其重点是观测将约束云层厚度,这反过来可以区分不同气氛模型。我们还讨论了该方法对有关不同轨道距离的外太阳系巨行星和绕轨非日型恒星的潜在前景。


Abstract

The recent transit observation of HD 209458 b-an extrasolar planet orbiting a Sun-like star-confirmed that it is a gas giant and determined that its orbital inclination is 85°. This inclination makes possible investigations of the planet atmosphere. In this paper we discuss the planet transmission spectra during a transit. The basic tenet of the method is that the planet atmosphere absorption features will be superimposed on the stellar flux as the stellar flux passes through the planet atmosphere above the limb. The ratio of the planet's transparent atmosphere area to the star area is small (~10^3to 10^4); for this method to work, very strong planet spectral features are necessary. We use our models of close-in extrasolar giant planets to estimate promising absorption signatures: the alkali metal lines; in particular, the Na I and K I resonance doublets; and the He I 2③S- 2③P triplet line at 1083.0 nm. If successful, observations will constrain the line-of-sight temperature, pressure, and density. The most important point is that observations will constrain the cloud depth, which in turn will distinguish between di†erent atmosphere models. We also discuss the potential of this method for extrasolar giant planets at different orbital distances and orbiting nonsolar-type stars. 

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Sara Seager

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