A ground-based near-infrared emission spectrum of the exoplanet HD 189733b

[摘要] Detection of molecules using infrared spectroscopy probes the conditions and compositions of exoplanet atmospheres. Water (H(2)O), methane (CH(4)), carbon dioxide (CO(2)), and carbon monoxide (CO) have been detected(1-5) in two hot Jupiters. These previous results relied on space-based telescopes that do not provide spectroscopic capability in the 2.4-5.2 mu m spectral region. Here we report ground-based observations of the dayside emission spectrum for HD189733b between 2.0-2.4 mu m and 3.1-4.1 mu m, where we find a bright emission feature. Where overlap with space-based instruments exists, our results are in excellent agreement with previous measurements(2,6). A feature at similar to 3.25 mu m is unexpected and difficult to explain with models that assume local thermodynamic equilibrium (LTE) conditions at the 1 bar to 1 x 10(-6) bar pressures typically sampled by infrared measurements. The most likely explanation for this feature is that it arises fromnon-LTE emission from CH(4), similar to what is seen in the atmospheres of planets in our own Solar System(7-9). These results suggest that non-LTE effects may need to be considered when interpreting measurements of strongly irradiated exoplanets.

[关键词] ATMOSPHERIC CIRCULATION;TRANSMISSION SPECTRUM;EXTRASOLAR PLANET;DAYSIDE SPECTRUM;HOT JUPITERS;WATER;METHANE;ABSORPTION;209458B;SODIUM