Emission Spectra of Gas Giant HD 209458b

The ground-based H, K, and L-band absolute emission spectra of HD 209458b

Authors:

Zellem et al

Abstract:

Here we explore the capabilities of NASA's 3.0 meter Infrared Telescope Facility (IRTF) and SpeX spectrometer and the 5.08 meter Hale telescope with the TripleSpec spectrometer with near-infrared H, K, and L-band measurements of HD 209458b's secondary eclipse. Our IRTF/SpeX data are the first absolute L-band spectroscopic emission measurements of any exoplanet other than the hot Jupiter HD 189733b. Previous measurements of HD 189733b's L-band indicate bright emission hypothesized to result from non-LTE CH4 ν3 fluorescence. We do not detect a similar bright 3.3 μm feature to ~3σ, suggesting that fluorescence does not need to be invoked to explain HD 209458b's L-band measurements. The validity of our observation and reduction techniques, which decrease the flux variance by up to 2.8 orders of magnitude, is reinforced by 1σ agreement with existent Hubble/NICMOS and Spitzer/IRAC1 observations which overlap the H, K, and L-bands, suggesting that both IRTF/SpeX and Palomar/TripleSpec can measure an exoplanet's emission with high precision.