Ground-based NIR emission spectroscopy of HD189733b

TL;DR

This study uses improved spectral analysis of multiple nights of data to confirm strong 3.3 micron emission from HD 189733b, suggesting non-LTE methane emission as a plausible source, and introduces a method for higher spectral resolution.

Contribution

An improved data analysis technique enabling higher spectral resolution in exoplanet emission spectroscopy and confirmation of non-LTE methane emission in HD 189733b.

Findings

Confirmed strong emission at ~3.3 microns.

Identified non-LTE methane emission as a plausible source.

Validated analysis method with independent spectroscopy.

Abstract

We investigate the K and L band dayside emission of the hot-Jupiter HD 189733b with three nights of secondary eclipse data obtained with the SpeX instrument on the NASA IRTF. The observations for each of these three nights use equivalent instrument settings and the data from one of the nights has previously reported by Swain et al (2010). We describe an improved data analysis method that, in conjunction with the multi-night data set, allows increased spectral resolution (R~175) leading to high-confidence identification of spectral features. We confirm the previously reported strong emission at ~3.3 microns and, by assuming a 5% vibrational temperature excess for methane, we show that non-LTE emission from the methane nu3 branch is a physically plausible source of this emission. We consider two possible energy sources that could power non-LTE emission and additional modelling is needed to obtain a detailed understanding of the physics of the emission mechanism. The validity of the data analysis method and the presence of strong 3.3 microns emission is independently confirmed by simultaneous, long-slit, L band spectroscopy of HD 189733b and a comparison star.