Ground- and Space-based Detection of the Thermal Emission Spectrum of the Transiting Hot Jupiter KELT-2Ab

TL;DR

This study detects water vapor in the atmosphere of the hot Jupiter KELT-2Ab using high-resolution ground-based spectroscopy, confirming planetary motion and combining data with space-based observations to analyze atmospheric composition.

Contribution

First detection of water vapor in KELT-2Ab's atmosphere using a spectroscopic binary approach with ground-based high-resolution data.

Findings

Water vapor detected at 3.8σ significance

Radial velocity of planet measured as 148 ± 7 km/s

Ground-based data provides constraints comparable to space-based observations

Abstract

We describe the detection of water vapor in the atmosphere of the transiting hot Jupiter KELT-2Ab by treating the star-planet system as a spectroscopic binary with high-resolution, ground-based spectroscopy. We resolve the signal of the planet's motion with deep combined flux observations of the star and the planet. In total, six epochs of Keck NIRSPEC $L$-band observations were obtained, and the full data set was subjected to a cross correlation analysis with a grid of self-consistent atmospheric models. We measure a radial projection of the Keplerian velocity, $K_P$, of 148 $\pm$ 7 km s$^{-1}$, consistent with transit measurements, and detect water vapor at 3.8$\sigma$. We combine NIRSPEC $L$-band data with $Spitzer$ IRAC secondary eclipse data to further probe the metallicity and carbon-to-oxygen ratio of KELT-2Ab's atmosphere. While the NIRSPEC analysis provides few extra constraints on the $Spitzer$ data, it does provide roughly the same constraints on metallicity and carbon-to-oxygen ratio. This bodes well for future investigations of the atmospheres of non-transiting hot Jupiters.