Molecular Signatures in the Near Infrared Dayside Spectrum of HD 189733b

TL;DR

This study presents near-infrared spectral measurements of HD 189733b's dayside, revealing molecular absorption features and estimating atmospheric composition and temperature structure.

Contribution

First detection and analysis of molecular signatures in the near-infrared spectrum of HD 189733b's dayside atmosphere.

Findings

Detection of H2O, CO, and CO2 absorption bands.

Estimated molecular mixing ratios for key gases.

Temperature decreases with altitude in the observed atmospheric layer.

Abstract

We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 microns using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ~0.01 < P < ~1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH4) at these pressures.