The High-Resolution Transmission Spectrum of HD 189733b Interpreted with Atmospheric Doppler Shifts from Three-Dimensional General Circulation Models

TL;DR

This study compares 3-D general circulation model predictions with high-resolution transmission spectra of HD 189733b, confirming atmospheric composition, wind patterns, and constraining the planet's rotation period, demonstrating the effectiveness of 3-D models in exoplanet characterization.

Contribution

First direct comparison of GCM-based spectra with high-res spectra of HD 189733b, validating 3-D models for interpreting atmospheric dynamics and composition.

Findings

Confirmed CO and H2O in atmosphere at 8.2σ

Detected km/s day-to-night winds at mbar pressures

Constrained rotation period between 1.2 and 4.69 days

Abstract

The signature of wind patterns caused by the interplay of rotation and energy redistribution in hot Jupiters is detectable at high spectral resolution, yet no direct comparison has been attempted between predictions from general circulation models (GCMs) and observed high-resolution spectra. We present the first of such comparisons on near-infrared transmission spectra of the hot Jupiter HD 189733b. Exploring twelve rotation rates and two chemical regimes, we have created model spectra from 3-D GCMs and cross-correlated them with the observed spectra. Comparing our models against those of HD 189733b, we obtain three key results: (1) we confirm CO and H$_2$O in the planet's atmosphere at a detection significance of 8.2$\sigma$; (2) we recover the signature of $\sim$km/s day-to-night winds at $\sim$mbar pressures; and (3) we constrain the rotation period of the planet to between 1.2 and 4.69 days (synchronous rotation (2.2 days) remains consistent with existing observations). Our results do not suffer from the shortcomings of 1-D models as cross correlation templates - mainly that these models tend to over-constrain the slower rotation rates and show evidence for anomalous blue shifts. Our 3-D models instead match the observed line-of-sight velocity of this planet by self-consistently including the effects of high-altitude day-to-night winds. Overall, we find a high degree of consistency between HD 189733b observations and our GCM-based spectra, implying that the physics and chemistry are adequately described in current 3-D forward models for the purpose of interpreting observations at high spectral resolution.