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

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 nearinfrared 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 8.2σ; (2) we recover the signature of ∼km/s day-to-night winds at ∼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.

Searching for thermal inversion agents in the transmission spectrum of KELT-20b/MASCARA-2b: detection of neutral iron and ionised calcium H&K lines

“…This has been predicted for a highly irradiated and fast-rotating planet where the zonal winds peak in the equator, which might result in a double-peak feature in the high-resolution spectroscopy analysis (e.g. Showman & Polvani 2011;Miller-Ricci Kempton & Rauscher 2012;Showman et al 2013;Showman, Lewis & Fortney 2015;Flowers et al 2019) or even a single blue-shifted signal as it was observed in WASP-76b when there is not enough gas to absorb the stellar light in the morning terminator (Ehrenreich et al 2020). The cause of 'delay' in the appearance of the weaker secondary signal is unclear and it is very unlikely that an unstable observational condition could cause this feature as it would affect all of the planetary signals.…”

A temperature inversion with atomic iron in the ultra-hot dayside atmosphere of WASP-189b

“…We then applied the −16 km s −1 ) derived using Kepler's third law with the orbital parameters from Anderson et al (2018). The small ∆ value could originate from several different sources, including the planetary atmospheric motion due to winds or rotation (Zhang et al 2017;Flowers et al 2019), the deviation of the absolute stellar RV relative to the measured RV sys (Yan et al 2019), the uncertainty in the transit ephemeris (e.g. according to the orbital parameters in Anderson et al (2018), the mid-transit time during our observations has an uncertainty of ∼ 300 s, which corresponds to a RV offset of 1.6 km s −1 at phases close to the secondary eclipse), and the eccentricity of the orbit.…”

Atmospheric Dynamics of Hot Giant Planets and Brown Dwarfs

“…Approaches to treating the opacities come in several flavors. The simplest is a dual-band (double grey) scheme, with one opacity band in the IR and one in the visible (e.g., Heng et al 2011a;Rauscher andMenou 2012a, 2013;Rauscher and Kempton 2014;Perna et al 2012;Tan and Komacek 2019;Flowers et al 2019). The advantage of this approach is its simplicity-it is ideal for wide parameter explorations, understanding dynamical processes, and capturing the bulk radiative budget, which is sufficient for many applications.…”

“…Detailed comparisons between IR lightcurve observations (obtained with Spitzer and Hubble) and GCM simulations including radiative transfer have been performed for a wide range of hot Jupiters, including HD 189733b Knutson et al 2012;Dobbs-Dixon and Agol 2013;Drummond et al 2018a;Steinrueck et al 2019;Flowers et al 2019), HD 209458b (Zellem et al 2014;Amundsen et al 2016;Drummond et al 2018b), WASP-43b (Kataria et al 2015;Stevenson et al 2017;, WASP-18b (Arcangeli et al 2019), WASP-19b (Wong et al 2016), HAT-P-7b (Wong et al 2016), WASP-103b , WASP-121b , HAT-P-2b , and HD 80606b . Most of these studies compute the radiative transfer driving the GCM assuming a solar-composition, cloud-free hydrogen atmosphere that is in local chemical equilibrium, and perform straight-up comparisons of the observed lightcurves to a nominal model, without any special attempts to search for an exact match via model tuning.…”

“…Motivated by these measurements, several GCMs investigations have explicitly determined the Doppler signatures that would result from the atmospheric circulation, and made predictions for various planets (Miller-Ricci Kempton and Rauscher 2012;Showman et al 2013a;Rauscher and Kempton 2014;Flowers et al 2019). These models show that at high altitude (pressures of ∼ 0.01-1 mbar, the approximate levels sensed by the Doppler measurements), the circulation tends to comprise a day-night flow at high latitudes combined with a superrotation at lower latitudes, yielding a net signature where the windflow is redshifted at low latitudes on the leading terminator and blue shifted everywhere else along the terminator.…”