Modeling the high-resolution emission spectra of clear and cloudy non-transiting hot Jupiters

TL;DR

This study models high-resolution emission spectra of non-transiting hot Jupiters, revealing how orbital inclination and cloud coverage affect spectral features and Doppler shifts, advancing atmospheric characterization methods.

Contribution

It introduces a 3D atmospheric model for non-transiting hot Jupiters incorporating cloud scattering and viewing geometry effects, which was not previously explored.

Findings

Cloud coverage increases Doppler shifts and flux variation.

Inclination decreases flux, spectral variation, and Doppler effects.

Models with clouds and varied viewing angles are essential for accurate spectra.

Abstract

The advent of high-resolution spectroscopy as a method for exoplanet atmospheric characterization has expanded our capability to study non-transiting planets, increasing the number of planets accessible for observation. Many of the most favorable targets for atmospheric characterization are hot Jupiters, where we expect large spatial variation in physical conditions such as temperature, wind speed, and cloud coverage, making viewing geometry important. Three-dimensional models have generally simulated observational properties of hot Jupiters assuming edge-on viewing, which neglects planets without near edge-on orbits. As the first investigation of how orbital inclination manifests in high-resolution emission spectra, we use a General Circulation Model to simulate the atmospheric structure of Upsilon Andromedae b, a non-transiting hot Jupiter. In order to accurately capture scattering from clouds, we implement a generalized two-stream radiative transfer routine for inhomogeneous multiple scattering atmospheres. We compare models with and without clouds, as cloud coverage intensifies spatial variations. Cloud coverage increases both the net Doppler shifts and the variation of the continuum flux amplitude over the course of the planet's orbit. As orbital inclination decreases, four key features also decrease in both the clear and cloudy models: 1) the average continuum flux level, 2) the amplitude of the variation in continuum with orbital phase, 3) net Doppler shifts of spectral lines, and 4) Doppler broadening in the spectra. Models capable of treating inhomogeneous cloud coverage and different viewing geometries are critical in understanding high-resolution emission spectra, enabling an additional avenue to investigate these extreme atmospheres.