Optical Transmission Spectra of Hot-Jupiters: Effects of Scattering

TL;DR

This paper develops new models for hot-Jupiter transmission spectra by incorporating multiple scattering effects, revealing how scattering influences spectral features and improves alignment with observations, especially in the optical range.

Contribution

It introduces a radiative transfer approach that accounts for scattering albedo effects, providing more accurate transmission spectra compared to previous models that used Beer-Lambert law.

Findings

Scattering increases transmitted flux and reduces transmission depth.

Significant differences between models with and without scattering below 1 micron.

Model comparisons with observations can improve atmospheric retrievals.

Abstract

We present new grids of transmission spectra for hot-Jupiters by solving the multiple scattering radiative transfer equations with non-zero scattering albedo instead of using the Beer-Bouguer-Lambert law for the change in the transmitted stellar intensity. The diffused reflection and transmission due to scattering increases the transmitted stellar flux resulting into a decrease in the transmission depth. Thus we demonstrate that scattering plays a double role in determining the optical transmission spectra -- increasing the total optical depth of the medium and adding the diffused radiation due to scattering to the transmitted stellar radiation. The resulting effects yield into an increase in the transmitted flux and hence reduction in the transmission depth. For a cloudless planetary atmosphere, Rayleigh scattering albedo alters the transmission depth up to about 0.6 micron but the change in the transmission depth due to forward scattering by cloud or haze is significant throughout the optical and near-infrared regions. However, at wavelength longer than about 1.2 $\mu$m, the scattering albedo becomes negligible and hence the transmission spectra match with that calculated without solving the radiative transfer equations. We compare our model spectra with existing theoretical models and find significant difference at wavelength shorter than one micron. We also compare our models with observational data for a few hot-Jupiters which may help constructing better retrieval models in future.