Diagnosing aerosols in extrasolar giant planets with cross-correlation function of water bands

TL;DR

This paper introduces a novel method using cross-correlation functions of water bands in high-resolution spectra to diagnose aerosol properties in exoplanet atmospheres, enhancing atmospheric characterization techniques.

Contribution

It demonstrates how comparing cross-correlation functions of water bands can reveal aerosol presence and properties in hot Jupiter atmospheres, a new application of the CCF method.

Findings

CCF contrast differences can reach about 100 ppm

Method can be applied with current high-resolution spectrographs

Aerosol properties can be constrained by comparing water band CCFs

Abstract

Transmission spectroscopy with ground-based, high-resolution instruments provides key insight into the composition of exoplanetary atmospheres. Molecules such as water and carbon monoxide have been unambiguously identified in hot gas giants through cross- correlation techniques. A maximum in the cross-correlation function (CCF) is found when the molecular absorption lines in a binary mask or model template match those contained in the planet. Here, we demonstrate how the CCF method can be used to diagnose broad-band spectroscopic features such as scattering by aerosols in high-resolution transit spectra. The idea consists in exploiting the presence of multiple water bands from the optical to the near-infrared. We produced a set of models of a typical hot Jupiter spanning various conditions of temperature and aerosol coverage. We demonstrate that comparing the CCFs of individual water bands for the models constrains the presence and the properties of the aerosol layers. The contrast difference between the CCFs of two bands can reach about 100 ppm, which could be readily detectable with current or upcoming high-resolution stabilized spectrographs spanning a wide spectral range, such as ESPRESSO, CARMENES, HARPS-N+GIANO, HARPS+NIRPS, SPIRou or CRIRES+.