Remote sensing of exoplanetary atmospheres with ground-based high-resolution near-infrared spectroscopy

TL;DR

This study assesses the potential of ground-based high-resolution near-infrared spectroscopy to retrieve detailed atmospheric properties of exoplanets, demonstrating the feasibility of temperature and molecular abundance estimations with simulated data.

Contribution

It introduces a method using optimal estimation and simulated spectra to evaluate the accuracy of atmospheric retrievals for exoplanets with upcoming ground-based instruments.

Findings

Temperature profiles can be accurately retrieved across a wide pressure range.

Simultaneous multi-wavelength observations improve molecular abundance estimates.

High signal-to-noise ratios are essential for reliable atmospheric parameter retrievals.

Abstract

Thanks to the advances in modern instrumentation we have learned about many exoplanets that span a wide range of masses and composition. Studying their atmospheres provides insight into planetary origin, evolution, dynamics, and habitability. Present and future observing facilities will address these important topics in great detail by using more precise observations, high-resolution spectroscopy, and improved analysis methods. We investigate the feasibility of retrieving the vertical temperature distribution and molecular number densities from expected exoplanet spectra in the near-infrared. We use the test case of the CRIRES+, instrument at the Very Large Telescope which will operate in the near-infrared between 1 and 5 micron and resolving powers of R=100000 and R=50000. We also determine the optimal wavelength coverage and observational strategies for increasing accuracy in the retrievals. We used the optimal estimation approach to retrieve the atmospheric parameters from the simulated emission observations of the hot Jupiter HD~189733b. The radiative transfer forward model is calculated using a public version of the tauREx software package. Our simulations show that we can retrieve accurate temperature distribution in a very wide range of atmospheric pressures between 1 bar and $10^{-6}$ bar depending on the chosen spectral region. Retrieving molecular mixing ratios is very challenging, but a simultaneous observations in two separate infrared regions around 1.6 micron and 2.3 micron helps to obtain accurate estimates; the exoplanetary spectra must be of relatively high signal-to-noise ratio S/N>10, while the temperature can already be derived accurately with the lowest value that we considered in this study (S/N=5).