Information Content Analysis for Selection of Optimal JWST Observing Modes for Transiting Exoplanet Atmospheres

TL;DR

This study uses an information content approach to identify optimal JWST observing modes for characterizing diverse exoplanet atmospheres, emphasizing broad wavelength coverage and mode combinations for efficient atmospheric parameter retrieval.

Contribution

It develops a systematic method to select the most effective JWST observing modes for different exoplanet atmospheric classes based on information content analysis.

Findings

Broader wavelength coverage across multiple modes is preferred over higher precision in a single mode.

NIRISS SOSS+NIRSpec G395 are the best modes for constraining key atmospheric parameters.

Using more than two modes can sometimes yield no additional information, favoring higher precision in fewer modes.

Abstract

The James Webb Space Telescope (JWST) is nearing its launch date of 2018, and will undoubtedly revolutionize our knowledge of exoplanet atmospheres. While several studies have explored what the limits of the telescope will be in terms of exoplanet characterization, less has been done to specifically identify which observing modes will be most useful for characterizing a diverse range of exoplanetary atmospheres. We use an information content based approach commonly used in the studies of Solar System atmospheres. We develop a system based upon these information content methods to trace the instrumental and atmospheric model phase space in order to identify which observing modes are best suited for particular classes of planets, focusing on transmission spectra. Specifically, the atmospheric parameter space we cover is T=600-1800 K, C/O=0.55-1, [M/H]=1-100$\times$Solar for a R=1.39 R$_J$, M=0.59 M$_J$ planet orbiting WASP-62-like star. We find that obtaining broader wavelength coverage over multiple modes is preferred over higher precision in a single mode given the same amount of observing time. Regardless of the planet temperature and composition, the best modes for constraining terminator temperatures, C/O ratios, and metalicity are NIRISS SOSS+NIRSpec G395. If the target's host star is dim enough such that the NIRSpec prism can be used, then it cam be used instead of NIRISS SOSS+NIRSpec G395. Lastly, observations that use more than two modes, should be carefully analyzed because sometimes the addition of a third mode results in no gain of information. In these cases, higher precision in the original two modes is favorable.