Grid-Based Atmospheric Retrievals for Reflected-Light Spectra of Exoplanets using PSGnest

Abstract

Techniques to retrieve the atmospheric properties of exoplanets via direct observation of their reflected light have often been limited in scope due to computational constraints imposed by the forward-model calculations. We have developed a new set of techniques which significantly decreases the time required to perform a retrieval while maintaining accurate results. We constructed a grid of 1.4 million pre-computed geometric albedo spectra valued at discrete sets of parameter points. Spectra from this grid are used to produce models for a fast and efficient nested sampling routine called PSGnest. Beyond the upfront time to construct a spectral grid, the amount of time to complete a full retrieval using PSGnest is on the order of seconds to minutes using a personal computer. An extensive evaluation of the error induced from interpolating intermediate spectra from the grid indicates that this bias is insignificant compared to other retrieval error sources, with an average coefficient of determination between interpolated and true spectra of 0.998. We apply these new retrieval techniques to help constrain the optimal bandpass centers for retrieving various atmospheric and bulk parameters from a LuvEx-type mission observing several planetary archetypes. We show that spectral observations made using a 20\% bandpass centered at 0.73 microns can be used alongside our new techniques to make detections of $H_{2}O$ and $O_2$ without the need to increase observing time beyond what is necessary for a signal-to-noise ratio of 10. The methods introduced here will enable robust studies of the capabilities of future observatories to characterize exoplanets.

32 pages, 17 figures. Accepted for publication in The Astronomical Journal

References in corpus (14)

• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• A statistical test for Nested Sampling algorithms
• Exo-Transmit: An Open-Source Code for Calculating Transmission Spectra for Exoplanet Atmospheres of Varied Composition
• Wind of Change: retrieving exoplanet atmospheric winds from high-resolution spectroscopy
• An Ensemble of Bayesian Neural Networks for Exoplanetary Atmospheric Retrieval
• A Library of Self-Consistent Simulated Exoplanet Atmospheres
• Neural posterior estimation for exoplanetary atmospheric retrieval
• Atmospheric Retrieval for Direct Imaging Spectroscopy of Gas Giants In Reflected Light II: Orbital Phase and Planetary Radius
• An Approach for Retrieving Temperatures and Abundances in Brown Dwarf Atmospheres
• Reflected spectroscopy of small exoplanets II: characterization of terrestrial exoplanets
• Retrieval Analysis of the Emission Spectrum of WASP-12b: Sensitivity of Outcomes to Prior Assumptions and Implications for Formation History
• Ground-Based Transmission Spectroscopy with FORS2: A featureless optical transmission spectrum and detection of H${}_2$O for the ultra-hot Jupiter WASP-103b
• Probing the capability of future direct imaging missions to spectrally constrain the frequency of Earth-like planets
• On the Dayside Atmosphere of WASP-12b

Cited by in corpus (1)

• Optimized Bandpasses for the Habitable Worlds Observatory's ExoEarth Survey