Understanding the Effects of Systematics in Exoplanetary Atmospheric Retrievals
arXiv:2106.12358 · doi:10.3847/1538-3881/ac173b
Abstract
Retrieval of exoplanetary atmospheric properties from their transmission spectra commonly assumes that the errors in the data are Gaussian and independent. However, non-Gaussian noise can occur due to instrumental or stellar systematics and merging discrete datasets. We investigate the effect of correlated noise and constrain the potential biases incurred in the retrieved posteriors. We simulate multiple noise instances of synthetic data and perform retrievals to obtain statistics of goodness-of-retrieval for varying noise models. We find that correlated noise allows for overfitting the spectrum, thereby yielding better goodness-of-fit on average but degrading the overall accuracy of retrievals. In particular, correlated noise can manifest as an apparent non-Rayleigh slope in the optical range, leading to an incorrect estimate of cloud/haze parameters. We also find that higher precision causes correlated results to be further off from the input values in terms of estimated errors. As such, we emphasize that caution must be taken in analyzing retrieved posteriors and that estimated parameter uncertainties are best understood as lower limits. Finally, we show that while correlated noise cannot be be reliably distinguished with HST observations, inferring its presence and strength may be possible with JWST observations.
25 pages, 26 figures, Submitted to AJ
References in corpus (12)
- Tau-REx I: A next generation retrieval code for exoplanetary atmospheres
- Using Stellar Limb-Darkening to Refine the Properties of HD 209458b
- A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
- Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
- Dos and don'ts of reduced chi-squared
- Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets
- Effects of a fully 3D atmospheric structure on exoplanet transmission spectra: retrieval biases due to day-night temperature gradients
- Updated Parameters and a New Transmission Spectrum of HD 97658b
- An Ensemble of Bayesian Neural Networks for Exoplanetary Atmospheric Retrieval
- An HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b
- WASP-52b. The effect of starspot correction on atmospheric retrievals
- Illusion and Reality in the Atmospheres of Exoplanets