Identifying and fitting eclipse maps of exoplanets with cross-validation
Monthly Notices of the Royal Astronomical Society, vol. 532, pp. 4350–4368
Abstract
ABSTRACT Eclipse mapping uses the shape of the eclipse of an exoplanet to measure its two-dimensional structure. Light curves are mostly composed of longitudinal information, with the latitudinal information only contained in the brief ingress and egress of the eclipse. This imbalance can lead to a spuriously confident map, where the longitudinal structure is constrained by out-of-eclipse data and the latitudinal structure is wrongly determined by the priors on the map. We present a new method to address this issue. The method tests for the presence of an eclipse mapping signal using k-fold cross-validation to compare the performance of a simple mapping model to the null hypothesis of a uniform disc. If a signal is found, the method fits a map with more degrees of freedom, optimizing its information content. The information content is varied by penalizing the model likelihood by a factor proportional to the spatial entropy of the map, optimized by cross-validation. We demonstrate this method for simulated data sets then apply it to three observational data sets. The method identifies an eclipse mapping signal for JWST MIRI/LRS observations of WASP-43b but does not identify a signal for JWST NIRISS/SOSS observations of WASP-18b or Spitzer Space Telescope observations of HD 189733b. It is possible to fit eclipse maps to these data sets, but we suggest that these maps are overfitting the eclipse shape. We fit a new map with more spatial freedom to the WASP-43b data set and show a flatter east–west structure than previously derived.
Authors 13
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Mark Hammond corresponding
Affiliation as printed
Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford , Oxford, OX1 3PU , UK
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Affiliation as printed
Department of Physics and Astronomy, University of Exeter , Exeter, EX4 4QL , UK
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Affiliation as printed
Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford , Oxford, OX1 3PU , UK
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Royal Observatory · University of Edinburgh
Affiliation as printed
Institute for Astronomy, University of Edinburgh , Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ , UK
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Technical University of Denmark
Affiliation as printed
National Space Institute, Technical University of Denmark , Elektrovej, DK-2800 Kgs. Lyngby , Denmark
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Université Côte d'Azur · Observatoire de la Côte d’Azur
Affiliation as printed
Observatoire de la Côte d’Azur, Université Côte d’Azur , Av. Valrose, F-06000 Nice , France
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Affiliation as printed
Astrophysics, Department of Physics, University of Oxford , Oxford, OX1 3PU , UK
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Affiliation as printed
BAER Institute, NASA Ames Research Center , Moffett Field, CA 94035 , USA
Space Science and Astrobiology Division, NASA Ames Research Center , Moffett Field, CA 94035 , USA
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Space Telescope Science Institute
Affiliation as printed
Space Telescope Science Institute , Baltimore, MD 21218 , USA
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University , P.O. Box 9513, NL-2300 RA Leiden , the Netherlands
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Max Planck Institute for Astronomy
Affiliation as printed
Max Planck Institute for Astronomy , 69117, Heidelberg , Germany
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Affiliation as printed
Trottier Institute for Research on Exoplanets, Université de Montréal , Montréal, Québec, QC H3A 2A7 , Canada
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Affiliation as printed
Department of Astronomy and Astrophysics, The University of Chicago , Chicago, IL 60637 , USA
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