A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST
Increasingly precise space-based photometry uncovers higher-order effects in transits, eclipses, and phase curves that can be used to characterize exoplanets in novel ways. The subtle signature induced by a rotationally deformed exoplanet is determined by the planet’s oblateness and rotational obliq...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/addb4e |
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| author | Shashank Dholakia Shishir Dholakia Benjamin J. S. Pope |
| author_facet | Shashank Dholakia Shishir Dholakia Benjamin J. S. Pope |
| author_sort | Shashank Dholakia |
| collection | DOAJ |
| description | Increasingly precise space-based photometry uncovers higher-order effects in transits, eclipses, and phase curves that can be used to characterize exoplanets in novel ways. The subtle signature induced by a rotationally deformed exoplanet is determined by the planet’s oblateness and rotational obliquity, which provide a wealth of information about a planet’s formation, internal structure, and dynamical history. However, oblateness and obliquity are often strongly degenerate and require sophisticated methods to convincingly constrain. We develop a new semianalytic model for an ellipsoidal object occulting a spherical body with arbitrary surface maps expressed in terms of spherical harmonics. We implement this model in an open-source J ax -based Python package eclipsoid ( https://github.com/shishirdholakia/eclipsoid ), allowing just-in-time compilation and automatic differentiation. We then estimate the precision obtainable with JWST observations of the long-period planet population and demonstrate the best current candidates for studies of oblateness and obliquity. We test our method on the JWST NIRSpec transit of the inflated warm Neptune WASP-107 b and place an upper bound on its projected oblateness of f < 0.23, which corresponds to a rotation period of P _rot > 13 hr if the planet is not inclined to our line of sight. Further studies of long-period exoplanets will necessitate discarding the assumption of planets as spherical bodies. Eclipsoid provides a general framework allowing rotational deformation to be modeled in transits, occultations, phase curves, transmission spectra, and more. https://github.com/shishirdholakia/eclipsoid/tree/main https://github.com/shashankdholakia/oblate-planets-paper/tree/main |
| format | Article |
| id | doaj-art-e6db85a435fc4e5bb19e4b04cbec94ff |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj-art-e6db85a435fc4e5bb19e4b04cbec94ff2025-08-20T03:31:33ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01987215010.3847/1538-4357/addb4eA General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWSTShashank Dholakia0https://orcid.org/0000-0001-9145-8444Shishir Dholakia1https://orcid.org/0000-0001-6263-4437Benjamin J. S. Pope2https://orcid.org/0000-0003-2595-9114School of Mathematics and Physics, The University of Queensland , St Lucia, QLD 4072, AustraliaCentre for Astrophysics, University of Southern Queensland , West Street, Toowoomba, QLD 4350, AustraliaSchool of Mathematics and Physics, The University of Queensland , St Lucia, QLD 4072, Australia; Centre for Astrophysics, University of Southern Queensland , West Street, Toowoomba, QLD 4350, Australia; School of Mathematical & Physical Sciences , 12 Wally’s Walk, Macquarie University, Macquarie Park, NSW 2113, AustraliaIncreasingly precise space-based photometry uncovers higher-order effects in transits, eclipses, and phase curves that can be used to characterize exoplanets in novel ways. The subtle signature induced by a rotationally deformed exoplanet is determined by the planet’s oblateness and rotational obliquity, which provide a wealth of information about a planet’s formation, internal structure, and dynamical history. However, oblateness and obliquity are often strongly degenerate and require sophisticated methods to convincingly constrain. We develop a new semianalytic model for an ellipsoidal object occulting a spherical body with arbitrary surface maps expressed in terms of spherical harmonics. We implement this model in an open-source J ax -based Python package eclipsoid ( https://github.com/shishirdholakia/eclipsoid ), allowing just-in-time compilation and automatic differentiation. We then estimate the precision obtainable with JWST observations of the long-period planet population and demonstrate the best current candidates for studies of oblateness and obliquity. We test our method on the JWST NIRSpec transit of the inflated warm Neptune WASP-107 b and place an upper bound on its projected oblateness of f < 0.23, which corresponds to a rotation period of P _rot > 13 hr if the planet is not inclined to our line of sight. Further studies of long-period exoplanets will necessitate discarding the assumption of planets as spherical bodies. Eclipsoid provides a general framework allowing rotational deformation to be modeled in transits, occultations, phase curves, transmission spectra, and more. https://github.com/shishirdholakia/eclipsoid/tree/main https://github.com/shashankdholakia/oblate-planets-paper/tree/mainhttps://doi.org/10.3847/1538-4357/addb4eExoplanetsExoplanet structureExoplanet astronomyExoplanet systemsOblatenessTransit photometry |
| spellingShingle | Shashank Dholakia Shishir Dholakia Benjamin J. S. Pope A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST The Astrophysical Journal Exoplanets Exoplanet structure Exoplanet astronomy Exoplanet systems Oblateness Transit photometry |
| title | A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST |
| title_full | A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST |
| title_fullStr | A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST |
| title_full_unstemmed | A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST |
| title_short | A General, Differentiable Transit Model for Ellipsoidal Occulters: Derivation, Application, and Forecast of Planetary Oblateness and Obliquity Constraints with JWST |
| title_sort | general differentiable transit model for ellipsoidal occulters derivation application and forecast of planetary oblateness and obliquity constraints with jwst |
| topic | Exoplanets Exoplanet structure Exoplanet astronomy Exoplanet systems Oblateness Transit photometry |
| url | https://doi.org/10.3847/1538-4357/addb4e |
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