JWST Panchromatic Study Reveals KELT-7 b is a Metal-Enriched Ultra-Hot Jupiter Orbiting a Young Star
This paper presents the first panchromatic JWST transmission spectrum of KELT-7 b, an ultra-hot Jupiter exoplanet. The researchers combined NIRISS and NIRSpec observations to study the planet's atmosphere. They identified and mitigated charge migration artifacts in NIRISS data between 1-1.5 μm using a novel "late-ramp-fit" method. The analysis revealed that KELT-7 is a young (640±100 Myr), metal-rich star ([Fe/H]=0.46±0.02). Atmospheric retrievals found strong evidence for H₂O, CO₂, and TiO, but no H⁻ or clouds. The study constrained a super-stellar metallicity (M/H=92× Solar) and C/O ≤0.9, suggesting enhanced metal accretion during the planet's later formation stages. General Circulation Models explained the lack of limb asymmetry through superrotating jet-driven horizontal mixing. The work demonstrates the value of broad wavelength coverage for exoplanet atmosphere studies.
Key quotes
We present the first panchromatic JWST transmission spectrum of an ultra-hot Jupiter, combining NIRISS and NIRSpec observations to constrain KELT-7 b's atmospheric properties.
Our free retrieval, two equilibrium retrievals, and self-consistent grid fit all prefer a high metallicity but find discrepant C/O ratios.
The stark contrast between our panchromatic analysis and prior analyses on subsets of these data demonstrates the value of broad wavelength coverage for the comprehensive study of exoplanet atmospheres.
We constrain a super-stellar M/H=92^{+24}_{-23}× Solar and C/O ≤0.9, suggesting enhanced metal accretion in the later stages of KELT-7 b's formation.
Using the transit-derived stellar mean density during stellar property inference reveals that KELT-7 is a 640±100 Myr-old, [Fe/H]=0.46±0.02 star.
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