A JWST Transiting Survey of FGK Stellar Limb Darkening: Empirical Evidence for Quadratic Laws and Atmospheric Model Comparisons
7 affiliations
- 1Johns Hopkins University
- 2Space Telescope Science Institute
- 3University of Oxford
- 4University of Exeter
- 5Arizona State University
- 6Johns Hopkins APL
- 7Princeton University
Abstract
We present a study of stellar limb darkening using JWST transit observations of seven exoplanets orbiting FGK host stars, spanning 4200–6800 K. The wide wavelength coverage and high S/N of NIRISS/SOSS and NIRSpec/PRISM enable precise constraints on the wavelength-dependent limb darkening. Using Bayesian model selection, we find that the quadratic limb-darkening law is statistically preferred over higher-order laws for most FGK stars, recovers consistent intensity profiles for >95% of the stellar disk area, and introduces a minimal bias in the derived transit depths of only ∼14 ppm (1 σ ) for 6/7 targets. This contrasts with previous studies relying on stellar models. We compare the empirically derived quadratic coefficients to predictions from the PHOENIX, MPS-ATLAS, MURaM, and Stagger stellar atmosphere grids. We introduce a quadratic limb-darkening parameterization in terms of limb intensity ( ℓ ) and curvature at mid- μ ( δ ), finding that empirical FGK limb darkening is generally more linear than models predict ( δ ≲ 0.1). We identify wavelength-independent offsets between data and model quadratic coefficients, minimized by adopting μ min = 0.2 in intensity calculations; we attribute this in part to models overpredicting limb darkening near the limb where the plane-parallel approximation breaks down. For spherical PHOENIX models, we derive a μ rescaling method using a τ = 1 photospheric radius. With these corrections, residual offsets are minimized and all stellar models achieve statistically acceptable fits. We provide recommended limb-darkening offset priors for use in JWST transit analyses, enabling more accurate constraints on exoplanet transmission spectra while accounting for residual stellar model uncertainties.
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BibTeX
@article{sing2026jwst,
title = {{A JWST Transiting Survey of FGK Stellar Limb Darkening: Empirical Evidence for Quadratic Laws and Atmospheric Model Comparisons}},
author = {David K. Sing and Joshua D. Lothringer and Jeff A. Valenti and Natalie H. Allen and Katherine A. Bennett and Carlos Gascón and Mei Ting Mak and Patrick McCreery and Sagnick Mukherjee and Lakeisha M. Ramos Rosado and Stephen P. Schmidt and Kevin B. Stevenson and Daniel P. Thorngren and Le-Chris Wang},
journal = {The Astronomical Journal},
year = {2026},
month = oct,
doi = {10.3847/1538-3881/aea21e},
url = {https://iopscience.iop.org/article/10.3847/1538-3881/aea21e},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A JWST Transiting Survey of FGK Stellar Limb Darkening: Empirical Evidence for Quadratic Laws and Atmospheric Model Comparisons
AU - David K. Sing
AU - Joshua D. Lothringer
AU - Jeff A. Valenti
AU - Natalie H. Allen
AU - Katherine A. Bennett
AU - Carlos Gascón
AU - Mei Ting Mak
AU - Patrick McCreery
AU - Sagnick Mukherjee
AU - Lakeisha M. Ramos Rosado
AU - Stephen P. Schmidt
AU - Kevin B. Stevenson
AU - Daniel P. Thorngren
AU - Le-Chris Wang
PY - 2026
DA - 2026/10/05
JO - The Astronomical Journal
DO - 10.3847/1538-3881/aea21e
UR - https://iopscience.iop.org/article/10.3847/1538-3881/aea21e
AB - We present a study of stellar limb darkening using JWST transit observations of seven exoplanets orbiting FGK host stars, spanning 4200–6800 K. The wide wavelength coverage and high S/N of NIRISS/SOSS and NIRSpec/PRISM enable precise constraints on the wavelength-dependent limb darkening. Using Bayesian model selection, we find that the quadratic limb-darkening law is statistically preferred over higher-order laws for most FGK stars, recovers consistent intensity profiles for >95% of the stellar disk area, and introduces a minimal bias in the derived transit depths of only ∼14 ppm (1 σ ) for 6/7 targets. This contrasts with previous studies relying on stellar models. We compare the empirically derived quadratic coefficients to predictions from the PHOENIX, MPS-ATLAS, MURaM, and Stagger stellar atmosphere grids. We introduce a quadratic limb-darkening parameterization in terms of limb intensity ( ℓ ) and curvature at mid- μ ( δ ), finding that empirical FGK limb darkening is generally more linear than models predict ( δ ≲ 0.1). We identify wavelength-independent offsets between data and model quadratic coefficients, minimized by adopting μ min = 0.2 in intensity calculations; we attribute this in part to models overpredicting limb darkening near the limb where the plane-parallel approximation breaks down. For spherical PHOENIX models, we derive a μ rescaling method using a τ = 1 photospheric radius. With these corrections, residual offsets are minimized and all stellar models achieve statistically acceptable fits. We provide recommended limb-darkening offset priors for use in JWST transit analyses, enabling more accurate constraints on exoplanet transmission spectra while accounting for residual stellar model uncertainties.
SN - 0004-6256
SN - 1538-3881
ER -