Limb-darkening coefficients for four-term and power-2 laws for the JWST mission adopting spherical PHOENIX models at high resolution

NIRCam, NIRISS, and NIRSpec passbands

¹ Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain
² Dept. Física Teórica y del Cosmos, Universidad de Granada, Campus de Fuentenueva s/n, 10871 Granada, Spain
³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA

^★ Corresponding author: claret@iaa.es

Received: 26 March 2025
Accepted: 21 May 2025

Abstract

Aims. Modeling observations of transiting exoplanets or close binary systems by comparing the observations with theoretical light curves requires precise knowledge of the distribution of specific intensities across the stellar disk. We aim to facilitate this type of research by providing extensive tabulations of limb-darkening coefficients for 11 frequently used near- and mid-infrared passbands on the NIRCam, NIRISS, and NIRSpec instruments installed on board the James Webb Space Telescope.

Methods. The calculation of the limb-darkening coefficients was based on spherically symmetric atmosphere models from the PHOENIX series, with a high spectral resolution (approximately 10⁶ wavelengths), and covering the wavelength range 0.1-6.0 μm. The models were computed for solar composition, and a microturbulent velocity of 1.0 kms^-1. We adopted two of the more accurate parametrizations for the coefficients: the four-term law, and the power-2 law. We applied the Levenberg-Marquardt least-squares minimization method, with a strategy to determine the critical value, μ_crit, of the cosine of the viewing angle near the limb that is designed to improve numerical accuracy.

Results. The limb-darkening coefficients were derived based on a total of 306 atmosphere models covering an effective temperature range of 2400-7800 K, and a log g interval between 3.0 and 5.5. We discuss the quality of the fits to the specific intensities provided by the power-2 and four-term laws, as well as by the often-used quadratic law. Based on a comparison, we recommend the use of the four-term or power-2 laws, in that order of preference.