Limb and Gravity-darkening Coefficients for the Space Mission CHEOPS

The goal of this Research Note is to provide the theoretical calculations of the limb-darkening coefficients and gravity-darkening coefficients (GDC) for the space mission CHEOPS. We use two stellar atmosphere models: ATLAS (plane-parallel) and PHOENIX with spherical symmetry covering a wide range of effective temperatures, local gravities, and hydrogen/metal. These grids cover 19 metallicities ranging from 10^-5 up to 10⁺¹ solar abundances, 0 ≤ log g ≤ 6.0 and 2300 K ≤ T_eff ≤ 50,000 K. The specific intensity distribution was fitted using six approaches: linear, quadratic, square root, logarithmic, power-2, and a series with four terms. The calculations of the GDC were performed for both stellar atmosphere models adopting an improved formulation.