The diameter of the CoRoT target HD 49933. Combining the 3D limb darkening, asteroseismology, and interferometry

Context. The interpretation of stellar pulsations in terms of internal structure depends on the knowledge of the fundamental stellar parameters. Long-base interferometers permit us to determine very accurate stellar radii, which are independent constraints for stellar models that help us to locate the star in the HR diagram.
Aims: Using a direct interferometric determination of the angular diameter and advanced three-dimensional (3D) modeling, we derive the radius of the CoRoT target HD 49933 and reduce the global stellar parameter space compatible with seismic data.
Methods: The VEGA/CHARA spectro-interferometer is used to measure the angular diameter of the star. A 3D radiative hydrodynamical simulation of the surface is performed to compute the limb darkening and derive a reliable diameter from visibility curves. The other fundamental stellar parameters (mass, age, and T_eff) are found by fitting the large and small p-mode frequency separations using a stellar evolution model that includes microscopic diffusion.
Results: We obtain a limb-darkened angular diameter of θ_LD = 0.445 ± 0.012 mas. With the Hipparcos parallax, we obtain a radius of R = 1.42 ± 0.04 R_⊙. The corresponding stellar evolution model that fits both large and small frequency separations has a mass of 1.20 ± 0.08 M_⊙ and an age of 2.7 Gy. The atmospheric parameters are T_eff = 6640 ± 100 K, log g = 4.21 ± 0.14, and [Fe/H] = -0.38.