Letter to the Editor

The diameter of the CoRoT target HD 49933

Combining the 3D limb darkening, asteroseismology, and interferometry

¹ Université Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, CNRS UMR 6202, BP 4229, 06304 Nice Cedex, France
e-mail: lbigot@oca.eu
² Université Nice-Sophia Antipolis, Observatoire de la Côte d’Azur, CNRS UMR 6525, BP 4229, 06304 Nice Cedex, France
³ UCBL/CNRS CRAL, 9 avenue Charles André, 69561 Saint Genis Laval Cedex, France
⁴ UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, 38041 Grenoble, France
⁵ CHARA and Department of Physics and Astronomy, Georgia State University, PO Box 4106, Atlanta, GA 30302-4106, USA
⁶ LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, 92195 Meudon, France
⁷ Georgia State University, PO Box 3969, Atlanta GA 30302-3969, USA
⁸ CHARA Array, Mount Wilson Observatory, 91023 Mount Wilson CA, USA
⁹ National Optical Astronomy Observatory, PO Box 26732, Tucson, AZ 85726, USA

Received: 26 May 2011
Accepted: 22 August 2011

Abstract

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.