The limb-darkened Arcturus: imaging with the IOTA/IONIC interferometer

¹ Observatoire de Paris, LESIA, CNRS/UMR 8109, 92190 Meudon, France e-mail: sylvestre.lacour@obspm.fr
² Sydney University, School of Physics, N.S.W. 2006, Australia
³ Laboratoire d'Astrophysique de Grenoble, CNRS/UMR 5571, 38041 Grenoble, France
⁴ Office National d'Études et de Recherches Aéronautiques, DOTA, 92322 Chatillon, France
⁵ Centre de Recherche Astrophysique de Lyon, CNRS/UMR 5574, 69561 Saint Genis Laval, France
⁶ Instituut voor Sterrenkunde, K.U. Leuven, 3001 Leuven, Belgium
⁷ University of Manchester, Jodrell Bank Centre for Astrophysics, Manchester, M13 9PL, UK
⁸ University of St Andrews, North Haugh, St Andrews, KY16 9SS, Scotland, UK
⁹ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
¹⁰ Institut d'Astrophysique Spatial, Université Paris-Sud, 91405 Orsay, France
¹¹ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA
¹² Department of Astronomy and Space Physics, Uppsala University, 75120 Uppsala, Sweden
¹³ Caltech/Michelson Science Center, Pasadena, CA, USA
¹⁴ Jet Propulsion Lab, M/S 301-451, 4800 Oak Grove Dr., Pasadena CA, 91109, USA

Received: 19 February 2008
Accepted: 31 March 2008

Abstract

Aims. We undertook an H band interferometric examination of Arcturus, a star frequently used as a spatial and spectral calibrator.

Methods. Using the IOTA 3 telescope interferometer, we performed spectro-interferometric observations (R≈35) of Arcturus. Atmospheric models and prescriptions were fitted to the data to derive the brightness distribution of the photosphere. Image reconstruction was performed using two software algorithms: Wisard and Mira.

Results. An achromatic power law proved to be a good model of the brightness distribution, with a limb darkening compatible with the one derived from atmospheric model simulations using our marcs model. A Rosseland diameter of 21.05±0.21 was derived, corresponding to an effective temperature of = 4295±26 K. No companion was detected from the closure phases, with an upper limit on the brightness ratio of 810^-4 at 1 AU. The dynamic range at such distance from the photosphere was established as 1.510^-4 (1rms). An upper limit of 1.710^-3 was also derived for the level of brightness asymmetries present in the photosphere.