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

Abstract

Aims. We undertook an 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 (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 21.050.21 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 at 1 AU. The dynamic range at such distance from the photosphere was established as 1.510 (1rms). An upper limit of 1.710 was also derived for the level of brightness asymmetries present in the photosphere. . © 2008 ESO.