The limb-darkened Arcturus: imaging with the IOTA/IONIC interferometer
Lacour, S × Meimon, S Thiebaut, E Perrin, G Verhoelst, Tijl Pedretti, E Schuller, P. A Mugnier, L Monnier, J Berger, J. P Haubois, X Poncelet, A Le Besnerais, G Eriksson, K Millan-Gabet, R Ragland, S Lacasse, M Traub, W #
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 Teff = 4295±26 K. No companion was detected from the closure phases, with an upper limit on the brightness ratio of 8×10-4 at 1 AU. The dynamic range at such distance from the photosphere was established as 1.5×10-4 (1σ rms). An upper limit of 1.7×10-3 was also derived for the level of brightness asymmetries present in the photosphere.