EDP Sciences
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Volume 485, Number 2, July II 2008
Page(s) 561 - 570
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:200809611
Published online 22 April 2008

A&A 485, 561-570 (2008)
DOI: 10.1051/0004-6361:200809611

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

S. Lacour1, 2, 3, S. Meimon4, E. Thiébaut5, G. Perrin1, T. Verhoelst6, 7, E. Pedretti8, P. A. Schuller9, 10, L. Mugnier4, J. Monnier11, J. P. Berger3, X. Haubois1, A. Poncelet1, G. Le Besnerais4, K. Eriksson12, R. Millan-Gabet13, S. Ragland9, M. Lacasse9, and W. Traub9, 14

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

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$\approx$35) of Arcturus. Atmospheric models and prescriptions were fitted to the data to derive the brightness distribution of the photosphere. Image reconstruction was performed using two software algorithms: WISARD and MIRA.
Results. An achromatic power law proved to be a good model of the brightness distribution, with a limb darkening compatible with the one derived from atmospheric model simulations using our mARCS model. A Rosseland diameter of 21.05$\pm$0.21 was derived, corresponding to an effective temperature of $T_{\rm
eff}$ = 4295$\pm$26 K. No companion was detected from the closure phases, with an upper limit on the brightness ratio of 8$\times$10-4 at 1 AU. The dynamic range at such distance from the photosphere was established as 1.5$\times$10-4 (1$\sigma\,$rms). An upper limit of 1.7$\times$10-3 was also derived for the level of brightness asymmetries present in the photosphere.

Key words: techniques: interferometric -- stars: fundamental parameters -- infrared: stars -- stars: individual: Arcturus

© ESO 2008

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