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Issue A&A
Volume 435, Number 1, May III 2005
Page(s) 289 - 301
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20042356



A&A 435, 289-301 (2005)
DOI: 10.1051/0004-6361:20042356

Is Arcturus a well-understood K giant?

Test of model atmospheres and potential companion detection by near-infrared interferometry
T. Verhoelst1, 2, P. J. Bordé3, G. Perrin2, L. Decin1, K. Eriksson4, S. T. Ridgway2, 5, P. A. Schuller3, W. A. Traub3, R. Millan-Gabet5, M. G. Lacasse3 and C. Waelkens1

1  Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
    e-mail: Tijl.verhoelst@ster.kuleuven.ac.be
2  Observatoire de Paris-Meudon, LESIA, 5 place Jules Janssen, 92195 Meudon, France
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4  Institute for Astronomy and Space Physics, Box 515, 75120 Uppsala, Sweden
5  National Optical Astronomy Observatories, PO Box 26732, Tucson, AZ 85726, USA

(Received 10 November 2004 / Accepted 23 January 2005)

Abstract
We present near-IR interferometric measurements of the K1.5 giant Arcturus ($\alpha$ Bootis), obtained at the IOTA interferometer with the FLUOR instrument, in four narrow filters with central wavelengths ranging from 2.03 $\mu$m to 2.39 $\mu$m. These observations were expected to allow us to quantify the wavelength dependence of the diameter of a typical K giant. They are compared to predictions from both plane-parallel and spherical model atmospheres. Unexpectedly, neither can explain the observed visibilities. We show that these data suggest the presence of a companion, in accordance with the Hipparcos data on this star, and discuss this solution with respect to Arcturus' single star status.


Key words: techniques: interferometric -- stars: individual: Arcturus -- stars: atmospheres -- stars: binaries: general

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© ESO 2005


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