Is Arcturus a well-understood K giant? Test of model atmospheres and potential companion detection by near-infrared interferometry

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 to 2.39 micron. 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 how 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.

arXiv comment15 pages, 14 figures, accepted for publication by Astronomy & Astrophysics

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• The limb-darkened Arcturus; Imaging with the IOTA/IONIC interferometer
• The K giant star Arcturus: the hybrid nature of its infrared spectrum
• Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 micron CO lines
• Beyond the Coronal Graveyard
• Astrophysics in 2005
• Temperature stratification of the atmosphere of Arcturus