Astronomy & Astrophysics

Free access article

A&A 408, 553-558 (2003)
DOI: 10.1051/0004-6361:20031002

$\textit$ $\mbox{$\textit{K}^{\prime}$ }$ -band IOTA interferometry of the circumstellar environment of R CrB

K. Ohnaka¹, U. Beckmann¹, J.-P. Berger^{2, 3}, M. K. Brewer⁴, K.-H. Hofmann¹, M. G. Lacasse², V. Malanushenko⁵, R. Millan-Gabet^{2, 6}, J. D. Monnier^{2, 7}, E. Pedretti², D. Schertl¹, F. P. Schloerb⁴, V. I. Shenavrin⁸, W. A. Traub², G. Weigelt¹ and B. F. Yudin⁸

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Laboratoire d'Astrophysique Observatoire de Grenoble, Domaine Universitaire, 414 rue de la Piscine, BP 53, 38041 Grenoble Cedex 9, France
⁴ Department of Physics and Astronomy, University of Massachusetts, Amherst, MA 01003, USA
⁵ Crimean Astrophysical Observatory, 98409 Crimea, Ukraine
⁶ California Institute of Technology, 770 S. Wilson Ave. MS 100-22, Pasadena, CA 91125, USA
⁷ University of Michigan, 941 Dennison Building, 500 Church Street, Ann Arbor, MI 48109-1090, USA
⁸ Sternberg Astronomical Institute, Universitetskii pr. 13, 119899 Moscow, Russia

(Received 28 March 2003 / Accepted 16 June 2003 )

Abstract
We report the first long-baseline interferometry of the circumstellar dust environment of R CrB. The observations were carried out with the Infrared Optical Telescope Array (IOTA), using our new $JH\mbox{$K^{\prime}$ }$ beam combiner which enables us to record fringes in the J, H, and $K^{\prime}$ bands simultaneously. The circumstellar dust envelope of R CrB is resolved at a baseline of 21 m along a position angle of ~ $170^{\circ}$ , and the visibilities in the J, H, and $K^{\prime}$ bands are $0.97 \pm 0.06$ , $0.78 \pm 0.06$ , and $0.61 \pm 0.03$ , respectively. These observed visibilities, together with the $K^{\prime}$ -band visibility obtained by speckle interferometry with baselines of up to 6 m, and the spectral energy distribution are compared with predictions from spherical dust shell models which consist of the central star and an optically thin dust shell. The comparison reveals that the observed J- and H-band visibilities are in agreement with those predicted by these models, and the inner radius and inner boundary temperature of the dust shell were derived to be 60-80 $R_{\star}$ and 950-1050 K, respectively. However, the predicted $K^{\prime}$ -band visibilities are found to be ~ 10% smaller than the one obtained with IOTA. Given the simplifications adopted in our models and the complex nature of the object, this can nevertheless be regarded as rough agreement. As a hypothesis to explain this small discrepancy, we propose that there might be a group of newly formed dust clouds, which may appear as a third visibility component.

Key words: techniques: interferometric -- stars: circumstellar matter -- stars: mass-loss -- stars: individual: R CrB -- stars: variable: general -- infrared: stars

Offprint request: K. Ohnaka, kohnaka@mpifr-bonn.mpg.de

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