Publications
of the
MPIfR Optical & Infrared Interferometry Group

K. Ohnaka, U. Beckmann, J.-P. Berger, M.K. Brewer, K.-H. Hofmann, M.G. Lacasse, R. Millan-Gabet, J.D. Monnier, E. Pedretti, D. Schertl, F.P. Schloerb, M. Scholz, W.A. Traub, G. Weigelt

JHK'-band IOTA interferometry of the Mira star T Cep and the cirmcumstellar environment of R CrB

In: Schielikke, R.E. (ed.): Short Contrib. Ann. Sci. Meeting Astron. Ges. Freiburg 2003. Astron. Nachr. 324, Suppl. Issue 3 (2003), p.61-62
The Sun and Planetary Systems - Paradigms for the Universe
Annual Scientific Meeting of the Astronomische Gesellschaft, Sep 15-20, 2003, Freiburg, Germany

Abstract

Our new IOTA JHK'-band beam combiner allows the simultaneous recording of spectrally dispersed J-, H- and K'-band Michelson interferograms. The beam combiner optics consists of an anamorphic cylindrical lens system and a prism. >From the interferograms of T Cep we derived the visibilities and the J-, H-, and K'-band uniform-disk diameters of 14.0 +- 0.6 mas, 13.7 +- 0.6 mas and 15.0 +- 0.6 mas, respectively. Angular Rosseland radii are derived from the measured visibilities by fitting theoretical center-to-limb intensity variations (CLVs) of different Mira models (Bessell, Scholz, and Wood 1996; Hofmann, Scholz, and Wood 1998). The available HIPPARCOS parallax (4.76 +- 0.75 mas) of T Cep allows us to determine linear radii. For example, from the K'-band visibility we derived a Rosseland radius of 329 +70/-50 Rsun, if we use the CLVs of the M-models as fit functions. This radius is in good agreement with the theoretical radius of 315 Rsun. Furthermore, we use the visibility ratios V(lambda_1)/V(lambda_2) to investigate the wavelength dependence of the stellar diameter. We also observed R~CrB and resolved its circumstellar dust envelope at a baseline of 21 m. The visibilities in the J, H, and K' bands are 0.97 +- 0.06, 0.78 +- 0.06, and 0.61 +- 0.03, respectively. These observed visibilities, together with the K'-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 visibilities are approximately 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 Rstar and 950 - 1050 K, respectively.