A&A 426, 279–296 (2004) Astronomy DOI: 10.1051/0004-6361:20041098 & c ESO 2004 Astrophysics Unveiling Mira stars behind the molecules, Confirmation of the molecular layer model with narrow band near-infrared interferometry G. Perrin1,S.T.Ridgway1,2, B. Mennesson3,W.D.Cotton4, J. Woillez1,5, T. Verhoelst1,6, P. Schuller7, V. Coud´e du Foresto1,W.A.Traub7, R. Millan-Gabet8, and M. G. Lacasse7 1 Observatoire de Paris, LESIA, UMR 8109, 92190 Meudon, France e-mail:
[email protected] 2 National Optical Astronomy Observatories, Tucson, AZ 85726-6732, USA 3 Jet Propulsion Laboratory, California Institute of Technology, MS 306-388, 4800 Oak Grove Drive, Pasadena, CA 91109, USA 4 National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA 5 Keck Observatory, 65-1120 Mamalahoa Highway, Kamuela, HI 96743, USA 6 Sterrenkunde Leuven, Leuven, Belgium 7 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA 8 Caltech/Michelson Science Center, Pasadena, CA 91125, USA Received 15 April 2004 / Accepted 15 June 2004 Abstract. We have observed Mira stars with the FLUOR beamcombiner on the IOTA interferometer in narrow bands around 2.2 µm wavelength. We find systematically larger diameters in bands contaminated by water vapor and CO. The visi- bility measurements can be interpreted with a model comprising a photosphere surrounded by a thin spherical molecular layer. The high quality of the fits we obtain demonstrates that this simple model accounts for most of the star’s spatial structure. For each star and each period we were able to derive the radius and temperature of the star and of the molecular layer as well as the optical depth of the layer in absorption and continuum bands.