Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models

We present K'-band observations of five Mira stars with the IOTA interferom eter. The interferograms were obtained with the FLUOR fiber optics beam com biner, which provides high-accuracy visibility measurements in spite of tim e-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU He r, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters 1 1.7 mas, 10.9 mas, 8.4 mas, 8.1 mas, and 7.9 mas (+/-0.3 mas), respectively . Simultaneous photometric observations yielded the bolometric fluxes. The derived angular Rosseland radii and the bolometric fluxes allowed the deter mination of effective temperatures. For instance, the effective temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland radius fo r R Aql of 250(-60)(+100) R-. was derived from the angular Rosseland radius of 5.5 +/- 0.2 mas and the HIPPARCOS parallax of 4.73 +/- 1.19 mas. The ob servations were compared with theoretical Mira star models of Bessel et al. [A&A 307 (1996) 481] and Hofmann et al. [A&A 339 (1998) 846]. The effectiv e temperatures of the M-type Miras and the linear radius of R Aql indicate fundamental mode pulsation. (C) 2002 Published by Elsevier Science B.V.