2005A&A...431.1019F

We present near-infrared K-band interferometric measurements of the Mira star RLeonis obtained in April 2001 and January 2002 with the VLTI, the commissioning instrument VINCI, and the two test siderostats. These epochs correspond to near-maximum stellar variability phases ∼0.08 and ∼1.02 (one cycle later), respectively. The April 2001 data cover a range of spatial frequencies (31-35 cycles/arcsecond) within the first lobe of the visibility function. These measurements indicate a center-to-limb intensity variation (CLV) that is clearly different from a uniform disk (UD) intensity profile. We show that these measured visibility values are consistent with predictions from recent self-excited dynamic Mira model atmospheres that include molecular shells close to continuum-forming layers. We derive high-precision Rosseland diameters of 28.5±0.4mas and 26.2±0.8mas for the April 2001 and January 2002 data, respectively. Together with literature estimates of the distance and the bolometric flux, these values correspond to linear radii of 350⁺⁵⁰_–40R_☉ and 320⁺⁵⁰_–40R_☉, and to effective temperatures of 2930±270K and 3080±310K, respectively.