The K-band intensity profile of R Leonis probed by VLTI/VINCI

We present near-infrared K-band interferometric measurements of the Mira star R Leonis 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 ± 0.4 mas and 26.2 ± 0.8 mas 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_-40⁺⁵⁰ R_⊙ and to effective temperatures of 2930 ± 270 K and 3080 ± 310 K, respectively.