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 \sim 0.08 and \sim 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 \pm 0.4 mas and 26.2 \pm 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 ^ { +50 } _ { -40 } R _ { \odot } and 320 ^ { +50 } _ { -40 } R _ { \odot } , and to effective temperatures of 2930 \pm 270 K and 3080 \pm 310 K , respectively .