| Abstract
| - We present diffraction-limited (30 mas resolution) bispectrum speckle interferometry of the Mira star R Leo with the 6 m SAO telescope. The speckle interfero grams were recorded through narrow-band interference filters with centre wavelength/bandwidth of 673 nm/8 nm (strong TiO absorption band), 656 nm/10 nm, 699 nm/6 nm and 781 nm/14 nm (moderate TiO absorption), 754 nm/6 nm (weak TiO absorption), and 1045 nm/9 nm (continuum). The reconstructed images show that the average uniform-disk diameters of R Leo are 60.6 mas ± 3.0 mas at 656 nm, 75.6 mas ± 3.7 mas at 673 nm, 52.5 mas ± 2.5 mas at 699 nm, 48.7 mas ± 2.3 mas at 754 nm, 55.0 mas ± 2.7 mas at 781 nm, and 37.9 mas ± 4.0 mas at 1045 nm. In all six observed wavelength bands the shape of R Leo shows no significant asymmetry. We compare our observations with Mira star models and check the ability of monochromatic linear diameters for discriminating between model representations of the observed star. Monochromatic $\tau_{\lambda}=1$ radii were derived from the observed visibilities by application of model-predicted center-to-limb variations of the intensity. Adopting the HIPPARCOS parallax we derived from the 1045 nm-observation a photospheric radius (Rosseland $\tau_{\rm Ross}=1$ radius) of R Leo of 417 $R_{odot} \pm 97 R_{odot}$ (19.2 mas ± 2.0 mas) indicating pulsation in the first-overtone mode. From JHKL photometry and the angular photospheric radius an effective temperature of $2590 \pm 180$ K at near maximum phase was obtained.
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