2001A&A...376..518H

We present diffraction-limited (30mas resolution) bispectrum speckle interferometry of the Mira star R Leo with the 6 m SAO telescope. The speckle interferograms were recorded through narrow-band interference filters with centre wavelength/bandwidth of 673nm/8nm (strong TiO absorption band), 656nm/10nm, 699nm/6nm and 781nm/14nm (moderate TiO absorption), 754nm/6nm (weak TiO absorption), and 1045nm/9nm (continuum). The reconstructed images show that the average uniform-disk diameters of R Leo are 60.6mas±3.0mas at 656nm, 75.6mas±3.7mas at 673nm, 52.5mas±2.5mas at 699nm, 48.7mas±2.3mas at 754nm, 55.0mas±2.7mas at 781nm, and 37.9mas±4.0mas at 1045nm. 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 τ_λ=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 1045nm-observation a photospheric radius (Rosseland τ_Ross=1 radius) of R Leo of 417R_☉±97R_☉ (19.2mas±2.0mas) indicating pulsation in the first-overtone mode. From JHKL photometry and the angular photospheric radius an effective temperature of 2590±180K at near maximum phase was obtained.