Multi-wavelength bispectrum speckle interferometry of R Leo and comparisonwith Mira star models

We present diffraction-limited (30 mas resolution) bispectrum speckle inter ferometry of the Mira star R Leo with the 6 m SAO telescope. The speckle in terferograms were recorded through narrow-band interference filters with ce ntre 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 i mages 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 a t 699 nm, 48.7 mas +/- 2.3 mas at 754 nm, 55.0 mas +/- 2.7 mas at 781 nm, a nd 37.9 mas +/- 4.0 mas at 1045 nm. In all six observed wavelength bands th e shape of R Leo shows no significant asymmetry. We compare our observation s with Mira star models and check the ability of monochromatic linear diame ters for discriminating between model representations of the observed star. Monochromatic tau (lambda) = 1 radii were derived from the observed visibi lities by application of model-predicted center-to-limb variations of the i ntensity. Adopting the HIPPARCOS parallax we derived from the 1045 nm-obser vation a photospheric radius (Rosseland tau (Ross) = 1 radius) of R Leo of 417 R. +/- 97 R. (19.2 mas +/- 2.0 mas) indicating pulsation in the first-o vertone mode. From JHKL photometry and the angular photospheric radius an e ffective temperature of 2590 +/- 180 K at near maximum phase was obtained.