1996A&A...316L..21W

We present the first diffraction-limited speckle masking observations of a Mira star with the Russian 6m SAO telescope. At 700 and 714nm wavelength a resolution of 1.22λ/D=30milli-arcsec was achieved. The reconstructed true images are the images with the highest resolution obtained up to now in this wavelength region. The speckle interferograms of R Cas were recorded through interference filters with center wavelength/bandwidth of 714nm/6nm (strong TiO band absorption) and 700nm/6nm (moderate TiO absorption). The two reconstructed images show that the azimuthally averaged 700 and 714nm uniform-disk diameters of R Cas are 36mas±2mas and 49mas±2mas, respectively. In the 700nm and 714nm images the disks of R Cas are non-uniform and elongated along position angle 52±7deg and 57±7deg, respectively. The size (ellptical uniform disk fit) of the elongated disks is about 33.3masx38.7mas (axial ratio 0.86) in the 700nm pseudo-continuum filter and 42.3masx55.6mas (axial ratio 0.76) in the 714nm TiO absorption band filter. We discuss briefly theoretical aspects of these and previous observations.