FIRST DIFFRACTION-LIMITED SPECKLE MASKING OBSERVATIONS OF THE MIRA VARIABLE R-CAS WITH THE 6 M SAO TELESCOPE

We present the first diffraction-limited speckle masking observations of a Mira star with the Russian 6 m SAO telescope. At 700 and 714 nm w avelength a resolution of 1,22 lambda/D = 30 milli-arcsec was achieved . The reconstructed true images are the images with the highest resolu tion obtained up to now in this wavelength region. The speckle interfe rograms of R Cas were recorded through interference filters with cente r wavelength/bandwidth of 714 nm/6 nm (strong TiO band absorption) and 700 nm/6 nm (moderate TiO absorption). The two reconstructed images s how that the azimuthally averaged 700 and 714 nm uniform-disk diameter s of R Gas are 36 mas +/- 2 mas and 49 mas +/- 2 mas, respectively. In the 700 nm and 714 nm images the disks of R Cas are non-uniform and e longated along position angle 52 degrees +/- 7 degrees and 57 degrees +/- 7 degrees, respectively. The size (elliptical uniform disk fit) of the elongated disks is about 33.3 mas x 38.7 mas (axial ratio 0.86) i n the 700 nm pseudo-continuum filter and 42.3 mas x 55.6 mas (axial ra tio 0.76) in the 714 nm TiO absorption band filter. We discuss briefly theoretical aspects of these and previous observations.