On the Gas Dynamic Features of the Interacting Binary System UU Cas

We present the results of spectroscopic observations and Ha Doppler tomography of the massive close binary system UU Cas where a giant star fills its Roche lobe (donor) and transfers material through the vicinity of the L-1 point onto a massive but rather compact stellar companion (accretor). The system has been observed at the 1.2 m telescope of the Kourovka Astronomical Observatory. By analyzing the obtained spectra and computed Doppler tomogram, we suggest that at least three elements of the gas dynamic pattern in the system contribute to the Balmer Ha emission line profiles. These elements are: the stream from the L-1 point, the stellar wind from the accretor, and the diffuse disk, surrounding the accretor. In combination with the estimates of the companions' masses, our findings indicate that the system is at the late stage of the first mass transfer phase of its evolution.