Fast Optical Variability of SS 433

We study the variability of the optical flux from the peculiar Galactic source SS 433 based on observations with the Russian-Turkish 1.5-m telescope. We describe in detail the technique of high-quality photometric measurements with a time resolution of 0.3-1 s using an ordinary CCD. Through test observations of nonvariable stars, we show that atmospheric turbulence introduces no significant distortions into the light curves. Therefore, such data are well suited for studying the aperiodic variability of various objects. A large set of light-curve measurements for SS 433 obtained in this way has allowed us to obtain the power spectra of its flux variability with a record sensitivity up to frequencies of similar to 0.5 Hz and to detect its break at a frequency of about 2.4 x 10(-3) Hz. We suggest that the detected break in the power spectrum results from the smoothing of the optical flux variability due to a finite size of the emitting region. Based on our measurement of the break frequency in the power spectrum, we have estimated the size of the accretion-disk photosphere to be approximate to 2 x 10(12) cm. We show that the amplitude of the variability in SS 433 decreases sharply during accretion-disk eclipses, but it does not disappear completely. This suggests that the size of the variable optical emission source is comparable to that of the normal star whose size is R-O approximate to 2 x 10(12) cm approximate to 30R(circle dot). The decrease in flux variability amplitude during eclipses shows the presence of a nonvariable optical emission component with a magnitude m(R) approximate to 13.2.