Because of their broad, often overlapping line profiles, measurement of spectrograms of OB double-lined binaries may be expected to give orbital velocities K that differ appreciably from their true values. For this reason, we have digitize and analyzed with the Victoria cross-correlation program VCROSS spectrograms obtained at the Lick Observatory of the detached OB eclipsing binaries CW Cep, V453 Cyg, V478 Cyg, U Oph, AG Per, and V760 Sco, as well as the semidetached system TT Aur and the contact system V382 Cyg. Synthetic binaries, with component lines having imposed velocities, formed from digitized photographic spectra of single stars of known rotational velocities, are employed to calibrate the procedures. According to the calibration, the values of K derived by the cross-correlation method are larger than the true values by an average of 2.0% for the primary components and 3.0% for the secondaries. The average luminosity ratio is 0.7. The values of K obtained for the eclipsing binaries by the calibrated cross-correlation procedure are, as expected, greater than the values obtained by oscilloscopic scanning of the same spectrograms. The differences are, on the average, 2.7% and 4.2% for the more and less luminous components, respectively. These results apply directly only to material similar to that studied by us. Although the values of K, and hence the masses and radii, obtained for these binaries are probably more reliable than earlier results, it is our conclusion that the elimination of systematic effects in the velocities of double-line OB binaries is a difficult task that we may not have accomplished completely. We recommend that, whatever scheme of observation and reduction is employed, calibration be carried out by means of synthetic binaries with given velocities of the components.
