The lack of close binaries among hot horizontal branch stars in NGC 6752

Aims. We present the results of a spectroscopic search for close binaries among horizontal branch (HB) stars in NGC 6752. Methods. We used the ESO VLT-FORS2 instrument to obtain medium resolution (R = 4100) spectra of 51 hot HB stars with 8000 K ≤ Teff ≤ 32 000 K during four consecutive nights. Eighteen of our targets are extreme horizontal branch (EHB) stars with Teff ≥ 22 000 K. Radial velocity variations were measured with cross-correlation techniques, previously evaluated the statistical and systematic errors associated with them. Results. No close binary system has been detected among our 51 targets. The data corrected for instrumental effects indicate that the radial velocity variations are always below ≈15 km s −1 (3σ level). From a statistical analysis of our results, we conclude that (at 95% confidence