Extreme Horizontal Branch stars in {omega} Cen

The observations performed consist of nearly 100 hours of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for aro und half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations.

Based on the spectroscopy, we derive reliable values of logg, Teff and logN(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48000 and 54000K.