Classification of EUV stellar sources detected by the ROSAT WFCI. Photometric and radial velocity studies

We present the results of high-precision UBV(RI), photometric observations and of spectroscopic radial velocity measurements obtained at the European Southers Observatory for a sample of 51 cool stars detected in the EW by th e ROSAT Wide Field Camera (WFC). Using also recent results from HIPPARCOS, we infer spectral ta-pes and investigate the single or binary nature of the sample stars. Optical variability, with periods in the 0.4-13 day range, h as been detected for the first time in 15 of these stars.