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This is the fifth paper in a series aimed at studying the chromospheres ofactive binary systems using several optical spectroscopic indicators to obtainor improve orbital solution and fundamental stellar parameters. We present herethe study of FF UMa (2RE J0933+624), a recently discovered, X-ray/EUV selected,active binary with strong H_alpha emission. The objectives of this work are, tofind orbital solutions and define stellar parameters from precise radialvelocities and carry out an extensive study of the optical indicators ofchromospheric activity. We obtained high resolution echelle spectroscopicobservations during five observing runs from 1998 to 2004. We found radialvelocities by cross correlation with radial velocity standard stars to achievethe best orbital solution. We also measured rotational velocity bycross-correlation techniques and have studied the kinematic by galactic space-velocity components (U, V, W) and Eggen criteria. Finally, we have determinedthe chromospheric contribution in optical spectroscopic indicators, from Ca IIH & K to Ca II IRT lines, using the spectral subtraction technique. We havefound that this system presents an orbital period variation, higher thanpreviously detected in other RS CVn systems. We determined an improved orbitalsolution, finding a circular orbit with a period of 3.274 days. We derived thestellar parameters, confirming the subgiant nature of the primary component andobtained rotational velocities (vsini), of 33.57 km/s and 32.38 km/s for theprimary and secondary components respectively. From our kinematic study, we candeduce its membership to the Castor moving group. Finally, the activity studyhas given us a better understanding of the possible mechanisms that produce theorbital period variation.

Multiwavelength optical observations of chromospherically active binary systems V. FF UMa (2RE J0933+624): a system with orbital period variation