  We report on the observation of vortex formation in a Bose-Einstein
condensate of Rb-87 atoms. Vortices are generated by superimposing an
oscillating excitation to the trapping potential introduced by an external
magnetic field. For small amplitudes of the external excitation field we
observe a bending of the cloud axis. Increasing the amplitude we observe
formation of a growing number of vortices in the sample. Shot-to-shot
variations in both vortex number and position within the condensed cloud are
observed, probably due to the intrinsic vortex nucleation dynamics. We discuss
the possible formation of vortices and anti-vortices in the sample as well as
possible mechanisms for vortex nucleation.
