  We investigate energetic stability of vortices near the surface of a
Bose-Einstein condensate. From an energy functional of a rotating Bose-Einstein
condensate, written in terms of variables local to the surface, and a suitable
trial wavefunction we calculate the energy of a moving vortex. The energetic
stability of the vortex is investigated in terms of the rotation frequency of
the confining potential. The critical frequency at which the vortices enter the
condensate is calculated and compared with the experiment where a reasonable
agreement is obtained.
