  Using 2D models of rotating stars, the interferometric measurements of alpha
Eri and its fundamental parameters corrected for gravitational darkening
effects we infer that the star might have a core rotating 2.7 times faster than
the surface. We explore the consequences on spectral lines produced by surface
differential rotation combined with the effects due to a kind of internal
differential rotation with rotational energies higher than allowed for rigid
rotation which induce geometrical deformations that do not distinguish strongly
from those carried by the rigid rotation.
