  Betelgeuse is an example of a cool super-giant displaying brightness
fluctuations and irregular surface structures. Simulations by Freytag et al.
(2002) of the convective envelope of the star have shown that the fluctuations
in the star's luminosity may be caused by giant cell convection. A related
question regarding the nature of Betelgeuse and supergiants in general is
whether these stars may be magnetically active. If so, that may in turn also
contribute to their variability. By performing detailed numerical simulations,
I find that both linear kinematic and non-linear dynamo action are possible and
that the non-linear magnetic field saturates at a value somewhat below
equipartition: in the linear regime there are two modes of dynamo action.
