  We treat a very crude model of an exploding star, in the weak field
approximation of the Brans-Dicke theory, in a scenario that resembles some
characteristics data of a Type Ia Supernova. The most noticeable feature, in
the electromagnetic component, is the relationship between the absolute
magnitude at maximum brightness of the star and the decline rate in one
magnitude from that maximum. This characteristic has become one of the most
accurate method to measure luminosity distances to objects at cosmological
distances. An interesting result is that the active mass associated with the
scalar field is totally radiated to infinity, representing a mass loss in the
ratio of the "tensor" component to the scalar component of 1 to $(2 \omega +
3)$ ($\omega$ is the Brans-Dicke parameter), in agreement with a general result
of Hawking. Then, this model shows explicitly, in a dynamical case, the
mechanism of radiation of scalar field, which is necessary to understand the
Hawking result.
