  Due to their high luminosity at maximum and degree of homogeneity, Type Ia
supernovae have been extensively used for cosmological purpouses, in particular
to estimate extragalactic distances and the Hubble constant. Recently the
number of Type Ia supernovae detected at high redshift has increased, opening
the possibility of determining the mass density parameter, the cosmological
constant and the deceleration parameter. The observed supernovae appear to be
further than expected -even for an empty Universe-, implying a low density
Universe and moreover an accelerating Universe. Among the various
uncertainties, we address the possibility that old supernovae are not equal to
current supernovae. From first principles, an evolution of progenitors with
time is expected. Additionally, some observations show a dependence of the
observed properties on galaxy type and colour. Our aim in this work is to study
the outcome of exploding CO white dwarfs following the evolution of the
progenitor intermediate mass stars with different masses and metallicities.
Once this influence of the progentitor has been determined, the observations
may be corrected. At the present stage of this project we are not able to
quantify this effect properly. One result is clear, that the differences at
maximum are expected to be small ($\sim$0.2 mag) but this is of the same order
as all the evidence for a positive cosmological constant ($\sim$0.25 mag).
