The kinematic approach to cosmological tests provides a direct evidence to
the present accelerating stage of the universe which does not depend on the
validity of general relativity, as well as on the matter-energy content of the
Universe. In this context, we consider here a linear two-parameter expansion
for the decelerating parameter, q(z)=q0+q1z, where q0 and q1 are
arbitrary constants to be constrained by the Union supernovae data. By assuming
a flat Universe we find that the best fit to the pair of free parameters is
(q0,q1) = (−0.73,1.5) whereas the transition redshift is zt=0.49−0.07+0.14 (1σ) −0.12+0.54 (2σ). This
kinematic result is in agreement with some independent analyzes and
accommodates more easily many dynamical flat models (like ΛCDM).Comment: 10 pages, 4 figures, 1 tabl