  Nonextensive formalism is a generalization of the Boltzmann-Gibbs statistics.
In this formalism the entropic index q is a quantity characterizing the degree
of nonextensivity, and is interpreted as a parameter of long-memory or
long-range interactions between the components of the system. Since its
proposition in 1988, this formalism has been applied to investigate a wide
variety of natural phenomena. In stellar astrophysics, theoretical distribution
function based on nonextensive formalism (q-distributions) has been
successfully applied to reproduce the distribution of stellar radial and
rotational velocity data. In this paper, we investigate the time variation of
the entropic index q obtained from the distribution of rotation, Vsini, for a
sample of 254 rotational data for solar-type stars from 11 open clusters aged
between 35.5Myr and 2.6Gyr. As a result, we have found an anti-correlation
between the entropic index q and the age of clusters, and that the distribution
of rotation Vsini for these stars becomes extensive for an age greater than
about 170Myr. Assuming that the parameter q is associated with long-memory
effects, we suggest that the memory of the initial angular momentum of
solar-type stars can be scaled by the entropic index q. We also propose a
physical link between the parameter q and the magnetic braking of stellar
rotation.

Solar and Stellar Astrophysics