A nonextensive approach to the stellar rotational evolution I. F and G type stars

Abstract

The pioneering study by Skumanich (1972) showed that the rotational velocity of G-type Main-Sequence (MS) stars decreases with stellar age according to $<v \sin i>$ $\propto$ $t^{-1/2}$. This relationship is consistent with simple theories of angular momentum loss from rotating stars, where an ionized wind is coupled to the star by a magnetic field. The present study introduces a new approach to the study of stellar rotational braking in unsaturated F and G type stars limited in age and mass, connecting angular momentum loss by magnetic stellar wind with Tsallis nonextensive statistical mechanics. As a result, we show that the rotation-age relationship can be well reproduced using a nonextensive approach from Tsallis nonextensive models. Here, the index $q$, which is related to the degree of nonextensivity, can be associated to the dynamo process and to magnetic field geometry, offering relevant information on the level of stellar magnetic braking for F- and G-type Main-Sequence stars.