A nonextensive view of the stellar braking indices

¹ Departamento de Física, Universidade Federal do Rio Grande do Norte - 59072-970 Natal, RN, Brazil
² Grupo de Astroestatística, Departamento de Física, Universidade do Estado do Rio Grande do Norte Mossoró-RN, Brazil

^(a) danielbrito@dfte.ufrn.br

Received: 3 April 2015
Accepted: 28 July 2015

Abstract

The present work is based on the effects of the magnetic braking for the angular-mometum loss evolution and, consequently, the relationship between stellar rotation and age. In general, this loss rate denoted by depends on the angular velocity Ω in the form , where q is a parameter from nonextensive statistical mechanics. In the context of the stellar rotation, this parameter is directly related to the braking index. For q equal to unity, the scenario of the saturation of the magnetic field is recovered. Such an approach was proposed and investigated by de Freitas and De Medeiros for unsaturated field stars. We propose a new nonextensive approach for the stellar rotational evolution based on the Reiners and Mohanty model. We developed a nonextensive version of Reiners and Mohanty torque, and compare it with the model proposed in de Freitas and De Medeiros, by using a sample of velocity for field F- and G- stars. As a result, we show that the Kawaler and Reiners-Mohanty models exhibit strong discrepancies in relation to the domain of validity of the entropic index q. These discrepancies are mainly due to sensitivity on the stellar radius. Our results also showed that the modified Kawaler prescription is consistent in a wider mass ranges, while the Reiners and Mohanty model is restricted to masses less than from G6 stars.