Time-dependent nonextensivity arising from the rotational evolution of solar-type stars

• Published in: arXiv.org 2013-12
• Main Authors: Silva, Jose R P, Nepomuceno, Mackson M F, Soares, Braulio B, de Freitas, Daniel B
• Format: Article
• Language: English
• Subjects: Angular momentum; Astrophysics; Braking; Distribution functions; Formalism; Open clusters; Parameters; Stars; Stellar age; Stellar evolution; Stellar rotation; Time dependence
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1308.6047

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.