A nonextensive view of the stellar braking indices

• Published in: arXiv.org
• Main Authors: de Freitas, D B, Cavalcante, F J, Soares, B B, Silva, J R P
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 10.08.2015
• Subjects: Angular velocity; Braking; Main sequence stars; Mathematical models; Parameters; Physics - Solar and Stellar Astrophysics; Stars; Statistical mechanics; Stellar age; Stellar evolution; Stellar rotation; Torque; Unity
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1508.02237

The present work is based on a description for the angular mometum loss rate due to magnetic braking for main-sequence stars on the relationship between stellar rotation and age. In general, this loss rate denoted by \(\mathrm dJ/\mathrm dt\) depends on angular velocity \(\Omega\) in the form \(\mathrm dJ/\mathrm dt\propto\Omega^{q}\), where \(q\) is a parameter extracted from nonextensive statistical mechanics. Already, in context of stellar rotation, this parameter is greater than unity and it is directly related to the braking index. For \(q\) equal to unity, the scenario of saturation of the magnetic field is recovered, otherwise \(q\) indicates an unsaturated field. This new approach have been proposed and investigated by de Freitas \& De Medeiros for unsaturated field stars. In present work, we propose a nonextensive approach for the stellar rotational evolution based on the Reiners \& Mohanthy model. In this sense, we developed a nonextensive version of Reiners \& Mohanthy torque and also compare this generalized version with the model proposed in de Freitas \& De Medeiros based on the spin-down Kawaler torque for the main-sequence stars with F and G spectral types. We use the same sample of \(\sim16 000\) field stars with rotational velocity \(v \sin i\) limited in age and mass. As a result, we show that the Kawaler and Reiners \& Mohanthy models exhibit strong discrepancies, mainly in relation to the domain of validity of the entropic index \(q\). These discrepancies are mainly due to sensitivity on the stellar radius. Finally, our results showed that modified Kawaler prescription is compatible with a wider mass range, while the Reiners \& Mohanty model is restricted to masses less than G6 stars.