Evolução do índice de freio magnético para estrelas do tipo solar
The present work is based on the effects of the magnetic brake for the evolution of the loss of angular momentum and, consequently, the relation between stellar rotation and age. In general, this loss rate defined by dJ=dt depends on the angular velocity in the form dJ=dt / q, where q is a para...
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| Formato: | doctoralThesis |
| Idioma: | por |
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Brasil
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/24146 |
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| Resumo: | The present work is based on the effects of the magnetic brake for the evolution of the loss
of angular momentum and, consequently, the relation between stellar rotation and age.
In general, this loss rate defined by dJ=dt depends on the angular velocity
in the form dJ=dt / q, where q is a parameter of non-extensive statistical mechanics. In the context
of stellar rotation, this parameter is directly related to the brake index. For q equal to
unity, the magnetic field saturation scenario is recovered. Such an approach was proposed
and investigated by de Freitas and De Medeiros for unsaturated field stars. We propose
a new non-extensive approach to the evolution of stellar rotation based on the Reiners
and Mohanty model. We have developed a non-extensive version of the Reiners and
Mohanty torque, and compared with the model proposed by de Freitas and De Medeiros,
using a velocity sample v sin i for ~ 16000 F and G field 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 the
sensitivity of the stellar rotation on the stellar radius . Our results also showed that the
modified Kawaler model is consistent within a wide mass range, while the Reiners and
Mohanty model is restricted to masses smaller than that of a G6 Main Sequence star. We also devoted part of this thesis to studying the evolutionary behavior of the
magnetic brake index for stars outside the Main Sequence. In this approach, we consider
that the brake index undergoes a variation along the evolution of the star, that is, it is not
a constant, but depends on the effect of I_. Thus, we justify the fact that G-type giant stars
are governed by the same Skumanich law. However, they must be corrected by one factor.
In this thesis, we show that this factor is due to the non-conservation of the volume of the star, which becomes more evident in later evolutionary stages, as is the case of the giants. We find that the effect of the variation of the moment of inertia (dI=dt) is more important when the volume of the star is not conserved. |
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