Banca de DEFESA: FRANCISCO JÂNIO CAVALCANTE

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
DISCENTE : FRANCISCO JÂNIO CAVALCANTE
DATA : 26/05/2017
HORA: 09:00
LOCAL: Auditório do DFTE
TÍTULO:

Evolution of the magnetic brake index for solar-type stars

PALAVRAS-CHAVES:

 Stellar rotation, magnetic braking, distribution and statistics.

PÁGINAS: 165
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
SUBÁREA: Física Geral
RESUMO:

The present work is based on the effects of the magnetic braking for the evolution of the loss of
angular momentum and, consequently, the relation between stellar rotation and age. In general, this
rate of loss defined by dJ/dt depends on the angular velocity Ω in the form dJ/dt ∝ Ω^{q}, where
q is a parameter of the non-extensive statistical mechanics. In the context of stellar rotation, this
parameter is directly related to the braking index. For q equal to the unit, the magnetic field
saturation scenario is recovered. Such an approach was proposed and investigated by de Freitas
and De Medeiros for unsaturated field stars. In this thesis, we propose a new non-extensive
approach to the evolution of stellar rotation based on the Reiners and Mohanty model. We
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 seni) for ~16000 stars
F and G field. 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 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 G6 stars.
We also devoted part of this thesis to studying the evolutionary behavior of the magnetic braking
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 dI /dt. 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 non-conservation of the volume of the star, which becomes more evident in later evolutionary
stages, as is the case of the giants. We found that the dI/dt effect is best considering that the star
volume is not conserved.

MEMBROS DA BANCA:
Interno - 1675216 - BRUNO LEONARDO CANTO MARTINS
Presidente - 1724218 - DANIEL BRITO DE FREITAS
Externo à Instituição - EDUARDO JANOT PACHECO - USP
Interno - 346785 - JOSE RENAN DE MEDEIROS
Externo à Instituição - MACKSON MATHEUS FRANÇA NEPOMUCENO - UFERSA