Rotação, atividade magnética e a ocorrência de jupiterianos quentes em estrelas frias
Rotation is fundamental in Stellar Astrophysics for being responsible for several phenomena with influence on the stellar formation and evolution, such as the generation and topology of the associated magnetic fields and the angular momentum transfer. It is known that stars undergo rotational bra...
Na minha lista:
Autor principal: | |
---|---|
Outros Autores: | |
Formato: | Dissertação |
Idioma: | por |
Publicado em: |
Brasil
|
Assuntos: | |
Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/26143 |
Tags: |
Adicionar Tag
Sem tags, seja o primeiro a adicionar uma tag!
|
Resumo: | Rotation is fundamental in Stellar Astrophysics for being responsible for several phenomena
with influence on the stellar formation and evolution, such as the generation
and topology of the associated magnetic fields and the angular momentum transfer. It
is known that stars undergo rotational braking as they evolve, showing a transition in
the values of rotational measurements from the F spectral type. A possible explanation
for this phenomenon is associated with magnetic activity, sustained by the dynamo process
and differential rotation, another possible explanation regards the dissipation due to
gravitational tides in the cases of binary stars or stars with detected exoplanets. In this
work, we developed a theoretical model to describe the frequency distributions of projected
rotational velocities, vsini, for approximately 10.000 stars of F, G, and K spectral
types, including a sample of solar twins. We studied the rotational braking due to magnetic
nature from the study of chromospheric activity by analyzing the log R0
HK indicator,
associated with the Ca II H and K lines, and the coronal activity through measurements
of X-ray flux. To study the gravitational mechanism we take into account a sample of
46 stars hosting extrasolar planets known as hot Jupiters (HJs), detected through transit
and radial velocity methods. We also explored the dependence between stellar rotation
and orbital parameters and discussed possible processes of formation and migration of
HJs, by analyzing the spin-orbit misalignment, or obliquity (λ), and the eccentricity of
these systems. Our theoretical model is valid since it recovers the Skumanich law, which
is fundamental in the context of gyrochronology, and properly describes the stars with low
rotation values. From the solar twins’ sample, we have also determined that the internal
distribution of angular momentum may be one of the factors associated with the rotational
transition observed between stars whose convective and radiative envelopes are found
in different depths. From the observational point of view, we did not notice a direct dependence
between rotation and the presence of HJs, however we showed a clear correlation
between the values of vsini and activity, so that the rotational braking is more probably
connected to the mass loss from magnetically-coupled winds. Exploring the planetary sample we noticed a slight tendency for more massive HJs to be found in aligned orbits.
Revisiting previous works, we have determined that stars with temperatures lower than
∼ 6020K and masses lower than ∼ 1.15M are found in approximately aligned systems,
whereas stars above these limits exhibit a great dispersion in the values of λ. We also
noticed a dependence between λ and the spectral type, where F stars show a great spread
in the obliquity values. These three results may be related to the fact that stars with
these characteristics undergo weak tidal dissipation due to their thin convective zones,
resulting in a slow orbital realignment in the respective systems. |
---|