Banca de DEFESA: JOÃO MARCELO MACHADO

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : JOÃO MARCELO MACHADO
DATA : 13/04/2018
HORA: 10:00
LOCAL: AUDITÓRIO DO DFTE
TÍTULO:

ROTATION, MAGNETIC ACTIVITY AND THE OCCURRENCE OF HOT JUPITERS IN COOL STARS

PALAVRAS-CHAVES:

stellar rotation, stellar activity, hot Jupiters

PÁGINAS: 110
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

Rotation is fundamental in Stellar Astrophysics for being responsible for several phenomena with impact 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 all 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 the 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 R’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.

MEMBROS DA BANCA:
Externo ao Programa - 4857669 - JEFFERSON SOARES DA COSTA
Presidente - 2496004 - JOSE DIAS DO NASCIMENTO JUNIOR
Interno - 2887830 - MATTHIEU SEBASTIEN CASTRO
Externo à Instituição - THARCISYO SA E SOUSA DUARTE - UFCA