Banca de DEFESA: BERNARDO FORTON ODLAVSON GONÇALVES

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : BERNARDO FORTON ODLAVSON GONÇALVES
DATE: 31/01/2023
TIME: 14:00
LOCAL: online
TITLE:

Investigating the rotation, the magnetism and the chemical abundances of solar-type stars through evolutionary models and spectroscopy: from the pre-main sequence to the red giant

KEY WORDS:

stars: evolution - stars: interiors - stars: magnetic field - stars: rotation - stars: solar-type

PAGES: 134
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

The study of the rotational evolution of the Sun and solar-type stars is undoubtedly one of the fields of stellar
astrophysics in major evidence today. There are numerous issues that are still far from being fully understood, which makes
research in this field intense and dynamic. Among these issues are the understanding of the phenomena that influence the
angular momentum of stars during their formation, still in the Pre-Main Sequence phase; the understanding of the
mechanisms that act in the stellar interiors throughout evolution, which end up determining, for example, the rotation profile
of a solid body observed on the Sun; or which transport mechanisms act in evolved stars, which undergo profound changes in
their structure, and manifest peculiar phenomena such as lithium enrichment and alterations in many chemical abundances. In
all cases, we know that stellar magnetism plays a prominent role, however, it is still far from being fully understood. In this
thesis we use models computed with the Toulouse-Geneva Stellar Evolution Code (TGEC) to study the rotational evolution of
four samples of solar-type stars, in addition to revisiting studies with analogous stars from open clusters. In our analysis, we
used two different magnetic brake prescriptions, which simulate the loss of angular momentum due to stellar winds.
Additionally, we also studied a sample of giant solar-type stars that are rich in lithium, investigating the possible relationship
with the magnetic character of some of these stars. As far as main sequence stars are concerned, we found some convergences
and some discrepancies between our models and the stellar samples studied. We found that the sample with seismological
data, composed of stars of intermediate and older ages, is not well restricted for a study on the rotation and magnetic
evolution of the Sun. The sample of low-activity stars appears to be affected by a decrease in magnetic braking despite
differences in metallicity, although targets with higher metallicity seem to better follow our evolutionary paths. Finally, wefound a mismatch between our rotation evolution tracks and the position of the youngest stars. As for lithium-rich giant stars,
we found that stars previously classified as red giants (RGB) may be in a different evolutionary state. Furthermore, we found
that most stars in our sample with surface magnetic field detection show at least moderate rotation speeds, but even then, we
were unable to detect a magnetic field in two rapidly rotating stars. Because of our small sample of magnetic giants, it is
difficult to determine whether the presence of a surface magnetic field and the Li-enrichment phenomena in giants could be
somehow linked.

COMMITTEE MEMBERS:
Externo à Instituição - JORGE LUIS MELENDEZ MORENO
Interno - 2496004 - JOSE DIAS DO NASCIMENTO JUNIOR
Externo à Instituição - LEO ALBERTO GIRARDI
Interno - 2887830 - MATTHIEU SEBASTIEN CASTRO
Interno - 1672854 - RAIMUNDO SILVA JUNIOR