Banca de DEFESA: BERNARDO FORTON ODLAVSON GONÇALVES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : BERNARDO FORTON ODLAVSON GONÇALVES
DATA : 10/09/2018
HORA: 09:00
LOCAL: AUDITÓRIO DO DFTE
TÍTULO:

Lithium-rich giant stars: a study of the chemical anomaly and the magnetic field of those objects

PALAVRAS-CHAVES:

 Stars: abundances. Stars: fundamental parameters. Stars: late-type. Stars: low-mass. Stars: magnetic field.

PÁGINAS: 80
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Física
RESUMO:

According to the standard theory of stellar evolution, low-mass stars (spectral type K and G) must reach the beginning of the main sequence (ZAMS) with Li abundance near the meteorological value, which is ∼3.3 dex, and hold a high abundance until they reach the first dredge-up zone in the Red Giant Branch (RGB). After completion of the dilution processes, in the red clump, such stars should present a relatively low Li abundance. However, approximately 1-2% of all observed K and G giant stars have an abnormally high Li abundance (≥ 1.5dex). It is possible to find in the literature many attempts to reconcile theory and observation, but none of them is capable of explaining all the scenarios in which these chemical anomalies occur.

 

Our work aims to present a new study of lithium-rich G and K spectral type stars and analyze the possible existence of particular characteristics to the lithium-rich stars that present detected magnetic field. We assemble a sample of 20 giant stars — taken from Charbonnel e Balachandran (2000), Kumar, Reddy e Lambert (2011), and Lèbre et al. (2009) — and calculate their fundamental parameters and the longitudinal magnetic field for a sub-sample of stars with observed high-resolution spectra available at PolarBase (Petit et al., 2014). Concerning the evolutionary states, we have used parallaxes recently provided by ESA’s Gaia spacecraft. To do so, we use the spectral analysis tool iSpec (Blanco-Cuaresma et al.,2014) and the Least-Squares Deconvolution (LSD) technique (Donati et al., 1997). We obtained results for fundamental parameters and Li abundance using the same procedure for all stars. Thus, we have the reliability in comparing stars from different samples that possibly had their spectra treated in different ways. We obtained relations between Li abundance, rotation velocity, and presence of a magnetic field according to what is predicted in the literature. We conclude that each star needs to be analyzed individually and with greater spectroscopic detail so that the real nature of its Li abundance is unraveled. The ¹²C/¹³C isotopic ratio, and the C/N elemental ratio, need to be investigated so that we can determine precisely the position of some stars (from our sample) on the H-R diagram.

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