Banca de DEFESA: JOSIAS VALENTIM SANTANA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSIAS VALENTIM SANTANA
DATE: 14/07/2022
TIME: 15:00
LOCAL: Zoom
TITLE:

Effects of radiative transfer on different techniques for tracking the magnetic field in the interstellar medium

KEY WORDS:

Magnetohydrodynamics; radiative transfer; numerical methods; Interstellar Medium

PAGES: 196
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Stellar clusters provide key information for studying from stellar origins to the Galactic structure, and even for fundamental
physics tests. In particular, Messier 67 (M67) is an important open cluster because it has similar metallicity and age to the Sun.
We present an observational study of different phenomena that can affect radial velocity (RV) measurements of stars
belonging to M67, for solving information about the cluster kinematics, as well as for a unique test of General Relativity.
Based on a recent technique, the difference between two independent RV measurements, spectroscopic and astrometric, of
stars belonging to a given cluster, allows empirically detecting, for example, the cluster’s global movement and the
gravitational redshift predicted by General Relativity. Spectroscopic and astrometric RV measurements were obtained from
public archives of the HARPS spectrometer and the Gaia satellite, respectively. Two initial samples, of 1278 and 144 stars,
were carefully selected, resulting in a final sample of 74 stars. We detected quantitatively the gravitational redshift (GR) in
M67, thus adding a new support to the General Theory of Relativity. We also detected for the first time an apparent rotational
(or shear) motion of M67, with a rotation gradient of ~ 66 m/s/pc. With these results, a new database with RV values
representing unbiased measurements are provided as a by-product of this Thesis. Finally, we calculated from newer data a
virial mass of 1980 +/- 100 M and a tidal radius of 14.2 +/- 0.3 pc for M67, in agreement with previous estimates. Overall, the
empirical determination of the cluster rotation is very useful for kinematic studies, either of the cluster itself or on its relation
with the Galactic structure. In addition, the present study contributes to fulfilling a gap among the tests of General Relativity,
since this theory has been little tested in stellar environments.

COMMITTEE MEMBERS:
Presidente - 3060853 - IZAN DE CASTRO LEÃO
Interno - 1675216 - BRUNO LEONARDO CANTO MARTINS
Interno - 346785 - JOSE RENAN DE MEDEIROS
Externo à Instituição - CARLOS EDUARDO FERREIRA LOPES - INPE
Externo à Instituição - DANIEL BRITO DE FREITAS - UFC