Desvio gravitacional relativístico em ambiente estelar e cinemática de aglomerados abertos - M67, um laboratório único

Abstract

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−1 pc−1 . 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.