Caracterização Espectroscópica de Estrelas FGK com Planetas Observadas pela Missão Kepler e de Anãs-M no Aglomerado das Plêiades Observadas pelo APOGEE

Abstract

The great statistic provided by the \textit {Kepler} mission, with the confirmation of over 4000 planets, shows the need to characterize the planets. A fundamental parameter to infer the nature of the planets is the planetary radii, derived through the stellar to planetary radii ratio. Recent works have shown that an accurate characterization of stellar parameters, such as the stellar radii, may reveal particularities of the planets once masked by the uncertainties in the stars radii. In this work, we analyzed Keck/HIRES optical spectra of a sample of 1305 FGK stars, hosting planets discovered by transits, and derived precise stellar parameters (effective temperature, surface gravity and metallicity), with the objective of investigating the relations between the stellar and planetary properties, and the architecture of planetary systems. The combination of the precise stellar parameters with Gaia distances allowed us to reach uncertainties of $\sim$2.8$\%$ and $\sim$3.7$\%$ for stellar and planetary radii, respectively. Analysis of the completeness corrected planetary radii distribution showed a bimodality for small planets ($R_{pl}$ $\leq$ 4$R_{\oplus}$), with peaks at 1.47 $\pm$ 0.05 $R_{\oplus}$ and 2.72 $\pm$ 0.10 $R_{\oplus}$, and a valley around $\sim$1.9$R_{\oplus}$. The high accuracy achieved in the determination of the planetary radii revealed a correlation in the $R_{pl}$ - orbital period plane, of the form $R_{pl}$ $\propto$ $P^{-0.11 \pm 0.03}$, which indicates that the position of the valley in the radii decreases as the orbital period increases. The obtained results are compatible with both the photoevaporation and core-powered mass-loss models of planet formation. Our results also showed that there is a correlation between stellar metalicities and planetary properties $R_{pl}$ and $P$ such that super-Earths and sub-Neptunes are preferably associated with stars with $[Fe/H]$ slightly above the solar metallicity ($[Fe/H]$ between 0 and 0.018 dex); the larger planets (sub-Saturns and Jupiters) are mostly associated with metal-rich stars ($[Fe/H]$ between 0.08 and 0.09 dex). On the other hand, we derived a critical period $P_{critical}$ $\sim$8 days, from which the stellar [Fe/H] increases reaching values of 0.056 $\pm$ 0.007 as the $P$ diminishes. Similarly, it is important to understand how the links between stellar and planetary characteristics extend to the M-dwarf star regime, as they represent about 70$\%$ of the stars of the Milky Way and, due to their low masses and small radii facilitate the detection of Earth-type exoplanets with both the radial velocity and transit techniques. In particular, M-dwarfs members of star clusters are of special interest as open clusters are used as calibrators by surveys, and are widely studied in the literature. In this thesis we performed a spectroscopic study of a sample of M-dwarfs, analyzing them in the infrared spectral region. We selected a sample of M-dwarfs, members of the young open cluster of the Pleiades, with photometric curves measured by the Kepler extended mission (K2). We used spectra obtained by the SDSS IV - APOGEE survey between 1.5 - 1.79 $\mu$m to determine their metallicities. The obtained results for the M-dwarfs of the Pleiades cluster are in agreement with the literature results, confirming the robustness of our analysis. A new result was the identification of the \textit{Zeeman} effect on some of the Fe I and FeH lines in most of the stars studied, opening the possibility of measuring magnetic fields from APOGEE spectra, which will have important consequences for the SDSS IV - APOGEE survey. Keywords: stars: fundamental parameters; stars: low-mass; infrared: stars; techniques: spectroscopic; open-cluster: Pleiades; planetary-systems