Stellar activity in exoplanet hosts

Most of the efforts on the search and characterization of Earth-like exoplanets are currently focused on low mass stars. These represent the vast majority of the population in our galaxy (about 75% of the stars have a lower mass than the Sun) and their interest lies in the fact that the photometric and spectroscopic signal of orbiting Earth-like planets is higher due to lower star-planet size and mass ratios. However, several important properties related to the structure and processes in this type of stars are still unknown, so a careful characterization is essential, especially for M-type stars, as one of the next steps in exoplanet sciences. Specifically, stellar activity effects, due to the presence of spots and faculae which have a different spectral and convective behavior than the quiet photosphere, introduce variations on photometric and spectroscopic measurements with a periodicity modulated by the stellar rotation. Their characterization is essential for exoplanet sciences. The availability of the most recent advances in observational equipment and techniques is allowing the amateur astronomy community to make significant contributions on the photometric follow up of exoplanet transits. In this work, a collaboration with the amateur astronomer Ramon Naves (Montcabrer Observatory) led to the discovery and analysis of the photometric variability of WASP-33 (Herrero et al. 2011), an A5-type star hosting a giant transiting planet with a period of 1.21986 days, then becoming the first exoplanet host with δ Scuti oscillations. The photometry was analysed with Lomb-Scargle periodograms and several methods of data weighting, revealing the possible commensurability of the photometric pulsations with the orbital period of the planet, thus suggesting some type of star-planet interactions. The oscillations show an amplitude and timescale that are of the same order that those typically produced by stellar activity, but in this case related to a phenomenon of pulsations in a relatively massive star. The characterization of stellar activity in low mass stars was carried out through several techniques that allowed us both to model and to simulate the relationships between the observational data and the stellar properties. Stellar activity in the photosphere is related to the magnetic field intensity, which is in turn modulated by the stellar rotation rate in terms of the dynamo action. Several empirical relations for G-, Kand M-type stars, where a convective envelope is present, allow to find correlations between certain activity indicators, such as the chromospheric log(R′ HK), and the rotation period of the star. These correlations allowed us to generate synthetic samples of stars with stochastic distributions of stellar and geometric properties, thus populating the activity v sin i diagram and allowing to estimate the inclination of the rotation axis, i, when accurate measurements of log(R′ HK) and the projected rotation rate, v sin i, are available. Assuming a spin-orbit alignment,