Name/Affiliation: Ignazio Pillitteri (INAF-Osservatorio Astronomico di Palermo)
The activity of stars hosting hot Jupiters
The activity of stars harboring hot Jupiters could be influenced by the close-in planets. Some cases of enhanced chromospheric activity are reported in literature that hint a magnetic origin. In X-rays, HD 189733 shows high features of activity that can be ascribed to the influence of the magnetic field of its planetary companion. I will report on the characterization of the corona of HD 189733 based on what we learned from three XMM-Newton observations. Through a wavelet analysis of a flare, we inferred a long magnetic loop of 2 R* to 4 R* and a local magnetic field of strength 40-100 G. The size of the flaring loop suggests a role of the hot Jupiter in triggering this kind of X-ray variability. HST-COS spectra of HD 189733 shows temporal variations in intensity and Doppler shifts of Si III and Si IV lines that can be ascribed to plasma flowing from the planetary atmosphere at well determined planetary phases. In another system, WASP-18, the very close hot Jupiter has likely suppressed any magnetic activity of the host star through strong tidal interaction with the upper layers of the stellar convective zone. In summary, star planet interaction can act in opposite directions enhancing or destroying the stellar activity, depending on different parameters, like star-planet separation, mass ratios, and inner stellar structure.