INAF-Osservatorio Astrofisico di Catania, Italy
Antonino Francesco Lanza shall introduce starspot occultations as a tool to detect surface brightness inhomogeneities in late-type stars with close-by transiting planets. Such occultations can be used to make precise measurements of the starspot recurrence at given longitudes or of stellar rotation us ing starspots as tracers. I report the intriguing cases of Kepler-17, Kepler-63, and HAT-P-11 where the rotation periods of occulted starspots show a commensurability within 1% with the orbital periods of their close-by massive planets, specifically with P_rot:P_orb ratios of 8:1, 4:7, and 6:1, respectively. Similar commensurabilities have been proposed to occur in several other stars hosting close-by planets, although with less precise measurements. They could be produced by tidal effects not accounted for by current tidal theories. A conjectural model is proposed to interpret such a phenomenon. It is based on the excitation of resonant oscillations in the interior magnetic field of a host star by a component of the planet tidal potential having a very low frequency in the reference frame rotating with the star itself. The advantages and the limitations of such an approach are briefly discussed.
Date: Thursday March 30, 2023 - 17:00 CET (online)