The GAPS programme with HARPS-N at TNG: VII. Putting exoplanets in the stellar context: Magnetic activity and asteroseismology of τ Bootis A ∗ ∗ ∗

Aims: We observed the τ Boo system with the HARPS-N spectrograph to test a new observational strategy aimed at jointly studying asteroseismology, the planetary orbit, and star-planet magnetic interaction. Methods: We collected high-cadence observations on 11 nearly consecutive nights and for each night averaged the raw FITS files using a dedicated software. In this way we obtained spectra with a high signal-to-noise ratio, used to study the variation of the Ca ii H&K lines and to have radial velocity values free from stellar oscillations, without losing the oscillations information. We developed a dedicated software to build a new custom mask that we used to refine the radial velocity determination with the HARPS-N pipeline and perform the spectroscopic analysis. Results: We updated the planetary ephemeris and showed the acceleration caused by the stellar binary companion. Our results on the stellar activity variation suggest the presence of a high-latitude plage during the time span of our observations. The correlation between the chromospheric activity and the planetary orbital phase remains unclear. Solar-like oscillations are detected in the radial velocity time series: we estimated asteroseismic quantities and found that they agree well with theoretical predictions. Our stellar model yields an age of 0.9 ± 0.5 Gyr for τ Boo and further constrains the value of the stellar mass to 1.38 ± 0.05 M⊙.