Evidence for Planet‐induced Chromospheric Activity on HD 179949

Abstract

We have detected the synchronous enhancement of Ca II H and K emission with the short-period planetary orbit in HD 179949. High-resolution spectra taken on three observing runs extending over more than a year show the enhancement coincides with ϕ ~ 0 (the sub-planetary point) of the 3.093 day orbit, with the effect persisting for more than 100 orbits. The synchronous enhancement is consistent with planet-induced chromospheric heating by magnetic rather than tidal interaction, but awaits confirmation by further observations. Independent observations are needed to determine whether the stellar rotation is synchronous with the planet's orbit. Of the five 51 Peg-type systems monitored, HD 179949 shows the greatest chromospheric H and K activity. Three others show significant nightly variations, but the lack of any phase coherence prevents us saying whether the activity is induced by the planet. Our two standards, τ Ceti and the Sun, show no such nightly variations. Revised periods and updated ephemerides for the planetary orbits are also included.