A search for CaII emission enhancement in stars resulting from nearby giant planets

We present a search for periodicities (P-chr) in the chromospheric Ca II in frared triplet emission of several stars (tau Boo, 51 Peg, v And, rho (1) C nc, rho CrB, 70 Vir and GL 876) which may be directly attributable to inter action with close-in giant planets. Activity enhancements could arise from increased non-radiative heating and dynamo action in planet-induced tidal b ulges (with P-chr approximate toP(orb)/2), or from interactions between the stellar and planetary magnetic fields (with P-chr approximate toP(orb)). W e compare both P-chr and the phase dependence of the activity with the plan etary orbital period P-orb, the orbital phase, and models. No significant P -chr or phase dependence attributable to planets can be clearly identified. We place approximate upper limits on the amplitude of any planet-induced a ctivity. We identify a possible stellar rotation period for GL 876, and sup port previous period determinations for four other stars. We discuss the re sults and possible directions of future research.