CI Tau light and radial velocity curves

Additionally, a detailed bisector analysis on cross-correlation functions was carried out to understand the cause of long-term periodicity. We detect coherent periods at ~6.6d, 9d, ~11.5d, ~14.2d, and ~25.2d, the last of which is seen consistently across all datasets. Bisector analysis of the cross-correlation functions provides strong hints for combined activity-induced and Doppler reflex signals in the radial velocities at a period of 25.2d.

Our analysis suggests that this periodicity is best explained by the presence of a 3.6+/-0.3M_Jup_ eccentric (e~0.58) planet at a semi-major axis of 0.17au. We report the detection of a massive inner planet in CI Tau. Our study outlines the difficulty of searching for disk embedded planets in the inner 0.1 au of young and active systems.

When searching for planets in actively accreting stars such as CI Tau, we demonstrate that the primary limitation is stellar activity rather than the precision of RV measurements provided by the instrument.