Amplitude Modulation of Short-Timescale Hot Spot Variability

TL;DR

This study analyzes short-timescale variability in the young star CI Tau, revealing amplitude modulation linked to stellar rotation and planetary accretion, which aids in distinguishing stellar activity from planetary signals.

Contribution

It demonstrates that small-amplitude variability shares the same periodic signatures as larger variations, connecting physical mechanisms across different timescales.

Findings

Variability amplitude shows periodic signatures matching stellar rotation.

Detected periods align with known star and planet orbital periods.

Physical mechanisms modulate brightness features across timescales.

Abstract

Variability of Classical T Tauri Systems (CTTS) occurs over a vast range of timescales. CTTS in particular are subject to variability caused by accretion shocks which can occur stochastically, periodically, or quasi-periodically on timescales over a few days. The detectability of young planets within these systems is likely hampered by activity; therefore, it is essential that we understand the origin of young star variability over a range of timescales to help disentangle stellar activity from signatures of planetary origin. We present analysis of the stochastic small-amplitude photometric variability in the K2 lightcurve of CI Tau occurring on timescales of $\lesssim$1 d. We find the amplitude of this variability exhibits the same periodic signatures as detected in the large-amplitude variability, indicating that the physical mechanism modulating these brightness features is the same. The periods detected are also in agreement with the rotation period of the star ($\sim$6.6 d), and orbital period of the planet ($\sim$9.0 d) known to drive pulsed accretion onto the star.