Star–Disk Interactions in Multiband Photometric Monitoring of the Classical T Tauri Star GI Tau

Abstract

Abstract The variability of young stellar objects is mostly driven by star–disk interactions. In long-term photometric monitoring of the accreting T Tauri star GI Tau, we detect extinction events with typical depths of mag that last for days to months and often appear to occur stochastically. In 2014–2015, extinctions that repeated with a quasi-period of 21 days over several months are the first empirical evidence of slow warps predicted by magnetohydrodynamic simulations to form at a few stellar radii away from the central star. The reddening is consistent with and, along with an absence of diffuse interstellar bands, indicates that some dust processing has occurred in the disk. The 2015–2016 multiband light curve includes variations in spot coverage, extinction, and accretion, each of which results in different traces in color–magnitude diagrams. This light curve is initially dominated by a month-long extinction event and a return to the unocculted brightness. The subsequent light curve then features spot modulation with a 7.03 day period, punctuated by brief, randomly spaced extinction events. The accretion rate measured from U-band photometry ranges from to M ⊙ yr−1 (excluding the highest and lowest 5% of high- and low- accretion rate outliers), with an average of M ⊙ yr−1. A total of 50% of the mass is accreted during bursts of M ⊙ yr , which indicates limitations on analyses of disk evolution using single-epoch accretion rates.