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

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 D ~ V 2.5 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 fi rst 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 = R 3.85 0.5 V 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 ́ - 1.3 10 8 to ́ - 1.1 10 10 M e yr − 1 ( excluding the highest and lowest 5% of high- and low- accretion rate outliers ) , with an average of ́ 4 .7 - 10 9 M e yr − 1 . A total of 50% of the mass is accreted during bursts of > ́ - 12.8 10 9 M e yr - 1 , which indicates limitations on analyses of disk evolution using single-epoch accretion rates.