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.
