Kavli Affiliate: Gregory J. Herczeg
| First 5 Authors: Mu-Tian Wang, Gregory J. Herczeg, Hui-Gen Liu, Min Fang, Doug Johnstone
| Summary:
EX Lup is the archetype for the class of young stars that undergoes repeated
accretion outbursts of $sim 5$ mag at optical wavelengths and that last for
months. Despite extensive monitoring that dates back 130 years, the accretion
history of EX Lup remains mostly qualitative and has large uncertainties. We
assess historical accretion rates of EX Lup by applying correlations between
optical brightness and accretion, developed on multi-band magnitude photometry
of the $sim 2$ mag optical burst in 2022. Two distinct classes of bursts
occur: major outbursts ($Delta Vsim5$ mag) have year-long durations, are
rare, reach accretion rates of $dot{M}_{rm acc}sim10^{-7}~M_odot~{rm
yr^{-1}}$ at peak, and have a total accreted mass of around 0.1 Earth masses.
The characteristic bursts ($Delta Vsim2$ mag) have durations of $sim 2-3$
months, are more common, reach accretion rates of $dot{M}_{rm
acc}sim10^{-8}~M_odot~{rm yr^{-1}}$ at peak, and have a total accreted mass
of around $10^{-3}$ Earth masses. The distribution of total accreted mass in
the full set of bursts is poorly described by a power law, which suggests
different driving causes behind the major outburst and characteristic bursts.
The total mass accreted during two classes of bursts is around two times the
masses accreted during quiescence. Our analysis of the light curves reveals a
color-dependent time lag in the 2022 post-burst light curve, attributed to the
presence of both hot and cool spots on the stellar surface.
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