Young Faithful: The Eruptions of EC 53 as It Cycles through Filling and Draining the Inner Disk

Kavli Affiliate: Gregory Herczeg

| First 5 Authors: Yong-Hee Lee, Doug Johnstone, Jeong-Eun Lee, Gregory Herczeg, Steve Mairs

| Summary:

While young stellar objects sometimes undergo bursts of accretion, these
bursts usually occur sporadically, making them challenging to study
observationally and to explain theoretically. We build a schematic description
of cyclical bursts of the young stellar object EC 53 using near-IR and sub-mm
monitoring obtained over six cycles, each lasting $approx530$ days. EC 53
brightens over $0.12$ yr by $0.3$ mag at 850 $mu$m, $2$ mag at 3.35 $mu$m,
and $1.5$ mag at near-IR wavelengths, to a maximum luminosity consistent with
an accretion rate of $sim8times10^{-6}$ M$_odot$ yr$^{-1}$. The emission
then decays with an e-folding timescale of $approx0.74$ yr until the accretion
rate is $sim1times10^{-6}$ M$_odot$ yr$^{-1}$. The next eruption then
occurs, likely triggered by the buildup of $sim5times10^{-6}$ M$_odot$ of
mass in the inner disk, enough that it becomes unstable and drains onto the
star. Just before outburst, when the disk is almost replenished, the near-IR
colors become redder, indicating an increase in the geometrical height of the
disk by this mass buildup. The reddening disappears soon after the initial
burst, as much of the mass is drained from the disk. We quantify physical
parameters related to the accretion process in EC 53 by assuming an
$alpha$-disk formulation, constrained by the observed disk properties and
accretion rate. While we can only speculate about the possible trigger for
these faithful eruptions, we hope that our quantified schematic will motivate
theorists to test the hypothesized mechanisms that could cause the cyclical
buildup and draining of mass in the inner disk.

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