The Eroding Disk of AU Mic

We report Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph imaging of AU Mic's debris disk from 2017 and archival data. Outward motion of the features in the southeast arm continues. At least three features have reached or exceeded projected escape velocity in the past decade, yielding a combined feature mass-loss rate of ∼1.2 × 10−7 MEarth yr−1, or ∼1.2 × 10−13 M⊙ yr−1, ∼10% of AU Mic's stellar wind mass-loss rate, and similar to the ratio of coronal mass ejection mass loss to the stellar wind mass-loss rate. We confirm the 2018 finding of feature height changes for one feature (B/SE4), but the HST data are too sparse to compare (yet) with the stellar activity cycle. Detection of what appears to be a chain of features in a second system suggests that the disk of AU Mic is not unique, although a larger sample of disks is required to quantify how common the phenomenon is.