The ASKAP Variables and Slow Transients Survey (VAST) is designed to detect highly variable and transient radio sources on timescales from 5 seconds to ∼5 years. Murphy et al. have recently presented initial results from the VAST Phase I Pilot Survey. An initial search revealed 28 highly variable and/or transient sources. One class of variable sources was stars, as illustrated above. (The X-axis is Modified Julian Day number: MJD 58600 corresponds to 27 April 2019 and MJD 59100 is 9 September 2020.)

VAST J052644.9−652650 is identified as AB Dor, a quadruple system composed of a K1V pre-main sequence star + M5.5V and M3.5 + M4.5 pair of binary systems The pre-main sequence star AB Dor A, is by far the brightest star in the system; it has a rotation period of 0.514 days, and shows optical super-flares and long-term X-ray variability. VLBI radio observations at 1.4 GHz, 8.4 GHz, and 22.3 GHz have revealed milliarcsecond radio structure. The source is detected in 11 epochs in Stokes I (total intensity) with a maximum flux density of 7.8 mJy/beam, and in three epochs in Stokes V (circular polarisation) showing both right- and left-handed circular polarisation with circular polarisation fraction ranging from 52% to 60%. We speculate that the three events with high circular polarisation are associated with known prominence formation seen in other young active stars.