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24th of September 2021
A VAST Pilot Survey star
by Murphy et al.
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, including a number of stars. 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 d, and shows optical super-flares and long-term X-ray variability. The left panel above shows the VAST Stokes I image for the epoch with the maximum flux density. The middle panel shows the Stokes V image for the same epoch where positive flux density corresponds to right handed circular polarisation and negative to left handed. The ellipse in the lower left corner of each radio image shows the FWHM of the restoring beam. The right panels show Stokes I contours at 30, 60, and 90 per cent of the peak Stokes I flux density overlaid on an RGB image of optical data from SkyMapper with red=i-band, green=r-band, blue=g-band. Saturated pixels are masked out. AB Dor, like all of the stars in the sample, shows radio emission with high fractional circular polarisation (> 30%), making this a useful tool for distinguishing these sources from extragalactic transients.

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