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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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