| 23rd of September 2021 |
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| A VAST Pilot Survey star |
| by Murphy et al. |
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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.
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.
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