Pritchard et al. present results from a circular polarisation survey for radio stars
Rapid ASKAP Continuum Survey (RACS).
Circular polarisation surveys are a promising method for widefield
detection of radio stars, as the synchrotron emission from background
Active Galactic Nuclei (AGN) is typically less than 2 per cent
circularly-polarised, and thus the number of false-positive matches
between stars and unrelated AGN is significantly reduced.
The team searched RACS for sources with fractional circular polarisation
above 6 per cent and, after excluding imaging artefacts, polarisation
leakage, and known pulsars, they identified radio emission coincident
with 33 known stars, 23 of which had no previous radio detections.
These range from M-dwarfs through to magnetic,
chemically peculiar A- and B-type stars.
Cool dwarfs typically
produce non-thermal radio emission in magnetically confined
The images above are of the binary system MV Vir / HD 124498
which comprises a K-type primary and an
unclassified secondary. The system exhibits strong chromospheric Ca
line emission and is a bright ultraviolet and X-ray source. RACS
detects 68 per cent left circularly-polarised emission from
the stellar system.
The RACS detection is the first radio detection of the star.
RACS data is shown in Stokes I (total intensity, left panel) and Stokes V
(circular polarisation, middle panel).
The ellipse in the lower left corner of each radio image shows
the restoring beam. The right panel shows the RACS Stokes I contours overlaid
on optical data from the
Panoramic Survey Telescope and
Rapid Response System 1 (Pan-STARRS1).
A neighbouring, unpolarised radio source is also visible in total
intensity, but not the cirular polarisation or optical image. The
high fractional polarisation of the detection is most easily explained
if originating from MV Vir, and as both stars are separated 11
arcsecond from the neighbouring source it is believed to be an
unrelated background object.
More details are given in
published in Monthly Notices of the Royal Astronomical Society.