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18th of March 2021
New radio stars
by Pritchard et al.
Pritchard et al. present results from a circular polarisation survey for radio stars in the 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 coronae. 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 the paper published in Monthly Notices of the Royal Astronomical Society.

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