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23rd of February 2022
RACS-mid and the Battle of the Planets
S. Duchesne & E. Lenc (CSIRO Space and Astronomy)
The Rapid ASKAP Continuum Survey (RACS) completed a second survey of the entire sky early in 2021. This time it observed at an ASKAP mid-band frequency rather than the lower-band used in the original RACS survey (we now refer to the original survey as RACS-low and the mid-band survey as RACS-mid). RACS-mid provides improved sensitivity and resolution and also surveyed a significantly larger portion of the sky, covering all declinations below +49 degrees. As a result of the rapid nature of the survey, the 15-minute RACS-mid snapshot images are sometimes inadvertently photo-bombed by a wandering planet as it passes through the field being observed. While inspecting RACS-mid images for quality checks, we found that over the two month period during which most of the survey was observed all seven planets (excluding Earth) were seen. Mercury and Venus appeared as a blur as they are fast movers in the sky. Jupiter is particularly elongated because of its radiation belts and they differ from the other planets in that they are also visible, albeit weakly, in circular polarisation. The more distant planets, Uranus and Neptune, are also more easily detected in RACS-mid compared to RACS-low because planetary emission is generally brighter at higher frequencies. In some cases we can also see background radio galaxies in the image, e.g., close to Mars, Jupiter and Neptune. While these planetary finds can be fun, just like photobombing during our own holiday snaps, they can also be an annoyance and may require re-observations (in case the planet was hiding a background object).

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