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4th of August 2021
ASKAP LMC and SUMSS comparison
by Pennock et al.
The Sydney University Molonglo Sky Survey (SUMSS) was carried out between 1997 and 2003 at 843 MHz with a beam size of 45 arcseconds × 45 arcseconds to create a catalogue that covers the whole sky South of a declination of = −30 degrees. The positions in the catalogue are accurate to within 1-–2 arcseconds for sources brighter than 20 mJy/beam and are always better than 10 arcsec. The SUMSS catalogue is therefore a good comparison for the new 888 MHz ASKAP catalogue of the Large Magellanic Cloud by Pennock et al.

In addition to a flux density comparison, as described in yesterday's ADAP, a comparison of the positional differences (as offsets in right ascension and declination, the celestial analogs of longitude and latitude respectively) between the new ASKAP catalogue and the previous SUMSS catalogue at 843 MHz are shown in the figure above. This shows that the positional offsets are well centred, with the mean offsets calculated to be (0.189 ± 0.054) arcsec and (0.088 ± 0.054) arcsec for RA and Dec, respectively. Overall, the ASKAP LMC astrometry is well-calibrated.

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