Flux density calibrators

At wavelengths shorter than a few centimetres, extra-galactic sources generally prove to be too variable to be useful as flux density calibrators. So at these wavelengths, the blackbody emission from the planets are often used as flux standards. The two most commonly used planets for the ATCA at 3mm are Mars and Uranus. Note Jupiter is too large for use as an ATCA flux density calibrator. Neptune would also be a possible flux density calibrator. However Neptune is quite close to and half the strength of Uranus, and so does not offer anything over Uranus.

Uranus is the preferred flux density calibrator for the ATCA. Mars is less suitable for a number of reasons: some models of Mars' average brightness temperature suggest variations in the temperature of up to 10% as a result of Mars' diurnal rotation, its distance from the Sun and the viewing geometry of Earth-based observers. Definitive measurements and confirmation of these models are poorly studied in the literature. Depending on its distance and the array configuration, structure on Mars is also readily detected with the ATCA: Mars has hot equatorial and cold polar regions.

Although Uranus or Mars (preferably Uranus) are the best flux density calibrators, frequently they may not be accessible to your observation. To account for this, the Narrabri Observatory regularly monitors some additional sources (usually 1253-055 and 1921-293) to allow them to be used as flux density calibrators. Be warned though that these sources can vary substantially on month timescales. If Uranus and Mars are not accessible to your observation, you should enquire about the next best source to be used for flux density bootstrapping.

Miriad manager