Short wavelength calibration

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C.1.2 Short wavelength calibration

The usual approach in this regime is to use (nearly) thermal sources in the Solar System. Their apparent brightness of course varies in time with their distance from the Earth (and Sun), and orientation if they are not perfect spheres with zero obliquity. However, most of them have almost constant surface properties, so once those properties are measured their apparent brightness distributions can in principle be predicted for any time, given an ephemeris.

In CASA all of the Solar System objects supported by setjy are lumped under one standard, ‘Butler-JPL-Horizons 2010’, since none of them are covered by more than one model yet. The model uses a uniform temperature disk whose semiaxes are set using ephemerides from the JPL-Horizons project. All of the objects are warm enough to put them in the Rayleigh-Jeans regime for ALMA, but the FD as a function of frequency is calculated using the full Planck equation. Synchrotron emission (the gas giants) is accounted for by using models that smoothly vary the brightness temperature with frequency.

Table C.2: Notable Solar System objects

Object	Notes

Mercury	Not yet included (phase angle)
Venus	Not yet included (phase angle)
Earth	Not yet included (very resolved)
Mars	Taken to be 210K (JPL ephemeris)
Jupiter	Model from B. Butler, λ ∈ [0.1,6.2] cm
Ceres	167K (Saint-Pe et al 1993)
Pallas	164K (Not yet scaled for its varying distance from the Sun. e = 0.231)
Juno	163K, but it has a large crater and temperature changes. (Lim et al. 2005)
Io	110K (Rathbun et al. 2004)
Europa	109K (Website 2)
Callisto	134K (±11 K, Moore et al. 2004,)
Ganymede	110K (Delitsky et al, 1998, J.Geophys.Res. 103 (E13))
Saturn	Not yet included (the rings, the rings)
Titan	76.6K (B. Butler)
Uranus	Model from B. Butler, λ ∈ [0.07,6.2] cm
Uranian moons	Not yet included (obliquity issues, esp. since the Voyager era was apx. 1 Uranian season ago.)
Neptune	Model from B. Butler, ν ∈ [4.0,1000.0] GHz (more refs in code comments)
Triton	38K (Website 3)
Pluto	35K (Altenhoff et al. 1988 + more refs in code comments.) setjy does not check whether Charon was in the field.

For most Solar System FD calibrators, the temperature reference will also be sent to the logger if casalog.filter(’INFO1’) (or lower) is run before running setjy. If there is a discrepancy between the logger note and this appendix, the logger note is more likely to be up to date.

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