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LABOCA Calibration

[ Zenith opacities  |  Flux calibrators  |  Pointing & Focus  |  Beam shape & Resolution  |  Array parameters ]

Intensity calibration

Pointing & Focus

Beam shape & angular resolution

From beam maps on Uranus the angular size of the telescope beam was measured for individual bolometers. After deconvolution by the planet size we found:

FWHM = 19.2″ ± 0.3″

The shape of the main beam is an almost circular Gaussian. At intensities below 3% of the peak, the beam starts to deviate from a Gaussian, with the first error beam pattern at a relative intensity of 1%. The support structure of the subreflector becomes visible at the 0.1% level.

The main beam area of the APEX/LABOCA beam is 420″² ± 11″², while the total beam area is 518″² ± 21″². This may lead to an overestimate of the total flux density of up to 20% for extended sources, and should be taken into account by the PI during the calibration of his/her data.

We provide a FITS file with the combined LABOCA beam pattern, based on these 30 Uranus beammaps: Laboca-beam-2007-11.fits.gz (courtesy of A. Weiß, MPIfR). Right-click on the link and then choose "Save link as...".

Note: A previous version of this section mentioned slightly different numbers. However, that numbers were obtained during the LABOCA commissioning, included less data sets (and only from Mars), and are therefore considered less reliable. The new numbers come from 30 Uranus beammaps obtained between 2007 and 2011.

Array parameters

For a multi-channel receiver, the array parameters include the relative offsets of the individual channels as well as their relative gains. Both can be estimated from fully sampled maps (for all channels) on strong compact objects.
We have summarized the array parameters for all observing periods from LABOCA commissioning until now. The channel offsets normally are expected to change only if physical work is done at the rerceiver itself (repair, upgrade, or maintenance). However, the relative gains, as well as the properties of individual channels (like cross-talk, excess noise, etc.) can also change with every warm-up of the instrument. The gains depend also on the bias voltages of the amplifier electronics boxes, which may change with time.