Heterodyne ITC

ACSIS can use 250 MHz or 1000 MHz sub-bands. In the case of HARP these can either be “chained” for higher resolution or overlapped as a 400 MHz or 1600 MHz “hybrid” band. Other receivers can use one of these “hybrid” modes without a loss of resolution.

Please see the ACSIS spectrometer information for more information, including the resolution constraints when observing multiple simultaneous frequencies.

Please select “Other” to enter a specific resolution in MHz or km/s. If a resolution is entered in terms of frequency, it corresponds to the sky frequency.

Some receivers have two mixers observing the same position in orthogonal polarizations. Normally the data are combined to reduce the integration time required, but you can use this option to see what the effect would be of processing each polarization individually.

Heterodyne receiver information

Continuum mode can be selected when you are interested in the continuum level (e.g. for planets) at the expense of reduced observing efficiency.

Heterodyne observing modes

Opacity conditions at JCMT are divided into 5 bands. You may select a band to use a representative value for that band or select “Other” to enter a specific 225 GHz opacity value.

Weather band information

Grid: the telescope moves to one or more individual points.
Jiggle: the secondary mirror of the telescope moves in a pre-defined pattern.
Raster: data are recorded while the telescope scans an area.

Heterodyne observing modes

Beam: the secondary mirror of the telescope “chops” a short distance (≤ 180 arc-seconds) to either side.
Position: the whole telescope moves between the source and offset position.
Frequency: the observing frequency alternates during the observation.

Heterodyne observing modes

In a basket-weaved observation the telescope scans the map area in two orthogonal directions (along the height and width) to minimize the effects of sky and system uncertainties.