Position angle of a prime focus receiver

To set the position angle of a prime focus receiver box and to track the parallactic angle change, the following options exists under obsinp (FSwitch, PSwitch):

None Just sets the position angle to the value given in StartPosAng (ATTENTION: SHOULD BE 0 FOR A MULTI-RECEIVER BOX!!)
Off Position angle is set according to the parallactic angle + Offset (StartPosAng) at the beginning of each subscan
Off (Scan) Position angle is set according to the parallactic angle + Offset (StartPosAng) at the beginning of a scan only
On Position angle is tracked continuously (+ Offset)

The default is None and StartPosAng = 0.0.

Please note, that in some rare cases (e.g., multi-feed OTF mapping) it is not necessarily the correct approach to simply correct for the parallactic angle. In example if one measures an OTF using the "descriptive" projection system, one would rather need to correct the feed angle in a way such that the beam pattern is always fixed with respect to the motion of the telescope position. This is currently not implemented, hence, for these rare cases we recommend to use the "absolute" projection.

 
information_for_astronomers/tracking_of_the_parallactic_angle.txt · Last modified: 2011/03/31 11:57 (external edit)     Back to top