Version 1.0 - CAJ, 2000-22-06
Version 1.1 - RFM, 2000-23-06
We sit the telescope still and let the sky go by!
A one-page summary of drift-scan observing is available here
General idea is that we take the telescope pointing South ie . 180. Azimuth and parked at 90. elevation. The receiver is then rotated to 79.1 degrees from the basic beam 2 up beam 4 down position (at 45 degrees), which gives 4 beams equally spaced in DEC. (A closer setting than the 60 degree rotation from 45 degrees used for RA scans).
Unfortunately we can't guarantee that the telescope will be parked at 180. Azimuth, and if it isn't the receiver should first be rotated to counteract the azimuth rotation and then taken around by 79.1 degrees.
The algorithm for the receiver rotation is therefore
If the azimuth is in the range 270 - 340 degrees, then this equation gives a value in or near the no go area (330 degrees to 30 degrees). We therefore make use of the rotational symmetry of the multibeam receiver and turn it through 180 degrees, giving the equation:
All results should be Modulo 360 - if you go all the way around to, say, 370 then subtract 360 to get 10. This should give results similar to those in table 1.
|Azimuth||Rotator Angle||Sched file to use|
There are two sched files available for use, one for each receiver position. Each scan is one hour long, so it is necessary to tell it to repeat a number of times using the 'Repeats:' box on tkmulti. Check this after starting, as it seems to have a habit of reverting to '1' - which means that the drift-scan will only run for an hour.
$ unit 1 disable fcc freq = 1405. bandwidth 64 config = mb4mod fcc_p_trk = disabled source = drft fitsname = drft79.mbf cycles = 720 az = 180. el = 90. fcc_rot = 79.1 track closef stop
$ unit 1 disable fcc freq = 1405. bandwidth 64 config = mb4mod fcc_p_trk = disabled source = drft fitsname = drft79.mbf cycles = 720 az = 180. el = 90. fcc_rot = 259.1 track closef stopTo start drift scanning: