MB Drift Scanning

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

rotation = 180.0 - azimuth + 79.1 + 45
or
rotation = 304.1 - azimuth

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:

rotation = 180.0 - azimuth + 259.1 + 45
or
rotation = 484.1 - azimuth

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.

Table 1 - Rough guide to rotator angles
Azimuth Rotator Angle Sched file to use
0 304.1 drift79.sch
30 274.1 drift79.sch
60 244.1 drift79.sch
90 214.1 drift79.sch
120 184.1 drift79.sch
150 154.1 drift79.sch
180 124.1 drift79.sch
210 94.1 drift79.sch
240 64.1 drift79.sch
270 214.1 drift259.sch
300 184.1 drift259.sch
330 154.1 drift259.sch

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.

DRIFT79.SCH (79 degree rotation)

 $ 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

DRIFT259.SCH (259 degree rotation)

 $ 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
 stop
To start drift scanning: After stopping the drift scanning, REMEMBER to reset the following equipment for pulsars!