The design for the ALPACA receiver includes a  parallactic rotator that can turn +/- 15 degrees about the center of the array.

Az velocities

The first plot shows the azimuth velocity for sources that transit close to za=0  (.ps) (.pdf)

• I've plots source tracks for 1,2,3, and 4 degrees away from za=0 (decs 14:21,15:21,16:21,17:21).
• The minimum za is 1.06 degrees
• the maximum az velocity is .4167 deg/sec
• a reasonable maximum tracking velocity is probably .35 deg/sec.
• The top frame is a linear scale, the bottom frame is a log scale.
• Disclaimer:
  
• we may be able to track at za< 2deg , but the pointing model does not have any source measurements at  these low za's.
• So i would say we have ok tracking down to za=2deg.

Parallactic angle rates

    AO40 will have a parallactic angle rotator that will go +/- 15 degrees.
The pulsar community said that we should be able to do a 10 minute integration (keeping the outer beams on the same spot on the sky)

The plots show the parallatic rotation rates, and allowable integration times for 30degree rotation (.ps) (.pdf)

• Page 1: parallactic rotation rate vs azimuth.
  
• The rates are plotted (in different colors) for declination's 08 thru 28 in 1 degree steps
• arecibo is at about 18:21:14.
• the leftmost set is 28 to 19 deg, the rightmost set is 08 to 17 deg.
• The maximum parallactic rotation rate (for sources within 1 deg or the AO latitude) is .225 deg/sec
• Page 2: parallactic rotation rate vs Hour Angle (in minutes).
• declination's 00:21:14 to 17:21:14 are plotted in 1 degree steps
• ha=0 is when the source transits.
  
• I've blown up the vertical scale a bit.
• Page 3: Integration time for a 30deg parallactic rotation for different source declinations.
• The horizontal axis is hour angle (minutes to transit).
• The vertical axis is the integration time for a 30 deg rotation (assuming it starts at the specified hour angle).
  
• I've plotted dec 00:21:14 to 17:21:14 in 1 degree steps.
• The top frame shows the entire data et
• The bottom frame is a blowup showing what happens around transit.
• Note:
• the diagonal lines on the right arise because the source sets before the 30deg rotation completes.
  
• Example:
• Top frame:
• the topmost black line is dec 00:21:14
• If you start at 30 minutes before transit,  you can track with the rotator for about 41 minutes
• Bottom frame:
• The bottom most line is dec 17:21:14
• If you start the rotation at transit (ha=0) you can track the rotator for about 2 minutes
  
• The dashed black line shows an integration time of 10 minutes (probably the longest pulsar integration..)

Summary:

• The maximum parallactic rotation rate is about .225 deg/sec
• Even if the rotator can go at .225 deg/sec, the 30 degree rotation will limit tracking to about 2 minutes.
  
• There are no restrictions on 10 minute tracks for all declination's at least 5 degrees from AO latitude.
• For declination's 14:21 to 22:21 the rotation time starts to be limited around 15 minutes before transit.

processing: x101/projects/ao40/rotation/ao40rotdoit.pro

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