# ALPACA Parallactic rotation

15feb16

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

• 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 telescope has a keyhole of about 1.09 degrees about the aoLat.
• so we could come close to tracking a source at 192114 or 172114
• 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: How long we can track a source while rotating  30 degrees in parallactic angle
• The horizontal axis is hour angle .. as minutes to transit.
• The Vertical axis is how long you can rotate assuming the rotator starts at -15 deg at the corresponding HA.
• I've plotted dec 00:21:14 to 17:21:14 in 1 degree steps.
• The downward sloping lines on the right come from the source setting before the rotation is complete.
• The top frame shows the entire dataset
• The bottom frame is a blowup showing what happens around transit.
• 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
• if the motion will track with a PI loop you'll need a maximum velocity greater than this.
• 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