ALPACA Parallactic rotation
The design for the ALPACA receiver includes
a parallactic rotator that can turn +/- 15 degrees about the
center of the array.
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
- The telescope has a keyhole of about 1.09 degrees about the
- so we could come close to tracking a source at 192114 or
- 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
- 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
- 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..)
- 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.