Pointing Mesh and Tracking Error Analysis for the Rigel Telescope in Sonoita, AZ

Pointing Model Look-up Table

A rough preliminary (15 degree) pointing mesh for the Rigel telescope was done on May 21 (day 141), 2002 which was used as a pointing model look-up table. The mesh showed fairly low blind pointing errors with a maximum

of approximately 15 arcmin and a maximum

of approximately 13 arcmin. Below are two views each of the look-up table for day 141. The x-axis indicates hour angle, the y-axis declination and the z-axis indicates error in hour angle for the first two graphs and error in declination for the next two.

Residual Pointing Errors

Residual pointing errors were then calculated using the pointing model look-up table. The resulting errors were acceptable considering the rough 15 degree pointing mesh used for the look-up table. There was a maximum

of approximately 3.5 arcmin and a maximum

of approximately 2.5 arcmin. This is a reduction of about 77% and 81% in the pointing errors respectively. Below are two views each of the secondary pointing mesh. Again, the x-axis indicates hour angle, the y-axis declination and the z-axis indicates error in hour angle for the first two graphs and error in declination for the next two.

Pointing Errors Test

Testing of the pointing mesh was then done by taking images in arbitrary regions of the sky and then analyzing the pointing accuracy. The test images had a maximum pointing error in declination of aproximately 1.5 arcmin and had a relatively flat distribution across a range of hour angles from -100 to +60 degrees. In a good pointing mesh the error distribution across the sky is relatively flat. Below is a graph of the errors in declination versus the hour angle for the preliminary pointing mesh (red diamonds) and the test images (blue circles). The error distribution for the test images is relatively flat as is expected.

Tracking Tests

Tracking was tested by taking images of a single target with an increasing integration time ranging from 10 s to 300 s. As the integration time increased, the tracking error is expected to compound resulting in a streaked image. The amount of streaking was determined by measuring the full width at half maximum of a single source that was well below saturation in each image. The change in the fwhm can be measured in arcmin and plotted as shown below. The tracking error was determined to be 0.011 arcmin/s, 0.001 arcmin/s above the specs required for the Rigel telescope of 0.01 arcmin/s.