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Pointing Model Offsets

In order to study the effects the pointing model may have on the offsets, new offsets were calculated with possible corrections from the effects of the hexapod trim values.

The following histograms show the distribution of the offsets before trim corrections, and with a trim correction of both addition and subtraction.

RA offset with: No correction, addition of a scaled (.0176 arcsec/micron) trim_dy value, subtraction of the scaled trim_dy value

Dec offset with: No correction, addition of a scaled (.0176 arcsec/micron) trim_dx value, subtraction of the scaled trim_dx value

The following plots show how adding the trim correction removes the correlation between trim values and the correspoding offsets. The
colors correspond to exposure IDs, approximately time, to help distinguish between exposure sets.

RA offset corrected with trim_dx value:

Red = Uncorrected
Blue = Corrected with trim_dx

Declination offset corrected with trim_dy value:

Red = Uncorrected
Blue = Corrected with trim_dy

By applying trim corrections, the offsets should no longer include the part of the offset due to hexapod corrections.
As can be seen, adding the correction makes each set of four data points taken in the same position much more horizontal, removing correlation with trim values.

After applying the correction, the offsets can then be reexamined for correlations with the telescopes position. The plots below illustrate the relations.

The following two plots show the Declination offsets plotted against the declination of the telescope. The color scale shows the HA of the telescope.

No correction, correction added

The following two plots show the RA offsets plotted against the declination of the telescope. The color scale shows the HA of the telescope.

No correction, correction added