The figure at right shows checks on the internal
astrometry between the D2.G and D2.R images.
The top left quarter shows the direction and size (greatly enlarged)
of the astrometric residuals as line segments. This plot is an
important diagnostic of astrometry because, while the residuals are
typically quite small, there are outliers in any distribution. As long
as these outliers are relatively isolated from each other and pointing
in random directions all is well. Conversely, if there are number
large residuals in close proximity to each other, all pointing the
same direction, this indicates a systematic misalignment between the
two images in question. The figure shows no such misalignments.
The bottom left quarter shows the astrometric residuals in
RA and Dec. The red histograms
show the relative distribution on the residuals in
both directions. The 68%-tile of the residuals is 0.060
The two right panels show the residuals in RA and Dec