Here are a few plots to illustrate the current status of the Relative Astrometry KPM. First we've constructed histograms of the RMS relative separation deltas for pairs of stars with ~ 5 arcmin of each other that fall within a 0.5-magnitude wide bin. To do so, we used Jim Bosch's pairwise matching script (jimBoschScript.py^{}) to select a list of 'safe' matches. Flags related to de-blending were applied based on a recommendation by Lauren MacArthur. The relevant quantities (id, coord_ra, coord_dec, object, visit, base_PsfFlux_mag) were read out of the GroupView object safeMatches into lists which were then pickled into a single file ListOfLists.pkl^{} to avoid having to re-run the Jim Bosch script.

To create the histograms using KPMScript_hist.py^{}, we first read the pickle file in and then find all matches within an Annulus of central radius D using simple squared Cartesian distance. For each pair, we check to see if a. Both members lie within a given magnitude bin, and b. Both members were observed on the same visit (not always true to the dithering). The spherical distance between the members of the pair is computed for each common visit and the RMS spread in separation measured for a given pair.

To create the scatter plot using KPMScript_scatter.py^{}, a similar routine is followed. However, no rejection is performed based on bins. Instead, all pairs of objects (regardless of magnitude) are used to compute the RMS RS scatter. The file Utilities.py^{} is used to email the user at the end of the script.

Descriptions of individual plots follow.

Plotted above is the histogram of point sources with PSF magnitudes from 16 (inclusive) to 16.5 (exclusive). The RMS of the relative separation from 36 pairs (across visits) is 10.05 mas (miliarcsec) which is well below the S15/S16 targets of 60 and 50 MAS respectively. In fact, the current value is almost within the final spec. Note also the percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 2.78%, well under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 16.5 (inclusive) to 17.0 (exclusive). The RMS of the relative separation from 124 pairs (across visits) is 9.89 mas which is within the final spec (10 mas). Note also the percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 5.65%, well under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 17.0 (inclusive) to 17.5 (exclusive). The RMS of the relative separation from 358 pairs (across visits) is 12.58 mas which is within the S20 AM1 spec (15 mas), but larger than the final target. However, the percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 4.19% which remains under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 17.5 (inclusive) to 18.0 (exclusive). The RMS of the relative separation from 871 pairs (across visits) is 11.77 mas which is within the S20 AM1 spec (15 mas), but larger than the final target. The percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 4.13%, which continues to remain under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 18.0 (inclusive) to 18.5 (exclusive). The RMS of the relative separation from 1664 pairs (across visits) is 12.42 mas which is within the S20 AM1 spec (15 mas), but larger than the final target. The percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 3.85%, which continues to remain under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 18.5 (inclusive) to 19.0 (exclusive). The RMS of the relative separation from 2905 pairs (across visits) is 11.95 mas which is within the S20 AM1 spec (15 mas), but larger than the final target. The percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 3.99%, which continues to remain under the final AF1 spec (10%).

Plotted above is the histogram of point sources with PSF magnitudes from 18.0 (inclusive) to 18.5 (exclusive). The RMS of the relative separation from 4963 pairs (across visits) is 12.43 mas which is within the S20 AM1 spec (15 mas), but larger than the final target. The percentage of targets with RMS relative separation (RMS RS) under AM1+AD1 is 3.12%, which continues to remain under the final AF1 spec (10%).

Next we show a scatter plot of the PSF magnitudes of all pairs of targets. The individual plot points are colored by the RMS RS and are also sized by the RMS RS (for additional clarity) i.e. bigger, darker points represent pairs with poorer RMS RS repeatability.

Notice that there is an indication of some sort of 'binning' in magnitudes. This behavior is much more evident in the D = 20 arcmin scatter plot (https://jira.lsstcorp.org/browse/DLP-311).

Vishal Kasliwal [X] has produced this figure using the scripts attached.

The brief summary is that we achieve 12.49 mas here, substantially better than the 60 mas requirement. Once Vishal Kasliwal [X] has his JIRA account up and running, he will update this issue with details of the data used and processing applied.