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XMM-Newton CCF Release Note
XMM-CCF-REL-197
OM Astrometry: new boresight
A. Talavera
September 26, 2005
1 CCF components
Name of CCF VALDATE List of Blocks
changed
CAL VERSION XSCS ag
XMM BORESIGHT 0019 2000-01-01T00:00:00 BORESIGHT No
2 Changes
The boresight of the Optical Monitor has been redened.
A statistical study of OM eld acquisition (FAQ) osets performed in nearly 1500 observations
in Revs. 207 - 860, shows a systematic average deviation of -2.29 and -2.32 arc sec in X and Y
axis respectively. These deviations have been introduced in the newsiam SAS task to compute the
corresponding new Euler angles. Angle  is modied by 2.3188 arc sec, angle  by -2.2865 and angle
by -1.3229e-02.
3 Scientic Impact of this Update
Astrometry in OM performed with SAS will improve.
1

XMM-Newton CCF Release XMM-CCF-REL-197 Page: 2
4 Estimated Scientic Quality
Cross-correlations with USNO Catalogue performed with SAS task omsrclistcomb in 905 observa-
tions using the current boresight, give average osets of -0.25 and -0.55 arc sec in right ascension
and declination respectively. The standard deviations of these osets are 4.0 and 2.8 arc sec.
Using this new boresight in the cross-correlations reduces these errors to average osets of -
0.22 and -0.40 with standard deviations of 1.8 and 2.1 arc sec in right ascension and declination
respectively.
5 Test procedures
The new CCF has been tested in two ways.
First, all FAQ's used to measure the deviation of the current boresight have been simulated using
the new CCF. (Note that the predicted positions of the acquisition stars are based in the boresight
Euler angles). The original deviation disappears in the simulation.
Secondly, SAS task omsrclistcomb , has been run in the observations used in the FAQ exercise,
to measure the deviations with respect to USNO catalogue. Only in 905 of them a correlation is
found (failures are due to few stars in the eld of view, as it may occur in the UV lters).
6 Summary of the test results
The average osets of the simulated FAQ are 0.02 and -0.09 arc sec in X and Y axis respectively.
The results of the cross correlation with USNO catalogue have been given before. Standard
deviation in the osets is reduced to 1.8 and 2.1 arc sec in right ascension and declination respectively.
7 Expected updates
No updates are expected in the near future.
8 Acknowledgments
Thanks to Chris Brindle and Simon Rosen for providing USNO catalogue input les for the cross
correlation.