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XMM­Newton CCF Release Note
XMM­CCF­REL­60
OM Photometry
R. Much / A. Talavera
February 15, 2001
1 CCF components
Name of CCF VALDATE List of Blocks
changed
CAL VERSION XSCS flag
OM COLORTRANS 0005 2000­01­01T00:00:00 COLORMAG No
OM PHOTTONAT 0003 2000­01­01T00:00:00 COINCIDENCE Yes
2 Changes
The structural changes are introduced to make the COLORTRANS file compatible to the CAL/SAS
changes which are required to improve on the OM photometry. To this aim coincidence loss correc­
tion is i ntroduced in PHOTTONAT file as well.
The keyword ALGOID is added to allow backwards compatibility. The APU­filter keywords
are added to the COLORMAG extension. The keyword contains the aperture radius used in the
photometric calibration analysis of the filter.
The additional column BRANCH is added to the COLORMAG extension. The value in column
BRANCH is used to indentify the different branches of the colour equations.
So far these changes only affect the structure of the COLORTRANS file. The actual values of
the colour transformation are not yet changed and still contain the numbers from the previous iss­
sue OM COLORTRANS 0004, which are a parametrization of the simulated colour transformation
based on inflight knowledge using the method by Harris. Therefore the ALGOID keyword is set
to 0. Once the improved COLORTRANS values are filled in, which will make use of the ground
calibration programme, the ALGOID keyword has to be set to 1. The new values are expected not
later than March 2001.
An additional extension COINCIDENCE was added. This extension contains the coefficients for
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XMM­Newton CCF Release XMM­CCF­REL­60 Page: 2
the empiric linearity correction curve. The coefficients in the CCF are the coefficients of a polynomial
function of the count to frame ratio (CFRR). The coefficients were derived in a comparison between
OM inflight and photometric ground based data. The accuracy of the coincidence loss correction is
improved. Currently the polynomial is of 4th order with only three independent coefficients. Due
to the boundary conditions a0 is fixed to 1 and a1 is fixed to minus the sum of the independent
coefficients.
3 Scientific Impact of this Update
None.
4 Estimated Scientific Quality
As before:
The colour transformation of model spectra was found to be generally good at the 0.1 mag level
or even better. However there are outliners, which need inspection. The colour transformation gets
worse as one goes towards late type spectra (B­V ? 1). Recommendation: assume accuracy of 0.5
if redder than B­V ?1.0.
The accuracy of U­B transformation is generally better than 0.1 mag, however there are again some
outliners, which need inspection. The U­V transformation is generally better than 0.1 mag, but
there are some outliners for U­V ? 1. B­V transformation is generally better than 0.05 mag for the
range \Gamma0:5 ! B \Gamma V ! 1. Towards the red, i.e. with increasing colour index the transformation gets
worse with B­V residuals up to ­0.3 mag. The V magnitude is good within 0.05 mag, with some
outliners with a residual up to 0.2 mag.
5 Acknowledgements
Thanks to Igor Antokhin for providing inputs to the linearity correction.