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Contamination of the ACA CCD can be revealed by seeing systematic
changes in the observed magnitude of individual guide stars that have
been repeatedly used during the course of the mission. The two
calibration fields pointing at the stars Ar Lac and Capella are ideal
for this investigation, as they have each been observed dozens of
times at fairly regular intervals since launch. In each field there
is a core set of guide stars that are typically used. We have
extracted data from the aspect Level-1 pipeline to determine the
average observed magnitude of all such guide stars. Those stars
which have at least one data point within both the first year of the
mission and after the second year are included.
The plot below shows the change in magnitude (with reference to
the mean within the first year) for all stars in the sample. There
is no obvious trend in delta magnitude with time. Fitting a line to
the data confirms that the change in average star magnitude is less
than 0.002 mags/year. Therefore there is no evidence for appreciable
optically obscuring contamination on the surface of the primary ACA
CCD.
Data
Analysis and data are in /proj/sot/ska/analysis/contam_aca
Aspect Information main page
Comments or questions: Aspect Help
Last modified:12/27/13
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