In the 'trace-*.ps' PostScript plot you will see a fit to the position of the 'trace' or 'star' file (2nd file on the command line) on the CCD for each echelle order (see Trace Plots ). Here is an example: trace-2336 (PS). A straight line connecting the endpoints of the trace has been subtracted from the fit for better visibility. At the top of each plot is RMS of each fit. Generally, this RMS number will be less than about 0.2 pixels. Values larger than 0.5 pixels may indicate problems.

When viewing the trace plot, check that solid line (the polynomial fit) goes through the cloud of points. These points are centroid calculations of the star position on the CCD. On occasion, this solid line will deviate significantly from the data points-- this could indicate a reduction problem. This may only affect one or a few orders, in which case the other orders may still have a good reduction.

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(April 2008)