Makee: Arclamp Wavelength Calibration: Residuals Table

The files "Arc-###.res" contain ASCII tables summarizing the final polynomial fits for the wavelength calibration in each order. Example:
 Final fit: ROW=  1  ORD= 6  WRMS=  0.0951  HIGH= -0.2393  NPT= 25  NREJ=  0
This shows the order number (row number), the polynomial order used (nominally 6th), the weighted root-mean-square in pixels, the highest residual in pixels, the number of points (arc lines) used in the final fit, and the number of points rejected in the final fit.

The is also a final summary line (for example):

Lo,Mdn,Hi:  R=  0.03  0.06  0.09  H=  0.07  0.24  0.39  Pt= 35 52 72  Rj= 0 0 2
which shows the lowest, median, and highest values for the RMS (R=), the highest rejection (H=), the number of points (Pt=), and the number rejected (Rj=). If you have many ".res" files you can get a quick summary check by going: "egrep Lo *.res".

The RMS values should stay below 0.15 pixels. The high values are generally less than about 0.3 pixels, but will never be above 0.4 since this is the rejection threshold. The number of points is usually about 20, and should normally not be below about 10 (with the exception of partial orders at the top or bottom of the CCD.) Number rejected should be less than a few.

Note that these pixel values are appropriate for a 3 pixel wide slit, although should be ok for a 2 or 4 pixel wide slit. Much wider slits would have larger deviations.

What to look for:

Back to makee home page.