Error Arrays

The ECHOMOP package can deal with errors from the following variety of sources:

• Errors on the flat field frame which should be provided in the flat-field frame error array. If no error array is provided then ECHOMOP will estimate the error using root-n statistics.

• Errors due to the readout-noise on CCD type detectors. The readout noise value is supplied as a parameter and is applied to the whole frame when calculating the variances on extracted pixels.

• Linear error sources determined manually may be treated by providing an error array associated with the object data frame. The values should represent an error source that does not vary with the intensity of the particular pixel involved.

  An example of this type of error source would be the bias subtraction. If many bias frames are available then error could be determined for each detector pixel. Supplying these errors as the object error array would then cause them to be correctly included in variance calculations during extraction.

• Multiplicative errors such as those due to errors on the balance factors (from the flat field) may be taken into account by incorporating the appropriate values in the error array supplied with the flat-field frame. You must ensure that these variances correctly represent the combined effect of both the flat-field noise and any additional multiplicative error sources.

• Errors due to sky modelling and subtraction are calculated and processed internally by the extraction task.

• Errors due to detected cosmic-ray hits are treated by ignoring the contaminated pixel and rescaling the variance on the remaining pixels in that wavelength increment.

• All output spectra have an error array associated with them, these error arrays always contain the variance for the parallel entry in the data arrays.