Measuring the calibration

To generate a new arc lines list file you will first need to reduce a flat-field frame as normal, then reduce an arc using the EXTRACT_SLICES recipe. This will extract the slices from the array, approximately align them in wavelength and apply the flat-field. The frame is now in the state that arc frames will be in when they are wavelength calibrated.

Extract a spectrum from the central slice, (or the one before if there are an even number of slices), so for UIST extract a spectrum from the 7th slice from the bottom. This is where iarc starts its fitting. Copy the spectrum to $ORAC_DATA_CAL/grisms/arcs/ and give it a meaningful name (e.g. short_K_Ar.sdf). This is not essential because the spectrum is not used for calibration but it will include all the headers describing the instrument configuration at the time, which may be useful for future reference.

Use FIGARO arc to wavelength calibrate the spectrum. The wavelength calibration should be in Angstroms. A 2nd or 3rd order fit is likely to be most appropriate. arc will generate a file called arlines.lis. This is the arc lines file that you want. Give it a more useful name (e.g. short_K_Ar.lis) and put it in $ORAC_DATA_CAL/grisms/.

In order for the calibration system to know about the file you will need to add it to the index.arlines file which you will find in the $ORAC_DATA_CAL directory.