Firehose stores all information about which flat, arc, and telluric files are paired with which science frames in an IDL structure for portability. The next step of the reduction process is to generate this structure, and then edit it to ensure it reflects the pairings you want (e.g. eliminating saturated tellurics, etc.). This procedure is done by a largely automated, and fairly complicated procedure. It performs the following procedures without user intervention:
- Read in the headers for all objects, and record telescope RA, DEC
- Check telescope pointing against the input Magellan object catalog, and assign each science target a unique object ID and common object name
- Cross-check pointing against a list of known A0V telluric calibrators; flag standards accordingly and record B and V mags if available.
- Assign ThAr arc frames to science and telluric exposures by checking for matches in telescope pointing, and asserting that lamps are on and mirrors in.
- Match telluric frames to science targets by searching for the closest match to each science target in UT obs, airmass, and sky angle
- Match flat field frames to each object or standard
These operations are all performed when the "Generate Structure" button is selected. You may select the "verbose" or "Loud" (= very verbose) buttons to produce more output, but these are mostly only useful for debugging purposes.
Once you have created the structure, it is advisable to inspect and (if appropriate) edit it by hand to ensure there are no errors. To do this, click "Edit Structure." You will be presented with a window that looks like the following:
The first column is an index number in the FIRE structure, used for bookkeeping. The second and third columns show the fits file and object name as determined by matching with the catalog, or, failing a match, form the OBJECT field in the header. The third column shows how firehose has classified the frame. All files classified as SCIENCE frames are tagged with an object ID, and grouped with telluric and arc calibrators, shown in the rightmost fields. Actual telluric frames are paired with an arc image.
You should check to make sure that the intended tellurics and arcs are matched with the right science frames, and that classifications are correct. By highlighting a line in the list and clicking a button at the top, you can change the relevant fields for an element of the FIRE structure. This is useful for example if you wish to delete a file from the reduction list (change exptype to TRASH or object ID to -1). Or, if name matching failed you can force objects to be grouped together by matching their object IDs and names. Or, you can split a single object pointing into individual subsets by assigning extra object IDs (e.g. by rotator angle, which is not considered by the automated object matching routines).
When you are happy with the structure, click "Done." Your changes will be committed, and the entire structure will be written to file for future use. You can save or reload the structure from disk at any time using the save and load buttons.
We are working on a utility to dump the contents of the structure to a text file that may be edited and read back in as a scriptable version of the pipeline; this feature will be available soon.