Whats the easiest way to extract night-only spectra from FUSE data?
Broadly speaking, there are two ways to exclude day-time photons from your data: either modify the screening files before running the pipeline or modify the IDFs afterward. If you are starting with raw files, simply change the keyword DAYNIGHT from BOTH to NIGHT in the scrn*.fit files (in the parmfiles directory), then run the pipeline as usual. Photons obtained during orbital day will be flagged as bad and excluded from the extracted spectrum. If you already have IDFs, you can use the IDL tool cf_edit to filter the data interactively. Another option is the C program idf_screen, which runs faster and (if you like) in batch mode. It is described on the FUSE Tools in C web page.
