Bias frames & subtraction

• Set some common parameter defaults for creating Hamamatsu bias frames and tell the script where to find raw data:

  iraf.gbias.rawpath="raw$"
  iraf.gbias.fl_over=yes
  iraf.gbias.fl_trim=yes
  iraf.gbias.biasrows="default"
  iraf.gbias.order=11
  iraf.gbias.low_reject=3.0
  iraf.gbias.high_reject=3.0
  iraf.gbias.niterate=5
  iraf.gbias.fl_vardq=yes
  

  The overscan fitting order is quite high for these Hamamatsu data, due to variable roll-off along columns (whose origin I don’t understand well).

  For the EEV detectors, I used to fit a constant value to a small overscan section that was unaffected by their strong charge transfer contamination, but this now seems much less of an issue and I am fitting the full height of the overscan region.

• Generate stacked bias frames:

  gbias @slow_bias.lis S20140919S0090_bias fl_inter-
  gbias @fast_bias.lis S20140926S0178_bias fl_inter-
  

  It’s best to run these commands interactively first time and inspect the overscan fit – but this means pressing ‘q’ about 60 times each and it’s not the most critical thing to show here, so I’ve left it out of the tutorial.

  If you do need to change any parameters after inspecting the fit, do it in the script above (to make the changes permanent), then you can disable fl_inter+ when re-running the script later and get the same results.

• Subtract the bias from the raw data files and attach an MDF extension to each one. This can be done using only the the bias & MDF options in gfreduce. Subtracting the bias separately from other gfreduce steps allows inspection and manual creation of a BPM before proceeding further.

  iraf.gfreduce.rawpath="raw$"
  iraf.gfreduce.mdfdir="scripts$"
  iraf.gfreduce.fl_gscrrej=no
  iraf.gfreduce.biasrows="default"
  iraf.gfreduce.order=11
  iraf.gfreduce.low_reject=3.0
  iraf.gfreduce.high_reject=3.0
  iraf.gfreduce.niterate=5
  iraf.gfreduce.fl_fulldq=yes
  iraf.gfreduce.fl_vardq=yes
  
  gfreduce @flat.lis bias=S20140919S0090_bias fl_addmdf+ fl_over+ fl_trim+ fl_bias+ fl_extract- fl_gsappwave- fl_wavtran- fl_skysub- fl_fluxcal- fl_inter-
  gfreduce @arc.lis bias=S20140926S0178_bias fl_addmdf+ fl_over+ fl_trim+ fl_bias+ fl_extract- fl_gsappwave- fl_wavtran- fl_skysub- fl_fluxcal- fl_inter-
  gfreduce @std.lis bias=S20140919S0090_bias fl_addmdf+ fl_over+ fl_trim+ fl_bias+ fl_extract- fl_gsappwave- fl_wavtran- fl_skysub- fl_fluxcal- fl_inter-
  

  (You can either type each gfreduce command as a single long line or split them with the continuation character \ for readability. Here I have kept them on one line just to make cutting & pasting easier for the tutorial).