Startup

To start the longslit pipeline, from an IDL prompt type:

IDL> firehose_ld

where the _ld stands for low-dispersion.  This should bring up the following window: 

SETUP DIRECTORIES: The first step is to enter in exposure file names for each of the fields listed.  The Raw directory should point to the folder where the 2D fits files reside.  The Reductions directory is where the final data and intermediary files for calibration are generated and stored.  The Raw and Reduction directories may be set to any location on disk where you want these files to reside.  FIREHOSE never over-writes raw data, but we advise against performing reductions in the raw data directory as a precaution.

OBJECT file: This denotes a science frame.  The software performs sky subtraction on a fram-by-frame basis, NOT with A-B-B-A sets.  Only one file at a time is handled although we will loop on these in the next release.

ARC file: This is a wavelength calibration image.  Our default is to use a NeNeAr combination, which has produced stable wavelength solutions.  An arc line identification plot for this lamp combination may be found here; associated references for the line lists are here.

BLUE and RED flats: As in many spectrographs which cover a large wavelength range, it is difficult to obtain a single flat field exposure the covers the full spectral range at adequate signal-to-noise ratio without saturating.  To work around this problem the pipeline takes in pairs of flats which we denote as "blue" and "red."  These are obtained using different voltage settings on the variable quartz lamp in the Baade dome. 

The "red" flat provides suitable counts for the red half of the spectrum but has too few counts in the blue; this is typically taken at low lamp voltage (we use 1.2 V).

The "blue" flat provides suitable counts in the blue half but saturates the red end of the spectrum.  This is taken at higher lamp voltage (i.e. hotter,we use 2.2 V)

Enter in file names for each of these; if you only have one flat then put the same name in both fields and it will be fine.  The software simply combines the two 2D frames, using a smooth weighting function to transition from one frame to the other without discontinuities.

Preferences

Once your file names are entered in, you will probably want to set preferences for the reduction stages.  To do this, select the "Options->Preferences" pane from the menu bar.  This will realize the following window:

A brief explanation of the options:

  • Arc line identification: firehose_ld will by default cross-correlate your arc frame against our NeNeAr template and attempt an automatic wavelength solution.  This works fairly well but not 100% of the time.  If you trust the software, you can choose "fully automated."  Or, you can choose "user reidentify."  The latter option generates a first guess ID of "good" lines, and then launches a GUI for the user to check centroiding, and generate the final wavelength fit.  Use of this GUI is documented in the Arcs page of the Wiki.
  • Flat field interaction: There is not much user-intervention allowed here, but if you choose "inspect results" an atv window will pop up to let you see the quality of the composite flat.  Usually this is mostly useful to see whether your red/blue transition row was chosen judiciously.
  • Red/blue transition row: As described above, firehose_ld generates a superflat from a composite of dome flats of different lamp voltages.  Depending on your exposure times, the temperature of the dome, etc, the row (i.e. the y pixel number) where the transition optimally blends from one flat to the other may vary.  We have chosen y=1150 as a default, but the user may set this to another value as needed.
  • Object finding: There are four modes available for defining the trace aperture, ranging from fully automated to fully manual.  In depth descriptions of each mode are provided on the object finding wiki page.
    • Fully automated: firehose will find the brightest object on the slit and trace it, with no user intervention and no feedback to the user.
    • Inspect results: as in "fully automated" except an xatv window launches with a black line indicating the trace center and a dotted line the +/- 2sigma aperture
    • User initial guess: Useful when the object is faint, or when your object is one of several on the slit.  The user defines the global position of the source of interest, and firehose then fits a detailed aperture model to this object.  Results are fed back to the user for inspection as in "inspect results."
    • User Specify: Here the user dictates the exact position and width of the aperture.  No automated post-fit is performed.
  • Extraction style: This allows the user to select between optimal / weighted extraction (default) and simple boxcar model where the flux is a straight sum of pixels at a given wavelength.
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