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The following sections describe the sequence of steps required for reducing FIRE data from scratch.
Data Preparation and Launching FIREHOSE
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Telluric Correction / Flux Calibration
Observations of A0V stars are used both for telluric absorption and relative flux calibration. The procedure is outlined in Vacca, Cushing, & Rayner (2003), and implemented in the xtellcor routine of their SpeX pipeline, Spextool. We have ported xtellcor for use with FIRE, and refer users to the relevant xtellcor documentation to see how this procedure is performed in practice.
To call xtellcor from firehose, select the Telluric tab, and then go in the file tree to the exposure you wish to correct. Double click and the xtellcor window should appear with all fields for the input files and B and V magnitudes of the standard correctly populated. If these fields are in error, you can browse to find the right files, and enter in the magnitudes by hand. The input files should be in the redux/Object directory and named Obj_0123.fits with '0123' replaced by the appropriate frame number.
Most Draper catalog telluric stars (i.e. the HD stars) will have both their B and V magnitudes tabulated in the structure. Some hipparcos stars do not have a B magnitude listed, but these can generally be found at the Gemini standards website.
Once the initial telluric calibration frame has been generated for a source visit, only the final correction is required (skipping the kernel calculation and line scaling steps). For subsequent corrections, firehose calls xtellcor_finish to speed up the processing.
Combining Orders and Exposures to 1D
Once you have completed telluric calibration (not before!), you are ready to combine the frames into a 1D spectrum. On the "Combine" tab, select the object(s) for which you intend to generate 1D spectra, and click "Combine to 1D." This procedure will average together the individual orders from all exposures on a given object, weighting optimally by signal to noise ratio. Then the orders of the combined spectrum are merged, again with inverse variance weighting, onto a single grid. The final output spectra are stored in the redux/FSpec subdirectory by object name. The files Objname_F.fits and Objname_E.fits are the flux and 1 sigma error spectra, respectively.
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Special Topics
Accessing 2D sky subtracted/Wavelength calibrated images
Firehose is optimized for point source subtraction. However it is occasionally useful to look at the 2D sky subtracted frame. This is handy wen the 1D frame has unusual residuals, or if you would like to generate your own customized routines for extracting extended or multiple sources (the pipeline *can* handle multiple point sources, but requires some hand holding).
If you would like to access the 2D data, there is an IDL function named "fire_show2D" which will return a 2D array with the sky subtracted data. This can only be done AFTER normal extraction is attempted, because local sky subtraction is performed at this time. For example, to look at the sky subtracted image of fire_0123.fits, you can call as follows from the redux directory:
IDL> skysub = fire_show2d('0123')
IDL> xatv, skysub, /block
If you wish to also look at the wavelength map, you can read this in directly from the arc file. Assuming that file fire_0123 was a long exposure with OH lines for calibration, we read in the arc solution:
IDL> logwv = xmrdfits("Arcs/ArcImg0123.fits.gz")
IDL> wv = 10^logwv
Using "Blank Sky" fields for Sky Subtraction on Extended Objects"
---IDL> xatv, skysub, wvimg=wv