Echelle - Data Reduction Guide

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This page last updated: June 29, 2006 - JMD
This page last checked: September 28, 2004 - JMD

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IRAF Reduction Script

An IRAF Reduction Script For ARC Echelle Data

Last updated 24 April 2003 by John Barentine

I have developed a protocol for reducing ARC Echelle data within IRAF, based on the pre-built IRAF scripts modified for the parameters of the Echelle. It is intended for casual or beginning Echelle users; more advanced users will probably want to further customize reductions for their own requirements.

I have thoroughly tested it under IRAF 2.11.3 on computers at APO, but have not yet tested it against the nuances of different IRAF installations. So for now it carries the caveat that it may not work under all flavors if IRAF, but half the reason for making it available to the Echelle community is in hopes it can be made more compliant.

The script assumes that the user has the following types of files in the same working directory:

• Object spectra
• Th-Ar lamp spectra
• Flats taken with and without the blue filter
• Biases

Click here to download the tarball containing all the necessary files. The README file contains installation instructions. Note that the script is written to include correcting for bias. Not all users take biases with the Echelle, so a minor bit of editing is needed to adapt the script to biasless data sets.

Once you have unpacked the tarball, view the script file itself, echred.cl. I have extensively commented it such that it's really not as much of a black box as it appears. Some familiarity with IRAF commands is useful but not required.

The result of operating on Echelle data with this script is fully calibrated, normalized 2-D output spectra from which scattered inter-order light has been subtracted. As the last step, the spectra are multiplied by a 2-D weighting function that is supposed to aid in the intercombination of the orders. That intercombination has not yet been implemented but is expected soon. Also there is currently no provision in this version of the script to do flux calibration of object spectra, but that is another likely addition sometime in 2003.

In writing this script I have been greatly aided by the ARCES Data Reduction Manual by Julie Thorburn (UChicago).