Brief Introduction to IRAF

Brief Introduction to IRAF and DS9

Last update: May 30, 2013

Data taking on the mountain is carried out within the IRAF environment. If you are not familiar with IRAF, it is essential that you learn at least the basic syntax and a few commands so you can run the science CCD and look at the data you take.

You can get help on a particular command, e.g. imexam, by typing

cl> help imexam

at an IRAF prompt.

IRAF is a bit like Latin: in the late 90s NOAO decided not to spend any more resources on further IRAF developement, even though their scientific staff were developing useful script packages to reduce and handle data coming from new NOAO instruments (e.g. CCD Mosaics, the Gemini Instruments). For a while, STScI also distributed IRAF packages which were the only way to handle Hubble Space Telescope data. So IRAF became a lingua franca, and several generations of astronomers became fluent in it.

Some of the most useful "tricks" to do things in IRAF are not written down anywhere, or are not particularly intuitive. Do not be shy about asking people for help.

At Steward, Skip Schaller and collaborators developed "ICE" which is a set of routines for taking data with CCDs. See this page for more information on using ICE with MAESTRO.

For basic introductions to getting started in IRAF, start with "A Beginner's Guide to Using IRAF" by Jeanette Barnes, which you can find HERE.

                At this writing, this guide seems to have disappeared from the NOAO IRAF documentation web sites.

          If you google "beginner's guide to iraf" you can find other more up-to-date pages with how-to guides for beginners, e.g.

           http://www.twilightlandscapes.com/IRAFtutorial/

Particularly easy to read documents for the beginner, especially if you are unfamiliar with CCDs, are:

A User's Guide to CCD Reductions with IRAF, Philip Massey, February 1997.
A User's Guide to Reducing Slit Spectra with IRAF, Phil Massey, Frank Valdes, Jeannette Barnes, April 1992.
A User's Guide to Reducing Echelle Spectra With IRAF, Daryl Willmarth and Jeannette Barnes, May 1994.

These documents have some obsolete sections, but are still good introductions for the rank beginner.

Ignore

the sections about setting up IRAF, it is already set up on the mountain computers.
the sections about how to mount 1600 bpi big reel magnetic tapes in IRAF and write to them; fortunately those days are over!
the sections about ximtool; we use ds9 now
the sections about IRAF image files, which refers to an old file format that NOAO originally adopted back when we all were using VAX computers. We use the fits file format exclusively now.

While you can reduce MAESTRO data completely in IRAF, the main shortcoming of IRAF is that propogation of errors is not an organic part of most of the reduction routines. On the other hand, almost anything you want to do to reduce your data will already be possible to do in IRAF. Most people will want to use IRAF for some steps of the reductions, and IDL or python for others. Notes on reducing MAESTRO data in various ways will be posted as they become available. Contributions are welcome.

Here is a summary of the most important IRAF commands you need for observing:

imheader          list image headers
hedit                 edit the header parameters of an image
hselect              list specific items from the image headers
display             display an image in a ds9 window
imexamine        general image analysis utility
imhist                 generate a histogram of the pixel values in an image
imstat               detailed statistics on an image or part thereof
implot                plot rows, columns, fit gaussians to portions of the data, etc.
splot                 similar to implot but with more functionality useful for spectral analysis
imarith                arithmetic operations between images (+,-,*,/)
imcombine          combine a list of images in various ways (average, median, etc)

IRAF commands are controlled by parameter files, which can be edited by the user. Be sure you understand how to list parameter files and edit them.

The recommended way to display images is to use DS9. If you are unfamiliar with DS9, check out the helpful documentation at

http://hea-www.harvard.edu/RD/ds9/site/Documentation.html

It's probably easiest to have someone show you how to display and image, change the gray scale, and zoom in and out if you are unfamiliar with ds9.