This Cookbook describes the basic concepts and methods used in optical astronomical spectroscopy; it is aimed at those new to the field. The term ‘spectroscopy’ covers quite a few areas, each within itself worthy of a Cookbook. For the sake of brevity, the scope of this document is limited to one-dimensional (1-D) and longslit (2-D) spectra, in the optical waveband, recorded with CCD detectors.
The reductions described in later sections of this document are the most-common, simple, and straightforward that you might encounter. Problems arising when real-world data deviate from this ideal case, and how to overcome them, are described.
If you are starting your work with 2-D longslit spectra it is still a good idea to read the sections of this guide dealing with 1-D spectra as many of the ideas and techniques are common to both and easier to understand in the first instance for 1-D data.
This Cookbook does not describe the preparation of CCD data in detail; an outline of what’s needed is given. Requirements for getting good extractions, in terms of calibration data, are also described.
Non-trivial spectroscopy—cross-dispersed, infrared etc.—are not covered by this Cookbook. See §1.2 (below) for some resources to help you in these areas.
The most obvious thing to do is read it. But no one ever does that—so which bits do you really need to read?
§3 is the starting point if you’re about to go observing for the first time.
The concepts used in spectrum extraction, problems and how to get around them, are covered in §4 for 1-D data and in §6 for longslit data.
Once you have an idea of what you’re doing, you’ll want to know how to do it; this is covered in §5 for 1-D data and in §7. These are worked examples of a complete reduction illustrating techniques described in §4 and §6
§8 gives some specific examples of recipes, and offers some problem-solving advice.
There is a glossary in this document. If you cannot find the term you want there, you might try the NASA Thesaurus:
A significant part of the process of spectrum extraction is the preparation of the CCD data frames. This subject is covered in the Starlink Cookbook, The 2-D CCD Reduction Cookbook (SC/5). Those planning to use IRAF1 should consult A User’s Guide to CCD Reductions with IRAF (UGCRI) by Philip Massey. UGCRI is useful to any user of CCD data, even those planning to use ccdpack or figaro, to do the preparation.
IRAF users should read the documents for spectral data reduction within IRAF: A User’s Guide to Reducing Slit Spectra With IRAF and Guide to the Slit Spectra Reduction Task DOSLIT. These give a comprehensive description of the IRAF approach to spectral data reductions. There is also a hypertext tutorial for DOSLIT at
You may be able to access a local copy of this tutorial, consult your system manager.
This Cookbook is the most basic introduction to spectroscopy, some guides for more specialised types of reductions are available:
1IRAF documents can be found in your IRAF installation; you do not need to get them from Tucson or a mirror. Check with your system manager for details.