This chapter deals with the analysis and reduction of spectral-line data after they have had the basic calibrations, described in Chapter 4, applied. Spectral-line software generally involves three-dimensional images, often called “cubes”, in which one of the three axes is frequency or velocity. Special programs are available to build, manipulate, and transpose these cubes and to display them properly. Most of the continuum software will work on data cubes or on appropriate two-dimensional subsets from a data cube. Spectral-line uv data can be read into from “uv” FITS tapes. Often, however, the data already exist on disk having been calibrated first within .
The data reduction process at this point has a number of stages, namely data preparation and assessment, self-calibration, continuum subtraction, imaging, display and manipulation of data cubes, and analysis. This chapter will address each of these areas in varying, but modest, detail on the assumption that the reader is somewhat familiar with the contents of previous chapters in this ookook. Some aspects of the art of spectral-line imaging are discussed in Chapters 17 and 18 of Synthesis Imaging in Radio Astronomy1 . A brief outline of the basic calibration process is given in Appendix A of this ookook and an outline of spectral-line analysis and calibration is given in Appendix B.