In addition to the above packages, most basic image manipulation software (e.g., display
) and spectral analysis software (e.g., splot
) available in PyRAF/IRAF/STSDAS
can be used on COS data, either directly through the PyRAF
FITS interface or by converting data to another format. Chapter 3 of the Introduction to HST Data Handbooks
includes information about how to display COS images and extracted spectra, as well as how and when to convert data formats, and a description of spectral analysis tasks. We present a brief summary of spectral display and analysis tasks in Section 5.1.3
In Chapter 3
, we gave detailed discussions of the use of the data reduction pipeline calcos
. This task is contained in the STSDAS
. Other tasks useful for reducing and analyzing COS data are contained in this package as well. A complete listing and brief description of these tasks is given in Table 5.1
. All of these tasks can be run in PyRAF
. Consult the on-line help for each task for more information. Some of these tasks will be discussed in greater detail in the remainder of this chapter.
COS spectral extractions, TIME-TAG
data, and most COS reference files are stored in FITS tables. (See Section 2.4.1
for a description of the structure of the table extension files for spectral extractions and TIME-TAG
data.) Tasks designed to handle this format can be used to examine and extract information from the tables. Here we give specific examples of the use of routines in ttools
to help you get started. A sample output is given after each command.
To use tread
to look at the contents of the table:
output indicates that some of the columns contain arrays of 16384 elements rather than a single value. For those columns, tread
displays the value of the first element in the array. e.g., the initial wavelength in this x1d
extraction is 1585.58 Angstroms. To plot an entire array, or plot one array against another, you can use a routine that operates on the table data directly:
You may want to change the parameter values in the supporting parameter sets axispar
, and pltpar
to adjust the plotting. Alternatively, you may find it easier to work with FITS images. To make FITS image files of the arrays:
lists some of the more useful PyRAF/IRAF/STSDAS
applications for displaying and analyzing COS spectral data.
is a powerful spectral fitting routine that provides the user with many options for modelling emission and absorption features, continuum, and extinction. The fitting parameters can be linked to each other (e.g., fixed wavelength ratio or fixed flux ratio for two emission lines) and constrained. Different algorithms can be selected to first explore chi-square space, then rapidly achieve convergence in the deepest minimum. The application is fully described in a help file.
COS spectra in tabular format are very similar to STIS spectra. The following examples illustrate the use of the sgraph
task to plot COS FUV and NUV tabular spectra using a row selector and specifying the columns (e.g., wavelength and flux) to plot.