An Astronomical Spectrum Analysis Package

Version : 1.0
Author(s) : Space Telescope Science Institute, Baltimore, MD (
License : copyright.aspec
Website :

Installs from Open Source Astronomy for Linux cd 2
Disk space required for installation is 11.22 Mb


The tasks in this package enable one to fit a model to a list of one or more input spectra. The model is constructed from a set of one or more components which can be defined interactively, or which can be read from an STSDAS binary table, called a component database. The various component parameters are fit using a choice of algorithms to one or more "domains" or portions of the input spectra. After a fit, the adjusted components may be written to an output database table and the model may be written out as a new spectrum.

The spectra can be imported from a variety of common formats, including ASCII tables, ST tables, FITS tables, and IRAF images. If fitting to more than one spectrum, they need not share the same dispersion relation. Since ASpec is intended to be a multi-wavelength analysis tool, a number of unit conventions are supported for input, output, and data display. (See the discussion of units below.) Various tasks in the TABLES "ttools" package may be used to access the parameter values in the database, either for further analysis or for reformating the results for publication.

There are at present two tasks, "autospec" and "vuespec", that can be used to build models of selected spectra. The interactive "vuespec" task contains essentially all the functionality of the other tasks, while the "autospec" task is more useful for building models that require a great deal of CPU time, and/or for building similar models for many spectra (e.g., of different targets) in succession. A productive approach for analyzing many archival spectra might be to use "vuespec" task on a representative spectrum to build a "template" component database, and then use that template with the "autospec" task to model the remainder of the spectra. On the other hand, "vuespec" offers a very powerful means to view the data, build and edit the components, and to control the fit process and evaluate the resulting model in real time.

There are other ancillary tasks with somewhat overlapping and/or complementary functionality. The component database may be built using the "populate" task, and the constraint expressions may be verified using the "express" task. The remaining tasks are really psets to specify defaults for the "autospec", "populate", and "vuespec" tasks.

More information about each task is available in the online help. This document provides a reference for the modelling process, including detailed descriptions of the fit algorithms, definitions of the available model components, and various internal mechanisms of the ASpec package. More detailed help, particularly for navigating the interactive "vuespec" task, may be accessed through the "Help" button in the "vuespec" workspace. Alternatively, you can direct your Web browser to URL