An Astronomical Spectrum Analysis Package
Version : 1.0
Author(s) : Space Telescope Science Institute, Baltimore, MD
License : copyright.aspec
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
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
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