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Astronomical Data Analysis Software and Systems IV
ASP Conference Series, Vol. 77, 1995
R. A. Shaw, H. E. Payne, and J. J. E. Hayes, eds.
ASpect: A Multi­Wavelength Spectrum Analysis Package
for IRAF
S. J. Hulbert, J. D. Eisenhamer, Z. G. Levay, and R. A. Shaw
Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD
21218
Abstract. ASpect is spectrum analysis package being developed at
ST ScI. We discuss the implementation of a GUI using the IRAF Object
Manager, the ASpect task design, and the mechanics of performing a fit
to a spectral feature with ASpect.
1. Introduction
ASpect is a spectrum and line analysis package being developed at ST ScI. AS­
pect is designed as an add­on package for IRAF and incorporates a variety of
analysis techniques for astronomical spectra. ASpect operates on spectra from
a wide variety of ground­based and space­based instruments, allowing simul­
taneous handling of spectra from different wavelength regimes. It accommo­
dates non­linear dispersion relations. ASpect provides a variety of functions,
individually or in combination, with which to fit spectral and continuum fea­
tures. It allows for the masking of known bad data. Most importantly, this
tool provides a powerful, intuitive graphical user interface (GUI) implemented
using the IRAF Object Manager and customized to handle the burden of data
input/output (I/O), on­line help, selection of relevant features for analysis, plot­
ting and graphical interaction, and database management. ASpect is scheduled
for release in late 1995.
2. ASpect GUI
The functional need for a full set of graphical I/O capabilities originally led
us to implement the ASpect GUI with the public­domain software, Tcl/Tk.
While Tcl/Tk provided the GUI functionality required for the task, this was
accomplished at the expense of working outside of the IRAF environment. With
the availability of the IRAF Object Manager, however, we now have access to
the necessary GUI elements within IRAF. As originally envisioned, ASpect is
an IRAF application--it is written is SPP and uses the IRAF Object Manager
to provide the GUI. In this scenario the ASpect task is the client; the Object
Manager is the server. At startup, the client application downloads a text file
that defines the GUI. The Object Manager interprets this GUI file using the
Tcl interpreter and then creates the GUI objects (each widget is an object). For
the duration of the task execution, the Object Manager manages the messages
between the graphical objects and the client application.
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3. ASpect Task Design
The ASpect task has been organized as a group of objects: each object is im­
plemented by a separate code library. Figure 1 shows a graphical representation
of the relationships between the ASpect objects and code libraries. In this fig­
ure, the connections show which objects are available for ``use'' by any given
object, i.e., the information ``flows'' towards the small circles at the ends of the
connections. For example, the fit library ``knows'' about the component and
spectrum objects but a given spectrum or component object knows nothing of
fitting. This approach enforces modularity and by requiring a set of well­defined
interfaces makes reuse of code more practical.
GUI
UI
Spectrum Component
Science
Utility
Task
Fit
Uses
Figure 1. Relationships between ASpect Objects and Code Libraries.
The highest level of objects are designed to bridge the gap between the user
and the actual task. The GUI object, which is created by the IRAF Object
Manager, manages all information passed between the UI object and the GUI.
The UI object consists primarily of the ``event loop'', which handles events from
the GUI. The UI object is solely responsible for setting UI parameters and all
GIO calls are isolated here.
The basic task functionality is implemented in the task object, which is
in turn dependent on a host of other objects and libraries. The task object
is the main procedure and all global variables are maintained here. The task
object manages a series of spectrum and component objects in the course of

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Figure 2. The ASpect workspace consists of a main window showing
a zoomed portion of the spectrum bordered by a menu bar and spec­
trum overview window across the top, a button bar to the left, and
a scroll bar, cursor readback display, and context­sensitive help box
along the bottom.
the analysis. The spectrum object merely defines a spectrum: a flux array, a
wavelength array, an error array, and a data mask array. A component object
is a collection of models for various features in a spectrum which are to be fit.
The actual fitting process is controlled by the data contained in the fit object.
The lowest level of objects provide support for all other parts of the ASpect
task. The science libraries consist of a set of routines that implement the basic
scientific functionality. In the case of fitting these consist of the actual fitting
functions, e.g., Gaussian absorption line or black­body continuum. The utility
library is a set of generic routines used by more than one part of ASpect.
4. Fitting Procedure
The set of actions that results in a fit to features in a spectrum consists of:
(1) selecting the region of the spectrum to be analyzed, (2) selecting the type
of component, (3) marking the region of the spectrum where the component is

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Figure 3. The component dialog box is used to display and edit
components and the parameters that define them.
relevant, (4) marking the region of the spectrum over which to do the fit, and
(5) initiating the fit. The initial spectral region selection is accomplished with
the pan and zoom capabilities of ASpect. The marker in the overview window
(see Figure 2) can be moved or resized. Alternately, a marker can be drawn
in the main window to zoom in on a particular part of the spectrum. The
type of component is selected in the component dialog box which is shown in
Figure 3. A pull down menu labeled ``Function'' is used to reveal a set of line and
continuum functional models. This function is mapped to a particular feature of
the spectrum by drawing out a box around the feature. The size and placement
of this marker is used to generate an initial guess for the parameter values of
the component. Once defined, the component is added to the component list
(seen in the top right­hand corner of the component dialog box). Additionally,
the guess is displayed graphically in the main window as a fit (of sorts). At this
point the user may edit the parameter values of an individual component as well
as certain fit­related constraints and limits. Any number of components can be
defined in this manner. When all components have been defined, one or more
fit regions are marked. These fit regions are the parts of the spectrum that will
be used in evaluating the fit. Finally, the fit is initiated using the fit dialog box.
Generic fit parameters, such as number of iterations and type of fit algorithm,
are also controlled from the fit dialog box. Once the fit is complete, the fit is
overplotted in the main window. As the fitting process is iterative, the user may
decide to repeat the fit after modifying any of the components or fit regions.
Acknowledgments. This ASpect project is funded under contract with
the NASA Astrophysical Data Program.