Spectral reduction and analysis packages are built into a number of commonly used, general purpose astronomical data processing packages, including IRAF and MIDAS. However, for compatibility with other IDL software efforts within the ISO mission, particularly the Interactive Analysis (IA) packages, and to deal with the complexity of the ISO pipeline data products which prevent their description and analyses using simple 1-dimensional spectra, ISAP is being developed in IDL. The starting point for ISAP is surrently the ISO data pipeline Auto Analysis Results (AARs) for SWS and LWS. Various calibration and auxiliary files, models of continuum and line sources, as well as observations from other telescopes such as IRAS and KAO can also be read into ISAP as either FITS or multi-column ASCII table files.
The Auto-Analysis Result (AAR) for SWS and LWS spectra, which is the final result of the standard pipeline processing, is not a simple single-valued spectrum like most astronomers are accustomed to for performing science analysis. It is a somewhat complex binary FITS table with data for 13 parameters for each detector element readout at each grating position. An SWS AAR contains 48 grating detector elements, and for SWS07, there are 4 FP detector elements. An LWS AAR contains 10 detectors for the grating. Spectral data points are present for each detector readout, which may represent numerous up and down directional scans over the spectral region of interest. More than one data point may be present at many wavelengths, and likewise data at any given wavelength may originate from different detectors. The spectral resolution and sampling (spacing between data points) varies with wavelength. The AAR often contains data for detectors not specified explicitly in the observer's AOT, often from a different grating order. Data for the grating and FP modes of the SWS07 AOT are contained in the same FITS table. Residual instrumental signatures which were not completely removed by the pipeline processing (e.g., fringing) are present in the AAR. Differences persist in detector calibration and responsivity which manifest as discontinuities in the continuum flux from one detector to another. For SWS, different data points are acquired from different aperture and grating order combinations, frequently leaving discontinuities in the AAR spectrum which have to be corrected. For spatially extended sources, flux differences due to different apertures are of course expected, but in such cases it is difficult to distinguish which portion of the flux change may be caused by this aperture effect and which portion may be due to uncertainties in flux calibration. Also, sometimes bad data points or entire bad scans are improperly filtered and passed through to the AAR stage.
ISAP's primary function is to simplify the process of visualizing, subsetting, rebinning, masking, combining scans with weighted means or medians, filtering, smoothing, fitting, and measuring the complex AAR spectra produced by the ISO spectrographs. With ISAP, the user can input an AAR FITS file, plot or overlay portions of the data using error bars where appropriate, sort, subset, filter, rebin, merge, and edit the scan data, measure continuum and lines, fit models, and write processed data to FITS and ASCII table files. A session history can be written to an ASCII file, and many processes appended a record of processing steps to the header which gets written to upon output to FITS. ISAP currently consists of about 110 routines which can be called from the command-line or scripts in IDL. There is also a user-friendly graphical user interface (GUI) which greatly simplifies removal or masking of bad data points, plotting and subsetting of spectral scans, and usage of the underlying data processing tasks. The result of a typical ISAP session is expected to be a "simple spectrum", single-valued and resampled to uniform wavelength separation if desired, that can be further analyzed either with other ISAP functions, native IDL functions, or exported to a different analysis package (e.g., IRAF, MIDAS) if desired. For details on the available functions and their origin, see the list of ISAP routines in the ISAP Reference Guide.
Additional functions planned or in ongoing development are listed here in order of current priority: 1) improved and simplified visualization and subsetting of the complex data structures; 2) instrument-specific corrections, especially interactive removal of fringing and corrections for calibration of point vs. extended sources; 3) improved error propagation (including correlated errors) for existing interpolation and fitting routines; 4) continuum and line fitting and measurement so users do not have to export data to another package for this basic functionality (and import back to make use of ISAP's unique ISO-specific routines; 5) basic continuum model generation (black-bodies, gray-bodies, etc.); 6) extensions to support SPD processing for LWS and comparisons between SPD and AAR data.
On-line help for using the individual routines in their command-line mode is provided using the standard IDL help widget, as well as through an on-line ISAP Reference Guide. Documentation for individual tasks are derived from the headers of the original IDL procedure code.
We also acknowledge support from the SWS IA3/CoCo group, in particular P. Roelfsema, D. Boxhorne (SRON), and Rik Huygen (K.U., Leuven).
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The ISAP User's Guide and Reference Guide are written primarily by S. Unger, E. Sturm and J. Mazzarella. The ISAP Programmers Guide is written by E. Sturm and B. Narron.