This software is available within the STSDAS package, version V1.3.2 or later, which is layered on the IRAF environment. STSDAS, and the companion TABLES external package, are available from the Space Telescope Science Institute. The software can be obtained electronically via anonymous ftp from node ftp.stsci.edu (130.167.1.2); follow the retrieval instructions in the README file in the software/stsdas/v1.3 directory. Information about the STSDAS and TABLES packages can be obtained by writing to the Science Software Group at STScI, or by accessing the STSDAS World Wide Web home page, with the URL http://ra.stsci.edu/STSDAS.html. Alternatively, users may obtain the nebular package for personal installation (i.e., without having to install STSDAS) by retrieving the files ``neb.tar" (the source code and documentation) and ``neb.README" (the installation instructions) from node ra.stsci.edu (130.167.1.101) in the directory pub/nebular. Note that this package requires both the IRAF core system (V2.10 or later) and the TABLES external package (V1.3.1 or later) to be installed. Users who wish only to make use of the relatively simple temden or ionic tasks may instead use the Mosaic interface, which can be accessed through URL http://ra.stsci.edu/NEBULAR.html.
Work is planned for a new task to derive the constant of interstellar
extinction (
) from multiple H I lines in the Balmer (and possibly
also Paschen) decrement, as well as the decrements of He I and
He II which are important for the UV. We also hope to offer tasks to
derive the abundances of several ions (including He
, He
, and
C), relative to H, from recombination lines.
We intend for this package to evolve and expand, particularly as the atomic
data improve. New A-values and collision strengths for various astrophysically
important ions are now appearing in the literature at a significant rate, due
to calculations from the OPACITY and IRON projects. Incorporation
of these new data is a continuing effort, and we are currently investigating
alternative techniques to parameterizing the T
-dependence of the collision
strengths in the program (i.e., using Lengendre or Chebyshev functions
instead of our current low-order polynomial functions). In addition, we will
be adding more ions, particularly with UV lines, as the atomic data become
available. Users of this package should
consult the on-line help for references to the latest updates to the
atomic data. We also intend to reconsider the current limitation of atomic
levels. Several ions, such as O and N, have UV lines of
significant strength in many nebulae arising from levels higher than the
five we currently treat: O III] 1660-6Å and N II] 2138-43Å,
for example. We plan to evaluate changing
the 5-level capability of the program to a larger number of levels,
to accomodate the next two higher levels of O and N which give
rise to these UV lines.
We hope that this package will be as useful to the astronomical community as it has been for our research efforts. We would be grateful for any comments, and for corrections to the source code or the documentation. Please send such comments/suggestions via electronic mail to shaw@stsci.edu and/or rjd@rice.edu.
Support for this software development was provided from the NASA Astrophysics Data Program through grant NAG5-1432 to the Space Telescope Science Institute. RJD also acknowledges AURA/STScI grant GO.4382.01.92A for support of his spectrophotometric studies of SMC N88A. We wish to thank the referee, Gary Ferland, for several useful comments and suggestions that improved this paper.
