Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.stecf.org/conferences/adass/adassVII/reprints/shawr1.ps.gz Äàòà èçìåíåíèÿ: Mon Jun 12 18:51:49 2006 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 03:10:17 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: redshift survey

Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Analysis Tools for Nebular Emission Lines
R. A. Shaw, M. D. De La Pe”na, R. M. Katsanis, and R. E. Williams
Space Telescope Science Institute, Baltimore, MD 21218, Email:
shaw@stsci.edu
Abstract. The nebular analysis package in STSDAS has been sub­
stantially enhanced, and now includes several new ions and diagnostics,
as well as updated atomic data for all supported ions. In addition, new
tasks are being added to compute, from ratios of recombination lines, cer­
tain nebular physical parameters and the abundances of He + and He +2
relative to H + .
1. Introduction
The nebular analysis package is a set of applications within IRAF/STSDAS for
computing physical parameters in emission line nebulae (such as electron density,
N e , and temperature, T e ), as well as ionic abundances of several elements relative
to ionized hydrogen. Nebular also provides utilities for exploring the range of
validity of the diagnostics themselves, and for employing them in the context of
a very simple nebular model. Several enhancements to the package have been
implemented since the original descriptive paper by Shaw & Dufour (1995) was
published, and the major new features are described here.
2. New Ions and Atomic Data
Thirteen new ions of C, N, O, Ne, Na, Mg, Al, Si, S, Cl, K, and Ca have been
added to the set of 21 previously supported in nebular. As a consequence, 15
new diagnostics for N e and T e are available, and they span a much greater range
of density, temperature, and ionization than in the previous version. The full set
of supported ions and diagnostics can be found from the nebular home page 1 .
Several new features have also been added, including the capability to compute
collisional line emissivities from up to eight (rather than the five previously sup­
ported) atomic levels, depending upon the availability of the supporting atomic
data. These low­lying levels arise from the same electron configurations as the
ground level. The atomic data for the various lines have been updated to the
best, most recent available as of mid­1996. These data have been appearing in
the literature at a rapid rate, owing to the success of the IRON project (Hummer
et al. 1993), a concerted international e#ort to compute precise atomic data for
iron­group ions of astrophysical interest. The collision strengths in particular
1 http://ra.stsci.edu/nebular/
192

Analysis Tools for Nebular Emission Lines 193
have been computed for most ions over a much wider range of T e , and are more
accurate by factors of 3 to 10. This improvement in the data quality permits the
calculation of reliable diagnostics over a much greater range of T e and N e . The
references to the atomic data are too numerous to include here (though they are
given in the nebular help documentation), but in general are at least as recent
as those given in the compilation by Pradhan and Peng (1995).
The T e and N e diagnostics of collisionally excited lines that are typically
used in the literature derive from ratios of specific line intensities (or ratios of
sums of intensities) which have a reasonably high emissivity, consistent with
being very sensitive to the diagnostic in question. These line intensity ratios
are generally the same for ions with a given ground state electron configuration.
Table 1 lists the line ratios that are traditional in this sense, where the notation
I i#j refers to the intensity of the transition from level i to j. The correspondence
of wavelength and transitions between energy levels for a given ion can be found
by running the ionic task.
Table 1. Traditional Diagnostic Ratios
Ground Traditional Ratio
Configuration Diagnostic
s 2 Ne I 4#1 / I 3#1
Te (I 4#1 + I 3#1 ) / I 5#1
p 1 Ne I 5#2 / I 4#2
p 2 Te (I 4#2 + I 4#3 ) / I 5#4
p 3 Ne I 3#1 / I 2#1
Te (I 2#1 + I 3#1 ) / (I 4#1 + I 5#1 )
Te a (I 2#1 + I 3#1 ) / (I 5#3 + I 5#2 + I 4#3 + I 4#2 )
p 4 Te (I 4#1 + I 4#2 ) / I 5#4
a For N 0 and O + .
Note that these traditional diagnostic ratios are not the only viable ratios to
use: some ratios, though perhaps not as sensitive to the diagnostic in question,
are useful if the spectral coverage or resolution is limited; others are simply better
for some purposes, such as the T e ­sensitive [O iii] ratio I(1660 + 1666)/I(4363).
Some nebular tasks, such as temden and ntcontour, now allow the user to
specify a transition other than the traditional (default) one.
3. Recombination Lines
The nebular package will soon include new tasks to accommodate the analysis
of recombination lines. Atomic data for H + , He + , and He +2 have been incorpo­
rated from Storey & Hummer (1995). Specifically, we adopt their tabulations
of emissivities, #, separately for Case A and Case B recombination. (The code

194 Shaw, De La Pe”na, Katsanis and Williams
interpolates in log­T e , log­# for intermediate values within their grid.) The re­
comb task will solve for the interstellar reddening and/or T e , given a list of
recombination line intensities for a single ion. The rec abund task will compute
the abundance of these ions with respect to H + from a list of recombination
lines. The abund task, which computes abundances from collisional lines in the
context of a simple model, is being enhanced to include the ionic abundance
calculations from recombination lines as well.
4. Exploration of the Diagnostics
The ntcontour task has been substantially enhanced, and is now more useful for
exploring new or traditional diagnostics from collisionally excited lines. This
task computes and plots curves that show the range of T e , N e , and/or intensity
ratios that are consistent with a specified diagnostic. A family of secondary
curves may optionally be plotted, where each curve may be specified explicitly
or as a set of successive, small di#erences from the reference ratio, giving the
appearance of contours. Though for all ions there are default diagnostics for
N e and/or T e , it is possible to customize the diagnostic to the ratio of any of
the supported transitions. In addition, the diagnostics may be plotted as N e vs.
T e , N e vs. I line , and T e vs. I line . This task may be run interactively, so that
it is possible to investigate many diagnostics quickly. Ntcontour is particularly
useful for determining the range of N e and T e where a particular diagnostic is
sensitive, for investigating non­traditional diagnostics, and for estimating the
consequences of a given level of uncertainty in an observed line ratio. Figure 1
shows an example plot of the default density­sensitive ratio for Al ii.
10 2 10 3 10 10 10 6
.25
.5
.75
1
1.25
1.5
1.75
Electron Density
Intensity
Ratio
Diagnostic Ratio Contour Plot
Al II: I(2661)/I(2670)
Primary = 10000.; Secondary = 5000. 20000.
Figure 1. Ratio of [Al ii] I(2661)/I(2670) vs. N e using ntcontour.

Analysis Tools for Nebular Emission Lines 195
5. Software Features
The nebular package has been substantially re­designed, and is largely table­
driven. For example, the atomic reference data are encapsulated in FITS binary
tables, and the data pedigree (including literature references) are documented in
header keywords. Fits to the collision strengths as a function of T e are evaluated
at run­time, so that the reference tables contain data in a form much as it
appears in the literature. These features provide great flexibility for anyone to
substitute improved atomic data, and allow for easy extensibility of the package
to accommodate high­quality data for more ions as they become available.
The data and associated functional fits for one or more atoms/ions of inter­
est are collected into persistent in­memory objects during the course of program
execution. The diagnostics for N e and T e are stored internally as strings con­
taining algebraic relations (in a form not unlike those given in Table 1), and are
evaluated at run­time. These features allow much greater flexibility in the appli­
cations to make use of relations between ions, such as the comparison of physical
diagnostics from similar ions, or the computation of relative abundances.
6. Software Availability
In their sum, the applications in the nebular package are a valuable set of tools
for nebular analysis: the derived quantities can be used directly or as input to
full photo­ionization models. Most of the enhancements described here have
already been incorporated into V2.0 of the nebular package; the new tasks for
analysis of recombination lines will be available in the next release. Nebular
is publically available, and is included in the STSDAS external package; the
new version will be found under the analysis package in STSDAS V2.0 and
later. Users who do not have STSDAS may obtain the new version for personal
installation from the nebular ftp 2 area. Note that nebular V2.0 requires that
IRAF V2.10.4 (or later) and TABLES V2.0 (or later) be installed. Some of the
tasks may alternatively be run via the Web from an HTML forms interface: view
the nebular home page for details.
Acknowledgments. Initial support for this software was provided through
the NASA Astrophysics Data Program. Support for these enhancements was
provided by an internal ST ScI research grant.
References
Hummer, D. G., Berrington, K. A., Eissner, W., Pradhan, A. K., Saraph, H. E.
& Tully, J. A. 1993, A&A, 279, 298
Pradhan, A. & Peng, J. 1995, in Proc. of the ST ScI, No. 8, eds. R. E. Williams
& M. Livio (Baltimore, Space Telescope Science Institute), 24
Shaw, R. A. & Dufour, R. J. 1995, PASP, 107, 896
Storey, P. J. & Hummer, D. G. 1995, MNRAS, 272, 41
2 ftp://ra.stsci.edu/pub/nebular/