| abund | stsdas.analysis.nebular | abund |
abund -- Derive ionic abundances in a 3-zone nebula
abund fluxtab diagtab
This task computes abundances in a nebular gas for several ions, given the electron temperatures (T_e) and densities (N_e) in three zones of low- medium- and high-ionization, and given the H-beta and ionic emission line fluxes. The abundances for each available ion are calculated within the 5-level atom approximation. (For more details about this approximation, type "help nlevel".) The user can specify a constant T_e and N_e for all calculations, or the T_e and N_e for each zone can be taken from the input table; these diagnostics can be calculated easily with the `zones' task.
The user specifies the names of an input table of emission line fluxes, and a table of electron temperatures and densities for each of three zones; the latter table will also serve as output for the results. If the two input table names are the same, then the all of the input columns are assumed to come from one table. The input tables may contain line fluxes for many nebulae and/or many regions within nebulae, one object/region per row. The flux for each emission line must be given in separate columns. The task locates particular emission line fluxes and temeratures/densities via names of specific columns in the input table(s). These columns have suggestive default names, but are entirely user-definable; see the "help" file for the `fluxcols' and `diagcols' psets. NOTE: the target name, region name, and the H-beta flux are required for all nebulae, and columns with that information must exist in the input table.
The emission line fluxes are derived from the input line fluxes, corrected for interstellar reddening. The reddening corrected line flux "I" is derived from the input line flux "F" by:
I(line) = F(line) * dex {-c * f(lambda)}
where "c" is the extinction constant (i.e. the logarithmic extinction at H-beta, 4861 Ang), and "f(lambda)" is derived from one of a few possible extinction functions. The choices for Galactic extinction are: Savage & Mathis (1979), Cardelli, Clayton, & Mathis (1989), and the function of Kaler (1976) which is based on Whitford (1958). The choices for extra-Galactic extinction laws are Howarth (1983) for the LMC, and Prevot et al. (1984) for the SMC. The value of "c" must be given in the input table if a correction for reddening is desired. However, the correction may be disabled if a correction flag (stored in another table column), is set to "yes". By default no reddening correction is performed unless a valid value for "c" is available, and unless the correction flag is set to "no" or is not present. The extinction law will default to that of Savage & Mathis ("gal") unless another choice is specified (one of "gal", "ccm", "jbk", "lmc", or "smc") in the input table.
The available ions, the emission line fluxes used, and the nebular ionization zone to which that ion is attributed, are listed below. Note that the calculated ionic abundance is the average of that derived from each of the emission lines for that ion. The emission lines used for each ion are listed by wavelength in Angstroms. It is often the case that some emission lines are unresolved at typical spectral resolutions. This circumstance is accomodated to some degree by specifying some fluxes as sums from closely spaced line pairs, which are denoted in the table below with a "+" sign between the two affected wavelengths.
Line Fluxes Often Used for Ionic Abundances
Ionization
Ion Spectrum Lines Used Zone
----------------------------------------------------
C(0) [C i] 9823 9849 Low
C(+1) C ii] 2326+28 Low
C(+2) C iii] 1907+09 Med
N(0) [N i] 5198+5200 Low
N(+1) [N ii] 5755, 6548, 6583 Low
N(+2) N iii] 1749+52 Med
N(+2) [N iv] 1483+1487 Med
O(0) [O i] 6300, 6363 Low
O(+1) [O ii] 3726+29, 7320+30 Low
O(+2) [O iii] 4363, 4959, 5007 Med
O(+3) [O iv] 1400+01+05+07 High
O(+4) [O v] 1214+1218 High
Ne(+2) [Ne iii] 3342, 3869, 3968 Med
Ne(+3) [Ne iv] 2423+25, 4724+25 High
Ne(+4) [Ne v] 2975, 3426, 3346 High
Na(+3) [Na iv] 2805, 3242, 3362 Med
Na(+5) [Na vi] 2569, 2871, 2970 High
Mg(+4) [Mg v] 2418, 2783, 2928 High
Mg(+6) [Mg vii] 2262, 2506, 2626 High
Al(+1) [Al ii] 1671, 2661+2670 Low
Si(+1) [Si ii] 2335+45+51 Low
Si(+2) Si iii] 1206, 1883+92 Low
S(+1) [S ii] 4068+76, 6716+31 Low
S(+2) [S iii] 6312, 9069, 9532 Med
S(+3) [S iv] 1405+1406+1417 High
Cl(+1) [Cl ii] 3679, 5807, 9383 Low
Cl(+2) [Cl iii] 3348, 5517+37 Med
Cl(+3) [Cl iv] 5323, 7531, 8045 Med
Ar(+2) [Ar iii] 5192, 7136, 7751 Med
Ar(+3) [Ar iv] 2854+68, 4711, 4740,
7170 Med
Ar(+4) [Ar v] 4626, 6435, 7006 High
K(+3) [K iv] 4511, 6102, 6796 High
K(+4) [K v] 2495, 2515, 4123, 4163 High
Ca(+4) [Ca v] 3996, 5309, 6087 High
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If a particular emission line flux is unavailable (e.g. the relevant line fluxes are INDEF, or the column name for that line flux is not found), that emission line is excluded from the calculations. If more than one emission line is available for a given ion, the task will compute a weighted average of the ionic abundance as determined for each of the input line fluxes; the weighting is approximately proportional to the relative line strengths.
The electron temperature and density is taken from the task parameters "t_e" and "n_e" if the parameter "constant=yes". In this case the T_e and N_e are assumed to be constant throughout the nebula. Alternatively, the electron temperature and density may be specified for each of three zones, in which case T_e and N_e are taken from the "diagtab" table from the columns named "Te_Low", "Ne_Low", etc. The column names can match the output of the `zones' task, if desired. If there is no valid T_e or N_e for a given zone, values are taken from the next-lowest ionization zone. It is therefore essential that a valid T_e and N_e exist for the low-ionization zone.
The output is to the "diagtab" table; the abundance for each ion is written to a separate column with names like, e.g. "Ni_(Si^+2)" for twice-ionized Silicon. The units are per unit ionized Hydrogen. The ionic abundances for each nebula/region are placed in separate rows.
To see how STSDAS binary Tables are used for this task, copy these example files to your IRAF current directory:
cl> copy nebular$data/flux.dat .
cl> copy nebular$data/flux.cols .
cl> tcreate flux.tab flux.cols flux.dat
(Type "help tcreate" for more information about making binary tables from ascii files.) You now have a test binary table called "flux.tab" in your current directory which can be used as input for the `zones' task.
1. Find the electron temperature and density, and then the ionic abundances in each of three zones from various diagnostic line fluxes for all objects in the table "flux.tab". The input/output table "abund.tab" contain columns listing T_e and N_e for each zone.
cl> zones flux.tab abund.tab objects="*"
cl> abund flux.tab abund.tab
You may wish to review & edit the adopted N_e and/or T_e with `tedit' after running `zones', but before running `abund'. You may then view the output table with `tread', or produce a printable ASCII file with, e.g.:
cl> tprint abund.tab > abund.ascii
2. Find the ionic abundances from various diagnostic line fluxes for objects in the table "flux.tab", assuming a constant T_e = 14,000 K, and N_e = 1500/cm^3 applies throughout the nebula. Store the results in new columns in the table "abund.tab".
cl> abund flux.tab abund.tab const+ t_e=14000. n_e=1500.
The 5-level atom program, upon which this package is based, was originally written by M.M. DeRobertis, R. Dufour, and R. Hunt. This package was written by R.A. Shaw (STScI); a description was published by R.A. Shaw & R.J. Dufour (1994). Type "help nlevel" for additional information about the N-level atom approximation, and for references to the atomic parameters and the other literature references. Support for this software development was provided by the Astrophysics Data Program through NASA grant NAG5-1432, and through STScI internal research funds.
diagcols, nlevel, fluxcols, ionic, temden, zones
For general information about tasks in the `nebular' package, type "help nebular opt=sysdoc".