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abund stsdas.analysis.nebular


NAME · USAGE_ · DESCRIPTION · PARAMETERS · EXAMPLES · BUGS
REFERENCES · SEE_ALSO

NAME

abund -- Derive ionic abundances in a 3-zone nebula

USAGE

abund fluxtab diagtab

DESCRIPTION

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
  ---------------------------------------------------------

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.

PARAMETERS

intable [string]
Input table of emission line fluxes. The line fluxes for different ions are stored in separate columns, and measurements for different objects are stored in separate rows.
diagtab [string]
Input table of electron temperatures and densities for each nebular zone. The T_e and N_e for each zone are stored in separate columns, and measurements for different objects are stored in separate rows. If the same as "fluxtab", all input will be taken from one table. This table also serves as the output for the ionic abundances for each object/region.
(diagcols = "") [pset]
Parameter set to specify column names for electron temperatures and densities for each nebular zone. No error is generated if a at least one T_e and one N_e column exists in the input table; rather, the calculation proceeds with fewer zones.
(fluxcols = "") [pset]
Parameter set to specify column names for certain line fluxes, the nebula name and the region code (which must both be present) in the input table. Otherwise, no error is generated if a named column does not exist in the input table; rather, the calculation proceeds as if the associated line flux is INDEF.
(faluminum = "") [pset]
Parameter set to specify column names for aluminum line fluxes.
(fargon = "") [pset]
Parameter set to specify column names for argon line fluxes.
(fcalcium = "") [pset]
Parameter set to specify column names for calcium line fluxes.
(fcarbon = "") [pset]
Parameter set to specify column names for carbon line fluxes.
(fchlorine = "") [pset]
Parameter set to specify column names for chlorine line fluxes.
(fmagnesium = "") [pset]
Parameter set to specify column names for magnesium line fluxes.
(fneon = "") [pset]
Parameter set to specify column names for neon line fluxes.
(fnitrogen = "") [pset]
Parameter set to specify column names for nitrogen line fluxes.
(foxygen = "") [pset]
Parameter set to specify column names for oxygen line fluxes.
(fpotassium = "") [pset]
Parameter set to specify column names for potassium line fluxes.
(fsilicon = "") [pset]
Parameter set to specify column names for silicon line fluxes.
(fsodium = "") [pset]
Parameter set to specify column names for sodium line fluxes.
(fsulfur = "") [pset]
Parameter set to specify column names for sulfur line fluxes.
(constant = no) [boolean]
Assume a constant T_e and N_e for the whole nebula? If set, the values will be obtained from the "t_e" and "n_e" task parameters.
(t_e = INDEF) [real]
If "constant=yes", T_e is assumed to have this constant value throughout the nebula, and diagnostics from the input table will be ignored.
(n_e = INDEF) [real]
If "constant=yes", N_e is assumed to have this constant value throughout the nebula, and diagnostics from the input table will be ignored.
(at_data = at_data) [string]
Atomic reference data directory name.

EXAMPLES

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.

BUGS

REFERENCES

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.

SEE ALSO

diagcols, nlevel, fluxcols, ionic, temden, zones

For general information about tasks in the `nebular' package, type "help nebular opt=sysdoc".


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