| ntplot | analysis.nebular | ntplot |
ntplot -- Plot curves on the N_e, T_e plane for observed diagnostic line ratios
ntplot intable
This task computes and plots curves that show the range of electron temperatures (T_e) and electron densities (N_e) that are consistent with various observed diagnostic line ratios. The diagnostics from an ionized nebular gas are computed within the N-level atom approximation. (For more details about this approximation, type "help nlevel".) The user specifies the name of the STSDAS binary table containing the observed line fluxes and ratios, and the task plots one curve in the N_e, T_e plane for each diagnostic. An optional output table will contain each of the computed curves, one per column. The output table is useful for identifying the individual curves, and for customized plotting (with, e.g., the `stplot.igi' task). This task is particularly useful for flagging unreasonable input line ratios, and for determining whether a detailed photoionization model is necessary for calculating the physical conditions and ionic abundances. If a detailed model is necessary, the output from this task will be useful for specifying the initial conditions; if not, the `zones' and `abund' tasks may be sufficient for determining the physical conditions and the ionic abundances.
The input table may contain line fluxes for many nebulae and/or many regions within a nebula, one object/region per row. A particular object in the table is selected with the "object" parameter. The flux for each emission line or line ratio must be given in separate columns. The task locates particular emission line fluxes via names of specific columns in the input table. These columns have suggestive default names, but are entirely user-definable; type "help fluxcols" for more details. (An example of an input table can be found in the file "nebular$data/flux.fits".) Note that the input table need not actually contain all the diagnostic lines specified in this p-set: if a named column is not found, the corresponding curve will be skipped. The plot limits can also be specified.
The diagnostic line ratios 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:
{-c * f(lambda)}
I(line) = F(line) * 10
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 diagnostic line ratios and the ionization potential of the associated ion are listed by ion below. The line ratio is in the form I(wave1)/I(wave2), where "wave1" and "wave2" are in units of Angstroms; ratios involving sums of line strengths are given as I(wave1+wave2)/I(wave3+wave4).
Table 1. Electron Density Diagnostics
Ion Spectrum Line Ratio I.P. Zone
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C(+1) C ii] I(2326) / I(2328) 11.3 Low
C(+2) C iii] I(1907) / I(1909) 24.4 Med
N(0) [N i] I(5198) / I(5200) 0.0 Low
N(+2) N iii] I(1749) / I(1752) 29.6 Med
O(+1) [O ii] I(3726) / I(3729) 13.6 Low
O(+3) O iv] I(1401) / I(1405) 54.9 High
Ne(+3) [Ne iv] I(2423) / I(2425) 63.5 High
Al(+1) [Al ii] I(2661) / I(2670) Low
Si(+2) Si iii] I(1883) / I(1892) 16.3 Low
S(+1) [S ii] I(6716) / I(6731) 10.4 Low
Cl(+2) [Cl iii] I(5517) / I(5537) 23.8 Med
Ar(+3) [Ar iv] I(4711) / I(4740) 40.9 Med
K(+4) [K v] I(6223) / I(6349) High
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Table 2. Electron Temperature Diagnostics
Ion Spectrum Line Ratio I.P. Zone
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N(+1) [N ii] I(6548+6583) / I(5755) 14.5 Low
O(+0) [O i] I(6300+6363) / I(5577) 0.0 Low
O(+1) [O ii] I(3726+3729) / I(7320+7330) 13.6 Low
O(+2) [O iii] I(4959+5007) / I(4363) 35.1 Med
Ne(+2) [Ne iii] I(3869+3969) / I(3342) 41.1 Med
Ne(+3) [Ne iv] I(2422+2425) / I(1601+1602) 63.5 High
Ne(+4) [Ne v] I(3426+3346) / I(2975) 97.0 High
Al(+1) [Al ii] I(2661+2670) / I(1671) 6.0 Low
Si(+2) Si iii] I(1883+1892) / I(1206) 16.3 Low
S(+1) [S ii] I(6716+6731) / I(4068+4076) 10.4 Low
S(+2) [S iii] I(9069+9532) / I(6312) 23.4 Med
Cl(+3) [Cl iv] I(7530+8045) / I(5323) 39.9 Med
Ar(+2) [Ar iii] I(7136+7751) / I(5192) 27.6 Med
Ar(+3) [Ar iv] I(4711+4740) / I(2854+2868) 40.9 Med
Ar(+4) [Ar v] I(6435+7006) / I(4626) 59.8 High
K(+3) [K iv] I(6102+6796) / I(4511) 46.0 Med
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Different line types in the plot are used to denote diagnostics from ions with different ionization potential, organized into three zones. Solid lines are used for low ionization species (I.P. < 20 eV), dashed lines for intermediate ionization (20 < I.P. < 50 eV), and dotted lines for the highest ionization diagnostics (I.P. > 50 eV).
1. Plot the range of electron densities and temperatures that are consistent with the diagnostic ratios found in the example input table for the object "Test_123". Adjust the density limits to 500 < N_e < 1.e4.
cl> tcopy nebular$data/flux.fits .
cl> ntplot flux.tab object=Test_123 min_dens=500. max_dens=1.e4
2. Plot curves in the N_e, T_e plane that are consistent with the diagnostic ratios found in the table nebula.tab, and store the results in the table curves.tab. Adjust the default plot limits to 100 < N_e < 1.e+6/cm^3 and 5000 < T_e < 30,000 K.
cl> ntplot nebula.tab outtab=curves.tab min_dens=100. \
>>> max_temp=3.e+4
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.
For general information about this package, type "help nebular opt=sysdoc".