NAME

temden -- Compute electron temperature or density from diagnostic line ratios.

USAGE

temden option ratio

DESCRIPTION

This task computes the electron temperature (T_e) given an electron density (N_e), or N_e given T_e, of an ionized nebular gas within the N-level atom approximation. The user specifies the quantity to be calculated, the reddening-corrected diagnostic line ratio, the name and the spectrum of the atom, and an assumed value for the quantity NOT being calculated. The task output lists the ion and the line ratio for which the calculation is performed, followed by the result of the calculation. These input task parameters, including those that are "hidden", are written back to the parameter file. The result is also stored in the task parameter "result" for ease of use in CL scripts.

The following table lists the default diagnostic line ratios in the form I(wave1)/I(wave2), where "wave1" and "wave2" are given in units of Angstroms.

	Table 1. Electron density diagnostics:

	  Ion             Line Ratio
	-------------------------------------
	  C ii]        I(2326) / I(2328)
	  C iii]       I(1907) / I(1909)
	 [N i]         I(5198) / I(5200)
	  N iii]       I(1749) / I(1752)
	  N iv]        I(1483) / I(1487)
	 [O ii]        I(3726) / I(3729)
	 [O iv]        I(1401) / I(1405)
	 [O v]         I(1214) / I(1218)
	[Ne iv]        I(2423) / I(2425)
	[Al ii]        I(2661) / I(2670)
	[Si ii]        I(2335) / I(2345)
	 Si iii]       I(1883) / I(1892)
	 [S ii]        I(6716) / I(6731)
	 [S iv]        I(1406) / I(1417)
	[Cl iii]       I(5517) / I(5537)
	[Ar iv]        I(4711) / I(4740)
	 [K v]         I(6223) / I(6349)

	Table 2. Electron temperature diagnostics:

	  Ion             Line Ratio
	-------------------------------------
         [C i]    I(9823+9849) / I(8728)
         [N i]    I(5198+5200) / I(10397+10407)
	 [N ii]   I(6548+6583) / I(5755)
	 [O i]    I(6300+6363) / I(5577)
	 [O ii]   I(3726+3729) / I(7320+7330)
	 [O iii]  I(4959+5007) / I(4363)
	[Ne iii]  I(3869+3969) / I(3342)
        [Ne iv]   I(2422+2425) / I(1601+1602)
	[Ne v]    I(3426+3346) / I(2975)
        [Na iv]   I(3242+3362) / I(2805)
        [Na vi]   I(2871+2970) / I(2569)
        [Mg v]    I(2783+2928) / I(2418)
        [Mg vii]  I(2506+2626) / I(2262)
        [Al ii]   I(2661+2670) / I(1671)
	 Si iii]  I(1883+1892) / I(1206)
	 [S ii]   I(6716+6731) / I(4068+4076)
	 [S iii]  I(9069+9532) / I(6312)
        [Cl iii]  I(5517+5537) / I(3353+3343)
	[Cl iv]   I(7530+8045) / I(5323)
	[Ar iii]  I(7136+7751) / I(5192)
	[Ar iv]   I(4711+4740) / I(2854+2868)
	[Ar v]    I(6435+7006) / I(4626)
         [K iv]   I(6102+6796) / I(4511)
         [K v]    I(4123+4163) / I(2515+2495)
        [Ca v]    I(5309+6087) / I(3996)

It is possible to customize the line ratio using the "transition" parameter and an expression for the ratio of interest. See the description of the "transition" parameter and the examples below. Note that the wavelengths corresponding to the various transitions can be obtained by running the "ionic" task.

PARAMETERS

option "density" [string]

Quantity to calculate: "temperature" or "density".

flxratio = "" [string]

Algebraic expression for the ratio of diagnostic line fluxes. The expression is evaluated with FORTRAN-like rules for supported operators and the order of their evaluation.

(atom = "oxygen") [string]

Name of the atom, which is one of: carbon, nitrogen, oxygen, neon, sodium, magnesium, aluminum, silicon, sulfur, chlorine, argon, potassium, or calcium.

(spectrum = 2) [int]

Spectrum number of the atom, e.g. "3" for [O iii], "2" for [S ii], etc. Must lie in the range 1 <= ion_stage <= 8.

(transition = "default") [string]

Expression for the transition, if not the "default". Transitions are specified with the special function "J" (for the emissivity): the arguments are the upper and lower levels of the transition. For example, the traditional density diagnostic of [O II] is the ratio of the intensities for the transition I(3->1) to that of I(2->1)--i.e., I(3726)/I(3729). The corresponding expression for would be "J(3,1)/J(2,1)". The expression is evaluated with FORTRAN-like expression rules.

(assume = INDEF) [real]

Value to assume for the quantity NOT being calculated. The units are 1/cm^3 if T_e is being calculated, or Kelvins if N_e is being calculated. Temperatures must lie in the range 500 to 1.e+5 K, and densities must lie in the range 1. to 1.e+8.

(result = INDEF) [real]

Result of the calculation. The units are 1/cm^3 if N_e is being calculated, or Kelvins if T_e is being calculated.

(verbose = no) [boolean]

Print verbose output for each iteration?

(at_data = at_data) [string]

Atomic reference data directory name.

EXAMPLES

1. Find the electron density from the [S II] diagnostic ratio I(6716)/I(6731) = 0.9 assuming an electron temerature of 10000 K.

    cl> temden density 0.9 atom=sulfur spectrum=2 assume=10000. 
    Density ratio [S ii]: I(6716)/I(6731) =   0.9
    Density: 910.344 /cm^3

2. Find the electron temperature from the [O III] diagnostic ratio I(4959+5007)/I(4363), given I(4959)=100., I(5007)=288., and I(4363)=7.405, and assuming an electron density of 1000/cm^3.

    cl> temden temerature "(100.+288.)/7.40" atom=oxygen \

    >>> spec=3 assume=1000.
    Temperature ratio [O iii]: I(4959+5007)/I(4363) = 52.432
    Temperature: 17158.3 K

3. Find the electron temperature from the custom [O III] diagnostic ratio I(1660+1666)/I(4363)=1.0, and assuming an electron density of 10,000/cm^3.

    cl> temden temerature 1.0 atom=oxygen spec=3 assume=1.e4 \

    >>> transition="(j(6,2)+j(6,3))/j(5,4)"
    Temperature ratio [O iii]: (J(6,2)+J(6,3))/J(5,4) = 1.
    Temperature: 17158.3 K

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

nlevel, ionic, zones

For further information type "help nebular opt=sysdoc".