Using emission models¶

The software tools offer three PAH emission models. With increasing complexity they are the ‘FixedTemperature’, ‘CalculatedTemperature’, and ‘Cascade’ model. The first simply multiplies a blackbody at fixed given temperature with the integrated cross-section of each vibrational transition. The second first calculates the maximum attained temperature from the provided input and subsequently multiplies a blackbody at that fixed temperature with the integrated cross-section of each vibrational transition. The third averages the total emission over the entire cooling cascade (time).

Emission models are handled by the ‘transitions’-instance. The ‘FixedTemperature’-model simply takes a temperature, in Kelvin, and, in their simplest form, both the ‘CalculatedTemperature’ and ‘Cascade’ models take an energy, in erg.

transitions->FixedTemperature,600D

transitions->CalculatedTemperature,6D*1.603D-12 ; 6 eV

transitions->Cascade,6D*1.603D-12 ; 6 eV

transitions.fixed_temperature(600)

transitions.calculatedtemperature(4.0 * 1.603e-12)

transitions.cascade(6 * 1.603e-12)

Both the ‘CalculatedTemperature’ and ‘Cascade’-methods accept the ‘Approximate’, ‘Star’, ‘StellarModel’, and ‘ISRF’-keywords. With the ‘Approximate’-keyword specified, calculations are performed using the PAH emission model from Bakes et al. (2001a, b). When the ‘Star’-keyword is set, a stellar blackbody at the provided temperature is used to calculate the average energy absorbed by each PAH utilizing the PAH absorption cross-sections from Draine & Li (2007). In case the ‘StellarModel’-keyword is provided as well, the input is considered to be a full-blown, for example, Kurucz stellar atmosphere model. In the IDL case, the ‘AmesPAHdbIDLSuite_CREATE_KURUCZ_STELLARMODEL_S’ helper routine is provided to assist with molding the model data into the proper input format. Lastly, with the ‘ISRF’-keyword set, the interstellar radiation field from Mathis et al. (1983) is used to calculate the average energy absorbed by each PAH.

transitions->CalculatedTemperature,17D3,/Star

transitions->Cascade,/Approximate,/ISRF

FTAB_EXT,'ckp00_17000.fits',[1,10],angstroms,flam,EXT=1

transitions->Cascade, $
              AmesPAHdbIDLSuite_CREATE_KURUCZ_STELLARMODEL_S(angstroms, $
                                                             flam), $
              /Star, $
              /StellarModel

transitions.calculatedtemperature(17000, star=True)

transitions.cascade(precision='approximate', field='ISRF')

The ‘Cascade’-method also accepts the ‘Convolve’-keyword. When set and combined with either the ‘Star’, optionally with the ‘StellarModel’-keyword, or ‘ISRF’-keyword, will instead of calculating the average absorbed photon energy for each PAH, convolve the PAH emission with the entire radiation field.

transitions->Cascade,17D3,/Star,/Convolve

transitions.cascade(17000,star=True,convolve=True)

NB This is computationally expensive.

The ‘transitions’-instance’s ‘Shift’-method can be used to redshift the fundamental transitions to simulate some anharmonic effects.

transitions->Shift,-15D

transitions.shift(-15)

NB Red-shifting the fundamental vibrational transitions should be done after applying one of the three emission models described above.