D. Cohen
29 Feb 2008

Some simple PrismSpect tests of recombination spectra in photoionized plasmas

H: 99.9% at.
C: 0.1% at.

n_i = 10^15 cm^-3
T_e = 5 eV

T_r = 150 eV
T_spec = 500 eV

I used the canned K-shell emission atm files 

I wanted a cold, highly ionized plasma of relatively low density to focus on the spectral signatures of recombination

Here’s some of the set-up screens for the baseline PrismSpect simulation: 

Note the carbon is nearly all H-like, but essentially none of it is bare. 

Note: The C VI K-edge is at 25.3 Angstroms; the edge that’s visible here, near 32 Angstroms, is the C V edge/RRC.   This reflects the fact that for a pure recombination spectrum, the strong features are from the i-1 ionization state. 

The lines at 40+ A are the resonance and intercombination lines of C V.  Presumably the forbidden line is absent because of the relatively high density, but I’m surprised that the intercombination line isn’t stronger, as G > 1 for photoionized plasmas.  

Turning up the radiation field (Tr=250) – still no bare C: 

Maybe the electron temperature is just too low.  Try Te=15eV.  But still Tr=250. ni=1e15.

OK, this made a huge difference; now bare C is dominant.

Though I’m somewhat surprised that it went from nothing to completely dominant going from just T_e=5eV to 15eV. 

Here’s the synthetic spectrum from this simulation: 

The RRC (at 25.3 A) is still very weak compared to Ly-alpha (near 33 A). 

Let’s convolve down to R=800

Doesn’t make much difference

But, when I integrate the power in a band around Ly-alpha and then around the RRC, I get just a factor of 4 ratio in integrated power: 

Hmmm… so there’s significant integrated power in the RRC… but it’s not highly peaked (though in linear space, it looks plausibly to have a width of ~kT. 

See what difference it makes to lower T to 10eV: 

Wow, Ionization completely different – back down to no bare C at all. 

Now try ni=1e13 and Te=10eV

same thing – still no bare C at all.