[Loops] EM loci

[Harry Warren]

Scott,

I think that you're ultimately correct that the DEM is not the "final
answer" to any questions in solar physics. If you think of what we're doing
as an iterative process, however, it does provide a useful starting point.

For example, if I gave you the intensities from some hot loops in an active
region:

Si VII 275.368   47.0 (erg/cm^2/s/sr)
Ca XV 200.972   238.9

How else would start to think about them? With the DEM you quickly see that
the amount of plasma at 4 MK appears to be much, much higher than it is at
0.6 MK, and that gets you thinking about physical models.

Of course at the end of the day, as you're saying, one needs to forward
model the observations.

Best wishes,

Harry

On 9/23/10 8:53 PM, "Scott W. McIntosh" <mscott at ucar.edu> wrote:

> Can I point out a paper to the list:
> 
> http://adsabs.harvard.edu/abs/2010ApJ...708.1238J
> 
> This paper encapsulates the problem in a concise form. I could point out a
> couple more, but those are nearly 10 years old now, wow how time flies. I have
> drawn my line in the sand with emission measures as a practical diagnostic -
> once we have a DEM/EM, etc what can we do with it? As far as I can tell there
> are only a few papers in the literature that deal with that particular issue
> in a real sense and those are from further back in the 80s [look for papers by
> Carole Jordan].
> 
> I am all for learning something about the solar plasma from a zeroth order
> approach. However, no EM/DEM/Line Ratio estimation deals with the real
> time-varying corona (or outer solar atmosphere as we need to deal with a
> intrinsically coupled system). By definition, these diagnostic deal with
> equilibrium processes and thermal populations - I am not entirely sure that we
> have that in place and if we do is, is that the process doing the "heavy
> lifting" or just the after effect procing the apparent stationary
> state.....there is strong evidence of non-thermal processes affecting the
> chromospheric, TR and coronal plasmas in the very same spectra from which such
> diagnostics are derived [probably even worse for broadband EUV imagers].
> 
> Sorry, to be a bummer!
> 
> -S. 

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