Applied Mathematics Seminar

I re-examine the simple question: How can we use the emitted photons to extract meaningful information on the (chromosphere,) transition region and corona? Using examples, I will conclude that the only safe way to proceed is through forward models, especially when the plasmas are unresolved. In this way, inherent non-uniqueness is handled by adding information through explicit physical assumptions and restrictions made in the modeling procedure. The alternative, "inverse" approaches rely (often implicitly) on more subjective choices that have little theoretical support. Although focussed on the transition region, there are implications for more general problems concerning the use of photons to diagnose conditions in astrophysical plasmas.