[Loops] [1112.2857] Monte Carlo Markov Chain DEM reconstruction of isothermal plasmas

[Fabio Reale]

Dear colleagues
      please find at the following link the preprint of a work accepted 
for publication in Astronomy & Astrophysics, showing tests on the 
capability of MCMC method to reconstruct isothermal DEMs:

http://arxiv.org/abs/1112.2857

The abstract is below.

Best regards
Fabio Reale


Monte Carlo Markov Chain DEM reconstruction of isothermal plasmas

E. Landi, F. Reale, P. Testa


In this paper, we carry out tests on the Monte Carlo Markov Chain (MCMC) 
technique with the aim of determining: 1) its ability to retrieve 
isothermal plasmas from a set of spectral line intensities, with and 
without random noise; 2) to what extent can it discriminate between an 
isothermal solution and a narrow multithermal distribution; and 3) how 
well it can detect multiple isothermal components along the line of 
sight. We also test the effects of 4) atomic data uncertainties on the 
results, and 5) the number of ions whose lines are available for the DEM 
reconstruction. We find that the MCMC technique is unable to retrieve 
isothermal plasmas to better than Delta log T = 0.05. Also, the DEM 
curves obtained using lines calculated with an isothermal plasma and 
with a Gaussian distribution with FWHM of log T = 0.05 are very similar. 
Two near-isothermal components can be resolved if their temperature 
separation is Delta log T = 0.2 or larger. Thus, DEM diagnostics has an 
intrinsic resolving power of log T = 0.05. Atomic data uncertainties may 
significantly affect both temperature and peak DEM values, but do not 
alter our conclusions. The availability of small sets of lines also does 
not worsen the performance of the MCMC technique, provided these lines 
are formed in a wide temperature range. Our analysis shows the present 
limitations in our ability to identify the presence of strictly 
isothermal plasmas in stellar and solar coronal spectra.