[Loops] [1111.3579] Post-flare UV light curves explained with thermal instability of loop plasma

[Fabio Reale]

Dear colleagues
     please find at the following link the preprint of a work accepted 
for publication in ApJ, showing interesting evidence of thermal 
instability in UV light curves late in a flare. This analysis is done on 
SoHO/SUMER data but may be useful for flare observations with SDO/EVE:

http://arxiv.org/abs/1111.3579

The abstract is below.

Best regards
Fabio Reale


Post-flare UV light curves explained with thermal instability of loop plasma

F. Reale, E. Landi, S. Orlando

In the present work we study the C8 flare occurred on September 26, 2000 
at 19:49 UT and observed by the SOHO/SUMER spectrometer from the 
beginning of the impulsive phase to well beyond the disappearance in the 
X-rays. The emission first decayed progressively through equilibrium 
states until the plasma reached 2-3 MK. Then, a series of cooler lines, 
i.e. Ca x, Ca vii, Ne vi, O iv and Si iii (formed in the temperature 
range log T = 4.3 - 6.3 under equilibrium conditions), are emitted at 
the same time and all evolve in a similar way. Here we show that the 
simultaneous emission of lines with such a different formation 
temperature is due to thermal instability occurring in the flaring 
plasma as soon as it has cooled below ~ 2 MK. We can qualitatively 
reproduce the relative start time of the light curves of each line in 
the correct order with a simple (and standard) model of a single flaring 
loop. The agreement with the observed light curves is greatly improved, 
and a slower evolution of the line emission is predicted, if we assume 
that the model loop consists of an ensemble of subloops or strands 
heated at slightly different times. Our analysis can be useful for flare 
observations with SDO/EVE.
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