Volume 537, January 2012
|Number of page(s)||11|
|Published online||25 January 2012|
Solar low-lying cool loops and their contribution to the transition region EUV output
1 INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
2 INAF-Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
Received: 28 June 2011
Accepted: 25 November 2011
Aims. We aim to investigate the increase of the differential emission measure (DEM) towards the chromosphere. In the past 30 years, small and cool magnetic loops (height ≲ 8 Mm, T ≲ 105 K) have been proposed as an explanation for this effect.
Methods. We present hydrodynamic simulations of low-lying cool loops in which we studied the loops’ conditions of existence and stability, and their contribution to the transition region EUV output.
Results. We find that stable, quasi-static cool loops (with velocities <1 km s-1) can be obtained under different and more realistic assumptions on the radiative loss function with respect to previous works. A mixture of the DEMs of these cool loops plus intermediate loops with temperatures between 105 and 106 K can reproduce the observed emission of the lower transition region at the critical turn-up temperature point (T ~ 2 × 105 K) and below T = 105 K.
Key words: Sun: transition region / Sun: UV radiation / hydrodynamics
© ESO, 2012
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