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.
Astronomy and Astrophysics
- Pub Date:
- January 2012
- Sun: transition region;
- Sun: UV radiation;
- Astrophysics - Solar and Stellar Astrophysics
- Accepted for publication in A&