Astron. Astrophys. 352, L99-L102 (1999)

5. Observational consequences

In order to calculate the ion populations along the loop for a given time we have to integrate the ionization equations, i.e.,

where and are the recombination and ionization coefficients of ionization stage i and is the volume number density of ion i. From the observed Doppler shifts in Fig. 1 we have selected the resonance line of C IV at 1548 Å, O VI 1032 Å, and Ne VIII 770 Å whose ion populations is going to be determined. This offers an easy comparison of Doppler shift observations and numerical predictions of the time evolution of observational signatures. Analyses also show that it is evident that strong deviations from the equilibrium values of the ion populations occur. We do not represent here a careful study of this deviation. We refer the detailed analysis of the evolution of the fractional ion populations with respect to the equilibrium values to a recent PhD thesis (Sarro 1998) devoted to the study of the evolution of the ionization state of several species in a loop subject to these kinds of energy perturbations.

Once the ion populations are computed, the emissivity of a given emission line per unit interval of wavelength in an optically thin, collisionally excited resonance line can be obtained by using the standard equation

Given a distribution of emissivities along the loop, the total intensity can be calculated as

where is the total length of the loop.

© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999
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