The Diagnostic Potential of Transition Region Lines under-going Transient Ionization in Dynamic Events

J.G. Doyle, A. Giunta, A. Singh, M.S. Madjarska, H. Summers, B.J. Kellett, M. O’Mullane

Figure 4. A contour plot of τth calculated using Equation 7. The black lines are the constant τs (=τob) obtained by the fitting procedure. The white stars are the derived values of Te and Ne for each burst, determined as in Fig. 3. The lower contour plot is an enlargement of the upper black rectangle showing the position of each burst labeled by numbers from 1 to 10.

Abstract

We discuss the diagnostic potential of high cadence ultraviolet spectral data when transient ionization is considered. For this we use high cadence UV spectra taken during the impulsive phase of a solar flare (observed with instruments on-board the Solar Maximum Mission) which showed excellent correspondence with hard X-ray pulses. The ionization fraction of the transition region ion O v and in particular the contribution function for the O v 1371 Å line are computed within the Atomic Data and Analysis Structure, which is a collection of fundamental and derived atomic data and codes which manipulate them. Due to transient ionization, the O v 1371 Å line is enhanced in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature than in ionization equilibrium. The rise time and enhancement factor depend mostly on the electron density. The fractional increase in the O v 1371 Å emissivity due to transient ionization can reach a factor of 2—4 and can explain the fast response in the line flux of transition regions ions during the impulsive phase of flares solely as a result of transient ionization. This technique can be used to diagnostic the electron temperature and density of solar flares observed with the forth-coming Interface Region Imaging Spectrograph

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Last Revised: 2012 April 30th