The Diagnostic Potential of Transition Region Lines Undergoing Transient Ionization in Dynamic Events
- 147 Downloads
We discuss the diagnostic potential of high cadence UV 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 to 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 two–four 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 diagnose the electron temperature and density of solar flares observed with the forthcoming Interface Region Imaging Spectrograph.
KeywordsAtomic processes Line: formation Sun: activity Sun: atmosphere
Research at the Armagh Observatory is grant-aided by the Northern Ireland Department of Culture, Arts and Leisure. We thank STFC for support via ST/J001082/1. MM and JGD thank the International Space Science Institute, Bern for the support of the team ‘Solar small-scale transient phenomena and their contribution to coronal heating’.
- McWhirter, R.W.P.: 1965, In: Huddlestone, R.H., Leonard, S.L. (eds.) Plasma Diagnostic Techniques, Academic Press, New York, 201. Google Scholar
- McWhirter, R.W.P., Summers, H.P.: 1984, In: Barnett, C.F., Harrison, M.F.A. (eds.) Applied Atomic Collision Physics, Volume 2: Plasmas, Academic Press, New York, 52 – 111. Google Scholar