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: http://star.arm.ac.uk/highlights/2013/637.html
Дата изменения: Mon Jul 29 17:10:26 2013 Дата индексирования: Fri Feb 28 01:17:21 2014 Кодировка: IBM-866 Поисковые слова: п п р р р р р р п п п ф ф ф ф ф |
Diagnosing Transient Ionization in Dynamic Events
Fig. 1. Line contribution function for Si IV 1394 Å and O IV 1401 Å in cmтИТ3 sтИТ1 at ionization equilibrium and for transient ionization. The electron density was fixed at 1010 cmтИТ3, with an initial starting temperature of 30 000K.
Abstract
Aims The present study aims to provide a diagnostic line ratio that will enable the observer to determine whether a plasma is in a state of transient ionization.
Methods We use the Atomic Data and Analysis Structure (ADAS) to calculate line contribution functions for two lines, Si IV 1394 Å and O IV 1401 Å, formed in the solar transition region. The generalized collisional-radiative theory is used. It includes all radiative and electron collisional processes, except for photon-induced processes. State-resolved direct ionization and recombination to and from the next ionization stage are also taken into account.
Results For dynamic bursts with a decay time of a few seconds, the Si IV 1394 Å line can be enhanced by a factor of 2тАУ4 in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature due to transient ionization compared to ionization equilibrium conditions. On the other hand, the O IV 1401 Å does not show such an enhancement. Thus the ratio of these two lines, which can be observed with the Interface Region Imaging Spectrograph, can be used as a diagnostic of transient ionization.
Conclusions We show that simultaneous high-cadence observations of two lines formed in the solar transition region may be used as a direct diagnostic of whether the observed plasma is in transient ionization. The ratio of these two lines can change by a factor of four in a few seconds owing to transient ionization alone.
Last Revised: 2013 July 29th |