Observational tests for nonequilibrium ionization in the solar corona

Details Observational tests for nonequilibrium ionization in the solar corona Observational tests for nonequilibrium ionization in the solar corona

May 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...427..453s&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 427, no. 1, p. 453-458

Astronomy and Astrophysics

Astrophysics

8

Nonequilibrium Ionization, Radiative Heat Transfer, Solar Corona, Solar Transition Region, Spatial Resolution, Ultraviolet Radiation, Density Distribution, Emissivity, Radioactive Decay, Soho Mission, Spectral Resolution, Temperature Gradients

Scientific paper

Nonequilibrium ionization may be produced by a variety of processes in the solar corona, for example, by mass flows through the large temperature gradients of the transition region or by impulsive heating and cooling. Any deviation from equilibrium ionization would have a strong effect on the radiation from the corona and on the interpretation of solar observations; hence, it is important to determine observational signatures of nonequilibrium. The temperature-sensitive line ratios can be used as such signatures. We examine the line ratios: C IV I(1548.2 A)/I(312.4 A), O IV I(789.4 A)/I(554.4 A), O V I(629.7 A)/I(172.2 A), O VI I(1031.9 A)/I(173.0 A) and O VI I(1031.9 A)/I(150.1 A). These line ratios are calculated for four coronal loop models that have a steady flow and that are known to have significant departures from equilibrium ionization. Our results indicate that, in general, nonequilibrium causes a considerable reduction in the line ratios, more than an order of magnitude in the downflowing leg of the loop model with the largest mass flows. We find that the C IV line ratio is the most sensitive to nonequilibrium. We discuss the implications of our results for observations, specifically, the observations expected from the upcoming SOHO mission.

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