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EUV analysis of an active region

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Abstract

A sequence of extreme ultraviolet (EUV) spectroheliograms of McMath region No. 10283 were obtained by the Harvard College Observatory experiment on OSO-6. The lines Ovi λ1032 Mg × λ625, Si xii λ499 and Fe xvi λ 335 were used to determine coronal temperatures and densities above the active region. A comparison of theoretical and observed line ratios yielded coronal temperatures of 2.2 to 2.3 × 106K above the active region and 2.0 to 2.1 × 106K in the surrounding area. The temperatures derived from ratios involving the O vi intensities are systematically higher than the others. This is attributed to an error in the theoretical O vi intensities.

The intensities observed above the limb are compared with intensities predicted with a simple model based on cylindrical geometry. The overall agreement shows that the assumption of an iso-thermal corona in hydrostatic equilibrium above the active region is a reasonable working hypothesis and that the adopted geometrical model for the electron density distribution is adequate.

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Authors and Affiliations

  1. Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory, 02138, Cambridge, Mass., U.S.A.

    Nirupama Raghavan & George L. Withbroe

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  1. Nirupama Raghavan
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  2. George L. Withbroe
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Now at the Indian Institute of Technology, New Delhi, India.

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Raghavan, N., Withbroe, G.L. EUV analysis of an active region. Sol Phys 43, 117–128 (1975). https://doi.org/10.1007/BF00155149

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  • DOI: https://doi.org/10.1007/BF00155149

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