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Title: Dynamical properties of the solar corona from the intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII

Abstract

We have studied the line profiles of the solar coronal forbidden lines Si VIII 1445.76 A, Fe XI 1467.08 A, and Fe XII 1242.03 A in quiet and active coronal regions from a survey of available limb spectral in the NRL Skylab data. The results show that the line widths of these lines are essentially the same in quiet-Sun regions as in active regions. For some active regions, however, the line widths are systematically narrower than those in quiet-Sun regions. In addition, the line widths are about the same in the height range from O'' to 30''. The widths are wider than the thermal Doppler widths at the ionization equilibrium temperature given by Jordan. The additional widths correspond to a nonthermal mas-motion velocity of 10--25 km s/sup -1/ at 1.7 x 10/sup 6/ K (Fe XII), 10--17 km s/sup -1/ at 1.5 x 10/sup 5/ K (Fe XI), and 10--20 km s/sup -1/ at 9.3 x 10/sup 5/ K (Si VIII). The intensities of the forbidden lines in active regions are about an order of magnitude greater than those in quiet-Sun regions. The distribution of column density calculated for the three different lines indicates that more plasma is near 1.7more » x 10/sup 6/ K than near 9.3 x 10/sup 5/ K at a given height. The observational results are discussed in terms of coronal heating mechanisms. The dissipation of acoustic waves does not provide a sufficient heating rate. The dissipation of three modes of hydromagnetic waves--the slow mode, the fast mode, and the Alfven mode--also cannot satisfactorily explain the observational results. It is difficult for heating by hydromagnetic waves to meet simultaneously the requirements of a large enough heating rate, a dissipation length comparable to the length of a coronal loop, and a velocity amplitude that agrees with observations.« less

Authors:
; ;
Publication Date:
Research Org.:
E. O. Hulburt Center for Space Research, Naval Research Laboratory, Washington
OSTI Identifier:
6271770
Resource Type:
Journal Article
Journal Name:
Astrophys. J.; (United States)
Additional Journal Information:
Journal Volume: 227:3
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; SOLAR CORONA; KINETICS; ULTRAVIOLET SPECTRA; DISSIPATION FACTOR; ENERGY LOSSES; EXTREME ULTRAVIOLET RADIATION; HYDROMAGNETIC WAVES; IONIZATION; LINE WIDTHS; MAGNETIC FIELDS; SOLAR ACTIVITY; SOLAR RADIATION; ELECTROMAGNETIC RADIATION; LOSSES; RADIATIONS; SPECTRA; ULTRAVIOLET RADIATION; 640104* - Astrophysics & Cosmology- Solar Phenomena

Citation Formats

Cheng, C., Doschek, G.A., and Feldman, U. Dynamical properties of the solar corona from the intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII. United States: N. p., 1979. Web. doi:10.1086/156811.
Cheng, C., Doschek, G.A., & Feldman, U. Dynamical properties of the solar corona from the intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII. United States. doi:10.1086/156811.
Cheng, C., Doschek, G.A., and Feldman, U. Thu . "Dynamical properties of the solar corona from the intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII". United States. doi:10.1086/156811.
@article{osti_6271770,
title = {Dynamical properties of the solar corona from the intensities and line widths of EUV forbidden lines of Si VIII, Fe XI, and Fe XII},
author = {Cheng, C. and Doschek, G.A. and Feldman, U.},
abstractNote = {We have studied the line profiles of the solar coronal forbidden lines Si VIII 1445.76 A, Fe XI 1467.08 A, and Fe XII 1242.03 A in quiet and active coronal regions from a survey of available limb spectral in the NRL Skylab data. The results show that the line widths of these lines are essentially the same in quiet-Sun regions as in active regions. For some active regions, however, the line widths are systematically narrower than those in quiet-Sun regions. In addition, the line widths are about the same in the height range from O'' to 30''. The widths are wider than the thermal Doppler widths at the ionization equilibrium temperature given by Jordan. The additional widths correspond to a nonthermal mas-motion velocity of 10--25 km s/sup -1/ at 1.7 x 10/sup 6/ K (Fe XII), 10--17 km s/sup -1/ at 1.5 x 10/sup 5/ K (Fe XI), and 10--20 km s/sup -1/ at 9.3 x 10/sup 5/ K (Si VIII). The intensities of the forbidden lines in active regions are about an order of magnitude greater than those in quiet-Sun regions. The distribution of column density calculated for the three different lines indicates that more plasma is near 1.7 x 10/sup 6/ K than near 9.3 x 10/sup 5/ K at a given height. The observational results are discussed in terms of coronal heating mechanisms. The dissipation of acoustic waves does not provide a sufficient heating rate. The dissipation of three modes of hydromagnetic waves--the slow mode, the fast mode, and the Alfven mode--also cannot satisfactorily explain the observational results. It is difficult for heating by hydromagnetic waves to meet simultaneously the requirements of a large enough heating rate, a dissipation length comparable to the length of a coronal loop, and a velocity amplitude that agrees with observations.},
doi = {10.1086/156811},
journal = {Astrophys. J.; (United States)},
number = ,
volume = 227:3,
place = {United States},
year = {1979},
month = {2}
}