Solar transition zone pressures from EUV observations of O IV and N IV

Details Solar transition zone pressures from EUV observations of O IV and N IV Solar transition zone pressures from EUV observations of O IV and N IV

Aug 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...259..366d&link_type=abstract

Astrophysical Journal, Part 1, vol. 259, Aug. 1, 1982, p. 366-371.

Astronomy and Astrophysics

Astronomy

25

Extreme Ultraviolet Radiation, Nitrogen, Oxygen Spectra, Radiation Pressure, Solar Spectra, Ultraviolet Astronomy, Faculae, Plasma Spectra, Solar Corona, Solar Instruments, Sunspots

Scientific paper

NRL High Resolution Telescope and Spectrograph observations of the O IV and N IV EUV lines emitted from the Sun are examined. The instrument provides stigmatic spectra with a spatial resolution of 1 arcsec and a spectral resolution of 0.05 A in the range 1170-1710 A. Intensity ratios of the intersystem lines of O IV near 1400 A are used as the primary diagnostic to measure electron pressures in a sunspot and plage. These ratios are strongly sensitive to electron pressure but are insensitive to the temperature structure of the emitting plasma. Average electron pressures of 9 x 10 to the 15th per cu cm K (1.2 dyn/sq cm) in a plage, 4 x 10 to the 15th per cu cm K (0.6 dyn/sq cm) in a sunspot and 2.2 x 10 to the 15th per cu cm K (0.3 dyn/sq cm) in high speed sunspot downflows are found. The ratio of I(Nv) + I(C IV) to I(N IV 1486A) is shown to be relatively insensitive to temperature and gives pressures consistent with those obtained from the O IV ratio. It is demonstrated that ratios of allowed lines such as C IV and Si IV to the O IV intersystem lines are temperature sensitive and hence are unreliable pressure diagnostics.

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