Plasma Laboratory - Weizmann Institute of Science


    author    = {R. Doron and G. A. Doschek and J. M. Laming and U. Feldman and A. K. Bhatia},
abstract = {UV emission from B-like N and O ions offers a rather rare opportunity for recording spectral lines in a narrow wavelength range that can potentially be used to derive temperatures relevant to the solar transition region. In these ions, the line intensity ratios of the type (2 s 2 p 2 -2 p 3 )/(2 s 2 2 p -2 s 2 p 2 ) are very sensitive to the electron temperature. In addition, the lines involving the ratios fall within a range of only ~12 Å; in N III the lines fall in the 980-992 Å range, and in O IV in the 780-791 Å range. In this work, we explore the use of these atomic systems, primarily in N III , for temperature diagnostics of the transition region by analyzing UV spectra obtained by the Solar Ultraviolet Measurement of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory . The N III temperature-sensitive line ratios are measured in more than 60 observations. The mean measured ratios are lower by ~30% than those predicted in the typical quiet Sun. Assuming an isothermal plasma, most of the measured ratios correspond to temperatures in the range 5.7 × 10 4 -6.7 × 10 4 K. This range is considerably lower than the calculated temperature of maximum abundance of N III , which is ~7.6 × 10 4 K. Detailed analysis of the spectra further indicates that the measured ratios are probably somewhat overestimated because of resonant scattering effects in the 2 s 2 2 p -2 s 2 p 2 lines and small blends in the 2 s 2 p 2 -2 p 3 lines. Actual lower ratios would only increase the discrepancy between the ionization balance calculations and present temperature measurements based on a collisional excitation model. In the case of the O IV spectra, we determine that because of the close proximity in wavelength of the weak line (2 s 2 p 2 -2 p 3 transitions) to a strong Ne VIII line, sufficiently accurate ratio measurements cannot be obtained.},
journal = {The Astrophysical Journal},
number = {2},
pages = {1121},
title = {Temperature Measurements in the Solar Transition Region Using N III Line Intensity Ratios},
url = {},
volume = {590},
year = {2003},

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