Abstract
Line ratios from the helium-like ions O vii and Ne ix are useful as plasma diagnostics for both flaring and nonflaring solar coronal active regions. The photon flux ratio, R, of the forbidden 1s/sup 2/ /sup 1/S/sub 0/-1s2s /sup 3/S/sub 1/ line to the intercombination 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 3/P/sub 1/ line in O vii is useful as a density diagnostic at coronal temperatures of approx.2 x 10/sup 6/ K. If the electron density n/sub e/ is less than n/sub e/*roughly-equal3 x 10/sup 9/ cm/sup -3/, Rroughly-equalR/sub 0/ (where R/sub 0/ is the low-density limit), and R decreases with increasing density. Uncertainties in R and R/sub 0/ both contribute to uncertainties in n/sub e/. R/sub 0/ uncertainties are especially important for nonflaring plasmas having n/sub e/roughly-equaln/sub e/*. We analyzed 29 nonflare X-ray spectra, each a sum of approx.10 scans by the SOLEX B spectrometer on the USAF P78-1 satellite, to conclude that R/sub 0/ is in the range 3.7--4.1 G, the photon flux ratio of the forbidden plus intercombination line to the resonance 1s/sup 2/ /sup 1/S/sub 0/-1s2p /sup 1/P/sub 1/ line, can be used as an indicator of whether or not the emitting plasma is in amore » state of ionization equilibrium. For both O vii and Ne ix, G is modified by resonance scattering in the solar atmosphere, which lowers the resonance line flux. This scattering allows us to estimate the column densities of O vii and Ne ix in the corona above the active region source. We also estimate the value of G in the absence of resonance scattering.« less
Paper version not known (
Free)
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call