Spectroscopic diagnostics of electron density in a flare ribbon by oxygen IV lines using Non-Maxwellian distribution

Abstract

By the line ratio of Oxygen IV 1399.776.50 Å and 1401.163 Å lines in a flare ribbon in the solar transition region, the principle of the electron density diagnostics using the collisional radiative model is discussed, and the relationship of the electron density with the line ratio is obtained, for both Maxwellian and Kappa distributions. By the observed line ratio, the diagnostic result of the electron density in the flare ribbon for the Maxwellian distribution are $\text{log}\hspace{0.17em}(N_e)={11.41}_{-0.33}^{+0.46}\text{\hspace{0.17em}c}{\text{m}}^{-3},$ ${11.42}_{-0.33}^{+0.46}\text{\hspace{0.17em}c}{\text{m}}^{-3}$ and ${11.45}_{-0.33}^{+0.46}\text{\hspace{0.17em}c}{\text{m}}^{-3}$ at the temperature of $\text{log}\hspace{0.17em}T=4.88$K, 5.0 K and 5.17 K, respectively, which are slightly smaller than reported ${11.96}_{-0.22}^{+0.35}\text{\hspace{0.17em}c}{\text{m}}^{-3}$ using the method of differential emission measure. The electron density for the Kappa distributions are $\text{log}\hspace{0.17em}(N_e)={11.18}_{-0.30}^{+0.42}\text{\hspace{0.17em}c}{\text{m}}^{-3},$${11.29}_{-0.31}^{+0.43}\text{\hspace{0.17em}c}{\text{m}}^{-3},$ and ${11.34}_{-0.32}^{+0.45}\text{\hspace{0.17em}c}{\text{m}}^{-3}$ for κ = 2, 3 and 5, respectively. With increasing κ, the electron density for the Kappa distribution will be close to that for the Maxwellian distribution. This discussion is significant in the electron density diagnostics in the solar transition region, which will be also important for diagnostics for non-Maxwellian distribution.

Keywords:

• Electron density
• flare ribbon
• non-Maxwellian distribution
• spectroscopic diagnostics

Additional information

Funding

The authors gratefully acknowledge the support of the National Natural Science Foundation of China [No. 11205047] and of Henan Province’s Education Department’s Key Project [No. 13A140271]. The authors also thank for the data from CHIANTI: An Atomic Database for Spectroscopic Diagnostics of Astrophysical Plasmas.