Study of the effect of opacity on the solar coronal X-ray Mg XII 0.842 nm spectral lines

Using the intensity ratio of the solar coronal X-ray Mg XII 0.842 nm doublet observed by using the SPIRIT instrumentation, we discuss the optical depth at the line center of the Mg XII emission lines. The optical depth at the line center of the (1/2 - 3/2) component that we calculated is 0.245. Using the measured abundance of magnesium and the results of ionization balance, we calculate the variation of electron density with the measured distance to the corona and estimate the average electron density to be n_e = 6.657 x 10⁸ cm^-3. Also we discuss the variation of the optical depth at the line center with the coronal temperature. This study will be significant to solar coronal plasma diagnostics.