The ratio of the Fe abundance in the photosphere to that in coronal flare plasmas is determined by X-ray lines within the complex at 6.7 keV ( 1.9 Å ) emitted during flares .
The line complex includes the He-like Fe ( Fe xxv ) resonance line w ( 6.70 keV ) and Fe K \alpha lines ( 6.39 , 6.40 keV ) , the latter being primarily formed by the fluorescence of photospheric material by X-rays from the hot flare plasma .
The ratio of the Fe K \alpha lines to the Fe xxv w depends on the ratio of the photospheric-to-flare Fe abundance , heliocentric angle \theta of the flare , and the temperature T _ { e } of the flaring plasma .
Using high-resolution spectra from X-ray spectrometers on the P78-1 and Solar Maximum Mission spacecraft , the Fe abundance in flares is estimated to be 1.6 \pm 0.5 and 2.0 \pm 0.3 times the photospheric Fe abundance , the P78-1 value being preferred as it is more directly determined .
This enhancement is consistent with results from X-ray spectra from the RHESSI spacecraft , but is significantly less than a factor 4 as in previous work .