Extended Data Figure 6: Effect of potential bias in the continuum-level estimate on the abundance measurement using weak emission lines.

a, Abundances of Cr (red), Mn (blue) and Fe (black) determined by intentionally adding a small offset to the continuum normalization (within ±3% of the measured value). The solid and dashed lines are obtained from our test analysis of the simulated CCD spectrum (Extended Data Fig. 5b) and the Hitomi spectrum, respectively. This illustrates that the CCD measurement of Cr and Mn abundances is sensitive to the accuracy of the continuum-level determination because of the weakness of the emission and the low spectral resolution. The Fe abundance is less subject to such uncertainty, even in the CCD measurement, owing to the much larger equivalent width of the emission. b, Abundance ratios of Cr/Fe (red) and Mn/Fe (blue), calculated using the values in a as a function of offset in the continuum level.